# ExtractComponents

VTKExamples/Cxx/Images/ExtractComponents

### Description

This example separates an image into the red channel, the green channel, and the blue channel using vtkImageExtractComponents.

Seealso

For the reverse operation, see CombiningRGBChannels.

### Code

ExtractComponents.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageExtractComponents.h>

    #include <vtkImageReader2Factory.h>
    #include <vtkImageReader2.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkRenderer.h>
    #include <vtkJPEGReader.h>
    #include <vtkImageActor.h>
    #include <vtkNamedColors.h>

    int main(int argc, char *argv[])
    {
      // Verify command line arguments
      if (argc != 2 )
      {
        std::cout << "Usage: " << argv[0] << " InputFilename" << std::endl;
        return EXIT_FAILURE;
      }

      // Read the image
      vtkSmartPointer<vtkImageReader2Factory> readerFactory =
        vtkSmartPointer<vtkImageReader2Factory>::New();
      vtkImageReader2 *reader = readerFactory->CreateImageReader2(argv[1]);
      reader->SetFileName(argv[1]);
      reader->Update();

      vtkSmartPointer<vtkImageExtractComponents> extractRedFilter =
        vtkSmartPointer<vtkImageExtractComponents>::New();
      extractRedFilter->SetInputConnection(reader->GetOutputPort());
      extractRedFilter->SetComponents(0);
      extractRedFilter->Update();

      vtkSmartPointer<vtkImageExtractComponents> extractGreenFilter =
        vtkSmartPointer<vtkImageExtractComponents>::New();
      extractGreenFilter->SetInputConnection(reader->GetOutputPort());
      extractGreenFilter->SetComponents(1);
      extractGreenFilter->Update();

      vtkSmartPointer<vtkImageExtractComponents> extractBlueFilter =
        vtkSmartPointer<vtkImageExtractComponents>::New();
      extractBlueFilter->SetInputConnection(reader->GetOutputPort());
      extractBlueFilter->SetComponents(2);
      extractBlueFilter->Update();

      // Create actors
      vtkSmartPointer<vtkImageActor> inputActor =
        vtkSmartPointer<vtkImageActor>::New();
      inputActor->GetMapper()->SetInputConnection(reader->GetOutputPort());

      vtkSmartPointer<vtkImageActor> redActor =
        vtkSmartPointer<vtkImageActor>::New();
      redActor->GetMapper()->SetInputConnection(extractRedFilter->GetOutputPort());

      vtkSmartPointer<vtkImageActor> greenActor =
        vtkSmartPointer<vtkImageActor>::New();
      greenActor->GetMapper()->SetInputConnection(extractGreenFilter->GetOutputPort());

      vtkSmartPointer<vtkImageActor> blueActor =
        vtkSmartPointer<vtkImageActor>::New();
      blueActor->GetMapper()->SetInputConnection(extractBlueFilter->GetOutputPort());

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double inputViewport[4] = {0.0, 0.0, 0.25, 1.0};
      double redViewport[4] = {0.25, 0.0, 0.5, 1.0};
      double greenViewport[4] = {0.5, 0.0, 0.75, 1.0};
      double blueViewport[4] = {0.75, 0.0, 1.0, 1.0};

      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      // Setup renderers
      vtkSmartPointer<vtkRenderer> inputRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      inputRenderer->SetViewport(inputViewport);
      inputRenderer->AddActor(inputActor);
      inputRenderer->ResetCamera();
      inputRenderer->SetBackground(colors->GetColor3d("Snow").GetData());

      vtkSmartPointer<vtkRenderer> redRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      redRenderer->SetViewport(redViewport);
      redRenderer->AddActor(redActor);
      redRenderer->ResetCamera();
      redRenderer->SetBackground(colors->GetColor3d("Tomato").GetData());

      vtkSmartPointer<vtkRenderer> greenRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      greenRenderer->SetViewport(greenViewport);
      greenRenderer->AddActor(greenActor);
      greenRenderer->ResetCamera();
      greenRenderer->SetBackground(colors->GetColor3d("Mint").GetData());

      vtkSmartPointer<vtkRenderer> blueRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      blueRenderer->SetViewport(blueViewport);
      blueRenderer->AddActor(blueActor);
      blueRenderer->ResetCamera();
      blueRenderer->SetBackground(colors->GetColor3d("Peacock").GetData());

      // Setup render window
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(1000, 250);
      renderWindow->AddRenderer(inputRenderer);
      renderWindow->AddRenderer(redRenderer);
      renderWindow->AddRenderer(greenRenderer);
      renderWindow->AddRenderer(blueRenderer);

      // 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();

      reader->Delete();
      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ExtractComponents)

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

    add_executable(ExtractComponents MACOSX_BUNDLE ExtractComponents.cxx )

    target_link_libraries(ExtractComponents ${VTK_LIBRARIES})

### Download and Build ExtractComponents

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

    cd ExtractComponents/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:

    ./ExtractComponents

WINDOWS USERS

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