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Topic: Fourier shift theorem
Replies: 1   Last Post: Dec 11, 2012 4:24 AM

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 mini Posts: 22 Registered: 9/18/08
Fourier shift theorem
Posted: Dec 10, 2012 6:22 PM

Dear all,

I'm currently trying to understand the 2d fourier shift theorem.

According to what I've learnd so far a translation in the image space leads to differences in phase but not the magnitude in frequency space.

I tried to demonstrate this with a little example but it only worked for shifts in rows but not in columns. Here's the little demo (I'm only showing the magnitude plots here)

clear all
close all
Iin = zeros(128);
Iin(10:20,10:20)=1;
figure,imagesc(Iin)
Y = fft(Iin);
figure, imagesc(fftshift(log10(abs(Y))));

Iin = zeros(128);
Iin(10:20,20:30)=1;
figure,imagesc(Iin)
Y = fft(Iin);
figure, imagesc(fftshift(log10(abs(Y))));

Iin = zeros(128);
Iin(20:30,10:20)=1;
figure,imagesc(Iin)
Y = fft(Iin);
figure, imagesc(fftshift(log10(abs(Y))));

In my opinion all 3 magnitude plots should yield the same result.
Can anyone explain me what I'm doing wrong here?

thank you very much for your help,
best regards,
Mini

Date Subject Author
12/10/12 mini
12/11/12 mini