Snake 算法或Active Contour Models。这类算法需要给出初始的轮廓，然后进行迭代，使轮廓沿能量降低的方向靠近，最后得到一个优化的边界。-Snake algorithm or Active Contour Models. Such algorithms need to give the initial profile, and then proceed to iteration, so that contours along the direction of lower energy around, and finally get an optimization of the border.