38、Auto-Encoder和Variational Auto-Encoder实战
作者：互联网
1、Auto-Encoder
降到自定义层
1 import os
2 import tensorflow as tf
3 import numpy as np
4 from tensorflow import keras
5 from tensorflow.keras import Sequential, layers
6 from PIL import Image
7 from matplotlib import pyplot as plt
8
9
10
11 tf.random.set_seed(22)
12 np.random.seed(22)
13 os.environ['TF_CPP_MIN_LOG_LEVEL'] = '2'
14 assert tf.__version__.startswith('2.')
15
16
17 def save_images(imgs, name): #将多张image保存为一张image
18 new_im = Image.new('L', (280, 280))
19
20 index = 0
21 for i in range(0, 280, 28):
22 for j in range(0, 280, 28):
23 im = imgs[index]
24 im = Image.fromarray(im, mode='L')
25 new_im.paste(im, (i, j))
26 index += 1
27
28 new_im.save(name)
29
30
31 h_dim = 20 #将原来的784维的数据降到20维数据，任意设定
32 batchsz = 512 #
33 lr = 1e-3 #学习率
34
35
36 (x_train, y_train), (x_test, y_test) = keras.datasets.fashion_mnist.load_data()
37 x_train, x_test = x_train.astype(np.float32) / 255., x_test.astype(np.float32) / 255.
38 # 不需要labels，所以不加载y
39 train_db = tf.data.Dataset.from_tensor_slices(x_train)
40 train_db = train_db.shuffle(batchsz * 5).batch(batchsz)
41 test_db = tf.data.Dataset.from_tensor_slices(x_test)
42 test_db = test_db.batch(batchsz)
43
44 print(x_train.shape, y_train.shape)
45 print(x_test.shape, y_test.shape)
46
47
48
49 class AE(keras.Model): #继承keras.Model
50
51 def __init__(self):
52 super(AE, self).__init__()
53
54 # Encoders 3层全连接层，输入维度为28x28，784
55 self.encoder = Sequential([
56 layers.Dense(256, activation=tf.nn.relu),
57 layers.Dense(128, activation=tf.nn.relu),
58 layers.Dense(h_dim) #降到自定义维度
59 ])
60
61 # Decoders 输入维度为h_dim，3个全连接层，升到高维
62 self.decoder = Sequential([
63 layers.Dense(128, activation=tf.nn.relu),
64 layers.Dense(256, activation=tf.nn.relu),
65 layers.Dense(784)
66 ])
67
68
69 def call(self, inputs, training=None): #前向传播过程
70 # [b, 784] => [b, 10] 降维
71 h = self.encoder(inputs)
72
73 # [b, 10] => [b, 784] 重建
74 x_hat = self.decoder(h)
75
76 return x_hat
77
78
79
80 model = AE() #创建模型
81 model.build(input_shape=(None, 784)) #这里要使用元组类型进行传入
82 model.summary()
83
84 optimizer = tf.optimizers.Adam(lr=lr) #优化器
85
86
87 for epoch in range(100):
88 for step, x in enumerate(train_db):
89
90 #先进行reshape，[b, 28, 28] => [b, 784]
91 x = tf.reshape(x, [-1, 784])
92
93 with tf.GradientTape() as tape: #梯度器，用来写要求梯度的函数
94 x_rec_logits = model(x)
95
96 rec_loss = tf.losses.binary_crossentropy(x, x_rec_logits, from_logits=True) #将图片的每一个点都当作一个分类问题
97 rec_loss = tf.reduce_mean(rec_loss) # 求均值
98
99 grads = tape.gradient(rec_loss, model.trainable_variables)
100 optimizer.apply_gradients(zip(grads, model.trainable_variables))
101
102
103 if step % 100 ==0:
104 print(epoch, step, float(rec_loss))
105
106
107 # evaluation 测试
108 x = next(iter(test_db))
109 logits = model(tf.reshape(x, [-1, 784]))
110 x_hat = tf.sigmoid(logits)
111 # [b, 784] => [b, 28, 28]
112 x_hat = tf.reshape(x_hat, [-1, 28, 28])
113
114 # [b, 28, 28] => [2b, 28, 28]
115 x_concat = tf.concat([x, x_hat], axis=0)
116 x_concat = x_hat
117 x_concat = x_concat.numpy() * 255.
118 x_concat = x_concat.astype(np.uint8)
119 save_images(x_concat, 'ae_images/rec_epoch_%d.png'%epoch)
2、Variational Auto-Encoder
h_dim一半是均值（小网络），一半是方差（小网络），解码器从h层进行采样。
从均值和方差进行sample采样时，loss对均值和方差是不可导的，所以将原来的均值和方差的分布变成均值加方差的分布。
1 import os
2 import tensorflow as tf
3 import numpy as np
4 from tensorflow import keras
5 from tensorflow.keras import Sequential, layers
6 from PIL import Image
7 from matplotlib import pyplot as plt
8
9
10 tf.random.set_seed(22)
11 np.random.seed(22)
12 os.environ['TF_CPP_MIN_LOG_LEVEL'] = '2'
13 assert tf.__version__.startswith('2.')
