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| import torch | |
| import torch._utils | |
| import torch.nn as nn | |
| import torchvision.models as models | |
| from typing import Tuple | |
| from config import Config | |
| class Encoder(nn.Module): | |
| def __init__(self, image_emb_dim: int, device: torch.device): | |
| """ Image encoder to obtain features from images. Contains pretrained Resnet50 with last layer removed | |
| and a linear layer with the output dimension of (BATCH, image_emb_dim) | |
| """ | |
| super(Encoder, self).__init__() | |
| self.image_emb_dim = image_emb_dim | |
| self.device = device | |
| # pretrained Resnet50 model with freezed parameters | |
| resnet = models.resnet50(weights=models.ResNet50_Weights.DEFAULT) | |
| for param in resnet.parameters(): | |
| param.requires_grad_(False) | |
| # remove last layer | |
| modules = list(resnet.children())[:-1] | |
| self.resnet = nn.Sequential(*modules) | |
| # define a final classifier | |
| self.fc = nn.Linear(in_features=resnet.fc.in_features, out_features=self.image_emb_dim) | |
| def forward(self, images: torch.Tensor) -> torch.Tensor: | |
| """ Forward operation of encoder, passing images through resnet and then linear layer. | |
| Args: | |
| > images (torch.Tensor): (BATCH, 3, 224, 224) | |
| Returns: | |
| > features (torch.Tensor): (BATCH, IMAGE_EMB_DIM) | |
| """ | |
| features = self.resnet(images) | |
| # features: (BATCH, 2048, 1, 1) | |
| features = features.reshape(features.size(0), -1).to(self.device) | |
| # features: (BATCH, 2048) | |
| features = self.fc(features).to(self.device) | |
| # features: (BATCH, IMAGE_EMB_DIM) | |
| return features | |
| class Decoder(nn.Module): | |
| def __init__(self, | |
| image_emb_dim: int, | |
| word_emb_dim: int, | |
| hidden_dim: int, | |
| num_layers: int, | |
| vocab_size: int, | |
| device: torch.device): | |
| """ | |
| Decoder taking as input for the LSTM layer the concatenation of features obtained from the encoder | |
| and embedded captions obtained from the embedding layer. Hidden and cell states are randomly initialized. | |
| Final classifier is a linear layer with output dimension of the size of a vocabulary. | |
| """ | |
| super(Decoder, self).__init__() | |
| self.config = Config() | |
| self.image_emd_dim = image_emb_dim | |
| self.word_emb_dim = word_emb_dim | |
| self.hidden_dim = hidden_dim | |
| self.num_layer = num_layers | |
| self.vocab_size = vocab_size | |
| self.device = device | |
| self.hidden_state_0 = nn.Parameter(torch.zeros((self.num_layer, 1, self.hidden_dim))) | |
| self.cell_state_0 = nn.Parameter(torch.zeros((self.num_layer, 1, self.hidden_dim))) | |
| self.lstm = nn.LSTM(input_size=self.image_emd_dim + self.word_emb_dim, | |
| hidden_size=self.hidden_dim, | |
| num_layers=self.num_layer, | |
| bidirectional=False) | |
| self.fc = nn.Sequential( | |
| nn.Linear(in_features=self.hidden_dim, out_featuers=self.vocab_size), | |
| nn.LogSoftmax(dim=2) | |
| ) | |
| def forward(self, | |
| embedded_captions: torch.Tensor, | |
| features: torch.Tensor, | |
| hidden: torch.Tensor, | |
| cell: torch.Tensor) -> Tuple[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]: | |
| """ | |
| Forward operation of (word-by-word) decoder. | |
| The LSTM input (concatenation of embedded_captions and features) is passed through LSTM and then linear layer. | |
| Args: | |
| > embedded_captions(torch.Tensor): (SEQ_LENGTH = 1, BATCH, WORD_EMB_DIM) | |
| > features (torch.Tensor): (1, BATCH, IMAGE_EMB_DIM) | |
| > hidden (torch.Tensor): (NUM_LAYER, BATCH, HIDDEN_DIM) | |
| > cell (torch.Tensor): (NUM_LAYER, BATCH, HIDDEN_DIM) | |
| Returns: | |
| > output (torch.Tensor): (1, BATCH, VOCAB_SIZE) | |
| > (hidden, cell) (torch.Tensor, torch.Tensor): (NUM_LAYER, BATCH, HIDDEN_DIM) | |
| """ | |
| lstm_input = torch.cat((embedded_captions, features), dim=2) | |
| output, (hidden, cell) = self.lstm(lstm_input, (hidden, cell)) | |
| # output : (SEQ_LENGTH, BATCH, HIDDEN_DIM) | |
| # hidden : (NUM_LAYER, BATCH, HIDDEN_DIM) | |
| output = output.to(self.device) | |
| output = self.fc(output) | |
| # output : (SEQ_LENGTH, BATCH, VOCAB_SIZE) | |
| return output, (hidden, cell) | |