低通滤波器，对图像滤波。采用opencv。其中包含二维高斯低通滤波器，衰减系数为2的二维指数低通滤波器，2阶巴特沃思低通滤波器，二维理想低通滤波器-Low-pass filter, the image filtering. Using opencv. Which contains two-dimensional Gaussian low-pass filter, the attenuation factor of 2 two-dimensional index of low-pass filte