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# Pass the list of images and the list of corresponding captions
train_dataset = make_dataset(list(train_data.keys()), list(train_data.values()))
valid_dataset = make_dataset(list(valid_data.keys()), list(valid_data.values()))
Building the model
Our image captioning architecture consists of three models:
A CNN: used to extract the image features
A TransformerEncoder: The extracted image features are then passed to a Transformer based encoder that generates a new representation of the inputs
A TransformerDecoder: This model takes the encoder output and the text data (sequences) as inputs and tries to learn to generate the caption.
def get_cnn_model():
base_model = efficientnet.EfficientNetB0(
input_shape=(*IMAGE_SIZE, 3), include_top=False, weights=\"imagenet\",
)
# We freeze our feature extractor
base_model.trainable = False
base_model_out = base_model.output
base_model_out = layers.Reshape((-1, base_model_out.shape[-1]))(base_model_out)
cnn_model = keras.models.Model(base_model.input, base_model_out)
return cnn_model
class TransformerEncoderBlock(layers.Layer):
def __init__(self, embed_dim, dense_dim, num_heads, **kwargs):
super().__init__(**kwargs)
self.embed_dim = embed_dim
self.dense_dim = dense_dim
self.num_heads = num_heads
self.attention_1 = layers.MultiHeadAttention(
num_heads=num_heads, key_dim=embed_dim, dropout=0.0
)
self.layernorm_1 = layers.LayerNormalization()
self.layernorm_2 = layers.LayerNormalization()
self.dense_1 = layers.Dense(embed_dim, activation=\"relu\")
def call(self, inputs, training, mask=None):
inputs = self.layernorm_1(inputs)
inputs = self.dense_1(inputs)
attention_output_1 = self.attention_1(
query=inputs,
value=inputs,
key=inputs,
attention_mask=None,
training=training,
)
out_1 = self.layernorm_2(inputs + attention_output_1)
return out_1
class PositionalEmbedding(layers.Layer):
def __init__(self, sequence_length, vocab_size, embed_dim, **kwargs):
super().__init__(**kwargs)
self.token_embeddings = layers.Embedding(
input_dim=vocab_size, output_dim=embed_dim
)
self.position_embeddings = layers.Embedding(
input_dim=sequence_length, output_dim=embed_dim
)
self.sequence_length = sequence_length
self.vocab_size = vocab_size
self.embed_dim = embed_dim
self.embed_scale = tf.math.sqrt(tf.cast(embed_dim, tf.float32))
def call(self, inputs):
length = tf.shape(inputs)[-1]
positions = tf.range(start=0, limit=length, delta=1)
embedded_tokens = self.token_embeddings(inputs)
embedded_tokens = embedded_tokens * self.embed_scale
embedded_positions = self.position_embeddings(positions)
return embedded_tokens + embedded_positions
def compute_mask(self, inputs, mask=None):
return tf.math.not_equal(inputs, 0)
class TransformerDecoderBlock(layers.Layer):
def __init__(self, embed_dim, ff_dim, num_heads, **kwargs):
super().__init__(**kwargs)
self.embed_dim = embed_dim
self.ff_dim = ff_dim
self.num_heads = num_heads
self.attention_1 = layers.MultiHeadAttention(
num_heads=num_heads, key_dim=embed_dim, dropout=0.1
)
self.attention_2 = layers.MultiHeadAttention(
num_heads=num_heads, key_dim=embed_dim, dropout=0.1
)
self.ffn_layer_1 = layers.Dense(ff_dim, activation=\"relu\")
self.ffn_layer_2 = layers.Dense(embed_dim)
self.layernorm_1 = layers.LayerNormalization()
self.layernorm_2 = layers.LayerNormalization()
self.layernorm_3 = layers.LayerNormalization()
self.embedding = PositionalEmbedding(
embed_dim=EMBED_DIM, sequence_length=SEQ_LENGTH, vocab_size=VOCAB_SIZE
)
self.out = layers.Dense(VOCAB_SIZE, activation=\"softmax\")