Create an aliased image in FD
I am trying to construct an aliasing image.

I=rgb2gray(imread('Liver.png')); % a 512*512 image 
subplot(1,2,1),imshow(I),title('Original image')  % shown on the left side of figure below


when you implement F=fftshift(fft2(I));, the corresponding axis represent the frequency range of [-255:256]/512; and the cut-off frequency U = V = 256/512 = 0.5;

based on Nyquist Sampling Theorem, the sampling periods in spatial domain should satisfy

delta_x&lt;=1/(2*U)=1;
delta_y&lt;=1/(2*V)=1;


to avoid the aliasing.

So if your bandwidth of recorder is 64 * 64, the corresponding point interval in spatial domain is 1 / (64/256) = 4. Thus,

Ia=imresize(I(1:4:end,1:4:end),[512 512]);
subplot(1,2,2),imshow(Ia),title('Aliased image') % shown on the right side of the figure below




You can observe the aliasing effect at the edge.