利用matlab编写的Butterworth低通滤波程序，可以运行，运行结果如截图源代码clear all;close all;P=input(input image data:);d=size(P);if(d(3)1) P=rgb2gray(P);endsubplot(131);imshow(P);title(原始图像);P1=imnoise(P,salt & pepper,0.02);subplot(132)imshow (P1);title(加入椒盐噪声后的图像);f=double(P1);g=fft2(f);%傅里叶变换g=fftshift(g);%转换数据矩阵M,N=size(g);D0=input(input nonnegative dhreshold D0=);n=input(input the order of filtering n=);n1=fix(M/2);n2= fix(N/2);for i=1:M for j=1:N
