说明：  一个通用的边缘提取函数。通过输入不同的参数，能够实现Sobel算子、Prewitt算子、Roberts算子、Marr算子和Canny边缘检测。
(a common edge extraction function. By entering different parameters to achieve Sobel operator, Prewitt operator, Roberts operator, Marr Operator and Canny edge detection.)