ITK/Examples/Registration/WatchRegistration

This example uses a command observer to visualize the iterations of the registration process.

Usage: WatchRegistration fixedImage movingImage

Try with these two images: BrainProtonDensitySliceBorder20.png and BrainProtonDensitySliceRotated10.png as follows

WatchRegistration BrainProtonDensitySliceBorder20.png BrainProtonDensitySliceRotated10.png

WatchRegistration.cxx

<source lang="cpp">

1. include "itkImageRegistrationMethod.h"
2. include "itkAffineTransform.h"
3. include "itkMattesMutualInformationImageToImageMetric.h"
4. include "itkRegularStepGradientDescentOptimizer.h"
5. include "itkNormalizeImageFilter.h"
6. include "itkDiscreteGaussianImageFilter.h"
7. include "itkResampleImageFilter.h"
8. include "itkCheckerBoardImageFilter.h"
9. include "itkFlipImageFilter.h"
10. include "itkImageFileReader.h"
11. include "itkImageToVTKImageFilter.h"
12. include "itkCenteredTransformInitializer.h"

1. include "vtkSmartPointer.h"
2. include "vtkRenderWindow.h"
3. include "vtkRenderer.h"
4. include "vtkInteractorStyleImage.h"
5. include "vtkRenderWindowInteractor.h"
6. include "vtkImageActor.h"
7. include "vtkImageMapper3D.h"

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

typedef itk::Image< PixelType, Dimension > InputImageType; typedef itk::Image< unsigned char, Dimension > OutputImageType;

// Command observer to visualize the evolution of the registration process. //

1. include "itkCommand.h"

template< typename TImage > class IterationUpdate : public itk::Command { public:

 typedef IterationUpdate          Self;
 typedef itk::Command             Superclass;
 typedef itk::SmartPointer<Self>  Pointer;
 itkNewMacro( Self );

protected:

 IterationUpdate() {};

public:

 typedef itk::Image< float, 2>                    InternalImageType;
 typedef itk::RegularStepGradientDescentOptimizer OptimizerType;
 typedef const OptimizerType *                    OptimizerPointer;
 typedef itk::ResampleImageFilter<
                           TImage,
                           TImage >               ResampleFilterType;
 typedef itk::AffineTransform< double, 2 >        TransformType;
 typedef itk::ImageToVTKImageFilter<TImage >      ConnectorType;
 typedef itk::FlipImageFilter<TImage>             FilterType;
 void Execute(itk::Object *caller, const itk::EventObject & event) ITK_OVERRIDE
   {
   Execute( (const itk::Object *) caller, event);
   }

 void Execute(const itk::Object * object, const itk::EventObject & event) ITK_OVERRIDE
   {
   OptimizerPointer optimizer = static_cast< OptimizerPointer >( object );
   if( !(itk::IterationEvent().CheckEvent( &event )) )
     {
     return;
     }

   m_Transform->SetParameters(optimizer->GetCurrentPosition());
   m_Filter->Update();
   m_Connector->SetInput(m_Filter->GetOutput());
   m_Connector->Update();
   m_ImageActor->GetMapper()->SetInputData(m_Connector->GetOutput());
   m_RenderWindow->Render();
   }
 void SetTransform(TransformType::Pointer &transform)
   {
   m_Transform = transform;
   }
 void SetFilter(typename FilterType::Pointer &filter)
   {
   m_Filter = filter;
   }
 void SetConnector(typename ConnectorType::Pointer &connector)
   {
   m_Connector = connector;
   }
 void SetImageActor(vtkImageActor *actor)
   {
   m_ImageActor = actor;
   }
 void SetRenderWindow(vtkRenderWindow *renderWindow)
   {
   m_RenderWindow = renderWindow;
   }
 TransformType::Pointer               m_Transform;
 typename FilterType::Pointer         m_Filter;
 typename ConnectorType::Pointer      m_Connector;
 vtkImageActor *                      m_ImageActor;
 vtkRenderWindow *                    m_RenderWindow;

