它的基本思想是：初始时，使用一个较大的阈值将两个目标分开，但目标间的间隙很大；在减小阈值的过程中，两个目标的边界会相向扩张，它们接触前所保留的最后像素集合就给出了目标间的最终边界，此时也就得到了阈值-Its basic idea is: the initial, use a larger threshold will separate the two objectives, but a large gap between the objectives　in the process of reducing the threshold, the two goals of the expansion of the border will be opposite, they contact reservations prior to the last pixel on the given set of final borders between the objectives at this time there have been threshold