【图像合成】基于DCGAN典型网络的MNIST字符生成（pytorch）

关于

近年来，基于卷积网络（CNN）的监督学习已经在计算机视觉应用中得到了广泛的采用。相比之下，无监督使用 CNN 进行学习受到的关注较少。在这项工作中，我们希望能有所帮助缩小了 CNN 在监督学习和无监督学习方面的成功之间的差距。我们介绍一类称为深度卷积生成的 CNN 对抗性网络（DCGAN），具有一定的架构限制，以及证明他们是无监督学习的有力候选人。训练在各种图像数据集上，我们展示了令人信服的证据，表明我们的深度卷积对抗对学习了从对象部分到生成器和鉴别器中的场景。此外，我们使用学到的新任务的特征 - 证明它们作为一般图像表示的适用性。（https://arxiv.org/pdf/1511.06434.pdf）

工具

数据集

方法实现

加载必要的库函数和自定义函数

python 复制代码

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


from torch.utils.data import DataLoader
from torchvision import datasets
from torchvision import transforms
from torchvision.utils import save_image

python 复制代码

def get_sample_image(G, n_noise):
    """
        save sample 100 images
    """
    z = torch.randn(100, n_noise).to(DEVICE)
    y_hat = G(z).view(100, 28, 28) # (100, 28, 28)
    result = y_hat.cpu().data.numpy()
    img = np.zeros([280, 280])
    for j in range(10):
        img[j*28:(j+1)*28] = np.concatenate([x for x in result[j*10:(j+1)*10]], axis=-1)
    return img

定义判别模型

python 复制代码

class Discriminator(nn.Module):
    """
        Convolutional Discriminator for MNIST
    """
    def __init__(self, in_channel=1, num_classes=1):
        super(Discriminator, self).__init__()
        self.conv = nn.Sequential(
            # 28 -> 14
            nn.Conv2d(in_channel, 512, 3, stride=2, padding=1, bias=False),
            nn.BatchNorm2d(512),
            nn.LeakyReLU(0.2),
            # 14 -> 7
            nn.Conv2d(512, 256, 3, stride=2, padding=1, bias=False),
            nn.BatchNorm2d(256),
            nn.LeakyReLU(0.2),
            # 7 -> 4
            nn.Conv2d(256, 128, 3, stride=2, padding=1, bias=False),
            nn.BatchNorm2d(128),
            nn.LeakyReLU(0.2),
            nn.AvgPool2d(4),
        )
        self.fc = nn.Sequential(
            # reshape input, 128 -> 1
            nn.Linear(128, 1),
            nn.Sigmoid(),
        )
    
    def forward(self, x, y=None):
        y_ = self.conv(x)
        y_ = y_.view(y_.size(0), -1)
        y_ = self.fc(y_)
        return y_

定义生成模型

python 复制代码

class Generator(nn.Module):
    """
        Convolutional Generator for MNIST
    """
    def __init__(self, input_size=100, num_classes=784):
        super(Generator, self).__init__()
        self.fc = nn.Sequential(
            nn.Linear(input_size, 4*4*512),
            nn.ReLU(),
        )
        self.conv = nn.Sequential(
            # input: 4 by 4, output: 7 by 7
            nn.ConvTranspose2d(512, 256, 3, stride=2, padding=1, bias=False),
            nn.BatchNorm2d(256),
            nn.ReLU(),
            # input: 7 by 7, output: 14 by 14
            nn.ConvTranspose2d(256, 128, 4, stride=2, padding=1, bias=False),
            nn.BatchNorm2d(128),
            nn.ReLU(),
            # input: 14 by 14, output: 28 by 28
            nn.ConvTranspose2d(128, 1, 4, stride=2, padding=1, bias=False),
            nn.Tanh(),
        )
        
    def forward(self, x, y=None):
        x = x.view(x.size(0), -1)
        y_ = self.fc(x)
        y_ = y_.view(y_.size(0), 512, 4, 4)
        y_ = self.conv(y_)
        return y_

模型超参数定义配置

python 复制代码

batch_size = 64

criterion = nn.BCELoss()
D_opt = torch.optim.Adam(D.parameters(), lr=0.001, betas=(0.5, 0.999))
G_opt = torch.optim.Adam(G.parameters(), lr=0.001, betas=(0.5, 0.999))

max_epoch = 30 # need more than 20 epochs for training generator
step = 0
n_critic = 1 # for training more k steps about Discriminator
n_noise = 100

D_labels = torch.ones([batch_size, 1]).to(DEVICE) # Discriminator Label to real
D_fakes = torch.zeros([batch_size, 1]).to(DEVICE) # Discriminator Label to fake

模型训练

python 复制代码

for epoch in range(max_epoch):
    for idx, (images, labels) in enumerate(data_loader):
        # Training Discriminator
        x = images.to(DEVICE)
        x_outputs = D(x)
        D_x_loss = criterion(x_outputs, D_labels)

        z = torch.randn(batch_size, n_noise).to(DEVICE)
        z_outputs = D(G(z))
        D_z_loss = criterion(z_outputs, D_fakes)
        D_loss = D_x_loss + D_z_loss
        
        D.zero_grad()
        D_loss.backward()
        D_opt.step()

        if step % n_critic == 0:
            # Training Generator
            z = torch.randn(batch_size, n_noise).to(DEVICE)
            z_outputs = D(G(z))
            G_loss = criterion(z_outputs, D_labels)

            D.zero_grad()
            G.zero_grad()
            G_loss.backward()
            G_opt.step()
        
        if step % 500 == 0:
            print('Epoch: {}/{}, Step: {}, D Loss: {}, G Loss: {}'.format(epoch, max_epoch, step, D_loss.item(), G_loss.item()))
        
        if step % 1000 == 0:
            G.eval()
            img = get_sample_image(G, n_noise)
            imsave('./{}_step{}.jpg'.format(MODEL_NAME, str(step).zfill(3)), img, cmap='gray')
            G.train()
        step += 1

测试生成效果

python 复制代码

# generation to image
G.eval()
imshow(get_sample_image(G, n_noise), cmap='gray')

模型和状态参量保存

python 复制代码

def save_checkpoint(state, file_name='checkpoint.pth.tar'):
    torch.save(state, file_name)


# Saving params.
# torch.save(D.state_dict(), 'D_c.pkl')
# torch.save(G.state_dict(), 'G_c.pkl')
save_checkpoint({'epoch': epoch + 1, 'state_dict':D.state_dict(), 'optimizer' : D_opt.state_dict()}, 'D_dc.pth.tar')
save_checkpoint({'epoch': epoch + 1, 'state_dict':G.state_dict(), 'optimizer' : G_opt.state_dict()}, 'G_dc.pth.tar')

应用

DCGAN作为一个成熟的生成模型，在自然图像，医学图像，医学电生理信号数据分析中，都可以用来实现数据的合成，达到数据增强的目的，同时，如何减少增强数据对于后端任务的不利干扰，也是一个需要关注的方面。