# ImageCorrelation

VTKExamples/Cxx/Images/ImageCorrelation

### Code

ImageCorrelation.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageShiftScale.h>
    #include <vtkImageCast.h>
    #include <vtkImageMapper3D.h>
    #include <vtkMath.h>
    #include <vtkImageData.h>
    #include <vtkPointData.h>
    #include <vtkDataArray.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageCorrelation.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkImageActor.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageCanvasSource2D> imageSource =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      imageSource->SetNumberOfScalarComponents(3);
      imageSource->SetScalarTypeToUnsignedChar();
      imageSource->SetExtent(0, 300, 0, 300, 0, 0);
      imageSource->SetDrawColor(0, 0, 0);
      imageSource->FillBox(0, 300, 0, 300);
      imageSource->SetDrawColor(255, 0, 0); //red
      imageSource->FillTriangle(10, 100,  190, 150,  40, 250);
      imageSource->Update();

      // Create an actor
      vtkSmartPointer<vtkImageActor> originalActor =
        vtkSmartPointer<vtkImageActor>::New();
      originalActor->GetMapper()->SetInputConnection(
        imageSource->GetOutputPort());

      // Create a kernel
      vtkSmartPointer<vtkImageCanvasSource2D> kernelSource =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      kernelSource->SetNumberOfScalarComponents(3);
      kernelSource->SetScalarTypeToUnsignedChar();
      kernelSource->SetExtent(0, 30, 0, 30, 0, 0);
      kernelSource->SetDrawColor(0, 0, 0);
      kernelSource->FillBox(0, 30, 0, 30);
      kernelSource->SetDrawColor(255, 0, 0); //red
      kernelSource->FillTriangle(10, 1,  25, 10,  1, 5);
      kernelSource->Update();

      // Create an actor
      vtkSmartPointer<vtkImageActor> kernelActor =
        vtkSmartPointer<vtkImageActor>::New();
      kernelActor->GetMapper()->SetInputConnection(
        kernelSource->GetOutputPort());

      // Compute the correlation
      vtkSmartPointer<vtkImageCorrelation> correlationFilter =
        vtkSmartPointer<vtkImageCorrelation>::New();
      correlationFilter->SetInputConnection(0, imageSource->GetOutputPort());
      correlationFilter->SetInputConnection(1, kernelSource->GetOutputPort());
      correlationFilter->Update();

      // At this point, corr pixels are doubles
      // So, get the scalar range
      vtkImageData* corr = correlationFilter->GetOutput();
      double corrRange[2];
      corr->GetPointData()->GetScalars()->GetRange( corrRange );

      // Rescale the correlation filter output. note that it implies
      // that minimum correlation is always zero.
      vtkSmartPointer<vtkImageShiftScale> imageScale =
        vtkSmartPointer<vtkImageShiftScale>::New();
      imageScale->SetInputConnection( correlationFilter->GetOutputPort( ));
      imageScale->SetScale( 255 / corrRange[1] );
      imageScale->SetOutputScalarTypeToUnsignedChar( );
      imageScale->Update();

      vtkSmartPointer<vtkImageCast> correlationCastFilter =
        vtkSmartPointer<vtkImageCast>::New();
      correlationCastFilter->SetInputConnection(imageScale->GetOutputPort());
      correlationCastFilter->SetOutputScalarTypeToUnsignedChar();
      correlationCastFilter->Update();

      // Create an actor
      vtkSmartPointer<vtkImageActor> correlationActor =
        vtkSmartPointer<vtkImageActor>::New();
      correlationActor->GetMapper()->SetInputConnection(
        correlationCastFilter->GetOutputPort());

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double originalViewport[4] = {0.0, 0.0, 0.33, 1.0};
      double kernelViewport[4] = {0.33, 0.0, 0.66, 1.0};
      double correlationViewport[4] = {0.66, 0.0, 1.0, 1.0};

      // Setup renderers
      vtkSmartPointer<vtkRenderer> originalRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      originalRenderer->SetViewport(originalViewport);
      originalRenderer->AddActor(originalActor);
      originalRenderer->ResetCamera();

      vtkSmartPointer<vtkRenderer> kernelRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      kernelRenderer->SetViewport(kernelViewport);
      kernelRenderer->AddActor(kernelActor);
      kernelRenderer->ResetCamera();

      vtkSmartPointer<vtkRenderer> correlationRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      correlationRenderer->SetViewport(correlationViewport);
      correlationRenderer->AddActor(correlationActor);
      correlationRenderer->ResetCamera();

      // Setup render window
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(900,300);
      renderWindow->AddRenderer(originalRenderer);
      renderWindow->AddRenderer(kernelRenderer);
      renderWindow->AddRenderer(correlationRenderer);

      // Setup render window interactor
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      vtkSmartPointer<vtkInteractorStyleImage> style =
        vtkSmartPointer<vtkInteractorStyleImage>::New();

      renderWindowInteractor->SetInteractorStyle(style);

      // Render and start interaction
      renderWindowInteractor->SetRenderWindow(renderWindow);
      renderWindowInteractor->Initialize();

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ImageCorrelation)

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

    add_executable(ImageCorrelation MACOSX_BUNDLE ImageCorrelation.cxx )

    target_link_libraries(ImageCorrelation ${VTK_LIBRARIES})

### Download and Build ImageCorrelation

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

    cd ImageCorrelation/build

If VTK is installed:

    cmake ..

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

    cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

    make

and run it:

    ./ImageCorrelation

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