Loss.py

from math import exp

import torch
import torch.nn as nn
import torch.nn.functional as F


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=1):
    _1D_window = gaussian(window_size, 1.5).unsqueeze(1)
    _2D_window = _1D_window.mm(_1D_window.t()).float().unsqueeze(0).unsqueeze(0)
    window = _2D_window.expand(channel, 1, window_size, window_size).contiguous()
    return window


def ssim(img1, img2, val_range, window_size=11, window=None, size_average=True, full=False):
    L = val_range

    padd = 0
    (_, channel, height, width) = img1.size()
    if window is None:
        real_size = min(window_size, height, width)
        window = create_window(real_size, channel=channel).to(img1.device)

    mu1 = F.conv2d(img1, window, padding=padd, groups=channel)
    mu2 = F.conv2d(img2, window, padding=padd, groups=channel)

    mu1_sq = mu1.pow(2)
    mu2_sq = mu2.pow(2)
    mu1_mu2 = mu1 * mu2

    sigma1_sq = F.conv2d(img1 * img1, window, padding=padd, groups=channel) - mu1_sq
    sigma2_sq = F.conv2d(img2 * img2, window, padding=padd, groups=channel) - mu2_sq
    sigma12 = F.conv2d(img1 * img2, window, padding=padd, groups=channel) - mu1_mu2

    C1 = (0.01 * L) ** 2
    C2 = (0.03 * L) ** 2

    v1 = 2.0 * sigma12 + C2
    v2 = sigma1_sq + sigma2_sq + C2
    cs = torch.mean(v1 / v2)  # contrast sensitivity

    ssim_map = ((2 * mu1_mu2 + C1) * v1) / ((mu1_sq + mu2_sq + C1) * v2)

    if size_average:
        ret = ssim_map.mean()
    else:
        ret = ssim_map.mean(1).mean(1).mean(1)

    if full:
        return ret, cs

    return ret


class MaskedMSELoss(nn.Module):
    def __init__(self):
        super(MaskedMSELoss, self).__init__()

    def forward(self, pred, target):
        assert pred.dim() == target.dim(), "inconsistent dimensions"
        valid_mask = (target > 0).detach()
        diff = target - pred
        diff = diff[valid_mask]
        self.loss = (diff ** 2).mean()
        return self.loss


class MaskedL1Loss(nn.Module):
    def __init__(self):
        super(MaskedL1Loss, self).__init__()

    def forward(self, pred, target):
        assert pred.dim() == target.dim(), "inconsistent dimensions"
        valid_mask = (target > 0).detach()
        diff = target - pred
        diff = diff[valid_mask]
        self.loss = diff.abs().mean()
        return self.loss