[Insight-users] Forward + Inverse FFT != Identity transform

[Julien Jomier]

Hi Jordi,

Actually the fix for gcc 3.4 was submitted after the 2.0.1 release. You 
can use the cvs version of ITK if you want.

Did you enable USE_FFTW when running CMake on Insight?
Can you post the linker errors you are getting?

thanks,

Julien

Jordi Inglada wrote:
> 
> Julien,
> 
> Thanks for your answer.
> 
> Julien Jomier wrote:
> 
>> Jordi, Stefan,
>>
>> We had the same issue here. One solution was to use FFTW and the
>> corresponding FFTW classes in ITK.
>>
> 
> I have just tried, but now is FFTW (version 3) which causes trouble. 
> First of all I had to add the following lines to 
> itkFFTWRealToComplexConjugateImageFilter.h in order to compile with gcc 
> 3.4 :
> 
> typedef typename Superclass::TInputImageType TInputImageType;
>  typedef typename Superclass::TOutputImageType TOutputImageType;
> 
> And now, the the fftwf_* functions seem not to be present into the 
> libfftw3.a file (at least, ld is no able to find them and 'nm libfftw3.a 
> |grep fftwf' says nothing).
> 
>> We didn't have time to dig into the possible bug using the VNL classes.
>> Did you submit a bug report on the bug tracker (www.itk.org/bug) yet?
>>
> 
> Not yet.
> 
> Jordi
> 
>> Julien
>>
>> Jordi Inglada wrote:
>> > Dear Stefan, all,
>> >
>> > Has there been a proposed solution to this problem? We are having
>> > similar problems : the FFT of a sinusoidal surface has not the expected
>> > shape (see the real, imaginary, and module parts of the FFT). We have
>> > used the FFTImageFilter.cxx example.
>> >
>> > Thanks for any advice.
>> >
>> > J. Inglada
>> >
>> > group at spellgen.com wrote:
>> >
>> >> Trying to debug a convolution routine for two images based on Fourier
>> >> transforms, I find that a forward FFT immediately followed by its
>> >> inverse does
>> >> not produce the image I started with. The code looks straightforward
>> >> enough -
>> >> it does the following:
>> >> 1. Read the image from a grayscale char-type file
>> >> 2. Resample to width and height both being powers of two.
>> >> 3. Forward transform (float)
>> >> 4. Another forward transform.
>> >> 5. Flip data in both dimensions
>> >> 6. Rescale to bring it into char range again
>> >> 7 Write the image.
>> >>
>> >> urls for the input (black with a white dot at the origin) and the 
>> output
>> >> images:
>> >> http://neuromagnetics.mc.vanderbilt.edu/out/itk/point.png
>> >> http://neuromagnetics.mc.vanderbilt.edu/out/itk/out.png
>> >>
>> >> The source code is there as well:
>> >> http://neuromagnetics.mc.vanderbilt.edu/out/itk/four2-example.cxx
>> >>
>> >> Any suggestions as to what is going on would be appreciated...
>> >>
>> >> Cheers,
>> >>
>> >> Stefan
>> >>
>> >>
>> >>
>> >> _______________________________________________
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>> >> Insight-users at itk.org
>> >> http://www.itk.org/mailman/listinfo/insight-users
>> >>
>> >
>> >
>> >
>> > 
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> 
>