卷积自编码器：用卷积层构建自编码器

当输入是图像时，使用卷积神经网络是更好的。卷积自编码器的编码器部分由卷积层和MaxPooling层构成，MaxPooling负责空域下采样。而解码器由卷积层和上采样层构成。50个epoch后，损失val_loss: 0.1018。

input_img = Input(shape=(28, 28, 1))

x = Convolution2D(16, (3, 3), activation='relu', padding='same')(input_img)
x = MaxPooling2D((2, 2), padding='same')(x)
x = Convolution2D(8, (3, 3), activation='relu', padding='same')(x)
x = MaxPooling2D((2, 2), padding='same')(x)
x = Convolution2D(8, (3, 3), activation='relu', padding='same')(x)
encoded = MaxPooling2D((2, 2), padding='same')(x)

x = Convolution2D(8, (3, 3), activation='relu', padding='same')(encoded)
x = UpSampling2D((2, 2))(x)
x = Convolution2D(8, (3, 3), activation='relu', padding='same')(x)
x = UpSampling2D((2, 2))(x)
x = Convolution2D(16, (3, 3), activation='relu')(x)
x = UpSampling2D((2, 2))(x)
decoded = Convolution2D(1, (3, 3), activation='sigmoid', padding='same')(x)

autoencoder = Model(inputs=input_img, outputs=decoded)
autoencoder.compile(optimizer='adadelta', loss='binary_crossentropy')

# 打开一个终端并启动TensorBoard，终端中输入 tensorboard --logdir=/autoencoder
autoencoder.fit(x_train, x_train, epochs=50, batch_size=256,
                shuffle=True, validation_data=(x_test, x_test),
                callbacks=[TensorBoard(log_dir='autoencoder')])

decoded_imgs = autoencoder.predict(x_test)

keras迁移学习——使用vgg19

keras预训练模型应用（3）：VGG19提取任意层特征