如何取出预先训练的keras模型的中间层

Question

I want to use VGG model (tensorflow or keras pretrained model) as a feature extractor; I load the VGG16 model :

IMG_SHAPE = (224, 224, 3)
vgg16 = tf.keras.applications.VGG16(input_shape = IMG_SHAPE,
                                    include_top=False,
                                    weights='imagenet')

Now if I have a batch of image

image_batch  =np.ones((5,224,224,3),np.float32)

I can get the last layer of VGG16 by

last_layer = vgg16(image_batch)

Does any one know to get the middle layers features given input images image_batch? That is I want to extract lower level features of the given images. Thank you very much!

Answer 1

You can do something like below:

IMG_SHAPE = (224, 224, 3)
model = tf.keras.applications.VGG16(input_shape = IMG_SHAPE,
                                    include_top=False,
                                    weights=None)
pretrain_model_path = "weights/vgg16_weights_tf_dim_ordering_tf_kernels_notop.h5"
model.load_weights(pretrain_model_path)
# print(model.summary())

image_batch = np.ones((5,224,224,3),np.float32)

last_layer = tf.keras.models.Model(inputs=model.input, outputs=model.get_layer('block5_pool').output)
res = last_layer.predict(image_batch)

But, how do you know what to pass in model.get_layer() ?

Answer - through model.summary()

If you print the output of model.summary() , you will get different layer names that you can pass in the model.get_layer() and get the output of that layer.

Layer (type)                 Output Shape              Param #   
=================================================================
input_17 (InputLayer)        (None, 224, 224, 3)       0         
_________________________________________________________________
block1_conv1 (Conv2D)        (None, 224, 224, 64)      1792      
_________________________________________________________________
block1_conv2 (Conv2D)        (None, 224, 224, 64)      36928     
_________________________________________________________________
block1_pool (MaxPooling2D)   (None, 112, 112, 64)      0         
_________________________________________________________________
block2_conv1 (Conv2D)        (None, 112, 112, 128)     73856     
_________________________________________________________________
block2_conv2 (Conv2D)        (None, 112, 112, 128)     147584    
_________________________________________________________________
block2_pool (MaxPooling2D)   (None, 56, 56, 128)       0         
_________________________________________________________________
block3_conv1 (Conv2D)        (None, 56, 56, 256)       295168    
_________________________________________________________________
block3_conv2 (Conv2D)        (None, 56, 56, 256)       590080    
_________________________________________________________________
block3_conv3 (Conv2D)        (None, 56, 56, 256)       590080    
_________________________________________________________________
block3_pool (MaxPooling2D)   (None, 28, 28, 256)       0         
_________________________________________________________________
block4_conv1 (Conv2D)        (None, 28, 28, 512)       1180160   
_________________________________________________________________
block4_conv2 (Conv2D)        (None, 28, 28, 512)       2359808   
_________________________________________________________________
block4_conv3 (Conv2D)        (None, 28, 28, 512)       2359808   
_________________________________________________________________
block4_pool (MaxPooling2D)   (None, 14, 14, 512)       0         
_________________________________________________________________
block5_conv1 (Conv2D)        (None, 14, 14, 512)       2359808   
_________________________________________________________________
block5_conv2 (Conv2D)        (None, 14, 14, 512)       2359808   
_________________________________________________________________
block5_conv3 (Conv2D)        (None, 14, 14, 512)       2359808   
_________________________________________________________________
block5_pool (MaxPooling2D)   (None, 7, 7, 512)         0         
=================================================================
Total params: 14,714,688
Trainable params: 14,714,688
Non-trainable params: 0

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