def valueBand(v0, delta=0.05):
    """
    Get the value band of the perturbation for a pixel with intensity of v0
    :param v0: the intensity of the target pixel
    :param delta: the difference constraint
    :return: a tuple containing the low edge and high edge of the value band
    """
    vl = max(v0 - delta, 0)
    vh = min(v0 + delta, 1)
    return vl, vh