Modify layer parameters in Keras

Question

I am interested in updating existing layer parameters in Keras (not removing a layer and inserting a new one instead, rather just modifying existing parameters).

I w

Answer 1

Well, if you would like to create the architecture of a new model based on an existing model, though with some modifications, you can use to_json and model_from_json() functions. Here is an example:

model = Sequential()
model.add(Conv2D(10, (3,3), input_shape=(100,100,3)))
model.add(Conv2D(40, (3,3)))

model.summary()

Model summary:

Layer (type)                 Output Shape              Param #   
=================================================================
conv2d_12 (Conv2D)           (None, 98, 98, 10)        280       
_________________________________________________________________
conv2d_13 (Conv2D)           (None, 96, 96, 40)        3640      
=================================================================
Total params: 3,920
Trainable params: 3,920
Non-trainable params: 0
_________________________________________________________________

Now we modify the number of filters of the first layer and create a new model based on the modified architecture:

from keras.models import model_from_json

model.layers[0].filters *= 2
new_model = model_from_json(model.to_json())
new_model.summary()

New model summary:

Layer (type)                 Output Shape              Param #   
=================================================================
conv2d_12 (Conv2D)           (None, 98, 98, 20)        560       
_________________________________________________________________
conv2d_13 (Conv2D)           (None, 96, 96, 40)        7240      
=================================================================
Total params: 7,800
Trainable params: 7,800
Non-trainable params: 0
_________________________________________________________________

You can also modify the output of model.to_json() directly without modifying the model instance.

---

You can easily use get_weights() method to get the current weights of the convolution layer. It would return a list of two numpy arrays. The first one corresponds to filter weights and the second one corresponds to bias parameters. Then you can use set_weights() method to set the new weights:

conv_layer = model.layers[random_conv_index]
weights = conv_layer.get_weights()
weights[0] *= factor  # multiply filter weights by `factor`
conv_layer.set_weights(weights)

As a side note, the filters attribute of a convolution layer which you have used in your code corresponds to the number of filters in this layer and not their weights.