本文共 6884 字,大约阅读时间需要 22 分钟。
上期我们介绍了
同样地,我们依旧通过实验来巩固我们刚刚所学的知识点。本次实验是基于Jupyer Notebook、Anaconda Python3.7与Keras环境。数据集是利用Minst手写体图像数据集。
1. # chapter5/5_3_GAN.ipynb2. import random 3. import numpy as np 4. from keras.layers import Input 5. from keras.layers.core import Reshape,Dense,Dropout,Activation,Flatten 6. from keras.layers.advanced_activations import LeakyReLU 7. from keras.layers.convolutional import Convolution2D, MaxPooling2D, ZeroPadding2D, Deconv2D, UpSampling2D 8. from keras.regularizers import * 9. from keras.layers.normalization import * 10. from keras.optimizers import * 11. from keras.datasets import mnist 12. import matplotlib.pyplot as plt 13. from keras.models import Model 14. from tqdm import tqdm 15. from IPython import display
1. 读取数据集
1. img_rows, img_cols = 28, 28 2. 3. # 数据集的切分与混洗(shuffle) 4. (X_train, y_train), (X_test, y_test) = mnist.load_data() 5. 6. X_train = X_train.reshape(X_train.shape[0], 1, img_rows, img_cols) 7. X_test = X_test.reshape(X_test.shape[0], 1, img_rows, img_cols) 8. X_train = X_train.astype('float32') 9. X_test = X_test.astype('float32') 10. X_train /= 255 11. X_test /= 255 12. 13. print(np.min(X_train), np.max(X_train)) 14. print('X_train shape:', X_train.shape) 15. print(X_train.shape[0], 'train samples') 16. print(X_test.shape[0], 'test samples')
0.0 1.0
X_train shape: (60000, 1, 28,28)
60000 train samples
10000 test samples
2. 超参数设置
1. shp = X_train.shape[1:] 2. dropout_rate = 0.25 3. 4. # 优化器 5. opt = Adam(lr=1e-4) 6. dopt = Adam(lr=1e-5)
3. 定义生成器
1. # 辨别是否来自真实训练集 2. d_input = Input(shape=shp) 3. H = Convolution2D(256, (5, 5), activation="relu", strides=(2, 2), padding="same")(d_input) 4. H = LeakyReLU(0.2)(H) 5. H = Dropout(dropout_rate)(H) 6. H = Convolution2D(512, (5, 5), activation="relu", strides=(2, 2), padding="same")(H) 7. H = LeakyReLU(0.2)(H) 8. H = Dropout(dropout_rate)(H) 9. H = Flatten()(H) 10. H = Dense(256)(H) 11. H = LeakyReLU(0.2)(H) 12. H = Dropout(dropout_rate)(H) 13. d_V = Dense(2,activation='softmax')(H) 14. discriminator = Model(d_input,d_V) 15. discriminator.compile(loss='categorical_crossentropy', optimizer=dopt) 16. discriminator.summary()
4. 定义辨别器
1. # 辨别是否来自真实训练集 2. d_input = Input(shape=shp) 3. H = Convolution2D(256, (5, 5), activation="relu", strides=(2, 2), padding="same")(d_input) 4. H = LeakyReLU(0.2)(H) 5. H = Dropout(dropout_rate)(H) 6. H = Convolution2D(512, (5, 5), activation="relu", strides=(2, 2), padding="same")(H) 7. H = LeakyReLU(0.2)(H) 8. H = Dropout(dropout_rate)(H) 9. H = Flatten()(H) 10. H = Dense(256)(H) 11. H = LeakyReLU(0.2)(H) 12. H = Dropout(dropout_rate)(H) 13. d_V = Dense(2,activation='softmax')(H) 14. discriminator = Model(d_input,d_V) 15. discriminator.compile(loss='categorical_crossentropy', optimizer=dopt) 16. discriminator.summary()
5. 构造生成对抗网络
1. # 冷冻训练层 2. def make_trainable(net, val): 3. net.trainable = val 4. for l in net.layers: 5. l.trainable = val 6. make_trainable(discriminator, False) 7. 8. # 构造GAN 9. gan_input = Input(shape=[100]) 10. H = generator(gan_input) 11. gan_V = discriminator(H) 12. GAN = Model(gan_input, gan_V) 13. GAN.compile(loss='categorical_crossentropy', optimizer=opt) 14. GAN.summary()
