利用点的八邻域信息，选择下一个点作为边界点，这个算法需要选择一个开始点，可以选择图像上是目标点，在最上，最左的点。然后查看它的八邻域的点，从右下方45°的位置开始寻找，如果是目标点，将沿顺时针90°作为下一次寻找的方向，如果不是，则逆时针45°继续寻找，一旦找到重复上面的过程。-By using eight neighborhood information,　the next point as the boundary point, the algorithm needs to choose a starting point, can　the image on the target, at the most, the left most point. Then look at the eight points neighborhood of it,　the lower right 45 degree position began to look for, if it is the target, will be along the clockwise 90 degrees as the next search direction, if not, then counter clockwise 45 degrees to find, once found to repeat the above process.