[Insight-users] RV: about HessianRecursiveGaussianImageFilter

[Neil Panjwani]

If you look at the relevant typedefs,

const     unsigned int        Dimension       =  3;
...
typedef   itk::FixedArray< InputPixelType, Dimension >  EigenValueArrayType;
typedef   itk::Image< EigenValueArrayType, Dimension > EigenValueImageType;
typedef
itk::SymmetricEigenAnalysisImageFilter<
HessianFilterType::OutputImageType, EigenValueImageType
>EigenAnalysisFilterType;

you see that the output of the EigenAnalysisFilterType is an image of Fixed
Arrays of dimension 3. In order to access each eigenvalue, you simply
traverse the image using an image iterator. When calling GetPixel(), you
will be returned a Fixed Array which contains all three eigenvalues. Read up
on the ITK software guide if you're unfamiliar with iterators and/or the
documentation for ITK for specific classes.

Here's what I would do:

// get output
EigenValueImageType::Pointer eigenImage = eigenAnalysisFilter->GetOutput();

// setup iterator
typedef itk::ImageRegionIterator<EigenValueImageType> EigenIteratorType;
EigenIteratorType
eigenImageIt(eigenImage,eigenImage->GetLargestPossibleRegion());

// iterate through image and get each eigen value
for (eigenImageIt.GoToBegin(); !eigenImageIt.IsAtEnd(); ++eigenImage)
{
 for (int i=0; i<3; i++)
{
  EigenValueArrayType eigenArray = eigenImageIt.Get();
  std::cout << eigenArray[i] << std::endl;
}
}

On Sat, May 14, 2011 at 1:41 PM, ra.corredor <ra.corredor at gmail.com> wrote:

> Hi Ivan,
>
> I'm just beginning  with ITK and I was testing your
> HessianMatrixEigenAnalysis.cxx code in order to obtain the Hessian matrix
> eigenvalues of a CT image. In my project, I need to save the three
> eigenvalues in a text file using several Sigma values (about 10 scales).
>
> You wrote in the last post that is possible to access these values using
> GetPixel, but what you mean is that eigenAnalysisFilter->GetOutput() is
> producing this vector image which can be accessed with getPixel or
> iteratiors?? I had some problems adding the little EigenValueAccessor class
> to my project, so I'm looking for alternative options for accessing
> eigenvalues.
>
> Is it possible to use MultiScaleHessianBasedMeasureImageFilter to get this
> info?
>
> Thank you !!
>
> Ricardo
> RaC
>
>
> -----
> Ricardo A Corredor
> RaC
> --
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