说明：  OTSU 算法可以说是自适应计算单阈值（用来转换灰度图像为二值图像）的简单高效方法。下面的代码最早由 Ryan Dibble提供，此后经过多人Joerg.Schulenburg, R.Z.Liu 等修改，补正。
(OTSU algorithm can be calculated adaptive threshold (for conversion to gray scale images binary images), a simple and efficient manner. The following code from the earliest to provide Ryan Dibble, after a more than Joerg.Schulenburg, R. Z. Liu amend the correction.)