# Copyright 2021 MosaicML. All Rights Reserved.
"""Core Progressive Resizing classes and functions."""
from __future__ import annotations
import logging
import textwrap
from functools import partial
from typing import Callable, Optional, Tuple
import torch
import torch.nn.functional as F
import torchvision.transforms.functional
from composer.core import Algorithm, Event, State
from composer.loggers import Logger
from composer.loss.utils import check_for_index_targets
log = logging.getLogger(__name__)
_VALID_MODES = ("crop", "resize")
T_ResizeTransform = Callable[[torch.Tensor], torch.Tensor]
__all__ = ["resize_batch", "ProgressiveResizing"]
[docs]def resize_batch(input: torch.Tensor,
target: torch.Tensor,
scale_factor: float,
mode: str = "resize",
resize_targets: bool = False) -> Tuple[torch.Tensor, torch.Tensor]:
"""Resize inputs and optionally outputs by cropping or interpolating.
Args:
input (torch.Tensor): input tensor of shape ``(N, C, H, W)``.
Resizing will be done along dimensions H and W using the constant
factor ``scale_factor``.
target (torch.Tensor): output tensor of shape ``(N, H, W)`` or
``(N, C, H, W)`` that will also be resized if ``resize_targets``
is ``True``,
scale_factor (float): scaling coefficient for the height and width of the
input/output tensor. 1.0 keeps the original size.
mode (str, optional): type of scaling to perform. Value must be one of ``'crop'`` or
``'resize'``. ``'crop'`` performs a random crop, whereas ``'resize'``
performs a nearest neighbor interpolation. Default: ``"resize"``.
resize_targets (bool, optional): whether to resize the targets, ``y``. Default: ``False``.
Returns:
X_sized: resized input tensor of shape ``(N, C, H * scale_factor, W * scale_factor)``.
y_sized: if ``resized_targets`` is ``True``, resized output tensor
of shape ``(N, H * scale_factor, W * scale_factor)`` or ``(N, C, H * scale_factor, W * scale_factor)``.
Depending on the input ``y``. Otherwise returns original ``y``.
Example:
.. testcode::
from composer.algorithms.progressive_resizing import resize_batch
X_resized, y_resized = resize_batch(X_example,
y_example,
scale_factor=0.5,
mode='resize',
resize_targets=False)
"""
# Verify dimensionalities are enough to support resizing
assert input.dim() > 2, "Input dimensionality not large enough for resizing"
if resize_targets is True:
assert target.dim() > 2, "Target dimensionality not large enough for resizing"
# Short-circuit if nothing should be done
if scale_factor >= 1:
return input, target
# Prep targets for resizing if necessary
if check_for_index_targets(target) and resize_targets is True:
# Add a dimension to match shape of the input and change type for resizing
y_sized = target.float().unsqueeze(1)
else:
y_sized = target
if mode.lower() == "crop" and resize_targets is False:
# Make a crop transform for X
resize_transform = _make_crop(tensor=input, scale_factor=scale_factor)
X_sized, y_sized = resize_transform(input), target
elif mode.lower() == "crop" and resize_targets is True:
# Make a crop transform for X and y
resize_transform, resize_y = _make_crop_pair(X=input, y=y_sized, scale_factor=scale_factor)
X_sized, y_sized = resize_transform(input), resize_y(y_sized)
elif mode.lower() == "resize":
# Make a resize transform (can be used for X or y)
resize_transform = _make_resize(scale_factor=scale_factor)
X_sized = resize_transform(input)
if resize_targets:
y_sized = resize_transform(y_sized)
else:
raise ValueError(f"Progressive mode '{mode}' not supported.")
# Revert targets to their original format if they were modified
if check_for_index_targets(target) and resize_targets is True:
# Convert back to original format for training
y_sized = y_sized.squeeze(dim=1).to(target.dtype)
# Log results
log.info(
textwrap.dedent(f"""\
Applied Progressive Resizing with scale_factor={scale_factor} and mode={mode}.
Old input dimensions: (H,W)={input.shape[2], input.shape[3]}.
New input dimensions: (H,W)={X_sized.shape[2], X_sized.shape[2]}"""))
return X_sized, y_sized
[docs]class ProgressiveResizing(Algorithm):
"""Apply Fastai's `progressive resizing <https://\\
github.com/fastai/fastbook/blob/780b76bef3127ce5b64f8230fce60e915a7e0735/07_sizing_and_tta.ipynb>`__ data
augmentation to speed up training.
Progressive resizing initially reduces input resolution to speed up early training.
Throughout training, the downsampling factor is gradually increased, yielding larger inputs
up to the original input size. A final finetuning period is then run to finetune the
model using the full-sized inputs.
