自已编写的求二值化阈值的函数.用5*5模板求局部灰值的平方各,然后求3*3邻域内的灰度熵,通过求熵的最大值对应的灰度值,来求阈值.-Prepared for their own binary threshold function. 5* 5 template partial gray value for each square, and then for 3* 3 gray neighborhood entropy, by seeking the maximum entropy of the gray value corresponding to demand threshold.