I = imread('saturn.tif');
J = imnoise(I,'salt & pepper',0.02);
%圖像添加鹽椒噪聲
subplot(121),imshow(J)
title('含有噪聲的原圖像')
J=double(J);
f=fft2(J);
g=fftshift(f);
[M,N]=size(f);
n=3;d0=20;
n1=floor(M/2);n2=floor(N/2);
for i=1:M
    for j=1:N
        d=sqrt((i-n1)^2+(j-n2)^2);
        h=1/(1+0.414*(d/d0)^(2*n));
        g(i,j)=h*g(i,j);
    end
end
g=ifftshift(g);
g=uint8(real(ifft2(g)));
subplot(122),imshow(g)
title('三階Butterworth濾波圖像')