[Insight-users] help: comparison FFTW/VNL

[Carlos Santos]

Hi Isabelle,

On 10/26/05, Renaud Isabelle <renauisa at yahoo.fr> wrote:
>
> I could not find any comment on differences between using
> itk::VnlFFTRealToComplexConjugateImageFilter and
> itk::FFTWRealToComplexConjugateImageFilter.
>
> - What is(are) the big difference(s)? What is the fastest between both?

FFTW claim to fame is that it is the "fastest fourier transform in the
west", since it is able to perform some code optimizations depending
on data size and platform. I don't know of any comparisons to VnlFFT,
though. There are some problems with the Vnl implementation that might
affect you:
http://www.itk.org/Bug/bug.php?op=show&bugid=1918&pos=0
http://www.itk.org/Bug/bug.php?op=show&bugid=2161&pos=2

>
> - BTW, what about having images of size of a power of 2? I tought that to
> compute fourier transform via FFT, it would be necessary to have a power of
> 2 of size.

Not necessarily. See http://www.eptools.com/tn/T0001/PT07.HTM for some
discussion.

> I am sorry but I am a bit confused between all of these notions
> (FFT,FFTW,VXL). Indeed, I have to adapt an algorithm written in matlab and
> in order to check out my implementation, I am comparing my results from itk
> and those from matlab.

Since version 6, matlab itself uses FFTW. The reasons for the change
are discussed at:
http://www.mathworks.com/company/newsletters/news_notes/clevescorner/winter01_cleve.html

Hope this helps,

Carlos

>
> Isabelle
>
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