You can use this program to choice how many threshold you need , and you can use the process to change original pictures to multi-layer colors.

otsu算法确定二值化阀值，最大类间方差是由日本学者大津(OTSU)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。 -In computer vision and image processing, Otsu s method is used to automatically perform histogram shape-based image thresholding,[1] or, the reduction of a graylevel image t