def ri2I(r, i):
    """Use the Lupton 2005 transformations listed at
    http://classic.sdss.org/dr7/algorithms/sdssUBVRITransform.html
    to transform r,i passbands into I.

    Returns array of I and float estimate of systematic RMS error of transformation.
    """
    I = r - 1.2444 * (r - i) - 0.382
    sigma = 0.0078
    return I, sigma
