import torch
import torch.nn.functional as F
import numpy as np
import json
import torchvision.transforms as transforms
import matplotlib.pyplot as plt
import matplotlib.cm as cm
import skimage.transform
import argparse
from scipy.misc import imread, imresize
from PIL import Image
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
def caption_image_beam_search(encoder, decoder, image_path, word_map, beam_size=3):
"""
Reads an image and captions it with beam search.
:param encoder: encoder model
:param decoder: decoder model
:param image_path: path to image
:param word_map: word map
:param beam_size: number of sequences to consider at each decode-step
:return: caption, weights for visualization
"""
k = beam_size
vocab_size = len(word_map)
# Read image and process
img = imread(image_path)
if len(img.shape) == 2:
img = img[:, :, np.newaxis]
img = np.concatenate([img, img, img], axis=2)
img = imresize(img, (256, 256))
img = img.transpose(2, 0, 1)
img = img / 255.
img = torch.FloatTensor(img).to(device)
normalize = transforms.Normalize(mean=[0.485, 0.456, 0.406],
std=[0.229, 0.224, 0.225])
transform = transforms.Compose([normalize])
image = transform(img) # (3, 256, 256)
# Encode
image = image.unsqueeze(0) # (1, 3, 256, 256)
encoder_out = encoder(image) # (1, enc_image_size, enc_image_size, encoder_dim)
enc_image_size = encoder_out.size(1)
encoder_dim = encoder_out.size(3)
# Flatten encoding
encoder_out = encoder_out.view(1, -1, encoder_dim) # (1, num_pixels, encoder_dim)
num_pixels = encoder_out.size(1)
# We'll treat the problem as having a batch size of k
encoder_out = encoder_out.expand(k, num_pixels, encoder_dim) # (k, num_pixels, encoder_dim)
# Tensor to store top k previous words at each step; now they're just <start>
k_prev_words = torch.LongTensor([[word_map['<start>']]] * k).to(device) # (k, 1)
# Tensor to store top k sequences; now they're just <start>
seqs = k_prev_words # (k, 1)
# Tensor to store top k sequences' scores; now they're just 0
top_k_scores = torch.zeros(k, 1).to(device) # (k, 1)
# Tensor to store top k sequences' alphas; now they're just 1s
seqs_alpha = torch.ones(k, 1, enc_image_size, enc_image_size).to(device) # (k, 1, enc_image_size, enc_image_size)
# Lists to store completed sequences, their alphas and scores
complete_seqs = list()
complete_seqs_alpha = list()
complete_seqs_scores = list()
# Start decoding
step = 1
h, c = decoder.init_hidden_state(encoder_out)
# s is a number less than or equal to k, because sequences are removed from this process once they hit <end>
while True:
embeddings = decoder.embedding(k_prev_words).squeeze(1) # (s, embed_dim)
awe, alpha = decoder.attention(encoder_out, h) # (s, encoder_dim), (s, num_pixels)
alpha = alpha.view(-1, enc_image_size, enc_image_size) # (s, enc_image_size, enc_image_size)
gate = decoder.sigmoid(decoder.f_beta(h)) # gating scalar, (s, encoder_dim)
awe = gate * awe
h, c = decoder.decode_step(torch.cat([embeddings, awe], dim=1), (h, c)) # (s, decoder_dim)
scores = decoder.fc(h) # (s, vocab_size)
scores = F.log_softmax(scores, dim=1)
# Add
scores = top_k_scores.expand_as(scores) + scores # (s, vocab_size)
# For the first step, all k points will have the same scores (since same k previous words, h, c)
if step == 1:
top_k_scores, top_k_words = scores[0].topk(k, 0, True, True) # (s)
else:
# Unroll and find top scores, and their unrolled indices
top_k_scores, top_k_words = scores.view(-1).topk(k, 0, True, True) # (s)
# Convert unrolled indices to actual indices of scores
prev_word_inds = top_k_words / vocab_size # (s)
next_word_inds = top_k_words % vocab_size # (s)
# Add new words to sequences, alphas
seqs = torch.cat([seqs[prev_word_inds], next_word_inds.unsqueeze(1)], dim=1) # (s, step+1)
seqs_alpha = torch.cat([seqs_alpha[prev_word_inds], alpha[prev_word_inds].unsqueeze(1)],
dim=1) # (s, step+1, enc_image_size, enc_image_size)
