[Insight-developers] Wrong behaviour of ImageFileReader when reading an itk::VectorImage<itk::FixedArray<double, 6>, 3> ?

[Karthik Krishnan]

On Fri, Jan 14, 2011 at 6:26 AM, Benoit Scherrer
<benoitscherrer at gmail.com>wrote:

> Hi,
>
> I wanted to use the type:
> typedef itk::VectorImage<itk::FixedArray<double, 6>, 3> TensorVectorImage;
> to make a vector image of tensors.
>
> Everything compiles well. But when i use the
> itk::ImageFileReader<TensorVectorImage>
> it seems that things goes wrong. When trying to iterate on the image :
>
> itk::ImageRegionConstIterator<TensorVectorImage>
>  it(image, image->GetLargestPossibleRegion());
>  while(!it.IsAtEnd())
> {
> itk::VariableLengthVector<itk::FixedArray<double, 6> > tensors = it.Get();
>                (...)
> ++it;
> }
>
> it compiles but during the execution goes out of the data bounds.
>
> By looking into ImageFileReader<TOutputImage,
> ConvertPixelTraits>::GenerateOutputInformation
> I found the lines:
>
>   if( strcmp( output->GetNameOfClass(), "VectorImage" ) == 0 )
>     {
>     typedef typename TOutputImage::AccessorFunctorType AccessorFunctorType;
>     AccessorFunctorType::SetVectorLength( output,
> m_ImageIO->GetNumberOfComponents() );
>     }
>
> So here m_ImageIO->GetNumberOfComponents() will returns 6 for a simple
> tensor file (Dimension
> of the VectorImage = 1), instead of 1 (after the offsets computed
> in ImageRegionConstIterator are wrong).
>
> So should ImageFileReader divides m_ImageIO->GetNumberOfComponents() by the
> number of components
> of TOutputImage::PixelType ? (i manually set it to 1 in the debugger, it's
> working. However i didn't tried
> with an image with 12 components, ie two tensors)
>
> Or is it a bad idea to use  itk::VectorImage<itk::FixedArray<double, 6>, 3>
>  ?
>

To make a VectorImage of tensors, you declare it simply as itk::VectorImage<
double, 3 > and set the VectorLength on the image to 6.

Or you could use itk::Image< FixedArray< double, 6 >, 3 >.

The two are equivalent.



> Thanks a lot
> Benoit
>
>
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