%例程4－27實現(xiàn)Butterworth低通濾波器

I = imread('eight.tif');
figure, imshow(I),
D = imnoise(I,'gaussian');
figure, imshow(D)
D=double(D);
F=fft2(D);                      %傅立葉變換
F=fftshift(F);                   %轉(zhuǎn)換數(shù)據(jù)矩陣
[N1,N2]=size(F);
n=2;
d0=40;
n1=fix(N1/2);
n2=fix(N2/2);
for i=1:N1
for j=1:N2
       d =sqrt((i-n1)^2+(j-n2)^2);
       h=1/(1+(d/d0)^(2*n));    %計算低通轉(zhuǎn)換函數(shù)
       FD(i,j)=h*F(i,j);        %低通濾波
end
end
FD=ifftshift(FD);
FD=ifft2(FD);
FD=uint8(real(FD));
figure,imshow(FD)