[Insight-users] problems filtering using GaussianBlurImageFunction

[Phillip Cheng]

Hello all,

I'm trying to get some code working that uses itkGaussianBlurImageFunction
to filter an image volume.  I can't just use itkDiscreteGaussianFilter
because I need to vary the width of the kernel throughout the image, based
on external data.

I didn't get the results I expected, probably because I don't really
understand how GaussianBlurImageFunction is supposed to work.  Appended are
two code samples, one using DiscreteGaussianFilter and the other using
GaussianBlurImageFunction, with the same kernel sizes.  I would like them to
give the same results, but they clearly do not.  The DiscreteGaussianFilter
gives results that appear correct; the GaussianBlurImageFunction seems to be
less blurred than what I expect.  I'm not sure how best to debug what's
going on.  Can anyone shed some light on this?

Thanks,

Phillip


==== Using DiscreteGaussianImageFilter:

#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkDiscreteGaussianImageFilter.h"

int main( int argc, char * argv[] )
{
  if( argc < 3 )
    {
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0] << "  inputImageFile  outputImageFile" <<
std::endl;
    return 1;
    }

  typedef itk::Image< float,  3 >   ImageType;
  typedef itk::ImageFileReader< ImageType >  ReaderType;
  typedef itk::ImageFileWriter< ImageType >  WriterType;

  ReaderType::Pointer reader = ReaderType::New();
  reader->SetFileName( argv[1] );

  typedef itk::DiscreteGaussianImageFilter< ImageType, ImageType >
FilterType;
  FilterType::Pointer filter = FilterType::New();
  filter->SetInput( reader->GetOutput() );
  filter->SetVariance(25.0);

  WriterType::Pointer writer = WriterType::New();
  writer->SetFileName( argv[2] );
  writer->SetInput( filter->GetOutput() );
  writer->Update();

  return 0;
}


==== Using GaussianBlurImageFunction:

#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkGaussianBlurImageFunction.h"
#include "itkImageRegionIterator.h"

int main( int argc, char * argv[] )
{
  if( argc < 3 ) {
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0] << "  inputImageFile  outputImageFile" <<
std::endl;
    return 1;
  }

  typedef itk::Image< float, 3 >   ImageType;
  typedef itk::ImageFileReader< ImageType >  ReaderType;
  typedef itk::ImageRegionIterator< ImageType > IteratorType;

  ReaderType::Pointer reader = ReaderType::New();
  reader->SetFileName( argv[1] );
  reader->Update();

  IteratorType it( reader->GetOutput(),
reader->GetOutput()->GetRequestedRegion() );
  ImageType::Pointer output = ImageType::New();
  output->SetRegions(reader->GetOutput()->GetRequestedRegion());
  output->SetOrigin(reader->GetOutput()->GetOrigin());
  output->SetSpacing(reader->GetOutput()->GetSpacing());
  output->Allocate();
  IteratorType out(output,reader->GetOutput()->GetRequestedRegion());

  typedef itk::GaussianBlurImageFunction< ImageType > GFunctionType;
  GFunctionType::Pointer gaussianFunction = GFunctionType::New();
  gaussianFunction->SetInputImage(reader->GetOutput());

  GFunctionType::ErrorArrayType setError;
  setError.Fill( 0.01 );
  gaussianFunction->SetMaximumError( setError );
  gaussianFunction->SetSigma(5.0);
  it.GoToBegin();
  out.GoToBegin();
  while (!it.IsAtEnd()) {
      out.Set(gaussianFunction->EvaluateAtIndex(it.GetIndex()));
      ++it;
      ++out;
  }

  typedef itk::ImageFileWriter < ImageType > WriterType;
  WriterType::Pointer writer = WriterType::New();
  writer->SetFileName(argv[2]);
  writer->SetInput(output);
  writer->Update();

  return 0;
}