[SIP-devel] images fft

[DRUEL J. <joc...@li...>]

Hi,
A function to obtain the frequency spectrum of an image.
My problem with scilab's fft function was that the result did not correspond 
to what I saw each time I performed a Fraunhoffer diffraction.

So I moved low frequencies from the edges to the center and added a few 
parameters to help visualisation of details in the spectrum.

I wrote this function to
1) illustrate (and simulate) diffraction by several openings.
2) for a double exposition speckle experiment: an object is lightened by a 
laser beam: a 1st picture of the speckle is taken with a CCD camera. The 
object is then moved of several microns. A 2nd picture is taken.
Adding the 2 pictures and then launching a fft transfrom will show fringes. 
The space between fringes is related to the object displacement.

I'm really not a fft specialist so don't hesitate to criticize this work.
I wanted too to:
1) calculate the spectrum of an image
2) modify the spectrum
3) apply a reverse fourier transform to see modifications on the original 
picture (strioscopy, foucaultage).
But I don't know how to perform a reverse fourier transform with scilab.

Best regards
Jocelyn
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