理想低通滤波器

I1 = imread('abc.jpg');
I2 = im2double(I1);
I3 = imnoise(I2,'gaussian',0.01);
I4 = imnoise(I3,'salt & pepper',0.01);
figure(1)
imshow(I1);
title('原始图像');
figure(2)
imshow(I4);
title('加噪声后的图像');
s = fftshift(fft2(I4));
[M,N]=size(s);
n1 = floor(M/2);
n2 = floor(N/2);
d0 = 40;
for i = 1:M
    for j = 1:N
        d=sqrt((n1 - i)^2+(n2 - j)^2);
        if d <= d0
            h = 1;
        else
            h = 0;
        s(i,j) = s(i,j)*h;
        end
    end
end
K = ifftshift(s);
T = im2uint8(real(ifft2(K)));
figure(3)
imshow(T);