[Insight-users] if there are somethings wrong with deform image using deform fields?

[Luis Ibanez]

Hi Han,

Your code looks good, except for the fact that you
are computing the displacement backwards

Instead of:

  displacement = fixedPoint -movingPoint;

You should do:

  displacement = movingPoint -fixedPoint;


This is clearer if you look at the source code
of the WarpImageFilter, to see how the displacement
is going to be used during resampling:


Insight/Code/BasicFilters/itkWarpImageFilter.txx
lines 202-231:

   while( !outputIt.IsAtEnd() )
     {
     // get the output image index
     index = outputIt.GetIndex();
     outputPtr->TransformIndexToPhysicalPoint( index, point );

     // get the required displacement
     displacement = fieldIt.Get();

     // compute the required input image point
     for(unsigned int j = 0; j < ImageDimension; j++ )
       {
       point[j] += displacement[j];
       }

     // get the interpolated value
     if( m_Interpolator->IsInsideBuffer( point ) )
       {
       PixelType value = static_cast<PixelType>(
         m_Interpolator->Evaluate( point ) );
       outputIt.Set( value );
       }
     else
       {
       outputIt.Set( m_EdgePaddingValue );
       }
     ++outputIt;
     ++fieldIt;
     progress.CompletedPixel();
     }




   Regards,


       Luis


----------------
Han D. F wrote:
>  I use the bspline deform field (which is computed from the bapline 
> registration algorithm) to wrap the image to the new image.
> When I use the the bspline parameters, the result is ok.
> when using the defor field, the result is wrong.
> Below is the code, id there is some thing wrong?
> thnanks
>  
> assuming the bsplineTransform is computed and I will compute the deform 
> field and warp to a new image.
> help me check the code and many thanks to your help
>  
> // define the  types for computing deform field
>  typedef itk::Point< float, ImageDimension > PointType;     
> typedef itk::Vector< float, ImageDimension > VectorType;
> typedef itk::Image< VectorType, ImageDimension > DeformationFieldType;
> DeformationFieldType::Pointer field = DeformationFieldType::New();
> field->SetRegions( fixedRegion );
> field->SetOrigin( fixedOrigin );
> field->SetSpacing( fixedSpacing );
> field->SetDirection( fixedDirection );
> field->Allocate();
> typedef itk::ImageRegionIterator< DeformationFieldType > FieldIterator;
> FieldIterator fi( field, fixedRegion );
> fi.GoToBegin();
> TransformType::InputPointType fixedPoint;
> TransformType::OutputPointType movingPoint;
> DeformationFieldType::IndexType index;
> VectorType displacement;
> // getting the deform field, I have see the result the computed 
> displacement  is right
> while( ! fi.IsAtEnd() )
> {
> index = fi.GetIndex();
> field->TransformIndexToPhysicalPoint( index, fixedPoint );
> movingPoint = bsplineTransform->TransformPoint( fixedPoint );
> displacement = fixedPoint -movingPoint ;
> fi.Set( displacement );
> //std::cout<<displacement<<std::endl;
> ++fi;
> 
> }
> 
> typedef itk::WarpImageFilter< FixedImageType,
> FixedImageType,
> DeformationFieldType > DeformFilterType;
> DeformFilterType::Pointer filter = DeformFilterType::New();
> //  fiil the deform filter,such as SetInterpolator,SetOutputSpacing,....
> 
> typedef itk::LinearInterpolateImageFunction<
> FixedImageType, double > InterpolatorType1;
> InterpolatorType1::Pointer interpolator1 = InterpolatorType1::New();
> filter->SetInterpolator( interpolator1 );
> filter->SetOutputSpacing( field->GetSpacing() );
> filter->SetOutputOrigin( field->GetOrigin() );
> filter->SetDeformationField( field );
> filter->SetInput( fixedReader->GetOutput() );
> 
> //define the writer
> 
> typedef itk::ImageFileWriter< FixedImageType > WriterType;
> WriterType::Pointer writer = WriterType::New();
> writer->SetFileName( argv[5] );
> writer->SetInput( filter->GetOutput() );
>  // try the wrap filter and get the result
> try
> {
> writer->Update();
> }
> catch( itk::ExceptionObject & excp )
> {
> std::cerr << "Exception thrown " << std::endl;
> std::cerr << excp << std::endl;
> }
> 
>  
> 
> 
> 
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