Keras: “must compile model before using it” despite compile() is used

Question

I want to create and train a CNN model in Keras for classification of banknotes. Creating models works fine with simple tutorials but not with the architecture I adopt from

Answer 1

Found my mistake - explanation for future reference.

The error origniates back in compile() where the first if-statement says:

if not self.built:
    # Model is not compilable because
    # it does not know its number of inputs
    # and outputs, nor their shapes and names.
    # We will compile after the first
    # time the model gets called on training data.
return

So I specified input_shape= and input_format=in the first Conv2D layer and everything works fine.