if mode == 'real':
           print('Building discriminator D(x)')
       elif mode == 'reconstructed':
           print('Building discriminator D(G(z))')
       else:
           raise NotImplementedError('Invalid discriminator mode specified.')

multiscale_discriminator的输入有2种，一种是generator生成的图G(z)，一种是来自真实图片的分布x

x2 = tf.layers.average_pooling2d(x, pool_size=3, strides=2, padding='same')
x4 = tf.layers.average_pooling2d(x2, pool_size=3, strides=2, padding='same')

print('Shape of x:', x.get_shape().as_list())
print('Shape of x downsampled by factor 2:', x2.