Is the fft2 output mirrored as in the fft?

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Andrea Muratori 2021-5-28

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回答： Manas Meena 2021-5-31

Hi,

I know that the fft algorithm gives a mirrored spectrum as output. Now, I'm working with the fft2 and I get a spectrum which seems to be symmetric but actually peaks has different heigths and slightly different positions.

My question: is this difference due to the double performing of the one dimensional fft (as by definition is fft2 = fft(fft(X).').' ) or the fft2 output is not symmetric as in the fft case?

Thanks

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Answer 1

Manas Meena 2021-5-31

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The spectrum seems to be symmetric but if you look at the spectrum matrix values you'll see that is not the case. This is caused by the round-off error. If you want to ensure a symmetric matrix you must specify the "symmetric" option on ifft2 function.

For example,

X = ifft2(Y,'symmetric')