说明：  大津法由大津于1979年提出，对图像Image，记t为前景与背景的分割阈值，前景点数占图像比例为w0， 平均灰度为u0；背景点数占图像比例为w1，平均灰度为u1
(Otsu method by Otsu in 1979 suggested that the image Image, remember t for the foreground and background segmentation threshold, the prospect of accounting for the image ratio of points w0, the average gray level for u0 background image representing the ratio of points w1, the average gray level for u1)