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课程：学堂在线的清华训练营《驭风计划：培养人工智能青年人才》（满分作业）
paper:《Show, Attend and Tell Neural Image Caption Generation with Visual Attention》
需要的理论知识：LSTM BLEU Resnet-101 COCO数据集 Attention beam算法
理论知识也可以参考博客：
《Show, Attend and Tell: Neural Image Caption Generation with Visual Attention》论文阅读（详细
《Show and Tell: A Neural Image Caption Generator》论文解读
项目配置、训练过程（环境：百度飞浆平台 V100 cuda9.2）：
conda create --prefix=/home/aistudio/external-libraries/caption python=3.6 -y conda init bash conda activate /home/aistudio/external-libraries/caption conda install pytorch=0.4.1 cuda92 -c https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/pytorch/linux-64/ -y pip install torchvision==0.2.2 numpy nltk tqdm h5py pillow matplotlib scikit-image scipy==1.1.0 -i https://pypi.tuna.tsinghua.edu.cn/simple python train.py > train_att.log python caption.py --img '/home/aistudio/data/data124850/test2014/COCO_test2014_000000090228.jpg' --model '../code/BEST_checkpoint_coco_5_cap_per_img_5_min_word_freq.pth.tar' --word_map '/home/aistudio/data/data124851/WORDMAP_coco_5_cap_per_img_5_min_word_freq.json'
实验结果示例：
图中的白色亮光是指注意力，很明显，可以看到对于清晰和明显的图片这个模型还是有较好的效果，注意力也能关注到图片中的重要部分，而且注意力是随着词的变化而改变位置的，例如第2张图，当词是a laptop的时候，注意力正好关注电脑；当词是wooden desk的时候，注意力正好关注着桌子。
核心代码：
import torch
from torch import nn
import torchvision
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
class Encoder(nn.Module):
"""
Encoder
"""
def __init__(self, encoded_image_size=14):
super(Encoder, self).__init__()
self.enc_image_size = encoded_image_size
# Pretrained ImageNet ResNet-101
# Remove linear and pool layers
resnet = torchvision.models.resnet101(pretrained=True)
modules = list(resnet.children())[:-2]
self.resnet = nn.Sequential(*modules)
# Resize image to fixed size to allow input images of variable size
self.adaptive_pool = nn.AdaptiveAvgPool2d((encoded_image_size, encoded_image_size))
self.fine_tune(fine_tune=True)
def forward(self, images):
"""
Forward propagation.
:param images: images, a tensor of dimensions (batch_size, 3, image_size, image_size)
:return: encoded images
"""
out = self.resnet(images) # (batch_size, 2048, image_size/32, image_size/32)
out = self.adaptive_pool(out) # (batch_size, 2048, encoded_image_size, encoded_image_size)
out = out.permute(0, 2, 3, 1) # (batch_size, encoded_image_size, encoded_image_size, 2048)
return out
def fine_tune(self, fine_tune=True):
"""
Allow or prevent the computation of gradients for convolutional blocks 2 through 4 of the encoder.
:param fine_tune: boolean
"""
for p in self.resnet.parameters():
p.requires_grad = False
# If fine-tuning, only fine-tune convolutional blocks 2 through 4
for c in list(self.resnet.children())[5:]:
for p in c.parameters():
p.requires_grad = fine_tune
class Attention(nn.Module):
"""
Attention Network.
"""
def __init__(self, encoder_dim, decoder_dim, attention_dim):
"""
:param encoder_dim: feature size of encoded images
:param decoder_dim: size of decoder's RNN
:param attention_dim: size of the attention network
"""
super(Attention, self).__init__()
self.encoder_att = nn.Linear(encoder_dim, attention_dim) # linear layer to transform encoded image
self.decoder_att = nn.Linear(decoder_dim, attention_dim) # linear layer to transform decoder's output
self.full_att = nn.Linear(attention_dim, 1) # linear layer to calculate values to be softmax-ed
self.relu = nn.ReLU()
self.softmax = nn.Softmax(dim=1) # softmax layer to calculate weights
def forward(self, encoder_out, decoder_hidden):
"""
Forward pass.
:param encoder_out: encoded images, a tensor of dimension (batch_size, num_pixels, encoder_dim)
:param decoder_hidden: previous decoder output, a tensor of dimension (batch_size, decoder_dim)
:return: attention weighted encoding, weights
"""
att1 = self.encoder_att(encoder_out) # (batch_size, num_pixels, attention_dim)
att2 = self.decoder_att(decoder_hidden) # (batch_size, attention_dim)
att = self.full_att(self.relu(att1 + att2.unsqueeze(1))).squeeze(2) # (batch_size, num_pixels)
alpha = self.softmax(att) # (batch_size, num_pixels)
z = (encoder_out * alpha.unsqueeze(2)).sum(dim=1) # (batch_size, encoder_dim)
return z, alpha
class DecoderWithAttention(nn.Module):
"""
Decoder.
