def _flatten_image_info(sim_dict):
    """
    Sim dict will have structure 
        {'g': {'param1': value1}, 'r': {'param1': value2} ...}
    This function will change the structure to
        {'param1_g': value1, 'param1_r': value2, ...}

    :param sim_dict: input sim_dict for ImageGenerator class
    :returns out_dict: flattened sim_dict
    """
    out_dict = {}
    for band, v in sim_dict.items():
        for sim_param, sim_value in v.items():
            out_dict[sim_param + '-' + band] = sim_value

    return out_dict