DCGAN

GAN的提出为使用神经网络进行图像生成打开了新世界的大门
而图像问题又与CNN有着很自然的关联
于是卷积与GAN的融合——DCGAN（Deep Convolution GAN）便诞生了

DCGAN是第一个将CNN应用于GAN取得成功的模型
它的主要特点是

  • 将判别器中的池化下采样改为带步长的卷积，将生成器中的上采样改为分数步长卷积，也即反卷积
  • 在模型中引入batchnorm（但生成器最后一层和判别器第一层不加入）
  • 移除了隐藏层的全连接层
  • 在生成器除最后一层外使用ReLU激活（原始GAN中使用了maxout）
  • 在判别器中使用LeakyReLU激活

Keras实现

代码中使用的是mnist数据集

此处代码中判别器没有用batchnorm，因为发现加了会造成判别器过强，进而导致collapse
可能是mnist数据集太简单造成的

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from keras.datasets import mnist
from keras.models import Model, Sequential
from keras.layers import Dense, Flatten, BatchNormalization, Reshape, Input, Activation, \
    Conv2D, Conv2DTranspose, Dropout
from keras.layers import LeakyReLU
from keras.optimizers import Adam
import numpy as np
import matplotlib.pyplot as plt

class DCGAN:
    def __init__(self):
        self.img_shape = (28, 28, 1)
        self.latent_dim = 100

        self.generator = self.buildGenerator()
        self.discriminator = self.buildDiscriminator()

        input = Input(shape=(self.latent_dim,))
        img = self.generator(input)

        # 在判别器compile之后设置trainable为False
        # 则使用train_on_batch时判别器仍可训练, 而训练生成器(GAN)时则判别器权重不变
        self.discriminator.trainable = False

        validity = self.discriminator(img)

        self.combined = Model(input, validity)
        self.combined.compile(loss='binary_crossentropy', optimizer=Adam(2e-4))

    def buildGenerator(self):
        model = Sequential()

        model.add(Dense(input_dim=self.latent_dim, units=7*7*256))
        model.add(BatchNormalization(momentum=0.8))
        model.add(Activation('relu'))

        model.add(Reshape((7, 7, 256)))

        model.add(Conv2DTranspose(filters=128, kernel_size=3, strides=2, padding='same'))
        model.add(BatchNormalization(momentum=0.8))
        model.add(Activation('relu'))

        model.add(Conv2DTranspose(filters=64, kernel_size=3, strides=2, padding='same'))
        model.add(BatchNormalization(momentum=0.8))
        model.add(Activation('relu'))

        model.add(Conv2DTranspose(filters=32, kernel_size=3, strides=1, padding='same'))
        model.add(BatchNormalization(momentum=0.8))
        model.add(Activation('relu'))

        model.add(Conv2DTranspose(filters=1, kernel_size=3, strides=1, padding='same'))
        model.add(Activation('tanh'))

        noise = Input(shape=(self.latent_dim,))
        img = model(noise)

        return Model(noise, img)

    def buildDiscriminator(self):
        model = Sequential()

        model.add(Conv2D(input_shape=self.img_shape, filters=64, kernel_size=3, strides=2, padding='same'))
        model.add(LeakyReLU(0.2))
        model.add(Dropout(0.4))

        model.add(Conv2D(filters=128, kernel_size=3, strides=2, padding='same'))
        model.add(LeakyReLU(0.2))
        model.add(Dropout(0.4))

        model.add(Conv2D(filters=256, kernel_size=3, strides=2, padding='same'))
        model.add(LeakyReLU(0.2))
        model.add(Dropout(0.4))

        model.add(Flatten())
        model.add(Dense(1, activation='sigmoid'))

        img = Input(shape=self.img_shape)
        validity = model(img)

        discriminator = Model(img, validity)
        discriminator.compile(optimizer=Adam(2e-4), loss='binary_crossentropy')

        return discriminator

    def trainModel(self, epochs, batch_size=64):
        (X_train, Y_train), (X_test, Y_test) = mnist.load_data()

