递归滤波(RF):对于离散信号,不能保护边缘的滤波器可以使用如下的一阶递归滤波器完成.该滤波器对指数衰减有无限脉冲响应-Recursive filtering (RF): For discrete signals, filters can not be used to protect the edge of a first-order recursive filter following the completion of the exponential decay of the filter