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input_dim=num_patches, output_dim=embedding_dim |
)(positions) |
x = x + position_embedding |
# Process x using the module blocks. |
x = blocks(x) |
# Apply global average pooling to generate a [batch_size, embedding_dim] representation tensor. |
representation = layers.GlobalAveragePooling1D()(x) |
# Apply dropout. |
representation = layers.Dropout(rate=dropout_rate)(representation) |
# Compute logits outputs. |
logits = layers.Dense(num_classes)(representation) |
# Create the Keras model. |
return keras.Model(inputs=inputs, outputs=logits) |
Define an experiment |
We implement a utility function to compile, train, and evaluate a given model. |
def run_experiment(model): |
# Create Adam optimizer with weight decay. |
optimizer = tfa.optimizers.AdamW( |
learning_rate=learning_rate, weight_decay=weight_decay, |
) |
# Compile the model. |
model.compile( |
optimizer=optimizer, |
loss=keras.losses.SparseCategoricalCrossentropy(from_logits=True), |
metrics=[ |
keras.metrics.SparseCategoricalAccuracy(name=\"acc\"), |
keras.metrics.SparseTopKCategoricalAccuracy(5, name=\"top5-acc\"), |
], |
) |
# Create a learning rate scheduler callback. |
reduce_lr = keras.callbacks.ReduceLROnPlateau( |
monitor=\"val_loss\", factor=0.5, patience=5 |
) |
# Create an early stopping callback. |
early_stopping = tf.keras.callbacks.EarlyStopping( |
monitor=\"val_loss\", patience=10, restore_best_weights=True |
) |
# Fit the model. |
history = model.fit( |
x=x_train, |
y=y_train, |
batch_size=batch_size, |
epochs=num_epochs, |
validation_split=0.1, |
callbacks=[early_stopping, reduce_lr], |
) |
_, accuracy, top_5_accuracy = model.evaluate(x_test, y_test) |
print(f\"Test accuracy: {round(accuracy * 100, 2)}%\") |
print(f\"Test top 5 accuracy: {round(top_5_accuracy * 100, 2)}%\") |
# Return history to plot learning curves. |
return history |
Use data augmentation |
data_augmentation = keras.Sequential( |
[ |
layers.Normalization(), |
layers.Resizing(image_size, image_size), |
layers.RandomFlip(\"horizontal\"), |
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 patch extraction as a layer |
class Patches(layers.Layer): |
def __init__(self, patch_size, num_patches): |
super(Patches, self).__init__() |
self.patch_size = patch_size |
self.num_patches = num_patches |
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_dims = patches.shape[-1] |
patches = tf.reshape(patches, [batch_size, self.num_patches, patch_dims]) |
return patches |
The MLP-Mixer model |
The MLP-Mixer is an architecture based exclusively on multi-layer perceptrons (MLPs), that contains two types of MLP layers: |
One applied independently to image patches, which mixes the per-location features. |
The other applied across patches (along channels), which mixes spatial information. |
This is similar to a depthwise separable convolution based model such as the Xception model, but with two chained dense transforms, no max pooling, and layer normalization instead of batch normalization. |
Implement the MLP-Mixer module |
class MLPMixerLayer(layers.Layer): |
def __init__(self, num_patches, hidden_units, dropout_rate, *args, **kwargs): |
super(MLPMixerLayer, self).__init__(*args, **kwargs) |
self.mlp1 = keras.Sequential( |
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