Pytorch 使用DCGAN生成MNIST手写数字 入门级教程

DCGAN的原理本文不再介绍，可以参考：DCGAN论文解读-----DCGAN原理简介与基础GAN的区别

之前发过一篇利用GAN生成手写数字的实战演示，具体参考：入门GAN实战---生成MNIST手写数据集代码实现pytorch

由于利用GAN生成的图像噪声较多，因此利用DCGAN再次完成该实验。两种方法区别不大，只是在定义生成器和鉴别器的时候稍有改动。具体演示如下：

1.加载MNIST手写数据集

    如果已经提前下载好MNIST手写数据集，记得把代码中的download改为False。具体MNIST数据集下载方法参考：深度学习入门--MNIST数据集及创建自己的手写数字数据集

# 加载数据
transform = transforms.Compose([transforms.ToTensor(),
                                transforms.Normalize(mean=0.5, std=0.5)])

train_ds = torchvision.datasets.MNIST('data/',
                                      train=True,
                                      transform=transform,
                                      download= True)
dataloader = torch.utils.data.DataLoader(train_ds, batch_size=64, shuffle=True)

2.定义生成器Generator

与基础GAN的生成器相比，利用了反卷积并添加了BN层

# 定义生成器
class Generator(nn.Module):
    def __init__(self):
        super(Generator,self).__init__()
        self.linear1 = nn.Linear(100, 256*7*7)  # 希望生成1*28*28的图片 7反卷积后14，再反卷积28 pytorch中channel在前
        self.bn1 = nn.BatchNorm1d(256*7*7)
        self.deconv1 = nn.ConvTranspose2d(256, 128,
                                          kernel_size=(3,3),
                                          stride=1,  
                                          padding=1 
                                          )   # 得到128*7*7的图像
        self.bn2 = nn.BatchNorm2d(128)
        self.deconv2 = nn.ConvTranspose2d(128, 64,
                                          kernel_size=(4,4),
                                          stride=2,
                                          padding=1  # 64*14*14
                                          )
        self.bn3 = nn.BatchNorm2d(64)
        self.deconv3 = nn.ConvTranspose2d(64, 1,
                                          kernel_size=(4, 4),
                                          stride=2,
                                          padding=1  # 1*28*28
                                          )
    def forward(self, x):
        x = F.relu(self.linear1(x))
        x = self.bn1(x)
        x = x.view(-1, 256, 7, 7)
        x = F.relu(self.deconv1(x))
        x = self.bn2(x)
        x = F.relu(self.deconv2(x))
        x = self.bn3(x)
        x = torch.tanh(self.deconv3(x))
        return x

3.定义鉴别器Discriminator

需要注意的是在生成器的输出层以及判别器的输入层不使用 BN

定义前向传播函数时，使用dropput是为了防止判别器随着训练判别能力越老越强，导致生成器损失过大

# 定义判别器
# input:1，28，28
class Discriminator(nn.Module):
    def __init__(self):
        super(Discriminator, self).__init__()
        self.conv1 = nn.Conv2d(1, 64, kernel_size=3, stride=2) # 第一层不适用bn  64，13，13
        self.conv2 = nn.Conv2d(64, 128, kernel_size=3, stride=2) #128，6，6
        self.bn = nn.BatchNorm2d(128)
        self.fc = nn.Linear(128*6*6, 1) # 输出一个概率值
    def forward(self, x):
        x = F.dropout2d(F.leaky_relu(self.conv1(x)))
        x = F.dropout2d(F.leaky_relu(self.conv2(x)))  # (batch, 128,6,6)
        x = self.bn(x)
        x = x.view(-1, 128*6*6)   # (batch, 128,6,6)--->  (batch, 128*6*6)
        x = torch.sigmoid(self.fc(x))
        return x

3.定义损失函数、训练过程与基础GAN的定义无差别

4.全部代码参考

import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim
import numpy as np
import matplotlib.pyplot as plt
import torchvision
from torchvision import transforms
# 加载数据
transform = transforms.Compose([transforms.ToTensor(),
                                transforms.Normalize(mean=0.5, std=0.5)])

train_ds = torchvision.datasets.MNIST('data/',
                                      train=True,
                                      transform=transform,
                                      download= True)
dataloader = torch.utils.data.DataLoader(train_ds, batch_size=64, shuffle=True)