"""
def __init__(self, cfg, encoder_dim=2048):
"""
:param attention_dim: size of attention network
:param embed_dim: embedding size
:param decoder_dim: size of decoder's RNN
:param vocab_size: size of vocabulary
:param encoder_dim: feature size of encoded images
:param dropout: dropout
"""
super(DecoderWithAttention, self).__init__()
self.encoder_dim = encoder_dim
self.decoder_dim = cfg['decoder_dim']
self.attention_dim = cfg['attention_dim']
self.embed_dim = cfg['embed_dim']
self.vocab_size = cfg['vocab_size']
self.dropout = cfg['dropout']
self.device = cfg['device']
self.attention = Attention(encoder_dim, self.decoder_dim, self.attention_dim) # attention network
self.embedding = nn.Embedding(self.vocab_size, self.embed_dim) # embedding layer
self.dropout = nn.Dropout(0.1)
self.decode_step = nn.LSTMCell(self.embed_dim + encoder_dim, self.decoder_dim, bias=True) # decoding LSTMCell
self.init_h = nn.Linear(encoder_dim, self.decoder_dim) # linear layer to find initial hidden state of LSTMCell
self.init_c = nn.Linear(encoder_dim, self.decoder_dim) # linear layer to find initial cell state of LSTMCell
self.f_beta = nn.Linear(self.decoder_dim, encoder_dim) # linear layer to create a sigmoid-activated gate
self.sigmoid = nn.Sigmoid()
self.fc = nn.Linear(self.decoder_dim, self.vocab_size) # linear layer to find scores over vocabulary
self.init_weights() # initialize some layers with the uniform distribution
# initialize some layers with the uniform distribution
self.embedding.weight.data.uniform_(-0.1, 0.1)
self.fc.bias.data.fill_(0)
self.fc.weight.data.uniform_(-0.1, 0.1)
def load_pretrained_embeddings(self, embeddings):
"""
Loads embedding layer with pre-trained embeddings.
:param embeddings: pre-trained embeddings
"""
self.embedding.weight = nn.Parameter(embeddings)
def fine_tune_embeddings(self, fine_tune=True):
"""
Allow fine-tuning of embedding layer? (Only makes sense to not-allow if using pre-trained embeddings).
:param fine_tune: Allow?
"""
for p in self.embedding.parameters():
p.requires_grad = fine_tune
def init_weights(self):
"""
Initializes some parameters with values from the uniform distribution, for easier convergence.
"""
self.embedding.weight.data.uniform_(-0.1, 0.1)
self.fc.bias.data.fill_(0)
self.fc.weight.data.uniform_(-0.1, 0.1)
def forward(self, encoder_out, encoded_captions, caption_lengths):
"""
Forward propagation.
:param encoder_out: encoded images, a tensor of dimension (batch_size, enc_image_size, enc_image_size, encoder_dim)
:param encoded_captions: encoded captions, a tensor of dimension (batch_size, max_caption_length)
:param caption_lengths: caption lengths, a tensor of dimension (batch_size, 1)
:return: scores for vocabulary, sorted encoded captions, decode lengths, weights, sort indices
"""
batch_size = encoder_out.size(0)
encoder_dim = encoder_out.size(-1)
vocab_size = self.vocab_size
# Flatten image
encoder_out = encoder_out.view(batch_size, -1, encoder_dim) # (batch_size, num_pixels, encoder_dim)
num_pixels = encoder_out.size(1)
# Sort input data by decreasing lengths;
caption_lengths, sort_ind = caption_lengths.squeeze(1).sort(dim=0, descending=True)
encoder_out = encoder_out[sort_ind]
encoded_captions = encoded_captions[sort_ind]
# Embedding
embeddings = self.embedding(encoded_captions) # (batch_size, max_caption_length, embed_dim)
# We won't decode at the <end> position, since we've finished generating as soon as we generate <end>
# So, decoding lengths are actual lengths - 1
decode_lengths = (caption_lengths - 1).tolist()
# Create tensors to hold word predicion scores and alphas
predictions = torch.zeros(batch_size, max(decode_lengths), vocab_size).to(self.device)
alphas = torch.zeros(batch_size, max(decode_lengths), num_pixels).to(self.device)
# Initialize LSTM state
mean_encoder_out = encoder_out.mean(dim=1)
h = self.init_h(mean_encoder_out) # (batch_size, decoder_dim)
c = self.init_c(mean_encoder_out)
for t in range(max(decode_lengths)):
batch_size_t = sum([l > t for l in decode_lengths])
preds, alpha, h, c = self.one_step(t, batch_size_t, embeddings, encoder_out, h, c)
predictions[:batch_size_t, t, :] = preds
alphas[:batch_size_t, t, :] = alpha
return predictions, encoded_captions, decode_lengths, alphas, sort_ind
def one_step(self, t, batch_size_t, embeddings, encoder_out, h, c):
"""
:param t:
:param batch_size_t:
:param embeddings:
:param encoder_out:
:param h:
:param c:
:return:
"""
attention_weighted_encoding, alpha = self.attention(encoder_out[:batch_size_t],
h[:batch_size_t])
gate = self.sigmoid(self.f_beta(h[:batch_size_t])) # gating scalar, (batch_size_t, encoder_dim)
attention_weighted_encoding = gate * attention_weighted_encoding
h, c = self.decode_step(
torch.cat([embeddings[:batch_size_t, t, :], attention_weighted_encoding], dim=1),
(h[:batch_size_t], c[:batch_size_t])) # (batch_size_t, decoder_dim)
preds = self.fc(self.dropout(h)) # (batch_size_t, vocab_size)
return preds, alpha, h, c
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