14
15
16 def save_images(imgs, name):
17 new_im = Image.new('L', (280, 280))
18
19 index = 0
20 for i in range(0, 280, 28):
21 for j in range(0, 280, 28):
22 im = imgs[index]
23 im = Image.fromarray(im, mode='L')
24 new_im.paste(im, (i, j))
25 index += 1
26
27 new_im.save(name)
28
29
30 h_dim = 20
31 batchsz = 512
32 lr = 1e-3
33
34
35 (x_train, y_train), (x_test, y_test) = keras.datasets.fashion_mnist.load_data()
36 x_train, x_test = x_train.astype(np.float32) / 255., x_test.astype(np.float32) / 255.
37 # we do not need label
38 train_db = tf.data.Dataset.from_tensor_slices(x_train)
39 train_db = train_db.shuffle(batchsz * 5).batch(batchsz)
40 test_db = tf.data.Dataset.from_tensor_slices(x_test)
41 test_db = test_db.batch(batchsz)
42
43 print(x_train.shape, y_train.shape)
44 print(x_test.shape, y_test.shape)
45
46 z_dim = 10
47
48 class VAE(keras.Model):
49
50 def __init__(self): #创建网络层
51 super(VAE, self).__init__() # 输入为784
52
53 # Encoder h_dim可以分为均值网络和方差方差
54 self.fc1 = layers.Dense(128) #h_dim的上一层
55 self.fc2 = layers.Dense(z_dim) # get mean prediction 分支结构，两个网络，得到均值 fc1->fc2
56 self.fc3 = layers.Dense(z_dim) # 得到方差 fc1->fc3
57
58 # Decoder
59 self.fc4 = layers.Dense(128)
60 self.fc5 = layers.Dense(784) #最后一层为784
61
62 def encoder(self, x):
63
64 h = tf.nn.relu(self.fc1(x))
65 # get mean
66 mu = self.fc2(h)
67 # get variance
68 log_var = self.fc3(h) #log方差，正无穷到负无穷
69
70 return mu, log_var
71
72 def decoder(self, z):
73
74 out = tf.nn.relu(self.fc4(z))
75 out = self.fc5(out)
76
77 return out
78
79 def reparameterize(self, mu, log_var): #从均值和方差进行sample采样时，loss对均值和方差是不可导的，所以将原来的均值和方差的分布变成均值加方差的分布。
80
81 eps = tf.random.normal(log_var.shape)
82
83 std = tf.exp(log_var*0.5)
84
85 z = mu + std * eps
86 return z
87
88 def call(self, inputs, training=None): # 网络层进行前向传播的过程
89
90 # [b, 784] => [b, z_dim], [b, z_dim] ，得到均值和方差的两个网络的logits
91 mu, log_var = self.encoder(inputs)
92 # reparameterization trick
93 z = self.reparameterize(mu, log_var)
94
95 x_hat = self.decoder(z)
96
97 return x_hat, mu, log_var
98
99
100 model = VAE()
101 model.build(input_shape=(4, 784))
102 optimizer = tf.optimizers.Adam(lr)
103
104 for epoch in range(1000):
105
106 for step, x in enumerate(train_db):
107
108 x = tf.reshape(x, [-1, 784])
109
110 with tf.GradientTape() as tape:
111 x_rec_logits, mu, log_var = model(x)
112
113 rec_loss = tf.nn.sigmoid_cross_entropy_with_logits(labels=x, logits=x_rec_logits)
114 rec_loss = tf.reduce_sum(rec_loss) / x.shape[0]
115
116 # compute kl divergence (mu, var) ~ N (0, 1) 计算KL散度 假设为正态分布
117 # https://stats.stackexchange.com/questions/7440/kl-divergence-between-two-univariate-gaussians
118 # KL(p,q)=logσ2σ1+σ21+(μ1−μ2)22σ22−12
119
120 kl_div = -0.5 * (log_var + 1 - mu**2 - tf.exp(log_var)) #两个正态分布的KL散度的计算
121 kl_div = tf.reduce_sum(kl_div) / x.shape[0] #求平均
122
123 loss = rec_loss + 1. * kl_div #重建误差加KL误差
124
125 grads = tape.gradient(loss, model.trainable_variables) #计算梯度
126 optimizer.apply_gradients(zip(grads, model.trainable_variables))
127
128
129 if step % 100 == 0:
130 print(epoch, step, 'kl div:', float(kl_div), 'rec loss:', float(rec_loss))
131
132
133 # evaluation
134 z = tf.random.normal((batchsz, z_dim))
135 logits = model.decoder(z) #随机给一个向量，因为解码器已经学习到了各个特征的分布，所以直接可以对新的图片进行生成
136 x_hat = tf.sigmoid(logits) #结果进行sigmod
137 x_hat = tf.reshape(x_hat, [-1, 28, 28]).numpy() *255. #还原到0-255
138 x_hat = x_hat.astype(np.uint8)
139 save_images(x_hat, 'vae_images/sampled_epoch%d.png'%epoch)
140
141 x = next(iter(test_db))
142 x = tf.reshape(x, [-1, 784])
143 x_hat_logits, _, _ = model(x)
144 x_hat = tf.sigmoid(x_hat_logits)
145 x_hat = tf.reshape(x_hat, [-1, 28, 28]).numpy() *255.
146 x_hat = x_hat.astype(np.uint8)
147 save_images(x_hat, 'vae_images/rec_epoch%d.png'%epoch)
标签：Auto,self,28,Encoder,test,train,tf,Variational,hat 来源： https://www.cnblogs.com/pengzhonglian/p/12163897.html