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# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
from __future__ import division
import torch
class ImageList(object):
"""
Structure that holds a list of images (of possibly
varying sizes) as a single tensor.
This works by padding the images to the same size,
and storing in a field the original sizes of each image
"""
def __init__(self, tensors, image_sizes):
"""
Arguments:
tensors (tensor)
image_sizes (list[tuple[int, int]])
"""
self.tensors = tensors
self.image_sizes = image_sizes
def to(self, *args, **kwargs):
cast_tensor = self.tensors.to(*args, **kwargs)
return ImageList(cast_tensor, self.image_sizes)
def to_image_list(tensors, size_divisible=0):
"""
tensors can be an ImageList, a torch.Tensor or
an iterable of Tensors. It can't be a numpy array.
When tensors is an iterable of Tensors, it pads
the Tensors with zeros so that they have the same
shape
"""
if isinstance(tensors, torch.Tensor) and size_divisible > 0:
tensors = [tensors]
if isinstance(tensors, ImageList):
return tensors
elif isinstance(tensors, torch.Tensor):
# single tensor shape can be inferred
assert tensors.dim() == 4
image_sizes = [tensor.shape[-2:] for tensor in tensors]
return ImageList(tensors, image_sizes)
elif isinstance(tensors, (tuple, list)):
max_size = tuple(max(s) for s in zip(*[img.shape for img in tensors]))
# TODO Ideally, just remove this and let me model handle arbitrary
# input sizs
if size_divisible > 0:
import math
stride = size_divisible
max_size = list(max_size)
max_size[1] = int(math.ceil(max_size[1] / stride) * stride)
max_size[2] = int(math.ceil(max_size[2] / stride) * stride)
max_size = tuple(max_size)
batch_shape = (len(tensors),) + max_size
batched_imgs = tensors[0].new(*batch_shape).zero_()
for img, pad_img in zip(tensors, batched_imgs):
pad_img[: img.shape[0], : img.shape[1], : img.shape[2]].copy_(img)
image_sizes = [im.shape[-2:] for im in tensors]
return ImageList(batched_imgs, image_sizes)
else:
raise TypeError("Unsupported type for to_image_list: {}".format(type(tensors)))
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