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Re: The question of FFT

From: Andreas Weber
Subject: Re: The question of FFT
Date: Sun, 4 Sep 2016 10:04:20 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.2.0

Am 04.09.2016 um 04:54 schrieb Yao-Wang Li:
> For a real function, for example, an image (u), Its Fourier transform
> should follow the Friedel symmetry, I mean the U(s) = U*(-s). Here,
> U(s) is the Fourier transform of u, and is a complex number. U*(s) is
> its conjugate. I tested two images in imagej, and it works. However, it
> is not happen in Octave, the real part is not equal and the imaginary
> part is not opposite. They should have the magnitude and opposite
> phase. That is what is my question. that is what I did in Octave.
> img1=imread("fibers01.tif");
> img2=imread("fibers02.tif");
> %Fourier transform
> img1_sf=fft2(double(img1));
> img2_sf=fft2(double(img2));

How have you checked, that the symmetry if not the case here?
If I try

x = rand (5, 5);
fft2 (x)

I can see the expected conjugate complex symmetry.
-- Andy

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