# Which sequences are incomplete (didn't reach <end>)?
incomplete_inds = [ind for ind, next_word in enumerate(next_word_inds) if
next_word != word_map['<end>']]
complete_inds = list(set(range(len(next_word_inds))) - set(incomplete_inds))
# Set aside complete sequences
if len(complete_inds) > 0:
complete_seqs.extend(seqs[complete_inds].tolist())
complete_seqs_alpha.extend(seqs_alpha[complete_inds].tolist())
complete_seqs_scores.extend(top_k_scores[complete_inds])
k -= len(complete_inds) # reduce beam length accordingly
# Proceed with incomplete sequences
if k == 0:
break
seqs = seqs[incomplete_inds]
seqs_alpha = seqs_alpha[incomplete_inds]
h = h[prev_word_inds[incomplete_inds]]
c = c[prev_word_inds[incomplete_inds]]
encoder_out = encoder_out[prev_word_inds[incomplete_inds]]
top_k_scores = top_k_scores[incomplete_inds].unsqueeze(1)
k_prev_words = next_word_inds[incomplete_inds].unsqueeze(1)
# Break if things have been going on too long
if step > 50:
break
step += 1
i = complete_seqs_scores.index(max(complete_seqs_scores))
seq = complete_seqs[i]
alphas = complete_seqs_alpha[i]
return seq, alphas
def visualize_att(image_path, seq, alphas, rev_word_map, smooth=True):
"""
Visualizes caption with weights at every word.
Adapted from paper authors' repo: https://github.com/kelvinxu/arctic-captions/blob/master/alpha_visualization.ipynb
:param image_path: path to image that has been captioned
:param seq: caption
:param alphas: weights
:param rev_word_map: reverse word mapping, i.e. ix2word
:param smooth: smooth weights?
"""
image = Image.open(image_path)
image = image.resize([14 * 24, 14 * 24], Image.LANCZOS)
words = [rev_word_map[ind] for ind in seq]
for t in range(len(words)):
if t > 50:
break
plt.subplot(np.ceil(len(words) / 5.), 5, t + 1)
plt.text(0, 1, '%s' % (words[t]), color='black', backgroundcolor='white', fontsize=12)
plt.imshow(image)
current_alpha = alphas[t, :]
if smooth:
alpha = skimage.transform.pyramid_expand(current_alpha.numpy(), upscale=24, sigma=8)
else:
alpha = skimage.transform.resize(current_alpha.numpy(), [14 * 24, 14 * 24])
if t == 0:
plt.imshow(alpha, alpha=0)
else:
plt.imshow(alpha, alpha=0.8)
plt.set_cmap(cm.Greys_r)
plt.axis('off')
plt.show()
if __name__ == '__main__':
parser = argparse.ArgumentParser(description='Show, Attend, and Tell - Tutorial - Generate Caption')
parser.add_argument('--img', '-i', help='path to image')
parser.add_argument('--model', '-m', help='path to model')
parser.add_argument('--word_map', '-wm', help='path to word map JSON')
parser.add_argument('--beam_size', '-b', default=5, type=int, help='beam size for beam search')
parser.add_argument('--dont_smooth', dest='smooth', action='store_false', help='do not smooth alpha overlay')
args = parser.parse_args()
# Load model
checkpoint = torch.load(args.model, map_location=str(device))
decoder = checkpoint['decoder']
decoder = decoder.to(device)
decoder.eval()
encoder = checkpoint['encoder']
encoder = encoder.to(device)
encoder.eval()
# Load word map (word2ix)
with open(args.word_map, 'r') as j:
word_map = json.load(j)
rev_word_map = {v: k for k, v in word_map.items()} # ix2word
# Encode, decode with attention and beam search
seq, alphas = caption_image_beam_search(encoder, decoder, args.img, word_map, args.beam_size)
alphas = torch.FloatTensor(alphas)
# Visualize caption and attention of best sequence
visualize_att(args.img, seq, alphas, rev_word_map, args.smooth)
