[Insight-users] Re : 3D Fourier Descriptors in itk? please help! how to get outer voxels of the segmented object?

[Luis Ibanez]

Hi Marion,


Thanks for the clarification.


1) The voxels located in the surface of your segmentation,
    will have 3D coordinates, so I would assume that your
    are calling "3D Fourier Descriptors" what we call
    "Spherical Harmonics".

      http://en.wikipedia.org/wiki/Spherical_harmonics

    You have a collection of points that you are going
    to approximate by a sum of basis functions of the
    angles Theta and Phi, where the basis functions are
    sines and cosines.

    Please let us know if that is what you have in mind.


2) There are multiple ways of extracting the voxels in
    the boundary of a segmentation. A common trick is
    to erode the segmentation and to subtract the eroded
    version it from the origin segmentation. That will
    leave you with an image where only the boundary
    pixels are ON.


    Luckly for your the following filters are available
    already in the Insight/Code/Review directory:


       A) itkBinaryContourImageFilter
       B) itkLabelContourImageFilter
       C) itkOptSimpleContourExtractorImageFilter


    Thanks go to Gaetan Lehmann who contributed these
    filters.

    You probably want to use (A) and/or (C).


     Regards,


         Luis



-------------------
Marion Rizet wrote:
> Hi Luis and thank you for your reply...I thought I will never get an answer.
>  
> sorry about my bad presentation of the question.
>  
> 1- I have a volume of a segmented object (3D image) and I would like to 
> compute the 3D fourier descriptors of the voxels which are located on 
> its surface.
>  
> 2-Now I 'm facing another problem which is how I can extract the surface 
> voxels?
> A possible way is to use triangleMeshToBinaryImageFilter but since I 
> have already a volume I don't want to extract the surface and then 
> convert the extracted surface to an image. Is there any fatest way to 
> get the outer voxels of the segmented object without converting it to a 
> mesh?
> hope I have made myself clear.
> / /
> Thanks
> Marion
> 
> --- En date de : *Mar 30.6.09, Luis Ibanez /<luis.ibanez at kitware.com>/* 
> a écrit :
> 
> 
>     De: Luis Ibanez <luis.ibanez at kitware.com>
>     Objet: Re: [Insight-users] Re : 3D Fourier Descriptors in itk?
>     please help!
>     À: "Marion Rizet" <marion.rizet at yahoo.fr>
>     Cc: "insight" <insight-users at itk.org>
>     Date: Mardi 30 Juin 2009, 21h31
> 
> 
> 
>     Hi Marion,
> 
> 
>                  Your email is contradictory.
> 
> 
>     First you say that you want:
> 
>       "Fourier descriptors of a volume (surface points)"
> 
>     but then you say that you want:
> 
>       "I'm looking for 3D fourier descriptors acting on voxels."
> 
> 
>     Please clarify,
> 
> 
> 
>     Also,
>     Would you consider using Spherical Harmonics
>     as approximation to the Surface (Mesh) ?
> 
> 
> 
>       Thanks
> 
> 
>         Luis
> 
> 
> 
>     -------------------
>     Marion Rizet wrote:
>      > Hi all,
>      > I've sent my question last week but till no reply. I post it here
>     again hoping I can get answer from you.
>      > Thanks for your time
>      > Marion
>      >
>      >
>      > --- En date de : *Ven 19.6.09, Marion Rizet
>     /<marion.rizet at yahoo.fr
>     <http://fr.mc246.mail.yahoo.com/mc/compose?to=marion.rizet@yahoo.fr>>/*
>     a écrit :
>      >
>      >
>      >     De: Marion Rizet <marion.rizet at yahoo.fr
>     <http://fr.mc246.mail.yahoo.com/mc/compose?to=marion.rizet@yahoo.fr>>
>      >     Objet: [Insight-users] 3D Fourier Descriptors in itk?
>      >     À: "insight" <insight-users at itk.org
>     <http://fr.mc246.mail.yahoo.com/mc/compose?to=insight-users@itk.org>>
>      >     Date: Vendredi 19 Juin 2009, 11h53
>      >
>      >     Dear all,
>      >     I would like to know is there any itk code or class to compute
>      >     Fourier descriptors of a volume (surface points). I’ve checked in
>      >     itk mailing list but I have only found the example
>      >     FourierDescriptors1.cxx, under:  Insight/Examples/Numerics.
>      >     the given code is designed for pixels but I'm looking for 3D
>     fourier
>      >     descriptors acting on voxels.
>      >     Thanks for your time and help.
>      >     Reagrds
>      >     Marion
>      >
>      >   
>      >   
>      >
>      >
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