ResNet也是相当经典的卷积神经网络，这里实现了18，34，50，101和152。
网络结构如下：
这里18和34用到的block是一样的，两层卷积。50，101和152用到的block是一样的，三层卷积，不过用到了1*1卷积来调整数据通道数。
猫狗大战的训练代码如下:
import torch import torch.nn as nn import torch.optim as optim from torch.utils.data import Dataset, DataLoader from PIL import Image import torchvision.transforms as transforms class BasicBlock(nn.Module): expansion = 1 def __init__(self, in_channels, out_channels, stride=1, downsample=None): super(BasicBlock, self).__init__() self.conv1 = nn.Conv2d(in_channels, out_channels, kernel_size=3, stride=stride, padding=1, bias=False) self.bn1 = nn.BatchNorm2d(out_channels) self.relu = nn.ReLU(inplace=True) self.conv2 = nn.Conv2d(out_channels, out_channels, kernel_size=3, stride=1, padding=1, bias=False) self.bn2 = nn.BatchNorm2d(out_channels) self.downsample = downsample def forward(self, x): identity = x out = self.conv1(x) out = self.bn1(out) out = self.relu(out) out = self.conv2(out) out = self.bn2(out) if self.downsample is not None: identity = self.downsample(x) out += identity out = self.relu(out) return out class Bottleneck(nn.Module): expansion = 4 def __init__(self, in_channels, out_channels, stride=1, downsample=None): super(Bottleneck, self).__init__() self.conv1 = nn.Conv2d(in_channels, out_channels, kernel_size=1, bias=False) self.bn1 = nn.BatchNorm2d(out_channels) self.conv2 = nn.Conv2d(out_channels, out_channels, kernel_size=3, stride=stride, padding=1, bias=False) self.bn2 = nn.BatchNorm2d(out_channels) self.conv3 = nn.Conv2d(out_channels, out_channels * self.expansion, kernel_size=1, bias=False) self.bn3 = nn.BatchNorm2d(out_channels * self.expansion) self.relu = nn.ReLU(inplace=True) self.downsample = downsample def forward(self, x): identity = x out = self.conv1(x) out = self.bn1(out) out = self.relu(out) out = self.conv2(out) out = self.bn2(out) out = self.relu(out) out = self.conv3(out) out = self.bn3(out) if self.downsample is not None: identity = self.downsample(x) out += identity out = self.relu(out) return out class ResNet(nn.Module): def __init__(self, block, layers, num_classes=1000): super(ResNet, self).__init__() self.in_channels = 64 self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3, bias=False) self.bn1 = nn.BatchNorm2d(64) self.relu = nn.ReLU(inplace=True) self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1) self.layer1 = self._make_layer(block, 64, layers[0]) self.layer2 = self._make_layer(block, 128, layers[1], stride=2) self.layer3 = self._make_layer(block, 256, layers[2], stride=2) self.layer4 = self._make_layer(block, 512, layers[3], stride=2) self.avgpool = nn.AdaptiveAvgPool2d((1, 1)) self.fc = nn.Linear(512 * block.expansion, num_classes) def _make_layer(self, block, out_channels, blocks, stride=1): downsample = None if stride != 1 or self.in_channels != out_channels * block.expansion: downsample = nn.Sequential( nn.Conv2d(self.in_channels, out_channels * block.expansion, kernel_size=1, stride=stride, bias=False), nn.BatchNorm2d(out_channels * block.expansion), ) layers = [] layers.append(block(self.in_channels, out_channels, stride=stride, downsample=downsample)) self.in_channels = out_channels * block.expansion for _ in range(1, blocks): layers.append(block(self.in_channels, out_channels)) return nn.Sequential(*layers) def forward(self, x): x = self.conv1(x) x = self.bn1(x) x = self.relu(x) x = self.maxpool(x) x = self.layer1(x) x = self.layer2(x) x = self.layer3(x) x = self.layer4(x) x = self.avgpool(x) x = torch.flatten(x, 1) x = self.fc(x) return x def resnet18(num_classes=1000): return ResNet(BasicBlock, [2, 2, 2, 2], num_classes) def resnet34(num_classes=1000): return ResNet(BasicBlock, [3, 4, 6, 3], num_classes) def resnet50(num_classes=1000): return ResNet(Bottleneck, [3, 4, 6, 3], num_classes) def resnet101(num_classes=1000): return ResNet(Bottleneck, [3, 4, 23, 3], num_classes) def resnet152(num_classes=1000): return ResNet(Bottleneck, [3, 8, 36, 3], num_classes) # 自定义数据集类 class CustomDataset(Dataset): def __init__(self, image_folder, transform=None): self.image_folder = image_folder self.transform = transform def __len__(self): return 20000 def __getitem__(self, index): image_name = str(index+1)+".jpg" image = Image.open(self.image_folder + '/' + image_name).convert('RGB') image = self.transform(image) if index < 10000: return image, 0 # cat else: return image, 1 # dog num_epochs = 10 # 创建ResNet模型和优化器 model = resnet50(num_classes=2) optimizer = optim.Adam(model.parameters(), lr=0.001) criterion = nn.CrossEntropyLoss() # 定义训练和测试数据集的转换方式 transform = transforms.Compose([ transforms.Resize((224, 224)), transforms.ToTensor(), transforms.Normalize(mean=[0.5, 0.5, 0.5], std=[0.5, 0.5, 0.5]) ]) # 加载数据集并进行训练 train_dataset = CustomDataset('./cat_vs_dog/train2', transform) train_loader = DataLoader(train_dataset, batch_size=64, shuffle=True) device = torch.device("cuda" if torch.cuda.is_available() else "cpu") model.to(device) for epoch in range(num_epochs): model.train() running_loss = 0.0 correct = 0 total = 0 for images, labels in train_loader: images = images.to(device) labels = labels.to(device) # 前向传播 outputs = model(images) loss = criterion(outputs, labels) # 反向传播和优化 optimizer.zero_grad() loss.backward() optimizer.step() running_loss += loss.item() _, predicted = torch.max(outputs.data, 1) total += labels.size(0) correct += (predicted == labels).sum().item() print(f"Epoch [{epoch + 1}/{num_epochs}], Loss: {running_loss / len(train_loader):.4f}, Accuracy: {(100 * correct / total):.2f}%") print('Training finished.') # 保存模型 torch.save(model.state_dict(), 'resnet.pth')