[Insight-users] Gradient anisotropic filter time step?

[Natarajan CS]

Hi Luis,
     thanks for the quick reply. Nope, I do not believe I have enabled this
flag. I am confused, I did take a look at the code snippet you suggested and
figured that time step is <= 1/2^(N+1) not 1/2^N (Judging from line 75
and/through 81). In reality I believe this has to be 1/2^N as you suggested,
at least if the implementation is same as Perona and Malik..

just in case my metadata looks as follows :

NDims = 3
DimSize = 256 256 256
ElementType = MET_SHORT
ElementDataFile = raw256.raw


Again, thanks for the help!

Cheers,

C.S.N



On Mon, Feb 15, 2010 at 2:00 PM, Luis Ibanez <luis.ibanez at kitware.com>wrote:

> 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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