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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