model.py

import torch
import torch.nn as nn
import torchvision.transforms.functional as TF

class DoubleConv(nn.Module):
    def __init__(self, in_channels, out_channels, dropout=False):
        super(DoubleConv, self).__init__()
        layers = [
            nn.Conv2d(in_channels, out_channels, kernel_size=3, stride=1, padding=1, bias=False),
            nn.BatchNorm2d(out_channels),
            nn.ReLU(inplace=True),
            nn.Conv2d(out_channels, out_channels, kernel_size=3, stride=1, padding=1, bias=False),
            nn.BatchNorm2d(out_channels),
            nn.ReLU(inplace=True),
        ]
        
        if dropout:
            layers.append(nn.Dropout(0.5))
        
        self.conv = nn.Sequential(*layers)

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

class UNET(nn.Module):
    def __init__(self, in_channels=3, out_channels=1, features=[64, 128, 256, 512]):
        super(UNET, self).__init__()
        self.ups = nn.ModuleList()
        self.downs = nn.ModuleList()
        self.pool = nn.MaxPool2d(kernel_size=2, stride=2)

        # Down part of UNET
        for feature in features:
            self.downs.append(DoubleConv(in_channels, feature, dropout=False))
            in_channels = feature

        # Up part of UNET
        for feature in reversed(features):
            self.ups.append(nn.ConvTranspose2d(feature * 2, feature, kernel_size=2, stride=2))
            self.ups.append(DoubleConv(feature * 2, feature, dropout=False))

        self.bottleneck = DoubleConv(features[-1], features[-1] * 2, dropout=False)
        self.final_conv = nn.Conv2d(features[0], out_channels, kernel_size=1)

    def forward(self, x):
        skip_connections = []

        for down in self.downs:
            x = down(x)
            skip_connections.append(x)
            x = self.pool(x)

        x = self.bottleneck(x)
        skip_connections = skip_connections[::-1]

        for idx in range(0, len(self.ups), 2):
            x = self.ups[idx](x)
            skip_connection = skip_connections[idx // 2]

            # Adjusting for size mismatch
            if x.size() != skip_connection.size():
                x = TF.resize(x, size=skip_connection.shape[2:])

            x = torch.cat((skip_connection, x), dim=1)
            x = self.ups[idx + 1](x)

        return self.final_conv(x)

def test():
    x = torch.randn((3, 1, 161, 161))
    model = UNET(in_channels=1, out_channels=1)
    preds = model(x)
    print(preds.shape)
    assert preds.shape == x.shape

if __name__ == "__main__":
    test()