def uv76_to_uv60(u76, v76):     # CIE1976 to CIE1960
    """ convert CIE1976 u'v' to CIE1960 uv coordinates
    :param u76: u' value (CIE1976)
    :param v76: v' value (CIE1976)
    :return: CIE1960 u, v """

    v60 = (2 * v76) / 3

    return u76, v60