def build_output_type_set(output_type_list, config):
    """Builds set of output types.

    Args:
        output_type_list: list, possible output image types.
        config: dict, user passed parameters.

    Returns:
        Set of requested output image types.
    """
    output_types = set()
    for output_type in output_type_list:
        if config["output_{}".format(output_type)]:
            output_types.add(output_type)
    return output_types