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

[Jordi Inglada]

Hi,

My link errors where solved by adding fftw3f to the link libraries. I 
had added fftw3, but forgot the other.

Sorry for increasing the entropy on the list!

So the conclusion is :
    - There may be a bug in the VnlFFT
    - Use the CVS version of the FFTWRealToComplexImageFilter which 
includes the fix for gcc 3.4
    - For FFTW :
                    - #define USE_FFTW
                    - add fftw3 and fftw3f to the link libraries.
                          

Jordi.

Julien Jomier wrote:

> 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
> >> >>
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> Insight-users mailing list
> >> >> Insight-users at itk.org
> >> >> http://www.itk.org/mailman/listinfo/insight-users
> >> >>
> >> >
> >> >
> >> >
> >> >
> >> 
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> >> >
> >> >
> >> >
> >> 
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> >> >
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> >> >
> >> > _______________________________________________
> >> > Insight-users mailing list
> >> > Insight-users at itk.org
> >> > http://www.itk.org/mailman/listinfo/insight-users
> >>
> >
> >
>


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