迭代式阈值选择是对双峰法的改进，先选择一个近似阈值，将图像分为两部分，计算两部分的均值，用两部分的均值的平均值作为新的分割阈值，重复操作直至均值不变。-Iterative threshold selection is an improvement on the bimodal method. First　an approximate threshold, divide the image into two parts, calculate the average of the two parts, use the mean of the two parts as the new threshold, and repeat until the mean value is not change.