# ImageStencil

VTKExamples/Cxx/Images/ImageStencil

### Description

This example creates a red image and a green image. It creates a mask that is half on and half off. It then combines the images according to the mask using an ImageStencil.

Seealso

ImageTransparency and Transparency

### Code

ImageStencil.cxx

    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageStencil.h>
    #include <vtkImageStencilData.h>
    #include <vtkImageToImageStencil.h>
    #include <vtkPointData.h>
    #include <vtkSmartPointer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkRenderer.h>
    #include <vtkImageActor.h>

    namespace
    {
    void CreateColorImage(vtkImageData*, unsigned int channel);
    void CreateMask(vtkImageData*);
    }

    int main(int, char *[])
    {
      vtkSmartPointer<vtkImageData> image1 = vtkSmartPointer<vtkImageData>::New();
      CreateColorImage(image1, 0); // Create a red image

      vtkSmartPointer<vtkImageData> image2 = vtkSmartPointer<vtkImageData>::New();
      CreateColorImage(image2, 1); // Create a green image

      vtkSmartPointer<vtkImageData> mask = vtkSmartPointer<vtkImageData>::New();
      CreateMask(mask);

      //vtkSmartPointer<vtkImageStencilData> stencilData = vtkSmartPointer<vtkImageStencilData>::New();
      vtkSmartPointer<vtkImageToImageStencil> imageToImageStencil = vtkSmartPointer<vtkImageToImageStencil>::New();
      imageToImageStencil->SetInputData(mask);
      imageToImageStencil->ThresholdByUpper(122);

      vtkSmartPointer<vtkImageStencil> stencil = vtkSmartPointer<vtkImageStencil>::New();
      stencil->SetInputConnection(2, imageToImageStencil->GetOutputPort());
      stencil->ReverseStencilOn();
      stencil->SetBackgroundInputData(image2);
      stencil->SetInputData(image1);
      stencil->Update();

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

      // Setup renderer
      vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
      renderer->AddActor(actor);
      renderer->ResetCamera();

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

      // 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->Start();

      return EXIT_SUCCESS;
    }

    namespace
    {
    void CreateColorImage(vtkImageData* image, const unsigned int channel)
    {
      unsigned int dim = 20;

      image->SetDimensions(dim, dim, 1);
      image->AllocateScalars(VTK_UNSIGNED_CHAR,3);

      for(unsigned int x = 0; x < dim; x++)
      {
        for(unsigned int y = 0; y < dim; y++)
        {
          unsigned char* pixel = static_cast<unsigned char*>(image->GetScalarPointer(x,y,0));
          pixel[0] = 0;
          pixel[1] = 0;
          pixel[2] = 0;

          pixel[channel] = 255;
        }
      }

      image->Modified();
    }

    void CreateMask(vtkImageData* image)
    {
      unsigned int dim = 20;

      image->SetDimensions(dim, dim, 1);
      image->AllocateScalars(VTK_UNSIGNED_CHAR, 1);

      for(unsigned int x = 0; x < dim; x++)
      {
        for(unsigned int y = 0; y < dim; y++)
        {
          unsigned char* pixel = static_cast<unsigned char*>(image->GetScalarPointer(x,y,0));
          if(x < dim/2)
          {
            pixel[0] = 0;
          }
          else
          {
            pixel[0] = 255;
          }
        }
      }

      image->Modified();
    }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ImageStencil)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkImagingCore
      vtkImagingStencil
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping ImageStencil: ${VTK_NOT_FOUND_MESSAGE}")
      return ()
    endif()
    message (STATUS "VTK_VERSION: ${VTK_VERSION}")
    if (VTK_VERSION VERSION_LESS "8.90.0")
      # old system
      include(${VTK_USE_FILE})
      add_executable(ImageStencil MACOSX_BUNDLE ImageStencil.cxx )
      target_link_libraries(ImageStencil PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(ImageStencil MACOSX_BUNDLE ImageStencil.cxx )
      target_link_libraries(ImageStencil PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS ImageStencil
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build ImageStencil

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

    cd ImageStencil/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:

    ./ImageStencil

WINDOWS USERS

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