        # Normalize [-1, 1]
        X_train = X_train / 127.5 - 1.
        X_train = np.expand_dims(X_train, axis=3)

        # 训练用的标签向量, valid为全1矩阵, fake为全0
        valid = np.ones((batch_size, 1))
        fake = np.zeros((batch_size, 1))

        for epoch in range(epochs):
            epoch += 1

            # 随机选取一个batch的图片 randint(low, high, num)
            idx = np.random.randint(0, X_train.shape[0], batch_size)
            orgImg = X_train[idx]

            # 生成标准正版态分布噪声作为输入
            noise = np.random.normal(0, 1, (batch_size, self.latent_dim))

            # generator以输入的随机噪声生成假图片
            genImg = self.generator.predict(noise)

            '''训练判别器D'''
            D_loss_real = self.discriminator.train_on_batch(orgImg, valid)
            D_loss_fake = self.discriminator.train_on_batch(genImg, fake)
            D_loss = 0.5 * np.add(D_loss_real, D_loss_fake)

            '''训练生成器G'''
            noise = np.random.normal(0, 1, (batch_size, self.latent_dim))
            G_loss = self.combined.train_on_batch(noise, valid)

            print("{} --- D loss: {:.4f} , G loss: {:.4f}".format(epoch, D_loss, G_loss))

            if epoch % 400 == 0:
                self.saveImage(epoch)

    def saveImage(self, epoch):
        r, c = 3, 3
        noise = np.random.normal(0, 1, (r * c, self.latent_dim))
        genImgs = self.generator.predict(noise)

        # Rescale images 0 - 1
        genImgs = 0.5 * genImgs + 0.5

        fig, axs = plt.subplots(r, c)
        cnt = 0
        for i in range(r):
            for j in range(c):
                axs[i, j].imshow(genImgs[cnt, :, :, 0], cmap='gray')
                axs[i, j].axis('off')
                cnt += 1
        fig.savefig('generated\\%d.png' % epoch)
        plt.close()

def main():
    gan = DCGAN()
    gan.trainModel(epochs=8000, batch_size=64)

if __name__ == '__main__':
    main()

Pytorch实现

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import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.optim import Adam
import torch.utils.data as Data
from torch.autograd import Variable
import torchvision
from torchvision import transforms
import numpy as np
import matplotlib.pyplot as plt

class Generator(nn.Module):
    def __init__(self, input_shape, output_shape):
        super().__init__()

        self.input_shape = input_shape
        self.output_shape = output_shape

        self.dense = nn.Sequential(
            nn.Linear(self.input_shape, 256 * 7 * 7),
            nn.BatchNorm1d(256 * 7 * 7, momentum=0.8),
        )

        self.conv1 = nn.Sequential(
            nn.ConvTranspose2d(256, 128, kernel_size=3, stride=2, padding=1, output_padding=1),
            nn.BatchNorm2d(128, momentum=0.8),
            nn.ReLU(),
        )

        self.conv2 = nn.Sequential(
            nn.ConvTranspose2d(128, 64, kernel_size=3, stride=2, padding=1, output_padding=1),
            nn.BatchNorm2d(64, momentum=0.8),
            nn.ReLU(),
        )

        self.conv3 = nn.Sequential(
            nn.ConvTranspose2d(64, 32, kernel_size=3, padding=1),
            nn.BatchNorm2d(32, momentum=0.8),
            nn.ReLU(),
        )

        self.conv4 = nn.Sequential(
            nn.ConvTranspose2d(32, 1, kernel_size=3, padding=1),
            nn.Sigmoid(),
        )

    def forward(self, tensor_input):
        x = self.dense(tensor_input)
        x = x.reshape(-1, 256, 7, 7)
        x = self.conv1(x)
        x = self.conv2(x)
        x = self.conv3(x)
        output = self.conv4(x)
        return output

