圖像頻域濾波的步驟： 

%% 頻域高斯低通濾波和頻域銳化的Matlab實現% Date:2017/2/5clc;clearall;I=imread('original_tletter.tif');I=double(I);[M,N]=size(I);m=(M+1)/2;n=(N+1)/2;d0=30;                      %截止頻率F=fftshift(fft2(I));        %空域轉頻域，平移中心H=zeros(M,N);G=zeros(M,N);fori=1:M  forj=1:N       d=(i-m)^2+(j-n)^2;       H(i,j)=exp(-d/(2*d0^2));%%高斯濾波函數       G(i,j)=H(i,j)*F(i,j);   endendO=ifft2(ifftshift(G));          %平移中心，頻域轉空域O=real(O);                       %取實數部分 subplot(1,2,1);imshow(I,[]);title('原始圖像');subplot(1,2,2);imshow(O,[]);title('頻域高斯低通濾波'); %% 采用二階巴特沃斯高通濾波器進行頻域濾波nn=2;d0 = 5;m = fix(M/2);n = fix(N/2);fori = 1:M   forj = 1:N        d = sqrt((i-m)^2+(j-n)^2);       if(d==0)            h=0;       else            h = 1/(1+0.414*(d0/d)/(2*nn));       end        result(i,j) = h*G(i,j);   end  end    result = ifftshift(result);    J2 = ifft2(result);    J3 = uint8(real(J2));    figure,    subplot(1,2,1),imshow(I),title('原始圖像');    subplot(1,2,2),imshow(J3),title('頻域銳化圖像');運行結果：