LeNet-5

搭建模型

上图是LeNet-5的示意图。LeNet-5是最早的卷积神经网络之一，最初用于手写输入图像(单通道)分类。网络结构信息(不使用连接表)如下：

Pytorch实现：

import torch
import torch.nn as nn
import torch.nn.functional as F
class LeNet5(nn.Module):
    def __init__(self):
        super(LeNet5, self).__init__()
        self.conv1 = nn.Conv2d(1, 6, 5)
        self.pool = nn.MaxPool2d(2, 2)
        self.conv2 = nn.Conv2d(6, 16, 5)
        self.fc1 = nn.Linear(16 * 5 * 5, 120)
        self.fc2 = nn.Linear(120, 84)
        self.fc3 = nn.Linear(84, 10)

    def forward(self, x):
        x = self.pool(F.relu(self.conv1(x)))
        x = self.pool(F.relu(self.conv2(x)))
        x = x.view(-1, 16 * 5 * 5)
        x = F.relu(self.fc1(x))
        x = F.relu(self.fc2(x))
        x = self.fc3(x)
        return x

让我们实例化LeNet5，并输入一个样本。

net = LeNet5()
print(net)
input = torch.rand(1, 1, 32, 32)   # 代表一个32x32黑白图像样本
print('\nImage batch shape:')
print(input.shape)

output = net(input)
print('\nRaw output:')
print(output)
print(output.shape)

输出：

LeNet(
  (conv1): Conv2d(1, 6, kernel_size=(5, 5), stride=(1, 1))
  (pool): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  (conv2): Conv2d(6, 16, kernel_size=(5, 5), stride=(1, 1))
  (fc1): Linear(in_features=400, out_features=120, bias=True)
  (fc2): Linear(in_features=120, out_features=84, bias=True)
  (fc3): Linear(in_features=84, out_features=10, bias=True)
)

Image batch shape:
torch.Size([1, 1, 32, 32])

Raw output:
tensor([[-0.0358, -0.0731, -0.1067,  0.0200,  0.0267, -0.0497, -0.0783,  0.0410,
         -0.0123, -0.0634]], grad_fn=<AddmmBackward>)
torch.Size([1, 10])

LeNet-5 三通道图像分类

接下来，我们将使用LeNet-5对CIFAR10数据集进行分类。CIFAR10是32x32三通道图像的数据集，有10类图像：6种动物（鸟、猫、鹿、狗、青蛙、马）和4种车辆（飞机、汽车、轮船、卡车）。

对于三通道图像，需对C1做以下改动：

import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim
from torch.utils.data import DataLoader
from torchvision import datasets
import torchvision.transforms as transforms


class LeNet5(nn.Module):
    def __init__(self):
        super(LeNet5, self).__init__()
        self.conv1 = nn.Conv2d(3, 6, 5)
        self.pool = nn.MaxPool2d(2, 2)
        self.conv2 = nn.Conv2d(6, 16, 5)
        self.fc1 = nn.Linear(16 * 5 * 5, 120)
        self.fc2 = nn.Linear(120, 84)
        self.fc3 = nn.Linear(84, 10)

    def forward(self, x):
        x = self.pool(F.relu(self.conv1(x)))
        x = self.pool(F.relu(self.conv2(x)))
        x = x.view(-1, 16 * 5 * 5)
        x = F.relu(self.fc1(x))
        x = F.relu(self.fc2(x))
        x = self.fc3(x)
        return x


def train_loop(dataloader, model, loss_fn, optimizer, device):
    running_loss = 0.0
    for i, data in enumerate(dataloader, 0):
        # 获取输入
        inputs, labels = data
        inputs = inputs.to(device)
        labels = labels.to(device)
        # 计算预测值和损失
        outputs = model(inputs)
        loss = loss_fn(outputs, labels)

        # 反向传播优化
        optimizer.zero_grad()
        loss.backward()
        optimizer.step()

        running_loss += loss.item()
        if (i + 1) % 100 == 0:
            print('[Batch%4d] loss: %.3f' %
                  (i + 1, running_loss / 100))
            running_loss = 0.0


def test_loop(dataloader, model, device):
    correct = 0
    total = 0
    with torch.no_grad():
        for data in dataloader:
            images, labels = data
            images = images.to(device)
            labels = labels.to(device)
            outputs = model(images)
            _, predicted = torch.max(outputs.data, 1)
            total += labels.size(0)
            correct += (predicted == labels).sum().item()

    print('Accuracy of the network on the 10000 test images: %d %%' % (
            100 * correct / total))


if __name__ == '__main__':
    # 设备
    device = 'cuda' if torch.cuda.is_available() else 'cpu'
    print(device)
    # 数据集
    transform = transforms.Compose(
        [transforms.ToTensor(),
         transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))])  # 标准化图像数据

    trainset = datasets.CIFAR10(root='./cifar10_data', train=True,
                                download=True, transform=transform)
    # 使用num_workers个子进程进行数据加载
    trainloader = DataLoader(trainset, batch_size=32,
                             shuffle=True, num_workers=2)

    testset = datasets.CIFAR10(root='./cifar10_data', train=False,
                               download=True, transform=transform)
    testloader = DataLoader(testset, batch_size=32,
                            shuffle=False, num_workers=2)
    # 超参数
    lr = 0.001
    epochs = 10
    # 模型实例
    model = LeNet5().to(device)
    # 损失函数实例
    loss_fn = nn.CrossEntropyLoss()
    # 优化器实例
    optimizer = optim.Adam(model.parameters(), lr=lr)

    for t in range(epochs):
        print(f"Epoch {t + 1}\n-------------------------------")
        train_loop(trainloader, model, loss_fn, optimizer, device=device)
        test_loop(testloader, model, device=device)
    print("Done!")

[1] https://pytorch.org/tutorials/beginner/introyt/introyt1_tutorial.html