[Insight-users] problem when calculating metric values between two images

[Ming Chao]

HI again,
For some reason, my message was discarded when I sent it to the mailing list
the first time. I am sending it again. The two images can be found:
http://www.stanford.edu/~mingchao/image/fixedImage.vtk
and
http://www.stanford.edu/~mingchao/image/movingImage16.vtk


Hi,

I followed a standard procedure to calculate the metric between two images.
However, I encountered a problem. Bascally I have two images which are
subregions of a big image. When I calculate the metric between these two
smaller images, the metric value is always -1 (I am using Normalized
Correlation Metric). The code is attached to the end of this message. And
the two images are attached as well. I don't understand what is wrong.
Thanks,
Ming


#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkMeanSquaresImageToImageMetric.h"
#include "itkNormalizedCorrelationImageToImageMetric.h "
#include "itkTranslationTransform.h"
#include "itkNearestNeighborInterpolateImageFunction.h"
#include "itkLinearInterpolateImageFunction.h"


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

  const     unsigned int   Dimension = 2;
  //typedef  unsigned char  PixelType;
  typedef  float  PixelType;

  typedef itk::Image< PixelType, Dimension >   ImageType;
  typedef itk::Image< PixelType, Dimension >   ImageType;


  typedef itk::ImageFileReader< ImageType >  ReaderType;

  ReaderType::Pointer fixedReader  = ReaderType::New();
  ReaderType::Pointer movingReader = ReaderType::New();

  fixedReader->SetFileName(  argv[ 1 ] );
  movingReader->SetFileName( argv[ 2 ] );

  try
    {
    fixedReader->Update();
    movingReader->Update();
    }
  catch( itk::ExceptionObject & excep )
    {
    std::cerr << "Exception catched !" << std::endl;
    std::cerr << excep << std::endl;
    }

  typedef itk::NormalizedCorrelationImageToImageMetric< ImageType, ImageType
>  MetricType;

  MetricType::Pointer metric = MetricType::New();



  typedef itk::TranslationTransform< double, Dimension >  TransformType;

  TransformType::Pointer transform = TransformType::New();



  typedef itk::NearestNeighborInterpolateImageFunction<
                                 ImageType, double >  InterpolatorType;

  InterpolatorType::Pointer interpolator = InterpolatorType::New();

  typedef TransformType::ParametersType ParametersType;
  ParametersType displacement( transform->GetNumberOfParameters() );
  displacement.Fill(  0.0  );

  metric->SetInterpolator( interpolator );
  metric->SetTransform( transform );

  //transform->SetIdentity();

  ImageType::ConstPointer fixedImage  = fixedReader->GetOutput();
  ImageType::ConstPointer movingImage = movingReader->GetOutput();

  metric->SetFixedImage(  fixedImage  );
  metric->SetMovingImage( movingImage );

  metric->SetFixedImageRegion(  fixedImage->GetBufferedRegion()  );

  try
    {
    metric->Initialize();
    }
  catch( itk::ExceptionObject & excep )
    {
    std::cerr << "Exception catched !" << std::endl;
    std::cerr << excep << std::endl;
    return -1;
    }

  const double value = metric->GetValue( displacement );

  std::cout << "metric value ==  " << value << std::endl;
  std::cout << "displacement = " << displacement << std::endl;

  return 0;
}
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