def read_catalog(catalog_file_path, sep=','):
    """ Read a Catalog file.
    A Catalog file is a tabular file containing 4 columns. These are
        (1) sample_id, (2) image_id, (3) image_src, and (4) mask_src,
        respectively.

    Args:
        catalog_file_path: Address of a catalog file.
        sep: A field seperator.

    Returns:
        return a list of lists, where each internal list contain for elements:
            (1) sample_id, (2) image_id, (3) image_src, and (4) mask_src.

    """
    data_sequence = []
    with open(catalog_file_path) as fin:
        for line in fin:
            line = line.strip()
            if line.startswith('#') or line == '':
                continue
            instance_info = [x.strip() for x in line.split(sep)]
            data_sequence.append(instance_info)
    return data_sequence