迭代法是基于逼近的思想，逼近的目标是使得：前景和背景的平均灰度值的平均值即为阈值。该方法的原理是：如果用某一阈值分割出的图像，其两部分平均值的中值，正好等于该阈值，那么这个阈值就是所求的阈值。-Iterative method is based on the approximation of the idea of ​ ​ approaching the goal is to make: the foreground and background is the average of the average gray value threshold. The principle is: if a threshold image segmentation, the average value of two parts, exactly equal to the threshold, then the threshold is the threshold requirements.