[Insight-users] FFT Confusion

[Gaëtan Lehmann]

I think Cory is working on the integration of this contribution in ITK.
This class should be part of it.

Cory, if you don't need this class, just let me know and I'll submit  
it to gerrit.

Gaëtan


Le 25 janv. 11 à 21:34, Bill Lorensen a écrit :

> Gaëtan ,
>
> I suggest submitting this and associated tests to gerrit.
>
> Bill
>
> 2011/1/25 Gaëtan Lehmann <gaetan.lehmann at jouy.inra.fr>:
>>
>> Le 25 janv. 11 à 15:28, David Doria a écrit :
>>
>>>> This is the "normal" FFT -- a real image produces a complex  
>>>> image, but
>>>> there is
>>>> complex conjugate symmetry of the first half of the transform  
>>>> because
>>>>
>>>> sin(-x) = - sin(x) (odd)
>>>> cos(-x) = cos(x)   (even)
>>>>
>>>> exp(ix) = cos(x) + isin(x)
>>>>
>>>> This complex conjugate symmetry is sometimes called Hermitian  
>>>> symmetry,
>>>> but I
>>>> have been told that is an incorrect term.
>>>>
>>>> Regards,
>>>> Matt
>>>
>>> Thanks Matt. Maybe you could explain this in the documentation of  
>>> the
>>> class (right now it is basically empty)? (and explain the choice of
>>> the name of the class too - i.e. why not just VnlFFTImageFilter? ).
>>>
>>> Also, should I just use UnaryFunctorImageFilter to compute the  
>>> complex
>>> conjugate of the resulting image? I'm surprised not to find a
>>> ConjugateImageFilter or similar.
>>
>> David,
>>
>> You will find one at
>>
>>  http://mima2.jouy.inra.fr/darcs/contrib-itk/deconv/itkComplexConjugateImageFilter.h
>>
>> Hopefully this class will be in ITK soon.
>>
>> Gaëtan
>>
>>
>>> For a normalized correlation of
>>> images A and B in the frequency domain, I believe you are supposed  
>>> to
>>> do
>>>
>>> FFT(A) * conj(FFT(B))
>>>
>>> Thanks,
>>>
>>> David
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>> --
>> 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://voxel.jouy.inra.fr  http://www.itk.org
>> http://www.mandriva.org  http://www.bepo.fr
>>
>>
>> _____________________________________
>> Powered by www.kitware.com
>>
>> Visit other Kitware open-source projects at
>> http://www.kitware.com/opensource/opensource.html
>>
>> Kitware offers ITK Training Courses, for more information visit:
>> http://www.kitware.com/products/protraining.html
>>
>> Please keep messages on-topic and check the ITK FAQ at:
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>>
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>>

-- 
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://voxel.jouy.inra.fr  http://www.itk.org
http://www.mandriva.org  http://www.bepo.fr

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