[Insight-users] Gradient anisotropic filter time step?

[Luis Ibanez]

Hi Natarajan,



                      "Glimpsing at the Source, leaves no doubt"


This is what the file:

           Insight/Code/BasicFilters/itkAnisotropicDiffusionImageFilter.txx

has in lines 75-82:


  if ( m_TimeStep >  (minSpacing / vcl_pow(2.0,
static_cast<double>(ImageDimension) + 1))  )
    {
    //    f->SetTimeStep(1.0 / vcl_pow(2.0,
static_cast<double>(ImageDimension)));
    itkWarningMacro( << "Anisotropic diffusion unstable time step: "
                     << m_TimeStep << std::endl
                     << "Stable time step for this image must be smaller than "
                     << minSpacing / vcl_pow(2.0,
static_cast<double>(ImageDimension+1)));
    }


In summary:

                    Timestep    <     pixelSpacing  /  ( 2^N )

where N is the image dimension (e.g. 3 for 3D images, and 2 for 2D images).




Did you enable the flag:

               UseImageSpacing  ?

If so, what is the pixel spacing of your image ?


      Regards,



            Luis


-------------------------------------------
On Mon, Feb 15, 2010 at 12:27 PM, Natarajan CS <csnataraj at gmail.com> wrote:
> Hello all,
>       Not sure if this is a bug or a implementation detail I am overlooking,
> I am tending towards the latter, so any info would be helpful !
>  I get  the following warning from the
> GradientAnisotropicDiffusionImageFilter (The filter is being applied to a
> 256^3 dataset of type short)
>
> WARNING: In
> /hpc/soft/natac0/itk/include/InsightToolkit/BasicFilters/itkAnisotropicDiffusionImageFilter.txx,
> line 78
> GradientAnisotropicDiffusionImageFilter (0xbc4120): Anisotropic diffusion
> unstable time step: 0.07
> Stable time step for this image must be smaller than 0.0625
>
> i was under the impression that the ITK implimentation was a explicit method
> with the time step requirement for 3D images is <= 1/8 and <= 1/4 for 2D. Am
> i completely off-track here?
>
> Appreciate any help!
>
> Thanks,
>
> C.S.N
>
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