Re: Questions about FFT2

[David Bateman]

Simoes Vincent wrote:
> Hi,
> I'm a frensh student in a school of image processing and i have to try
> to do image processing with a FPGA.
> 
> For that, i need to use the fft2. I know how to do a fft2 on your
> software using fft2() and ifft2() but i can't use it on a FPGA. Thus, i
> want to rewrite the function fft2 and ifft2. I have try with the
> formuls, I have done that on a image 512x512 divided on matrice 8x8 to
> do several fft2. But it takes too long to be interessant for me !
> That's why i'm writing to you about your function fft2. Can you tell me
> how you do it ? Maybe give me your algorithm as your software is a free one.
> After the installation of octave, i have found some files which can help
> me for sure but i dont know how to open it, it is fft2.oct and
> ifft2.oct. I hope you can help me on this subject.
> 
> Moreover, i want to congrats you for your software, it is very useful to
> work on my own at home and to avoid Matlab, witch is too expensive for a
> single person.
> 
> I look forward to hearing from you soon
> Thanks a lot for your help
> 
> SIMOES Vincent
> 

Octave uses FFTW or FFTPACK for this. You're better using the code from
there and asking their authors.. However having myself been in teams
implementing FFTs on FPGA, perhaps you should look at the fixed point
radix-4 FFT implementation that uses the octave-forge fixed point toolbox at

http://octave.svn.sourceforge.net/viewvc/octave/trunk/octave-forge/main/fixed/examples/ffft.cc?revision=HEAD&view=markup

If you want bit accurate modelling of what will happen when you
implement the FFT on your FPGA you really should be modelling in fixed
point in any case, and the code in the octave-forge fixed point toolbox
might help there.

D.