[Insight-users] ReleaseDataFlag() strikes again ! : Problem with bspline interpolation and VTKImageToImageFilter

[Luis Ibanez]

Hi Michael,

Thanks for your detailed report.
We wish all problem reports were as specific as yours.


I was able to reproduce the problem you pointed out. Effectively,
when the BSpline interpolator is used, the outpur values are
all set to the default value. This does not occur with the
linear interpolator.



However the real culprit of this undesirable effect seems to be
the innocent-looking call to "ReleaseDataFlag()" in

 >    vtk2itk->GetImporter()->SetReleaseDataFlag(true);

This call authorizes the itkVTKImporter filter to release its
memory as soon as the next filter in the pipeline runs its Update()
method.

Some ITK filters however are not well suited for supporting this
call in their predecessors. This typically happens when the filter
has internal calls to Update() othere than their own. Filters having
internal pipelines are an example of this condition.


Removing the call to ReleaseDataFlagOn() solves the problem in this
case.



Please let us know if you find further problems,


     Luis



----------------------
Michael Kuhn wrote:
> Hi,
> 
> I have a problem using the bspline interpolation, which I think is 
> related to the VTKImageToImageFilter. If I'm trying to transform an 
> image (which originates from a VTKImageToImageFilter) using a resample 
> image filter and a bspline interpolator, the output is the default pixel 
> value for all the pixels. Using a linear interpolator, the problem does 
> not occur. Since I've already successfully transformed images with a 
> bspline interpolator that did not originate from a 
> VTKImageToImageFilter, I think the problem is related to that one.
> 
> I have quickly set up a  simple program that demonstrates the problem 
> (see code below). It generates vtk image data (a cube) and transforms it 
> by an identity transform. Using a linear interpolator, the output is the 
> original cube, using a bspline interpolator it consists only of 1 values 
> (which is the default pixel value) (comment and uncomment the BSPLINE 
> BLOCK and LINEAR BLOCK to see the difference):
> 
> Thanks,
> 
> Michael
> 
> 
> 
> #include "itkImage.h"
> #include "itkLinearInterpolateImageFunction.h"
> #include "itkBSplineInterpolateImageFunction.h"
> #include "itkVTKImageToImageFilter.h"
> #include "itkResampleImageFilter.h"
> #include "itkAffineTransform.h"
> 
> int main(int argc, char** argv) {
>    vtkImageData* data = vtkImageData::New();
>    data->SetDimensions(12, 12, 12);
>    data->SetScalarTypeToShort();
>    data->AllocateScalars();
>    for (int x = 0; x < 12; x++) {
>        for (int y = 0; y < 12; y++) {
>            for (int z = 0; z < 12; z++) {
>                short* tmp = (short*)data->GetScalarPointer(x, y, z);
>                if (x >= 2 && x < 10 && y >= 2 && y < 10 && z >= 2 && z < 
> 10)
>                {
>                    *tmp = 5;
>                } else {
>                    *tmp = 0;
>                }
>            }
>        }
>    }
> 
>    typedef itk::Image<short, 3> ImageType;
>    typedef itk::VTKImageToImageFilter<ImageType> VTK2ITKType;
>    VTK2ITKType::Pointer vtk2itk = VTK2ITKType::New();
>    vtk2itk->GetImporter()->SetReleaseDataFlag(true);
>    vtk2itk->SetInput(data);
>    vtk2itk->GetImporter()->Update();
>    ImageType::Pointer image1 = vtk2itk->GetImporter()->GetOutput();
> 
> 
>    typedef itk::ResampleImageFilter<ImageType, ImageType> 
> ResampleFilterType;
>    ResampleFilterType::Pointer resampleFilter = ResampleFilterType::New();
>        // BSPLINE BLOCK
>    typedef itk::BSplineInterpolateImageFunction<ImageType, double, double>
>        BSplineType;
>    BSplineType::Pointer interpolator = BSplineType::New();
>    interpolator->SetSplineOrder(3);
>        /*
>    // LINEAR BLOCK
>    typedef itk::LinearInterpolateImageFunction<ImageType, double>
>        LinearType;
>    LinearType::Pointer interpolator = LinearType::New();
>    */  
>    typedef itk::AffineTransform<double, 3> AffineType;
>    AffineType::Pointer affineTransform = AffineType::New();
> 
>    AffineType::ParametersType affineParams(12);
>    affineParams[0] = 1;
>    affineParams[1] = 0;
>    affineParams[2] = 0;
>    affineParams[3] = 0;
>    affineParams[4] = 1;
>    affineParams[5] = 0;
>    affineParams[6] = 0;
>    affineParams[7] = 0;
>    affineParams[8] = 1;
>    affineParams[9] = 0;
>    affineParams[10] = 0;
>    affineParams[11] = 0;
> 
>    affineTransform->SetParameters(affineParams);
>    resampleFilter->SetInterpolator(interpolator);
>    resampleFilter->SetTransform(affineTransform);
>    resampleFilter->SetInput(image1);
> 
>    resampleFilter->SetOutputOrigin(image1->GetOrigin());
>    resampleFilter->SetOutputSpacing(image1->GetSpacing());
>    resampleFilter->SetSize(image1->GetBufferedRegion().GetSize());
>    resampleFilter->SetDefaultPixelValue(1);
>    resampleFilter->Update();
>    ImageType::Pointer image2 = resampleFilter->GetOutput();
> 
>    for (int x = 0; x < 12; x++) {
>        for (int y = 0; y < 12; y++) {
>            for (int z = 0; z < 12; z++) {
>                ImageType::IndexType idx;
>                idx[0] = x;
>                idx[1] = y;
>                idx[2] = z;
>                cout << image2->GetPixel(idx) << " ";
>            }
>            cout << endl;
>        }
>        cout << endl;
>        cout << endl;
>    }
> 
>    return 0;
> }
> 
> 
> 
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