说明：  最大类间方差法原理：最大类间方差法是由日本学者大津于1979年提出的,是一种自适应的阈值确定的方法,又叫大津法,简称OTSU。它是按图像的灰度特性,将图像分成背景和目标2 部分。
(Otsu method works: Otsu method by Otsu, Japan scholars put forward in 1979, is an adaptive method of determining the threshold, also known as Otsu method, referred to OTSU. It is based on gray-scale image features, the image into the background and objectives 2.)