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data_loader.py
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data_loader.py
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import torch
import torchvision.transforms as transforms
import torch.utils.data as data
import os
import pickle
import string
import numpy as np
import nltk
from PIL import Image
from build_vocab import Vocabulary
from coco.pycocotools.coco import COCO
class CocoDataset(data.Dataset):
"""COCO Custom Dataset compatible with torch.utils.data.DataLoader."""
def __init__(self, root, json, vocab, transform=None):
"""Set the path for images, captions and vocabulary wrapper.
Args:
root: image directory.
json: coco annotation file path.
vocab: vocabulary wrapper.
transform: image transformer.
"""
self.root = root
self.coco = COCO( json )
self.ids = list( self.coco.anns.keys() )
self.vocab = vocab
self.transform = transform
def __getitem__(self, index):
"""Returns one data pair ( image, caption, image_id )."""
coco = self.coco
vocab = self.vocab
ann_id = self.ids[index]
caption = coco.anns[ann_id]['caption']
img_id = coco.anns[ann_id]['image_id']
filename = coco.loadImgs(img_id)[0]['file_name']
if 'val' in filename.lower():
path = 'val2014/' + filename
else:
path = 'train2014/' + filename
image = Image.open( os.path.join( self.root, path ) ).convert('RGB')
if self.transform is not None:
image = self.transform( image )
# Convert caption (string) to word ids.
tokens = str( caption ).lower().translate( None, string.punctuation ).strip().split()
caption = []
caption.append(vocab('<start>'))
caption.extend([vocab(token) for token in tokens])
caption.append(vocab('<end>'))
target = torch.Tensor(caption)
return image, target, img_id, filename
def __len__(self):
return len( self.ids )
def collate_fn(data):
"""Creates mini-batch tensors from the list of tuples (image, caption).
We should build custom collate_fn rather than using default collate_fn,
because merging caption (including padding) is not supported in default.
Args:
data: list of tuple (image, caption).
- image: torch tensor of shape (3, 256, 256).
- caption: torch tensor of shape (?); variable length.
Returns:
images: torch tensor of shape (batch_size, 3, 256, 256).
targets: torch tensor of shape (batch_size, padded_length).
lengths: list; valid length for each padded caption.
img_ids: image ids in COCO dataset, for evaluation purpose
filenames: image filenames in COCO dataset, for evaluation purpose
"""
# Sort a data list by caption length (descending order).
data.sort( key=lambda x: len( x[1] ), reverse=True )
images, captions, img_ids, filenames = zip( *data ) # unzip
# Merge images (from tuple of 3D tensor to 4D tensor).
images = torch.stack(images, 0)
img_ids = list( img_ids )
filenames = list( filenames )
# Merge captions (from tuple of 1D tensor to 2D tensor).
lengths = [len(cap) for cap in captions]
targets = torch.zeros(len(captions), max(lengths)).long()
for i, cap in enumerate(captions):
end = lengths[i]
targets[i, :end] = cap[:end]
return images, targets, lengths, img_ids, filenames
def get_loader(root, json, vocab, transform, batch_size, shuffle, num_workers):
"""Returns torch.utils.data.DataLoader for custom coco dataset."""
# COCO caption dataset
coco = CocoDataset(root=root,
json=json,
vocab=vocab,
transform=transform)
# Data loader for COCO dataset
# This will return (images, captions, lengths) for every iteration.
# images: tensor of shape (batch_size, 3, 224, 224).
# captions: tensor of shape (batch_size, padded_length).
# lengths: list indicating valid length for each caption. length is (batch_size).
data_loader = torch.utils.data.DataLoader(dataset=coco,
batch_size=batch_size,
shuffle=shuffle,
num_workers=num_workers,
collate_fn=collate_fn)
return data_loader