Fine tuning VGG16

[jroberayalas]

Hi,

Just a quick question, I'm trying to fine tune the VGG16 as suggested in the notebook 2.4. However, I got an error: The shape of the input to "Flatten" is not fully defined (got (None, None, 512). Make sure to pass a complete "input_shape" or "batch_input_shape" argument to the first layer in your model.. Not sure if anyone can give me a hint on this. My code is shown below:

from keras.applications import VGG16

model = VGG16(include_top=False)
for layer in model.layers:
    layer.trainable = False

top_model = Sequential()
top_model.add(Flatten(input_shape=model.output_shape[1:]))
top_model.add(Dense(768, activation='sigmoid'))
top_model.add(Dropout(0.0))
top_model.add(Dense(768, activation='sigmoid'))
top_model.add(Dropout(0.0))
top_model.add(Dense(n_labels, activation='softmax'))

model.add(top_model)

train_model(model,
            (X_train_gte5, y_train_gte5),
            (X_test_gte5, y_test_gte5), nb_classes)