};

int main( int argc, char *argv[] ) {

 InputImageType::Pointer  fixedImage = InputImageType::New();
 InputImageType::Pointer movingImage = InputImageType::New();

 if (argc > 2)
   {
   typedef itk::ImageFileReader<InputImageType> ReaderType;
   ReaderType::Pointer fixedReader = ReaderType::New();
   fixedReader->SetFileName( argv[1] );
   fixedReader->Update();
   fixedImage = fixedReader->GetOutput();

   ReaderType::Pointer movingReader = ReaderType::New();
   movingReader->SetFileName( argv[2] );
   movingReader->Update();
   movingImage = movingReader->GetOutput();
   }
 else
   {
   std::cout << "Usage: " << argv[0] << " fixedImage movingImage" << std::endl;
   return EXIT_FAILURE;
   }

 // Use floats internally
 typedef   float                       InternalPixelType;
 typedef itk::Image< float, Dimension> InternalImageType;

 // Normalize the images
 typedef itk::NormalizeImageFilter<InputImageType, InternalImageType> NormalizeFilterType;
 NormalizeFilterType::Pointer fixedNormalizer =
   NormalizeFilterType::New();
 NormalizeFilterType::Pointer movingNormalizer =
   NormalizeFilterType::New();

 fixedNormalizer->SetInput(  fixedImage);
 movingNormalizer->SetInput( movingImage);

 // Smooth the normalized images
 typedef itk::DiscreteGaussianImageFilter<InternalImageType,InternalImageType> GaussianFilterType;
 GaussianFilterType::Pointer fixedSmoother  =
   GaussianFilterType::New();
 GaussianFilterType::Pointer movingSmoother =
   GaussianFilterType::New();

 fixedSmoother->SetVariance( 3.0 );
 fixedSmoother->SetInput( fixedNormalizer->GetOutput() );
 movingSmoother->SetVariance( 3.0 );
 movingSmoother->SetInput( movingNormalizer->GetOutput() );

 // Set up registration
 typedef itk::AffineTransform< double, Dimension >           TransformType;
 typedef itk::RegularStepGradientDescentOptimizer OptimizerType;
 typedef itk::LinearInterpolateImageFunction<
                                   InternalImageType,
                                   double             >      InterpolatorType;
 typedef itk::MattesMutualInformationImageToImageMetric<
                                         InternalImageType,
                                         InternalImageType >    MetricType;
 typedef itk::ImageRegistrationMethod<
                                   InternalImageType,
                                   InternalImageType >       RegistrationType;
 typedef itk::CenteredTransformInitializer<
                                 TransformType,
                                 InputImageType,
                                 InputImageType >
                                           InitializerType;

 InitializerType::Pointer    initializer = InitializerType::New();
 TransformType::Pointer      transform     = TransformType::New();
 OptimizerType::Pointer      optimizer     = OptimizerType::New();
 InterpolatorType::Pointer   interpolator  = InterpolatorType::New();
 RegistrationType::Pointer   registration  = RegistrationType::New();

 // Set up the registration framework
 initializer->SetFixedImage( fixedImage );
 initializer->SetMovingImage( movingImage );
 initializer->SetTransform( transform );

 transform->SetIdentity();
 initializer->GeometryOn();
 initializer->InitializeTransform();

 registration->SetOptimizer(     optimizer     );
 registration->SetTransform(     transform     );
 registration->SetInterpolator(  interpolator  );

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

 registration->SetMetric( metric );
 registration->SetFixedImage( fixedSmoother->GetOutput() );
 registration->SetMovingImage(movingSmoother->GetOutput() );

 // Update to get the size of the region
 fixedNormalizer->Update();
 InputImageType::RegionType fixedImageRegion =
      fixedNormalizer->GetOutput()->GetBufferedRegion();
 registration->SetFixedImageRegion( fixedImageRegion );

 typedef RegistrationType::ParametersType ParametersType;
 ParametersType initialParameters( transform->GetNumberOfParameters() );

