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# Copyright (c) 2023 Amphion.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
# This code is modified from https://github.com/Po-Hsun-Su/pytorch-ssim
import torch
import torch.nn.functional as F
from torch.autograd import Variable
from math import exp
def gaussian(window_size, sigma):
gauss = torch.Tensor(
[
exp(-((x - window_size // 2) ** 2) / float(2 * sigma**2))
for x in range(window_size)
]
)
return gauss / gauss.sum()
def create_window(window_size, channel):
_1D_window = gaussian(window_size, 1.5).unsqueeze(1)
_2D_window = _1D_window.mm(_1D_window.t()).float().unsqueeze(0).unsqueeze(0)
window = Variable(
_2D_window.expand(channel, 1, window_size, window_size).contiguous()
)
return window
def _ssim(img1, img2, window, window_size, channel, size_average=True):
mu1 = F.conv2d(img1, window, padding=window_size // 2, groups=channel)
mu2 = F.conv2d(img2, window, padding=window_size // 2, groups=channel)
mu1_sq = mu1.pow(2)
mu2_sq = mu2.pow(2)
mu1_mu2 = mu1 * mu2
sigma1_sq = (
F.conv2d(img1 * img1, window, padding=window_size // 2, groups=channel) - mu1_sq
)
sigma2_sq = (
F.conv2d(img2 * img2, window, padding=window_size // 2, groups=channel) - mu2_sq
)
sigma12 = (
F.conv2d(img1 * img2, window, padding=window_size // 2, groups=channel)
- mu1_mu2
)
C1 = 0.01**2
C2 = 0.03**2
ssim_map = ((2 * mu1_mu2 + C1) * (2 * sigma12 + C2)) / (
(mu1_sq + mu2_sq + C1) * (sigma1_sq + sigma2_sq + C2)
)
if size_average:
return ssim_map.mean()
else:
return ssim_map.mean(1)
class SSIM(torch.nn.Module):
def __init__(self, window_size=11, size_average=True):
super(SSIM, self).__init__()
self.window_size = window_size
self.size_average = size_average
self.channel = 1
self.window = create_window(window_size, self.channel)
def forward(self, fake, real, bias=6.0):
fake = fake[:, None, :, :] + bias # [B, 1, T, n_mels]
real = real[:, None, :, :] + bias # [B, 1, T, n_mels]
self.window = self.window.to(dtype=fake.dtype, device=fake.device)
loss = 1 - _ssim(
fake, real, self.window, self.window_size, self.channel, self.size_average
)
return loss
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