Keras TensorFlow 混编中 trainable=False设置无效

这是最近碰到一个问题,先描述下问题:
首先我有一个训练好的模型(例如vgg16),我要对这个模型进行一些改变,例如添加一层全连接层,用于种种原因,我只能用TensorFlow来进行模型优化,tf的优化器,默认情况下对所有tf.trainable_variables()进行权值更新,问题就出在这,明明将vgg16的模型设置为trainable=False,但是tf的优化器仍然对vgg16做权值更新

以上就是问题描述,经过谷歌百度等等,终于找到了解决办法,下面我们一点一点的来复原整个问题。

trainable=False 无效

首先,我们导入训练好的模型vgg16,对其设置成trainable=False

from keras.applications import VGG16
import tensorflow as tf
from keras import layers
# 导入模型
base_mode = VGG16(include_top=False)
# 查看可训练的变量
tf.trainable_variables()
[<tf.Variable 'block1_conv1/kernel:0' shape=(3, 3, 3, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv1/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block1_conv2/kernel:0' shape=(3, 3, 64, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv2/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block2_conv1/kernel:0' shape=(3, 3, 64, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv1/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block2_conv2/kernel:0' shape=(3, 3, 128, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv2/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block3_conv1/kernel:0' shape=(3, 3, 128, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv2/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv2/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv3/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv3/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block4_conv1/kernel:0' shape=(3, 3, 256, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv2/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv2/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv3/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv3/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv2/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv2/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv3/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv3/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block1_conv1_1/kernel:0' shape=(3, 3, 3, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv1_1/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block1_conv2_1/kernel:0' shape=(3, 3, 64, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv2_1/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block2_conv1_1/kernel:0' shape=(3, 3, 64, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv1_1/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block2_conv2_1/kernel:0' shape=(3, 3, 128, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv2_1/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block3_conv1_1/kernel:0' shape=(3, 3, 128, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv1_1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv2_1/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv2_1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv3_1/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv3_1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block4_conv1_1/kernel:0' shape=(3, 3, 256, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv1_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv2_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv2_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv3_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv3_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv1_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv1_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv2_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv2_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv3_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv3_1/bias:0' shape=(512,) dtype=float32_ref>]
# 设置 trainable=False
# base_mode.trainable = False似乎也是可以的
for layer in base_mode.layers:
    layer.trainable = False

设置好trainable=False后,再次查看可训练的变量,发现并没有变化,也就是说设置无效

# 再次查看可训练的变量
tf.trainable_variables()
[<tf.Variable 'block1_conv1/kernel:0' shape=(3, 3, 3, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv1/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block1_conv2/kernel:0' shape=(3, 3, 64, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv2/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block2_conv1/kernel:0' shape=(3, 3, 64, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv1/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block2_conv2/kernel:0' shape=(3, 3, 128, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv2/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block3_conv1/kernel:0' shape=(3, 3, 128, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv2/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv2/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv3/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv3/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block4_conv1/kernel:0' shape=(3, 3, 256, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv2/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv2/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv3/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv3/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv2/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv2/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv3/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv3/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block1_conv1_1/kernel:0' shape=(3, 3, 3, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv1_1/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block1_conv2_1/kernel:0' shape=(3, 3, 64, 64) dtype=float32_ref>,
 <tf.Variable 'block1_conv2_1/bias:0' shape=(64,) dtype=float32_ref>,
 <tf.Variable 'block2_conv1_1/kernel:0' shape=(3, 3, 64, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv1_1/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block2_conv2_1/kernel:0' shape=(3, 3, 128, 128) dtype=float32_ref>,
 <tf.Variable 'block2_conv2_1/bias:0' shape=(128,) dtype=float32_ref>,
 <tf.Variable 'block3_conv1_1/kernel:0' shape=(3, 3, 128, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv1_1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv2_1/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv2_1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block3_conv3_1/kernel:0' shape=(3, 3, 256, 256) dtype=float32_ref>,
 <tf.Variable 'block3_conv3_1/bias:0' shape=(256,) dtype=float32_ref>,
 <tf.Variable 'block4_conv1_1/kernel:0' shape=(3, 3, 256, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv1_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv2_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv2_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block4_conv3_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block4_conv3_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv1_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv1_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv2_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv2_1/bias:0' shape=(512,) dtype=float32_ref>,
 <tf.Variable 'block5_conv3_1/kernel:0' shape=(3, 3, 512, 512) dtype=float32_ref>,
 <tf.Variable 'block5_conv3_1/bias:0' shape=(512,) dtype=float32_ref>]

解决的办法

解决的办法就是在导入模型的时候建立一个variable_scope,将需要训练的变量放在另一个variable_scope,然后通过tf.get_collection获取需要训练的变量,最后通过tf的优化器中var_list指定需要训练的变量

from keras import models
with tf.variable_scope('base_model'):
    base_model = VGG16(include_top=False, input_shape=(224,224,3))
with tf.variable_scope('xxx'):
    model = models.Sequential()
    model.add(base_model)
    model.add(layers.Flatten())
    model.add(layers.Dense(10))
# 获取需要训练的变量
trainable_var = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES, 'xxx')
trainable_var
[<tf.Variable 'xxx_2/dense_1/kernel:0' shape=(25088, 10) dtype=float32_ref>,
 <tf.Variable 'xxx_2/dense_1/bias:0' shape=(10,) dtype=float32_ref>]
# 定义tf优化器进行训练,这里假设有一个loss
loss = model.output / 2; # 随便定义的,方便演示
train_step = tf.train.AdamOptimizer().minimize(loss, var_list=trainable_var)

总结

  • 在keras与TensorFlow混编中,keras中设置trainable=False对于TensorFlow而言并不起作用
  • 解决的办法就是通过variable_scope对变量进行区分,在通过tf.get_collection来获取需要训练的变量,最后通过tf优化器中var_list指定训练
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