سير العمل البرمجي · تنبؤ Paeth في PNG

def paeth(left, above, upper_left):
    if any(type(v) is not int or not 0 <= v <= 255
           for v in (left, above, upper_left)):
        raise ValueError("byte integers required")
    p = left + above - upper_left
    dl, da, dc = abs(p-left), abs(p-above), abs(p-upper_left)
    if dl <= da and dl <= dc: return left
    if da <= dc: return above
    return upper_left