[Insight-users] Filtering a tensor component accessed with NthElementImageAdaptor

[Jim Miller]

Vicente,

In your set of print statements, can you do a

m_ImageAdaptor->Print(std::cout);

I'd like to see what the spacing is that gets printed here.  Perhaps the
adaptor has a different spacing stored than the image it is adapting.  The
call to GetSpacing() delegates to the adapted image.  But the call to
Print() will print the ivar of the adaptor not the adapted image.

Jim




On 5/5/06, Vicente Grau <vgrauc at googlemail.com> wrote:
>
> Dear all,
>
> I am writing a filter to calculate the gradient structure tensor. This
> involves calculating an NxN matrix for each voxel of the image, and then
> applying a gaussian filter to each one of the components of the matrix (
> i.e., taking one component of the matrix at every voxel to create a new
> image, and applying a gaussian filter on this new image). Based on
> HessianRecursiveGausianImageFilter, I am using NthElementImageAdaptor and
> three instances of RecursiveGaussianImageFilter to filter in the x, y and z
> directions. As I saw in previous submissions to the list, I defined the
> first of the gaussian filters to accept the adaptor as an input.
> I have been getting errors in the results (basically, the filters behave
> as if the pixel spacing were always [1 1 1], though it's not), so I wrote
> this very simple piece of code to check that image spacing has the expected
> values. I have attached the code below. It works by reading a tensor image
> from a file, and applying a gaussian filter to the first component of the
> tensor (of course, I would have to define things as filter direction, sigma,
> etc., but here I just wanted to check the spacing). The input image is all
> zeros, though I don't think this matters in this case. With an input image
> with spacing [2 2 2], the program output is:
>
> m_ImageAdaptor->GetSpacing(): [2, 2, 2]
> m_ComponentFilter->GetOutput()->GetSpacing(): [1, 1, 1]
>
> which is exactly the same error I got in my structure tensor calculation
> program. It seems that the output of the filter has a different spacing from
> the input, so when I attach a second filter to the output of the first one,
> the result is wrong. Could anybody tell me what I am doing wrong here?
> Thanks a lot,
>
> Vicente
>
> /**************************** Code follows ***********************/
>
> #include "itkSymmetricSecondRankTensor.h"
> #include "itkImage.h"
> #include "itkImageFileReader.h"
> #include "itkRecursiveGaussianImageFilter.h"
> #include "itkNthElementImageAdaptor.h"
>
>
>
> int main( int argc, char *argv[] )
> {
>     const     unsigned int        Dimension       = 3;
>     typedef   double              InputPixelType;
>
>     typedef itk::Image< itk::SymmetricSecondRankTensor< InputPixelType,
> Dimension > , Dimension > InputImageType;
>     typedef itk::Image< InputPixelType, Dimension >   OutputImageType;
>
>     typedef   itk::ImageFileReader< InputImageType >  ReaderType;
>     ReaderType::Pointer   reader = ReaderType::New();
>    reader->SetFileName( argv[1] );
>
>     typedef itk::NthElementImageAdaptor< InputImageType, InputPixelType >
> OutputImageAdaptorType;
>     OutputImageAdaptorType::Pointer  m_ImageAdaptor =
> OutputImageAdaptorType::New();
>     m_ImageAdaptor->SetImage( reader->GetOutput() );
>     m_ImageAdaptor->Allocate();
>     m_ImageAdaptor->SelectNthElement( 0 );
>
>     typedef itk::RecursiveGaussianImageFilter< OutputImageAdaptorType,
> OutputImageType >    ComponentFilterType;
>     ComponentFilterType::Pointer m_ComponentFilter  =
> ComponentFilterType::New();
>     m_ComponentFilter->SetInput( m_ImageAdaptor );
>
>     m_ComponentFilter->Update();
>
>     std::cout << "m_ImageAdaptor->GetSpacing(): " <<
> m_ImageAdaptor->GetSpacing() << std::endl;
>     std::cout << "m_ComponentFilter->GetOutput()->GetSpacing(): " <<
>
> m_ComponentFilter->GetOutput()->GetSpacing() << std::endl;
>
>   return EXIT_SUCCESS;
> }
>
>
>
>
>
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>
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