Get the output and gradients of output of a convolutional layer.

    Parameters:
    ----------
    net: Block
        Network to use for visualization.
    image: NDArray
        Preprocessed image to use for visualization.
    class_id: int
        Category ID this image belongs to. If not provided,
        network's prediction will be used.
    conv_layer_name: str
        Name of the convolutional layer whose output and output's gradients need to be acptured.

def get_conv_out_grad(net, image, class_id=None, conv_layer_name=None):
    """Get the output and gradients of output of a convolutional layer.

    Parameters:
    ----------
    net: Block
        Network to use for visualization.
    image: NDArray
        Preprocessed image to use for visualization.
    class_id: int
        Category ID this image belongs to. If not provided,
        network's prediction will be used.
    conv_layer_name: str
        Name of the convolutional layer whose output and output's gradients need to be acptured."""
    return _get_grad(net, image, class_id, conv_layer_name, image_grad=False)