6. 训练
1. # 描绘损失收敛过程 2. def plot_loss(losses): 3. display.clear_output(wait=True) 4. display.display(plt.gcf()) 5. plt.figure(figsize=(10,8)) 6. plt.plot(losses["d"], label='discriminitive loss') 7. plt.plot(losses["g"], label='generative loss') 8. plt.legend() 9. plt.show() 10. 11. 12. # 描绘生成器生成图像 13. def plot_gen(n_ex=16,dim=(4,4), figsize=(10,10) ): 14. noise = np.random.uniform(0,1,size=[n_ex,100]) 15. generated_images = generator.predict(noise) 16. 17. plt.figure(figsize=figsize) 18. for i in range(generated_images.shape[0]): 19. plt.subplot(dim[0],dim[1],i+1) 20. img = generated_images[i,0,:,:] 21. plt.imshow(img) 22. plt.axis('off') 23. plt.tight_layout() 24. plt.show() 25. 26. # 抽取训练集样本 27. ntrain = 10000 28. trainidx = random.sample(range(0,X_train.shape[0]), ntrain) 29. XT = X_train[trainidx,:,:,:] 30. 31. # 预训练辨别器 32. noise_gen = np.random.uniform(0,1,size=[XT.shape[0],100]) 33. generated_images = generator.predict(noise_gen) # 生成器产生样本 34. X = np.concatenate((XT, generated_images)) 35. n = XT.shape[0] 36. y = np.zeros([2*n,2]) # 构造辨别器标签 one-hot encode 37. y[:n,1] = 1 38. y[n:,0] = 1 39. 40. make_trainable(discriminator,True) 41. discriminator.fit(X,y, epochs=1, batch_size=32) 42. y_hat = discriminator.predict(X)
1. # 计算辨别器的准确率 2. y_hat_idx = np.argmax(y_hat,axis=1) 3. y_idx = np.argmax(y,axis=1) 4. diff = y_idx-y_hat_idx 5. n_total = y.shape[0] 6. n_right = (diff==0).sum() 7. 8. print( "(%d of %d) right" % (n_right, n_total))
1. def train_for_n(nb_epoch=5000, plt_frq=25,BATCH_SIZE=32): 2. for e in tqdm(range(nb_epoch)): 3. 4. # 生成器生成样本 5. image_batch = X_train[np.random.randint(0,X_train.shape[0],size=BATCH_SIZE),:,:,:] 6. noise_gen = np.random.uniform(0,1,size=[BATCH_SIZE,100]) 7. generated_images = generator.predict(noise_gen) 8. 9. # 训练辨别器 10. X = np.concatenate((image_batch, generated_images)) 11. y = np.zeros([2*BATCH_SIZE,2]) 12. y[0:BATCH_SIZE,1] = 1 13. y[BATCH_SIZE:,0] = 1 14. 15. # 存储辨别器损失loss 16. make_trainable(discriminator,True) 17. d_loss = discriminator.train_on_batch(X,y) 18. losses["d"].append(d_loss) 19. 20. # 生成器生成样本 21. noise_tr = np.random.uniform(0,1,size=[BATCH_SIZE,100]) 22. y2 = np.zeros([BATCH_SIZE,2]) 23. y2[:,1] = 1 24. 25. # 存储生成器损失loss 26. make_trainable(discriminator,False) # 辨别器的训练关掉 27. g_loss = GAN.train_on_batch(noise_tr, y2) 28. losses["g"].append(g_loss) 29. 30. # 更新损失loss图 31. if e%plt_frq == plt_frq-1: 32. plot_loss(losses) 33. plot_gen() 34. train_for_n(nb_epoch=1000, plt_frq=10,BATCH_SIZE=128)
从模型输出的loss我们可以知道生成器与辨别器两者拟合的loss并不是特别地好,因此我们可以通过调参来解决。主要调参方向有以下四点:
1. batch size
2. adam优化器的learning rate
3. 迭代次数nb_epoch
4. 生成器generator和辨别器discriminator的网络结构
好了,到这里,我们就已经将生成对抗网络(GAN)的知识点讲完了。大家在掌握了整个流程之后,就可以将笔者的代码修改成自己所需要的场景,进而训练自己的GAN模型了。
最后,笔者在本章介绍的GAN只是2014年的开山之作,后面有很多人基于GAN提出了许多有趣的实验,但是所用的网络原理都差不多,这里就不一一赘述了。而且GAN的应用范围非常广阔,比如市面上很火的“换脸”软件,大多都是基于GAN的原理去做的。甚至我们也可以利用GAN去做数据增强,比如在我们缺少训练集的时候,可以考虑用GAN去生成一些数据,扩充我们的训练样本。
下一期,我们将讲授
李宏毅老师的无监督学习讲座的PPT总结
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