Problem with ifftn and ifftshift??
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Hi there I was wondering if someone could help me. I am using the fftn fftshift functions as part of my alogrithm;
tmp = fftn(MAT); Adash = fftshift(tmp);
Adashup=ifftshift(Adash);
Adashup2new = ifftn(Adashup);
However, When I took everything else out and left these in as a tester I noticed that instead of the above taking me back to the original MAT, it alters the numbers quite a lot. What am I doing wrong?? Example original file MAT has a min of 0 and a max of 1.0856, however the file Adashup2new has a min of -6.792 and a max of 1.0856
2 Comments
Mehri Mehrnia
on 14 Oct 2023
why we should use fftshit?when I dont use fftshit, scale is good and untouched
Walter Roberson
on 14 Oct 2023
fft() returns back the 2-sided fft. By convention, the order of frequency bins returns back from fft() of real input signals is like
0, 1, 2, 3, 4, ... n-1, n, conj(-n), conj(-(n-1)), ... conj(-(4)), conj(-(3)), conj(-(2)), conj(-1)
but people often prefer to visualize it in the order
conj(-(n-1)), ... conj(-(4)), conj(-(3)), conj(-(2)), conj(-1), 0, 1, 2, 3, 4, ... n-1, n
The change is not mathematically significant: it is just easier for people to look at the plots.
Accepted Answer
Nitin
on 26 Jun 2013
Sounds like Imaginary components are there due to round off errors, try extracting the real part
f = real(ifft2(F));
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