def check_photometry_categorize(x, y, levels, tags=None):
    '''Put every point in its category.
    levels must be sorted.'''
    x = numpy.asarray(x)
    y = numpy.asarray(y)
    ys = y.copy()
    ys.sort()
    m = ys[len(ys) // 2:].mean()
    y /= m
    m = 1.0
    s = ys[len(ys) // 2:].std()
    result = []
    if tags is None:
        tags = list(six.moves.range(len(levels) + 1))
    for l, t in zip(levels, tags):
        indc = y < l
        if indc.any():
            x1 = x[indc]
            y1 = y[indc]
            result.append((x1, y1, t))
            x = x[~indc]
            y = y[~indc]
    else:
        result.append((x, y, tags[-1]))
    return result, (m, s)