Example:
.. testcode::
from composer.algorithms import ProgressiveResizing
from composer.trainer import Trainer
progressive_resizing_algorithm = ProgressiveResizing(
mode='resize',
initial_scale=1.0,
finetune_fraction=0.2,
resize_targets=False
)
trainer = Trainer(
model=model,
train_dataloader=train_dataloader,
eval_dataloader=eval_dataloader,
max_duration="1ep",
algorithms=[progressive_resizing_algorithm],
optimizers=[optimizer]
)
Args:
mode (str, optional): Type of scaling to perform. Value must be one of ``'crop'`` or ``'resize'``.
``'crop'`` performs a random crop, whereas ``'resize'`` performs a bilinear
interpolation. Default: ``"resize"``.
initial_scale (float, optional): Initial scale factor used to shrink the inputs. Must be a
value in between 0 and 1. Default: ``0.5``.
finetune_fraction (float, optional): Fraction of training to reserve for finetuning on the
full-sized inputs. Must be a value in between 0 and 1. Default: ``0.2``.
resize_targets (bool, optional): If True, resize targets also. Default: ``False``.
"""
def __init__(self,
mode: str = 'resize',
initial_scale: float = .5,
finetune_fraction: float = .2,
resize_targets: bool = False):
if mode not in _VALID_MODES:
raise ValueError(f"mode '{mode}' is not supported. Must be one of {_VALID_MODES}")
if not (0 <= initial_scale <= 1):
raise ValueError(f"initial_scale must be between 0 and 1: {initial_scale}")
if not (0 <= finetune_fraction <= 1):
raise ValueError(f"finetune_fraction must be between 0 and 1: {finetune_fraction}")
self.mode = mode
self.initial_scale = initial_scale
self.finetune_fraction = finetune_fraction
self.resize_targets = resize_targets
[docs] def match(self, event: Event, state: State) -> bool:
"""Run on Event.AFTER_DATALOADER.
Args:
event (:class:`Event`): The current event.
state (:class:`State`): The current state.
Returns:
bool: True if this algorithm should run now
"""
return event == Event.AFTER_DATALOADER
[docs] def apply(self, event: Event, state: State, logger: Optional[Logger] = None) -> None:
"""Applies ProgressiveResizing on input images.
Args:
event (Event): the current event
state (State): the current trainer state
logger (Logger): the training logger
"""
input, target = state.batch_pair
assert isinstance(input, torch.Tensor) and isinstance(target, torch.Tensor), \
"Multiple tensors not supported for this method yet."
# Calculate the current size of the inputs to use
initial_size = self.initial_scale
finetune_fraction = self.finetune_fraction
scale_frac_elapsed = min([state.get_elapsed_duration().value / (1 - finetune_fraction), 1])
# Linearly increase to full size at the start of the fine tuning period
scale_factor = initial_size + (1 - initial_size) * scale_frac_elapsed
new_input, new_target = resize_batch(input=input,
target=target,
scale_factor=scale_factor,
mode=self.mode,
resize_targets=self.resize_targets)
state.batch = (new_input, new_target)
if logger is not None:
logger.data_batch({
"progressive_resizing/height": new_input.shape[2],
"progressive_resizing/width": new_input.shape[3],
"progressive_resizing/scale_factor": scale_factor
})
def _make_crop(tensor: torch.Tensor, scale_factor: float) -> T_ResizeTransform:
"""Makes a random crop transform for an input image."""
Hc = int(scale_factor * tensor.shape[2])
Wc = int(scale_factor * tensor.shape[3])
top = torch.randint(tensor.shape[2] - Hc, size=(1,))
left = torch.randint(tensor.shape[3] - Wc, size=(1,))
resize_transform = partial(torchvision.transforms.functional.crop,
top=int(top),
left=int(left),
height=Hc,
width=Wc)
return resize_transform
def _make_crop_pair(X: torch.Tensor, y: torch.Tensor,
scale_factor: float) -> Tuple[T_ResizeTransform, T_ResizeTransform]:
"""Makes a pair of random crops for an input image X and target tensor y such that the same region is selected from
both."""
# New height and width for X
HcX = int(scale_factor * X.shape[2])
WcX = int(scale_factor * X.shape[3])
# New height and width for y
Hcy = int(scale_factor * y.shape[2])
Wcy = int(scale_factor * y.shape[3])
# Select a corner for the crop from X
topX = torch.randint(X.shape[2] - HcX, size=(1,))
leftX = torch.randint(X.shape[3] - WcX, size=(1,))
# Find the corresponding point for X
height_ratio = y.shape[2] / X.shape[2]
width_ratio = y.shape[3] / X.shape[3]
topy = int(height_ratio * topX)
lefty = int(width_ratio * leftX)
# Make the two transforms
resize_X = partial(torchvision.transforms.functional.crop, top=int(topX), left=int(leftX), height=HcX, width=WcX)
resize_y = partial(torchvision.transforms.functional.crop, top=topy, left=lefty, height=Hcy, width=Wcy)
return resize_X, resize_y
def _make_resize(scale_factor: float) -> T_ResizeTransform:
"""Makes a nearest-neighbor interpolation transform at the specified scale factor."""
resize_transform = partial(F.interpolate, scale_factor=scale_factor, mode='nearest')
return resize_transform