# 定义生成器
class Generator(nn.Module):
    def __init__(self):
        super(Generator,self).__init__()
        self.linear1 = nn.Linear(100, 256*7*7) 
        self.bn1 = nn.BatchNorm1d(256*7*7)
        self.deconv1 = nn.ConvTranspose2d(256, 128,
                                          kernel_size=(3,3),
                                          stride=1,  
                                          padding=1  
                                          )   # 得到128*7*7的图像
        self.bn2 = nn.BatchNorm2d(128)
        self.deconv2 = nn.ConvTranspose2d(128, 64,
                                          kernel_size=(4,4),
                                          stride=2,
                                          padding=1  # 64*14*14
                                          )
        self.bn3 = nn.BatchNorm2d(64)
        self.deconv3 = nn.ConvTranspose2d(64, 1,
                                          kernel_size=(4, 4),
                                          stride=2,
                                          padding=1  # 1*28*28
                                          )
    def forward(self, x):
        x = F.relu(self.linear1(x))
        x = self.bn1(x)
        x = x.view(-1, 256, 7, 7)
        x = F.relu(self.deconv1(x))
        x = self.bn2(x)
        x = F.relu(self.deconv2(x))
        x = self.bn3(x)
        x = torch.tanh(self.deconv3(x))
        return x

# 定义判别器
# input:1，28，28
class Discriminator(nn.Module):
    def __init__(self):
        super(Discriminator, self).__init__()
        self.conv1 = nn.Conv2d(1, 64, kernel_size=3, stride=2) # 第一层不适用bn  64，13，13
        self.conv2 = nn.Conv2d(64, 128, kernel_size=3, stride=2) #128，6，6
        self.bn = nn.BatchNorm2d(128)
        self.fc = nn.Linear(128*6*6, 1) # 输出一个概率值
    def forward(self, x):
        x = F.dropout2d(F.leaky_relu(self.conv1(x)))
        x = F.dropout2d(F.leaky_relu(self.conv2(x)))  # (batch, 128,6,6)
        x = self.bn(x)
        x = x.view(-1, 128*6*6)   # (batch, 128,6,6)--->  (batch, 128*6*6)
        x = torch.sigmoid(self.fc(x))
        return x


# 初始化模型
device = 'cuda' if torch.cuda.is_available() else 'cpu'
gen = Generator().to(device)
dis = Discriminator().to(device)

# 损失计算函数
loss_function = torch.nn.BCELoss()

# 定义优化器
d_optim = torch.optim.Adam(dis.parameters(), lr=1e-5)
g_optim = torch.optim.Adam(gen.parameters(), lr=1e-4)

def generate_and_save_images(model, epoch, test_input):
    predictions = np.squeeze(model(test_input).cpu().numpy()) 
    fig = plt.figure(figsize=(4, 4))
    for i in range(predictions.shape[0]):
        plt.subplot(4, 4, i + 1)
        plt.imshow((predictions[i] + 1) / 2, cmap='gray')  
        plt.axis("off")
    
    plt.show()

test_input = torch.randn(16, 100, device=device)

# 开始训练
D_loss = []
G_loss = []
# 训练循环
for epoch in range(30):
    d_epoch_loss = 0
    g_epoch_loss = 0
    count = len(dataloader)
    # 对全部的数据集做一次迭代
    for step, (img, _) in enumerate(dataloader):
        img = img.to(device)  
        size = img.shape[0]    # 返回img的第一维的大小
        random_noise = torch.randn(size, 100, device=device)  

        d_optim.zero_grad()  # 将上述步骤的梯度归零
        real_output = dis(img)  # 对判别器输入真实的图片，real_output是对真实图片的预测结果
        d_real_loss = loss_function(real_output,
                                    torch.ones_like(real_output, device=device)
                                    )
        d_real_loss.backward() #求解梯度

        # 得到判别器在生成图像上的损失
        gen_img = gen(random_noise)
        fake_output = dis(gen_img.detach())  
        d_fake_loss = loss_function(fake_output,
                                    torch.zeros_like(fake_output, device=device))
        d_fake_loss.backward()

        d_loss = d_real_loss + d_fake_loss
        d_optim.step()  # 优化

        # 得到生成器的损失
        g_optim.zero_grad()
        fake_output = dis(gen_img)
        g_loss = loss_function(fake_output,
                               torch.ones_like(fake_output, device=device))
        g_loss.backward()
        g_optim.step()

        with torch.no_grad():
            d_epoch_loss += d_loss.item()  
            g_epoch_loss += g_loss.item()
    with torch.no_grad():
        d_epoch_loss /= count
        g_epoch_loss /= count
        D_loss.append(d_epoch_loss)
        G_loss.append(g_epoch_loss)
        generate_and_save_images(gen, epoch, test_input)
    print('Epoch:', epoch)
plt.plot(D_loss, label='D_loss')
plt.plot(G_loss, label='G_loss')
plt.legend()
plt.show()

5.训练结果展示