[Insight-developers] Consistency in the output of forward/inverse FFT image filters

[Gaëtan Lehmann]

Le 18 août 11 à 21:14, Cory Quammen a écrit :

> Kevin Hobbs brought up a good point in a recent post to the ITK users
> list regarding the output of the forward FFT filter. Right now, the
> output of this filter is quite different if FFTW is enabled. This is
> because FFTW computes only about half of the output image because of
> the Hermitian symmetry inherent in the Fourier transform of a real
> signal, while the FFT routine in VNL computes the full output image.
> Kevin pointed out that to effectively work with the output of this
> filter, one must know whether the output is in the half or full image
> format, and one must explicitly check in the code whether FFTW is
> enabled to check that. I agree with him that this is undesirable.
>
> To make the FFT filters' behaviors consistent regardless of whether
> FFTW is enabled, I propose that all FFT filters include an option to
> produce the full output image. By default, all the FFT filters would
> produce the half output (what FFTW produces). The inverse filters
> would also have an option to specify whether their input is in the
> half or full output format.
>
> Does this sound like a good idea? I'm happy to work on a patch for
> this change if there are no objections.
>

Hi Cory,

It's a very good idea.

What would you think of adding a new filter to produce the full image  
from the half output of the fft filter instead of adding an option to  
the fft filter?
Also, would that behavior make sense when working on complex images?

Regards,

Gaëtan



-- 
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://mima2.jouy.inra.fr  http://www.itk.org
http://www.bepo.fr

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