说明：  双峰法是一种简单的阈值分割方法，即如果灰度级直方图呈现明显的双峰状，则选双峰之间的谷底所对应的灰度级作为阈值分割。
(Two peaks is a simple threshold segmentation method, that is, if the gray level histogram showed a clear bimodal shape, then choose between the two peaks corresponding to the bottom of the gray level as threshold segmentation.)