def simple_atmo_opstring(haze, contrast, bias):
    """Make a simple atmospheric correction formula."""
    gamma_b = 1 - haze
    gamma_g = 1 - haze / 3.0
    ops = (
        'gamma g {gamma_g}, gamma b {gamma_b}, sigmoidal rgb {contrast} {bias}'
        .format(gamma_g=gamma_g, gamma_b=gamma_b, contrast=contrast, bias=bias)
        )
    return ops