 // rotation matrix (identity)
 initialParameters[0] = 1.0;  // R(0,0)
 initialParameters[1] = 0.0;  // R(0,1)
 initialParameters[2] = 0.0;  // R(1,0)
 initialParameters[3] = 1.0;  // R(1,1)

 // translation vector
 initialParameters[4] = 0.0;
 initialParameters[5] = 0.0;

 registration->SetInitialTransformParameters( initialParameters );

 const unsigned int numberOfPixels = fixedImageRegion.GetNumberOfPixels();
 const unsigned int numberOfSamples =
                       static_cast< unsigned int >( numberOfPixels * 0.05 );

 metric->SetNumberOfHistogramBins( 26 );
 metric->SetNumberOfSpatialSamples( numberOfSamples );

 optimizer->MinimizeOn();
 optimizer->SetMaximumStepLength( 2.00 );
 optimizer->SetMinimumStepLength( 0.001 );
 optimizer->SetNumberOfIterations( 1000 );

 const unsigned int numberOfParameters =  transform->GetNumberOfParameters();
 typedef OptimizerType::ScalesType       OptimizerScalesType;
 OptimizerScalesType optimizerScales( numberOfParameters );
 double translationScale = 1.0 / 1000.0;
 optimizerScales[0] =  1.0;
 optimizerScales[1] =  1.0;
 optimizerScales[2] =  1.0;
 optimizerScales[3] =  1.0;
 optimizerScales[4] =  translationScale;
 optimizerScales[5] =  translationScale;

 optimizer->SetScales( optimizerScales );

 TransformType::Pointer finalTransform =
   TransformType::New();
 finalTransform->SetParameters( initialParameters );
 finalTransform->SetFixedParameters( transform->GetFixedParameters() );

 typedef itk::ResampleImageFilter< InputImageType, InputImageType >
   ResampleFilterType;
 ResampleFilterType::Pointer resample =
   ResampleFilterType::New();
 resample->SetTransform( finalTransform );
 resample->SetInput( movingImage);
 resample->SetSize( fixedImage->GetLargestPossibleRegion().GetSize() );
 resample->SetOutputOrigin( fixedImage->GetOrigin() );
 resample->SetOutputSpacing( fixedImage->GetSpacing() );
 resample->SetOutputDirection( fixedImage->GetDirection() );
 resample->SetDefaultPixelValue( 100 );
 resample->Update();

 // Set up the visualization pipeline
 typedef itk::CheckerBoardImageFilter< InputImageType > CheckerBoardFilterType;
 CheckerBoardFilterType::Pointer checkerboard =
   CheckerBoardFilterType::New();
 CheckerBoardFilterType::PatternArrayType pattern;
 pattern[0] = 4;
 pattern[1] = 4;

 checkerboard->SetCheckerPattern( pattern );
 checkerboard->SetInput1( fixedImage);
 checkerboard->SetInput2( resample->GetOutput());

 typedef itk::FlipImageFilter< InputImageType> FlipFilterType;
 FlipFilterType::Pointer flip =
   FlipFilterType::New();
 bool flipAxes[3] = { false, true, false };
 flip->SetFlipAxes(flipAxes);
 flip->SetInput(checkerboard->GetOutput());
 flip->Update();

 // VTK visualization pipeline
 typedef itk::ImageToVTKImageFilter<InputImageType > ConnectorType;
 ConnectorType::Pointer connector =
   ConnectorType::New();
 connector->SetInput(flip->GetOutput());

 vtkSmartPointer<vtkImageActor> actor =
   vtkSmartPointer<vtkImageActor>::New();
 connector->Update();
 actor->GetMapper()->SetInputData(connector->GetOutput());
 vtkSmartPointer<vtkRenderWindow> renderWindow =
   vtkSmartPointer<vtkRenderWindow>::New();
 vtkSmartPointer<vtkRenderer> renderer =
   vtkSmartPointer<vtkRenderer>::New();
 renderer->SetBackground(.4, .5, .6);
 renderer->AddActor(actor);
 renderWindow->SetSize(640, 480);;
 renderWindow->AddRenderer(renderer);
 renderWindow->Render();

