用matlab实现的中心加权滤波函数，中心权重为3，滤波窗口为3*3，参数可自行修改，可进一步改成可变参数函数。cwm_test为测试程序。-Weighted with matlab filter function to achieve the center, the center weight of 3, 3* 3 filter window, parameters can modify, change the variable argument function further.