[Insight-users] VNLFFT vs. FFTW

[Cory Quammen]

Kevin,

I've created an issue in the new ITK bug tracker here:

https://itk.icts.uiowa.edu/jira/browse/ITK-270

I've observed the doubling along the x-axis you report when using
FFTW. I'm investigating now.

Cory

On Tue, Aug 2, 2011 at 10:41 AM, Kevin H. Hobbs <hobbsk at ohio.edu> wrote:
> I'm doing
>
> 1.
> read -> FFT -> FFTShift -> modulus -> log -> file1
>
> Using the file to make a mask and then doing:
>
> 2.
> read_mask -> FFTShift
>                     \
>                      --> mask -> iFFT -> file2
>                     /
>          read -> FFT
>
> When I use FFTW I have to do UpdateLargestPossibleRegion() at the end of
> 1. or the mask in 2. fails complaining about the regions being at least
> partially outside.. well duh FFTW uses symmetry to only make half the
> output. But then file2 gets doubled along the x-axis with vertical lines
> of junk (I'm surprised it worked at all).
>
> I switched to using the VNL classes and all is well, I suppose I could
> crop the masked image if I know that the iFFT is the FFTW class... but
> that seems like a bit of a kludge.
>
> It should probably be a bug that a program writen with
> itk::FFTRealToComplexConjugateImageFilter and
> itk::FFTComplexConjugateToRealImageFilter will fail based on weather itk
> was made with FFTW.
>
>
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-- 
Cory Quammen
Research Associate
Department of Computer Science
University of North Carolina at Chapel Hill
http://www.cs.unc.edu/~cquammen