filter

代码说明：

  对一幅数字图像采用理想低通、Butterworth低通 、Gaussian低通滤波器进行平滑；对一幅数字图像采用理想高通、Butterworth高通 、Gaussian高通滤波器进行平滑。 (The ideal of a digital image using low pass, Butterworth low-pass, Gaussian smoothing low pass filter on a digital image using the ideal high-pass, Butterworth high-pass, Gaussian high-pass filter smoothing. )