[Insight-developers] GradientVectorFlowImageFilter internal image type

[Gaëtan Lehmann]

Le 10 janv. 09 à 16:20, Karthik Krishnan a écrit :

> Gaëtan Lehmann wrote:
>>  template <class TInputImage, class TOutputImage, class  
>> TInternalPixel=double>
>>  class ITK_EXPORT GradientVectorFlowImageFilter : public  
>> ImageToImageFilter<TInputImage, TOutputImage>
>>
>> There shouldn't be any backward compatibility issue that way. I  
>> don't know well that class though, so I have an important question:
>> Does that change look reasonable? I mean, is it relevant to use a  
>> different internal pixel type than double - float for example?
> I don't think it makes sense to use the class with any internal  
> pixel type other than float or double. Actually, the input images  
> (and output images) supplied should also be float/double. The filter  
> internally computes the laplacian image using the internal pixel  
> type. Double precision is also needed to account for the diffusion  
> of the gradient vectors.
>
> I would just wrap the class for double and float alone.

My problem comes from this method:

     itkSetMacro(LaplacianFilter, LaplacianFilterPointer);

The LaplacianFilter currently uses double as pixel type, whatever are  
the input or the output image types, so that method expose a filter  
type which is not available most of the time, because the default real  
type wrapped in wrapitk is float. The result is a warning at build  
time and an unusable SetLaplacianFilter() in the target languages.  
Changing the internal pixel type (used in the laplacian filter type)  
to the one used in the input and the output image would avoid the  
problem with the SetLaplacianFilter() method.
An easy way to fix the problem, but if it produce wrong result because  
the double precision is required for the internal image type, that's  
also a wrong way to fix that problem.

With that fix, I would wrap the types

   itk::GradientVectorFlowImageFilter< itk::Image<float, 2>,  
itk::Image<float, 2>, float >
   itk::GradientVectorFlowImageFilter< itk::Image<float, 3>,  
itk::Image<float, 3>, float >

by default, and/or

   itk::GradientVectorFlowImageFilter< itk::Image<double, 2>,  
itk::Image<double, 2>, double >
   itk::GradientVectorFlowImageFilter< itk::Image<double, 3>,  
itk::Image<double, 3>, double >

if the user has chosen to wrap double.
But does it make sense to have itk::Image<float, 2> used for the  
laplacian, when input and output image are itk::Image<float, 2>?

>
>
> thx
> --
> karthik
>>
>> Regards,
>>
>> Gaëtan
>>
>>
>> ------------------------------------------------------------------------
>>
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>>
>
> -- 
> Karthik Krishnan
> R & D Engineer,
> Kitware Inc,
> Ph:  518 371 3971 x119
> Fax: 518 371 3971
>

-- 
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.mandriva.org
http://www.itk.org  http://www.clavier-dvorak.org

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