[X, Y] = meshgrid(-128:1:127, -128:1:127);
ddk = X.*X + Y.*Y;

load bacteria

figure
subplot(1,2,1)
imagesc(bacteria); axis image; colormap gray

subplot(1,2,2)
bacedge = ifft2(fft2(double(bacteria)).*fftshift(ddk));
imagesc(abs(bacedge)); axis image; colormap gray