# ImageDifference

VTKExamples/Cxx/Images/ImageDifference

### Description

This example makes a large square and a smaller square and subtracts them, leaving the outline of a square.

### Code

ImageDifference.cxx

    #include <vtkVersion.h>
    #include <vtkSmartPointer.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageDifference.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkProperty.h>
    #include <vtkRenderer.h>
    #include <vtkImageActor.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageCanvasSource2D> source1 =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      source1->SetScalarTypeToUnsignedChar();
      source1->SetNumberOfScalarComponents(3);
      source1->SetExtent(0, 100, 0, 100, 0, 0);
      source1->SetDrawColor(0,0,0,1);
      source1->FillBox(0, 100, 0, 100);
      source1->SetDrawColor(255,0,0,1);
      source1->FillBox(10, 90, 10, 90);
      source1->Update();

      // Create another image
      vtkSmartPointer<vtkImageCanvasSource2D> source2 =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      source2->SetScalarTypeToUnsignedChar();
      source2->SetNumberOfScalarComponents(3);
      source2->SetExtent(0, 100, 0, 100, 0, 0);
      source2->SetDrawColor(0,0,0,1);
      source2->FillBox(0, 100, 0, 100);
      source2->SetDrawColor(255,0,0,1);
      source2->FillBox(20, 80, 20, 80);
      source2->Update();

      vtkSmartPointer<vtkImageDifference> differenceFilter =
        vtkSmartPointer<vtkImageDifference>::New();

      differenceFilter->SetInputConnection(source1->GetOutputPort());
    #if VTK_MAJOR_VERSION <= 5
      differenceFilter->SetImage(source2->GetOutput());
    #else
      differenceFilter->SetImageConnection(source2->GetOutputPort());
    #endif
      differenceFilter->Update();

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double leftViewport[4] = {0.0, 0.0, 0.33, 1.0};
      double centerViewport[4] = {0.33, 0.0, 0.66, 1.0};
      double rightViewport[4] = {0.66, 0.0, 1.0, 1.0};

      // Setup render window
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();

      // Setup renderers
      vtkSmartPointer<vtkRenderer> leftRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderWindow->AddRenderer(leftRenderer);
      leftRenderer->SetViewport(leftViewport);
      vtkSmartPointer<vtkImageActor> leftActor =
        vtkSmartPointer<vtkImageActor>::New();
      leftActor->GetMapper()->SetInputConnection(source1->GetOutputPort());
      leftRenderer->AddActor(leftActor);

      vtkSmartPointer<vtkRenderer> centerRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderWindow->AddRenderer(centerRenderer);
      centerRenderer->SetViewport(centerViewport);
      vtkSmartPointer<vtkImageActor> centerActor =
        vtkSmartPointer<vtkImageActor>::New();
      centerActor->GetMapper()->SetInputConnection(source2->GetOutputPort());
      centerRenderer->AddActor(centerActor);

      vtkSmartPointer<vtkRenderer> rightRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderWindow->AddRenderer(rightRenderer);
      rightRenderer->SetViewport(rightViewport);
      vtkSmartPointer<vtkImageActor> rightActor =
        vtkSmartPointer<vtkImageActor>::New();
      rightActor->GetMapper()->SetInputConnection(differenceFilter->GetOutputPort());
      rightRenderer->AddActor(rightActor);

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

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

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ImageDifference)

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

    add_executable(ImageDifference MACOSX_BUNDLE ImageDifference.cxx )

    target_link_libraries(ImageDifference ${VTK_LIBRARIES})

### Download and Build ImageDifference

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

    cd ImageDifference/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:

    ./ImageDifference

WINDOWS USERS

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