cyclegan.py

import torch
import torch.nn as nn


class ConvBlock(nn.Module):
    def __init__(self, in_channels, out_channels, down=True, use_act=True, **kwargs):
        super().__init__()
        self.conv = nn.Sequential(
            nn.Conv2d(in_channels, out_channels, padding_mode="reflect", **kwargs)
            if down
            else nn.ConvTranspose2d(in_channels, out_channels, **kwargs),
            nn.InstanceNorm2d(out_channels),
            nn.ReLU(inplace=True) if use_act else nn.Identity(),
        )

    def forward(self, x):
        return self.conv(x)


class ResidualBlock(nn.Module):
    def __init__(self, channels):
        super().__init__()
        self.block = nn.Sequential(
            ConvBlock(channels, channels, kernel_size=3, padding=1),
            ConvBlock(channels, channels, use_act=False, kernel_size=3, padding=1),
        )

    def forward(self, x):
        return x + self.block(x)


class Generator(nn.Module):
    def __init__(self, img_channels, num_features=64, num_residuals=9):
        super().__init__()
        self.initial = nn.Sequential(
            nn.Conv2d(
                img_channels,
                num_features,
                kernel_size=7,
                stride=1,
                padding=3,
                padding_mode="reflect",
            ),
            nn.InstanceNorm2d(num_features),
            nn.ReLU(inplace=True),
        )
        self.down_blocks = nn.ModuleList(
            [
                ConvBlock(
                    num_features, num_features * 2, kernel_size=3, stride=2, padding=1
                ),
                ConvBlock(
                    num_features * 2,
                    num_features * 4,
                    kernel_size=3,
                    stride=2,
                    padding=1,
                ),
            ]
        )
        self.res_blocks = nn.Sequential(
            *[ResidualBlock(num_features * 4) for _ in range(num_residuals)]
        )
        self.up_blocks = nn.ModuleList(
            [
                ConvBlock(
                    num_features * 4,
                    num_features * 2,
                    down=False,
                    kernel_size=3,
                    stride=2,
                    padding=1,
                    output_padding=1,
                ),
                ConvBlock(
                    num_features * 2,
                    num_features * 1,
                    down=False,
                    kernel_size=3,
                    stride=2,
                    padding=1,
                    output_padding=1,
                ),
            ]
        )

        self.last = nn.Conv2d(
            num_features * 1,
            img_channels,
            kernel_size=7,
            stride=1,
            padding=3,
            padding_mode="reflect",
        )

    def forward(self, x):
        x = self.initial(x)
        for layer in self.down_blocks:
            x = layer(x)
        x = self.res_blocks(x)
        for layer in self.up_blocks:
            x = layer(x)
        return torch.tanh(self.last(x))


class Block(nn.Module):
    def __init__(self, in_channels, out_channels, stride):
        super().__init__()
        self.conv = nn.Sequential(
            nn.Conv2d(
                in_channels,
                out_channels,
                4,
                stride,
                1,
                bias=True,
                padding_mode="reflect",
            ),
            nn.InstanceNorm2d(out_channels),
            nn.LeakyReLU(0.2, inplace=True),
        )

    def forward(self, x):
        return self.conv(x)


class Discriminator(nn.Module):
    def __init__(self, in_channels=3, features=[64, 128, 256, 512]):
        super().__init__()
        self.initial = nn.Sequential(
            nn.Conv2d(
                in_channels,
                features[0],
                kernel_size=4,
                stride=2,
                padding=1,
                padding_mode="reflect",
            ),
            nn.LeakyReLU(0.2, inplace=True),
        )

        layers = []
        in_channels = features[0]
        for feature in features[1:]:
            layers.append(
                Block(in_channels, feature, stride=1 if feature == features[-1] else 2)
            )
            in_channels = feature
        layers.append(
            nn.Conv2d(
                in_channels,
                1,
                kernel_size=4,
                stride=1,
                padding=1,
                padding_mode="reflect",
            )
        )
        self.model = nn.Sequential(*layers)

    def forward(self, x):
        x = self.initial(x)
        return torch.sigmoid(self.model(x))