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# Copyright (c) 2023-2024, Zexin He
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import torch
import torch.nn as nn
__all__ = ['PixelLoss']
class PixelLoss(nn.Module):
"""
Pixel-wise loss between two images.
"""
def __init__(self, option: str = 'mse'):
super().__init__()
self.loss_fn = self._build_from_option(option)
@staticmethod
def _build_from_option(option: str, reduction: str = 'none'):
if option == 'mse':
return nn.MSELoss(reduction=reduction)
elif option == 'l1':
return nn.L1Loss(reduction=reduction)
else:
raise NotImplementedError(f'Unknown pixel loss option: {option}')
@torch.compile
def forward(self, x, y):
"""
Assume images are channel first.
Args:
x: [N, M, C, H, W]
y: [N, M, C, H, W]
Returns:
Mean-reduced pixel loss across batch.
"""
N, M, C, H, W = x.shape
x = x.reshape(N*M, C, H, W)
y = y.reshape(N*M, C, H, W)
image_loss = self.loss_fn(x, y).mean(dim=[1, 2, 3])
batch_loss = image_loss.reshape(N, M).mean(dim=1)
all_loss = batch_loss.mean()
return all_loss
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