How to modify layers of pretrained models in Keras like Inception-v3?

问题

I want to use Inception-v3 with pretrained weights on ImageNet to take inputs that are not just 3 channel RGB images but have more channels, such that the dimension is (224, 224, x!=3), and then assigning a self-defined set of weights to the following Conv2D layer. I was trying to change the input layer and the subsequent Conv2D layer such that it suits my needs, but I could not find a structured way of doing so.

I tried building a custom Conv2d tensor with Conv2D(...)(input) and assigning that to the corresponding layer of Inception, but this fails because it requires actual layers, while the above instruction yields a tensor. For all it matters, Conv2D(...)(Input) and Inception.layers[1].output yields the correct same output (which it should be since I just want to change the input dimensions and weights), the question is how to wrap the new Conv2D input-output mapping as a layer and replace it in Inception?

I could try hacking my way through this, but generally I wondered if there is a swift and elegant way of reassigning certain layers in those pretrained models with custom specifications.

Thank you!

Edit: What works is inserting these lines at line 394 of the inception_v3.py from Keras, disabling the exception for more than 3 channel inputs and then simply calling the constructor with the desired input. (Note that Original calls the original InceptionV3 constructor)

Code:

original_model = Original(weights='imagenet', include_top=False, input_shape=(299, 299, 3))
weights = model.get_weights()
original_weights = original_model.get_weights()

for i in range(1, len(original_weights)):
       weights[i] = original_weights[i]
averaged_weights = np.mean(weights[0], axis=2)[:, :, None, :]
replicated_weights = np.repeat(averaged_weights, 20, axis=2)
weights[0] = replicated_weights

Then I can call

InceptionV3(weights='imagenet', include_top=False, input_shape=(299, 299, 20))

This work and gives the desired result, but seems very hacky.

来源：https://stackoverflow.com/questions/49339355/how-to-modify-layers-of-pretrained-models-in-keras-like-inception-v3

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