model.py

import torch
import torch.nn as nn

class DownBlock(nn.Module):
    def __init__(self, in_filters, out_filters, normal=True):
        super().__init__()
        layers = [nn.Conv2d(in_filters, out_filters, kernel_size=4, stride=2, padding=1, padding_mode='reflect', bias=not normal)]
        if normal:
            layers.append(nn.InstanceNorm2d(out_filters, affine=True))
        layers.append(nn.LeakyReLU(0.2, inplace=True))
        self.block = nn.Sequential(*layers)
        
    def forward(self, x):
        return self.block(x)
    
class UpBlock(nn.Module):
    def __init__(self, in_filters, out_filters, dropout=0.0):
        super().__init__()
        layers = [
            nn.ConvTranspose2d(in_filters, out_filters, 4, 2, 1, bias=False),
            nn.InstanceNorm2d(out_filters, affine=True),
            nn.ReLU(inplace=True),
        ]
        if dropout:
            layers.append(nn.Dropout(dropout))
        self.model = nn.Sequential(*layers)
        
    def forward(self, x, skip_input):
        x = self.model(x)
        x = torch.cat((x, skip_input), 1)
        return x

class Generator(nn.Module):
    def __init__(self, input_channels, features=[64, 128, 256, 512, 512, 512, 512]):
        super().__init__()
        self.encoder = nn.ModuleList()
        self.decoder = nn.ModuleList()
        
        for idx, feature in enumerate(features):
            if idx == 0:
                self.encoder.append(DownBlock(input_channels, feature, normal=False))
            else:
                self.encoder.append(DownBlock(input_channels, feature))
            input_channels = feature
            
        self.bottleneck = DownBlock(512, 512, normal=False)
        self.final = nn.Sequential(
            nn.ConvTranspose2d(128, 3, 4, 2, 1),
            nn.Tanh()
        )
        
        input_channels = features[-1]
        for idx, feature in enumerate(reversed(features)):
            if idx == 0:
                self.decoder.append(UpBlock(input_channels, feature, dropout=0.5))
            elif idx < 3:
                self.decoder.append(UpBlock(input_channels*2, feature, dropout=0.5))
            else:
                self.decoder.append(UpBlock(input_channels*2, feature))
            input_channels = feature
            
    def forward(self, x):
        skips = []
        for layer in self.encoder:
            x = layer(x)
            skips.append(x)
        x = self.bottleneck(x)
        skips = skips[::-1]
        
        for idx, layer in enumerate(self.decoder):
            x = layer(x, skips[idx])
        x = self.final(x)
        return x