链码（又称为freeman码）是用曲线起始点的坐标和边界点方向代码来描述曲线或边界的方法，常被用来在图像处理、计算机图形学、模式识别等领域中表示曲线和区域边界。本例用C++实现图像八方向链码的边界跟踪算法。(freeman　is a method to describe a curve or boundary by using the coordinates of the starting point of the curve and the direction code of the boundary point)