def relativeSize(bbox1, bbox2):
    """
    Calculate the relative size of bbox1 to bbox2.

    :return: (sx, sy) where bbox1_width = sx * bbox2_width, etc.

    """
    sx = (bbox1[2]-bbox1[0]) / (bbox2[2]-bbox2[0])
    sy = (bbox1[3]-bbox1[1]) / (bbox2[3]-bbox2[1])

    return (sx, sy)