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x_test shape: (10000, 32, 32, 3) - y_test shape: (10000, 1)
Configure the hyperparameters
learning_rate = 0.001
weight_decay = 0.0001
batch_size = 64
num_epochs = 50
dropout_rate = 0.2
image_size = 64 # We'll resize input images to this size.
patch_size = 2 # Size of the patches to be extract from the input images.
num_patches = (image_size // patch_size) ** 2 # Size of the data array.
latent_dim = 256 # Size of the latent array.
projection_dim = 256 # Embedding size of each element in the data and latent arrays.
num_heads = 8 # Number of Transformer heads.
ffn_units = [
projection_dim,
projection_dim,
] # Size of the Transformer Feedforward network.
num_transformer_blocks = 4
num_iterations = 2 # Repetitions of the cross-attention and Transformer modules.
classifier_units = [
projection_dim,
num_classes,
] # Size of the Feedforward network of the final classifier.
print(f\"Image size: {image_size} X {image_size} = {image_size ** 2}\")
print(f\"Patch size: {patch_size} X {patch_size} = {patch_size ** 2} \")
print(f\"Patches per image: {num_patches}\")
print(f\"Elements per patch (3 channels): {(patch_size ** 2) * 3}\")
print(f\"Latent array shape: {latent_dim} X {projection_dim}\")
print(f\"Data array shape: {num_patches} X {projection_dim}\")
Image size: 64 X 64 = 4096
Patch size: 2 X 2 = 4
Patches per image: 1024
Elements per patch (3 channels): 12
Latent array shape: 256 X 256
Data array shape: 1024 X 256
Note that, in order to use each pixel as an individual input in the data array, set patch_size to 1.
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 Feedforward network (FFN)
def create_ffn(hidden_units, dropout_rate):
ffn_layers = []
for units in hidden_units[:-1]:
ffn_layers.append(layers.Dense(units, activation=tf.nn.gelu))
ffn_layers.append(layers.Dense(units=hidden_units[-1]))
ffn_layers.append(layers.Dropout(dropout_rate))
ffn = keras.Sequential(ffn_layers)
return ffn
Implement patch creation as a layer
class Patches(layers.Layer):
def __init__(self, patch_size):
super(Patches, self).__init__()
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_dims = patches.shape[-1]
patches = tf.reshape(patches, [batch_size, -1, patch_dims])
return patches
Implement the patch encoding layer
The PatchEncoder layer will linearly transform a patch by projecting it into a vector of size latent_dim. In addition, it adds a learnable position embedding to the projected vector.
Note that the orginal Perceiver paper uses the Fourier feature positional encodings.
class PatchEncoder(layers.Layer):
def __init__(self, num_patches, projection_dim):
super(PatchEncoder, self).__init__()
self.num_patches = num_patches
self.projection = layers.Dense(units=projection_dim)
self.position_embedding = layers.Embedding(
input_dim=num_patches, output_dim=projection_dim
)
def call(self, patches):
positions = tf.range(start=0, limit=self.num_patches, delta=1)
encoded = self.projection(patches) + self.position_embedding(positions)
return encoded
Build the Perceiver model