pyramid_loss.py

#code from https://gist.github.com/alper111/b9c6d80e2dba1ee0bfac15eb7dad09c8
#by alper111
import torch
import torch.nn.functional as F


def gauss_kernel(size=5, device=torch.device('cpu'), channels=3):
    kernel = torch.tensor([[1., 4., 6., 4., 1],
                           [4., 16., 24., 16., 4.],
                           [6., 24., 36., 24., 6.],
                           [4., 16., 24., 16., 4.],
                           [1., 4., 6., 4., 1.]])
    kernel /= 256.
    kernel = kernel.repeat(channels, 1, 1, 1)
    kernel = kernel.to(device)
    return kernel


def downsample(x):
    return x[:, :, ::2, ::2]


def upsample(x):
    cc = torch.cat([x, torch.zeros(x.shape[0], x.shape[1], x.shape[2], x.shape[3], device=x.device)], dim=3)
    cc = cc.view(x.shape[0], x.shape[1], x.shape[2] * 2, x.shape[3])
    cc = cc.permute(0, 1, 3, 2)
    cc = torch.cat([cc, torch.zeros(x.shape[0], x.shape[1], x.shape[3], x.shape[2] * 2, device=x.device)], dim=3)
    cc = cc.view(x.shape[0], x.shape[1], x.shape[3] * 2, x.shape[2] * 2)
    x_up = cc.permute(0, 1, 3, 2)
    return conv_gauss(x_up, 4 * gauss_kernel(channels=x.shape[1], device=x.device))


def conv_gauss(img, kernel):
    img = F.pad(img, (2, 2, 2, 2), mode='reflect')
    out = F.conv2d(img, kernel, groups=img.shape[1])
    return out


def laplacian_pyramid(img, kernel, max_levels=3):
    current = img
    pyr = []
    for level in range(max_levels):
        filtered = conv_gauss(current, kernel)
        down = downsample(filtered)
        up = upsample(down)
        diff = current - up
        pyr.append(diff)
        current = down
    return pyr


class LapLoss(torch.nn.Module):
    def __init__(self, max_levels=3, channels=3, device=torch.device('cpu')):
        super(LapLoss, self).__init__()
        self.max_levels = max_levels
        self.gauss_kernel = gauss_kernel(channels=channels, device=device)

    def forward(self, inp, target):
        pyr_input = laplacian_pyramid(img=inp, kernel=self.gauss_kernel, max_levels=self.max_levels)
        pyr_target = laplacian_pyramid(img=target, kernel=self.gauss_kernel, max_levels=self.max_levels)
        return sum(F.l1_loss(a, b) for a, b in zip(pyr_input, pyr_target))