def iteration_layers(model, speedup, session, indepth_layer=None):
    """
    Define the the layers whose activations are enhanced and visualized.

    Parameters:
        model: Inception5h model
        speedup: selects subset of layers to give results faster
    Returns: layer tensors to iterate through
    """
    if speedup is True:
        layer_names_reduced = ['conv2d1',
                               'conv2d2',
                               'mixed3b',
                               'mixed4b',
                               'mixed5b']
        layer_tensors = [session.graph.get_tensor_by_name(name + ":0") for name in layer_names_reduced]
    else:
        layer_tensors = model.layer_tensors

    return layer_tensors