def uv60_to_xy(u60, v60):       # CIE1960 to CIE1931
    """ convert CIE1960 uv to CIE1931 xy coordinates
    :param u60: u value (CIE1960)
    :param v60: v value (CIE1960)
    :return: CIE1931 x, y """
    denominator = (((6 * u60) / 2) - (12 * v60) + 6)

    if denominator == 0.0:
        x, y = 0.0, 0.0
    else:
        x = ((18 * u60) / 4) / denominator
        y = (3 * v60) / denominator

    return x, y