[Insight-users] FFT in 3D not working?

[Luis Ibanez]

Hi Monica,


There was a bug in the netlib function that VnlFFT uses for computing
the Fourier Transform. This bug has been fixed very recently.
(last week).


You may want to checkout the current CVS version of ITK in order to
get this bug fix.


Note that this bug was for the VnlFFT version.
The FFTW version should have worked anyways,
did you tried with the FFTW version ?


    Please let us know,


      Thanks


         Luis


---------------------------
mhg at unizar.es wrote:
> Dear Insight users,
> 
> I am trying to use the class itkVnlFFTRealToComplexConjugateImageFilter.h
> to get the fft transform of a 3D image. I wrote the code presented avobe
> using itk version 2.01 to write the real part of the Fourier transform
> of a 3D image. I tested my code with a second order derivative kernel
> of 64 x 64 x 64. In the following direction I posted the results:
> 
> http://webmail.unizar.es/DescargarFicheros.php?id0=1157193166.php3NXuyp&idn0=real1.vtk&id1=1157193166.php5tbxOn&idn1=real2.vtk& 
> 
> 
> where real1.vtk is the file with the itk computed result and real2.vtk 
> is the
> file computed with the fft implemented in vtk. Looking at these results 
> you can
> appreciate that the image computed with the itk code is not correct.
> 
> Maybe there is an error in my code or maybe you already fixed this bug 
> in latest
> releases of itk. I would appreciate if any of you can tell me what is 
> the reason
> why my code is not working.
> 
> Best, Monica.
> 
> #include "itkVnlFFTRealToComplexConjugateImageFilter.h"
> #include "itkFFTWRealToComplexConjugateImageFilter.h"
> #include "itkComplexToRealImageFilter.h"
> #include "itkComplexToImaginaryImageFilter.h"
> 
> using namespace std;
> 
> typedef FloatPixelType PixelType;
> typedef FloatImageType ImageType;
> typedef FloatIteratorType IteratorType;
> typedef FloatNeighborhoodIteratorType NeighborhoodIteratorType;
> typedef FloatNumericTraits NumericTraits;
> 
> typedef itk::VnlFFTRealToComplexConjugateImageFilter< PixelType, 3 >
> FFTFilterType;
> typedef FFTFilterType::OutputImageType ComplexImageType;
> typedef itk::ComplexToRealImageFilter< ComplexImageType, ImageType >
> RealFilterType;
> typedef itk::ComplexToImaginaryImageFilter< ComplexImageType, ImageType >
> ImaginaryFilterType;
> 
> typedef FloatReaderType ReaderType;
> typedef FloatWriterType WriterType;
> 
> void usage()
> {
>  cerr << "Usage: fftDemo [input] [output]" << endl;
>  exit(1);
> }
> 
> int main( int argc, char **argv )
> {
>  if( argc < 3 )
>    usage();
> 
>  char *input_name = NULL, *output_name = NULL;
>  input_name  = argv[1];
>  argc--;
>  argv++;
>  output_name = argv[1];
>  argc--;
>  argv++;
> 
>  // Reading the images
>  ReaderType::Pointer sourceR = ReaderType::New();
>  sourceR->SetFileName( input_name );
>  sourceR->Update();
> 
>  FFTFilterType::Pointer fft = FFTFilterType::New();
> 
>  fft->SetInput( sourceR->GetOutput() );
>  try
>  {
>    fft->Update();
>  }
>  catch( itk::ExceptionObject & excp )
>  {
>    std::cerr << "Error: " << std::endl;
>    std::cerr << excp << std::endl;
>  }
> 
>  RealFilterType::Pointer realFilter = RealFilterType::New();
>  realFilter->SetInput( fft->GetOutput() );
>  realFilter->Update();
> 
>  WriterType::Pointer writer = WriterType::New();
>  writer->SetFileName( output_name );
>  writer->SetInput( realFilter->GetOutput() );
>  writer->Update();
> 
>  return 0;
> }
> 
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