[Insight-users] Mutual Information with Mask

[Xabier Artaechevarria Artieda]

Hi ITK users,

I am trying to obtain the Mutual Information of two images in a  
certain region, applying a mask. I get the error:

itk::ERROR: MutualInformationImageToImageMetric(0x6bc6c0): All the  
sampled point mapped to outside of the moving image

I think the problem is in the way I set the mask, because:
  1. I get no errors if I do not set it.
  2. The error comes out even if I try to calculate the metric between  
an image and itself.
  3. I have also checked the mask by writing it to a file, and it looks ok.

Below are the last lines of my code. As I said, ?mask.tif? is in fact  
a binary image with around one third of the values set to 1, the rest  
are 0s.

Am I missing some extra step? What might be wrong?
Thanks in advance for your help,
Xabi

// set the mask as the output of a certain filter
   spatialObjectMask->SetImage( filter->GetOutput() );

// write the mask to check the it is correct
   typedef itk::ImageFileWriter< ImageMaskType >  WriterType;
   WriterType::Pointer writer  = WriterType::New();
   writer->SetFileName("mask.tif");
   writer->SetInput(dilateFilter->GetOutput());
   writer->Update();

//set the mask
   MImetric->SetFixedImageMask( spatialObjectMask );
   MImetric->SetMovingImageMask( spatialObjectMask );

//initialize metric
   MImetric->Initialize();

//set 0 displacement to translation transform and get metric value
   typedef TransformType::ParametersType ParametersType;
   ParametersType displacement( transform->GetNumberOfParameters() );
   displacement.Fill(0.0);
   double value =MImetric->GetValue( displacement );
   std::cout << "MI metric  " << value << std::endl;



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