class Discriminator(nn.Module):
    def __init__(self, input_shape):
        super().__init__()

        self.input_shape = input_shape

        self.conv1 = nn.Sequential(
            nn.Conv2d(self.input_shape[0], 64, kernel_size=3, stride=2, padding=1),
            nn.LeakyReLU(negative_slope=0.2),
            nn.Dropout2d(0.4),
        )

        self.conv2 = nn.Sequential(
            nn.Conv2d(64, 128, kernel_size=3, stride=2, padding=1),
            nn.LeakyReLU(negative_slope=0.2),
            nn.Dropout2d(0.4),
        )

        self.conv3 = nn.Sequential(
            nn.Conv2d(128, 256, kernel_size=3, stride=1, padding=1),
            nn.LeakyReLU(negative_slope=0.2),
            nn.Dropout2d(0.4),
        )

        self.dense = nn.Sequential(
            nn.Flatten(),
            nn.Linear(256 * 7 * 7, 1024),
            nn.LeakyReLU(negative_slope=0.2),
            nn.Linear(1024, 1),
            nn.Sigmoid(),
        )

    def forward(self, img):
        x = self.conv1(img)
        x = self.conv2(x)
        x = self.conv3(x)
        output = self.dense(x)

        return output

class DCGAN():
    def __init__(self):
        self.cuda_on = torch.cuda.is_available()

        self.input_shape = 100
        self.img_shape = (1, 28, 28)

        self.generator = Generator(self.input_shape, self.img_shape)
        self.discriminator = Discriminator(self.img_shape)

        self.optim_G = Adam(self.generator.parameters(), lr=2e-4)
        self.optim_D = Adam(self.discriminator.parameters(), lr=2e-4)
        self.loss_adver = nn.BCELoss()

        if self.cuda_on:
            self.generator.cuda()
            self.discriminator.cuda()
            self.loss_adver.cuda()

    def getDataloader(self, batch_size):
        mnist = torchvision.datasets.MNIST(
            root='./data/', train=True,
            transform=transforms.Compose([
                transforms.ToTensor(),
            ])
        )
        loader = Data.DataLoader(dataset=mnist, batch_size=batch_size, shuffle=True)
        return loader

    def train(self, epochs=1, batch_size=32):
        loader = self.getDataloader(batch_size)

        for epoch in range(epochs):
            for step, (img_real, _) in enumerate(loader):
                num = img_real.shape[0]

                valid = torch.ones((num, 1), dtype=torch.float32)
                fake = torch.zeros((num, 1), dtype=torch.float32)
                z = torch.randn(num, self.input_shape)

                if self.cuda_on:
                    valid = valid.cuda()
                    fake = fake.cuda()
                    z = z.cuda()
                    img_real = img_real.cuda()

                img_gen = self.generator(z)

                '''Train Discriminator'''
                D_loss_real = self.loss_adver(self.discriminator(img_real), valid)
                D_loss_fake = self.loss_adver(self.discriminator(img_gen), fake)
                D_loss = (D_loss_real + D_loss_fake) / 2

                self.optim_D.zero_grad()
                D_loss.backward(retain_graph=True)
                self.optim_D.step()

                '''Train Generator'''
                G_loss = self.loss_adver(self.discriminator(img_gen), valid)

                self.optim_G.zero_grad()
                G_loss.backward()
                self.optim_G.step()

                print('Epoch:', epoch+1, ' Step:', step, ' D_loss:', D_loss.item(), ' G_loss:', G_loss.item())

                if (step+1) % 400 == 0:
                    torchvision.utils.save_image(
                        img_gen.data[:9], 'gen\\{}_{}.png'.format(epoch, step), nrow=3)

if __name__ == '__main__':
    gan = DCGAN()
    gan.train(epochs=10, batch_size=64)