 // Set up the iteration event observer
 IterationUpdate<InputImageType>::Pointer observer =
   IterationUpdate<InputImageType>::New();
 optimizer->AddObserver( itk::IterationEvent(), observer );

 observer->SetTransform(finalTransform);
 observer->SetFilter(flip);
 observer->SetConnector(connector);
 observer->SetImageActor(actor);
 observer->SetRenderWindow(renderWindow);
 try
   {
   registration->Update();
   std::cout << "Optimizer stop condition: "
             << registration->GetOptimizer()->GetStopConditionDescription()
             << std::endl;
   }
 catch( itk::ExceptionObject & err )
   {
   std::cout << "ExceptionObject caught !" << std::endl;
   std::cout << err << std::endl;
   return EXIT_FAILURE;
   }
 std::cout << "Final Transform: " << finalTransform << std::endl;

 ParametersType finalParameters = registration->GetLastTransformParameters();
 std::cout << "Final Parameters: " << finalParameters << std::endl;

 unsigned int numberOfIterations = optimizer->GetCurrentIteration();
 double bestValue = optimizer->GetValue();

 // Print out results
 std::cout << std::endl;
 std::cout << "Result = " << std::endl;
 std::cout << " Iterations    = " << numberOfIterations << std::endl;
 std::cout << " Metric value  = " << bestValue          << std::endl;
 std::cout << " Numb. Samples = " << numberOfSamples    << std::endl;

 // Interact with the image
 vtkSmartPointer<vtkRenderWindowInteractor> interactor =
   vtkSmartPointer<vtkRenderWindowInteractor>::New();
 vtkSmartPointer<vtkInteractorStyleImage> style =
   vtkSmartPointer<vtkInteractorStyleImage>::New();
 interactor->SetInteractorStyle(style);
 interactor->SetRenderWindow(renderWindow);
 interactor->Start();

 return EXIT_SUCCESS;

} </source>

CMakeLists.txt

<syntaxhighlight lang="cmake"> cmake_minimum_required(VERSION 3.9.5)

project(WatchRegistration)

find_package(ITK REQUIRED) include(${ITK_USE_FILE}) if (ITKVtkGlue_LOADED)

 find_package(VTK REQUIRED)
 include(${VTK_USE_FILE})

else()

 find_package(ItkVtkGlue REQUIRED)
 include(${ItkVtkGlue_USE_FILE})
 set(Glue ItkVtkGlue)

endif()

add_executable(WatchRegistration MACOSX_BUNDLE WatchRegistration.cxx) target_link_libraries(WatchRegistration

 ${Glue}  ${VTK_LIBRARIES} ${ITK_LIBRARIES})

</syntaxhighlight>

Download and Build WatchRegistration

Click here to download WatchRegistration. and its CMakeLists.txt file. Once the tarball WatchRegistration.tar has been downloaded and extracted,

cd WatchRegistration/build 

• If ITK is installed:

cmake ..

• If ITK is not installed but compiled on your system, you will need to specify the path to your ITK build:

cmake -DITK_DIR:PATH=/home/me/itk_build ..

Build the project,

make

and run it:

./WatchRegistration

WINDOWS USERS PLEASE NOTE: Be sure to add the VTK and ITK bin directories to your path. This will resolve the VTK and ITK dll's at run time.

Building All of the Examples

Many of the examples in the ITK Wiki Examples Collection require VTK. You can build all of the the examples by following these instructions. If you are a new VTK user, you may want to try the Superbuild which will build a proper ITK and VTK.

ItkVtkGlue

ITK >= 4

For examples that use QuickView (which depends on VTK), you must have built ITK with Module_ITKVtkGlue=ON.

ITK < 4

Some of the ITK Examples require VTK to display the images. If you download the entire ITK Wiki Examples Collection, the ItkVtkGlue directory will be included and configured. If you wish to just build a few examples, then you will need to download ItkVtkGlue and build it. When you run cmake it will ask you to specify the location of the ItkVtkGlue binary directory.