models.py

from torch import nn
import torch
from torchvision import models
import torchvision
from torch.nn import functional as F


def conv3x3(in_, out):
    return nn.Conv2d(in_, out, 3, padding=1)


class ConvRelu(nn.Module):
    def __init__(self, in_: int, out: int):
        super(ConvRelu, self).__init__()
        self.conv = conv3x3(in_, out)
        self.activation = nn.ReLU(inplace=True)

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


class DecoderBlockLinkNet(nn.Module):
    def __init__(self, in_channels, n_filters):
        super().__init__()

        self.relu = nn.ReLU(inplace=True)

        # B, C, H, W -> B, C/4, H, W
        self.conv1 = nn.Conv2d(in_channels, in_channels // 4, 1)
        self.norm1 = nn.BatchNorm2d(in_channels // 4)

        # B, C/4, H, W -> B, C/4, 2 * H, 2 * W
        self.deconv2 = nn.ConvTranspose2d(in_channels // 4, in_channels // 4, kernel_size=4,
                                          stride=2, padding=1, output_padding=0)
        self.norm2 = nn.BatchNorm2d(in_channels // 4)

        # B, C/4, H, W -> B, C, H, W
        self.conv3 = nn.Conv2d(in_channels // 4, n_filters, 1)
        self.norm3 = nn.BatchNorm2d(n_filters)

    def forward(self, x):
        x = self.conv1(x)
        x = self.norm1(x)
        x = self.relu(x)
        x = self.deconv2(x)
        x = self.norm2(x)
        x = self.relu(x)
        x = self.conv3(x)
        x = self.norm3(x)
        x = self.relu(x)
        return x

class LinkNet34(nn.Module):
    def __init__(self, num_classes=1, num_channels=3, pretrained=True):
        super().__init__()
        assert num_channels == 3
        self.num_classes = num_classes
        filters = [64, 128, 256, 512]
        resnet = models.resnet34(pretrained=pretrained)

        self.firstconv = resnet.conv1
        self.firstbn = resnet.bn1
        self.firstrelu = resnet.relu
        self.firstmaxpool = resnet.maxpool
        self.encoder1 = resnet.layer1
        self.encoder2 = resnet.layer2
        self.encoder3 = resnet.layer3
        self.encoder4 = resnet.layer4

        # Decoder
        self.decoder4 = DecoderBlockLinkNet(filters[3], filters[2])
        self.decoder3 = DecoderBlockLinkNet(filters[2], filters[1])
        self.decoder2 = DecoderBlockLinkNet(filters[1], filters[0])
        self.decoder1 = DecoderBlockLinkNet(filters[0], filters[0])

        # Final Classifier
        self.finaldeconv1 = nn.ConvTranspose2d(filters[0], 32, 3, stride=2)
        self.finalrelu1 = nn.ReLU(inplace=True)
        self.finalconv2 = nn.Conv2d(32, 32, 3)
        self.finalrelu2 = nn.ReLU(inplace=True)
        self.finalconv3 = nn.Conv2d(32, num_classes, 2, padding=1)

    # noinspection PyCallingNonCallable
    def forward(self, x):
        # Encoder
        x = self.firstconv(x)
        x = self.firstbn(x)
        x = self.firstrelu(x)
        x = self.firstmaxpool(x)
        e1 = self.encoder1(x)
        e2 = self.encoder2(e1)
        e3 = self.encoder3(e2)
        e4 = self.encoder4(e3)

        # Decoder with Skip Connections
        d4 = self.decoder4(e4) + e3
        d3 = self.decoder3(d4) + e2
        d2 = self.decoder2(d3) + e1
        d1 = self.decoder1(d2)

        # Final Classification
        f1 = self.finaldeconv1(d1)
        f2 = self.finalrelu1(f1)
        f3 = self.finalconv2(f2)
        f4 = self.finalrelu2(f3)
        f5 = self.finalconv3(f4)

        if self.num_classes > 1:
            x_out = F.log_softmax(f5, dim=1)
        else:
            x_out = f5
        return x_out