FFT

+================+       +================+
|                |       |. . . . . . . . |
|      ===       |  ---> || | | | | | | | |
|                |       |' ' ' ' ' ' ' ' |
+================+       +================+ 

mat = zeros(100,100);
iCentre=20; jCentre=70;
for i=iCentre-5:iCentre+5, for j=jCentre-3:jCentre+3, mat(i,j)=1; end, end;
matfft = fft(mat);
matffts = fftshift(matfft);
matabs = log(abs(matffts)+1);
matabsMin = min(matabs);
matabsMax = max(matabs);
subplot(1,2,1), imshow(mat);
subplot(1,2,2), imshow(matabs, [matabsMin, matabsMax]);