[Insight-users] I have a problem With FFT in ITK

[Simon Warfield]

Luis Ibanez wrote:
>
> Hi Simon,
>
> We know that a problem exists at the level of using FFT filters
> in ITK that are based on the VNL ones. However, we didn't get to
> find the source of the problem.
>
> It may well be that the ITK FFT filters are missing some operation
> that is required for the good use of the vnl FFT; or it may be an
> actual bug in the VNL implementation.
>
> The observation is that when you take an image, computes its FFT
> and then apply the inverse FFT, you don't recover the original
> image. The returned image is structured in different blocks and
> it has non-zero values in places where it should be zero.
>
> The simplest way to test this is with the examples:
>
>    Insight/Examples/Filtering/
>                  FFTDirectInverse.cxx
>                  FFTDirectInverse2.cxx
>
>
> The first one uses VNL,
> while the second one uses FFTW.
>
>
> If you have any suggestions on what may be the source
> of the problem we will be happy to give them a try.

I don't have an idea about what might be going wrong with the VNL FFT, 
but there is a bug in the CMake configuration file for FFTW.
line 15 of
InsightToolkit-2.8.1/CMake/FindFFTW.cmake
  defines a boolean option for FFTW_INCLUDE_PATH.  This line should be 
deleted.
The later FIND_PATH in the same file will allow the FFTW_INCLUDE_PATH to 
be set.


--
Simon