from typing import Tuple


def get_subpixel_indices(col_num: int) -> Tuple[int, int, int]:
    """Return a 3-tuple of 1-indexed column indices representing subpixels of a single pixel."""
    offset = (col_num - 1) * 2
    red_index = col_num + offset
    green_index = col_num + offset + 1
    blue_index = col_num + offset + 2
    return red_index, blue_index, green_index