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We see that different filters in the kernel have different locality spans, and this pattern is likely to evolve with more training.
Final notes
There's been a recent trend on fusing convolutions with other data-agnostic operations like self-attention. Following works are along this line of research:
ConViT (d'Ascoli et al.)
CCT (Hassani et al.)
CoAtNet (Dai et al.)
Image classification with a Transformer that leverages external attention.
Introduction
This example implements the EANet model for image classification, and demonstrates it on the CIFAR-100 dataset. EANet introduces a novel attention mechanism named external attention, based on two external, small, learnable, and shared memories, which can be implemented easily by simply using two cascaded linear layers ...
pip install -U tensorflow-addons
Setup
import numpy as np
import tensorflow as tf
from tensorflow import keras
from tensorflow.keras import layers
import tensorflow_addons as tfa
import matplotlib.pyplot as plt
Prepare the data
num_classes = 100
input_shape = (32, 32, 3)
(x_train, y_train), (x_test, y_test) = keras.datasets.cifar100.load_data()
y_train = keras.utils.to_categorical(y_train, num_classes)
y_test = keras.utils.to_categorical(y_test, num_classes)
print(f\"x_train shape: {x_train.shape} - y_train shape: {y_train.shape}\")
print(f\"x_test shape: {x_test.shape} - y_test shape: {y_test.shape}\")
x_train shape: (50000, 32, 32, 3) - y_train shape: (50000, 100)
x_test shape: (10000, 32, 32, 3) - y_test shape: (10000, 100)
Configure the hyperparameters
weight_decay = 0.0001
learning_rate = 0.001
label_smoothing = 0.1
validation_split = 0.2
batch_size = 128
num_epochs = 50
patch_size = 2 # Size of the patches to be extracted from the input images.
num_patches = (input_shape[0] // patch_size) ** 2 # Number of patch
embedding_dim = 64 # Number of hidden units.
mlp_dim = 64
dim_coefficient = 4
num_heads = 4
attention_dropout = 0.2
projection_dropout = 0.2
num_transformer_blocks = 8 # Number of repetitions of the transformer layer
print(f\"Patch size: {patch_size} X {patch_size} = {patch_size ** 2} \")
print(f\"Patches per image: {num_patches}\")
Patch size: 2 X 2 = 4
Patches per image: 256
Use data augmentation
data_augmentation = keras.Sequential(
[
layers.Normalization(),
layers.RandomFlip(\"horizontal\"),
layers.RandomRotation(factor=0.1),
layers.RandomContrast(factor=0.1),
layers.RandomZoom(height_factor=0.2, width_factor=0.2),
],
name=\"data_augmentation\",
)
# Compute the mean and the variance of the training data for normalization.
data_augmentation.layers[0].adapt(x_train)
Implement the patch extraction and encoding layer
class PatchExtract(layers.Layer):
def __init__(self, patch_size, **kwargs):
super(PatchExtract, self).__init__(**kwargs)
self.patch_size = patch_size
def call(self, images):
batch_size = tf.shape(images)[0]
patches = tf.image.extract_patches(
images=images,
sizes=(1, self.patch_size, self.patch_size, 1),
strides=(1, self.patch_size, self.patch_size, 1),
rates=(1, 1, 1, 1),
padding=\"VALID\",
)
patch_dim = patches.shape[-1]
patch_num = patches.shape[1]
return tf.reshape(patches, (batch_size, patch_num * patch_num, patch_dim))
class PatchEmbedding(layers.Layer):
def __init__(self, num_patch, embed_dim, **kwargs):
super(PatchEmbedding, self).__init__(**kwargs)
self.num_patch = num_patch
self.proj = layers.Dense(embed_dim)
self.pos_embed = layers.Embedding(input_dim=num_patch, output_dim=embed_dim)
def call(self, patch):
pos = tf.range(start=0, limit=self.num_patch, delta=1)
return self.proj(patch) + self.pos_embed(pos)
Implement the external attention block