# ImageLuminance

VTKExamples/Cxx/Images/ImageLuminance

### Description

There are two ways to convert images to greyscale:

- vtkImageLuminance uses the luminance equation for properly weighting the R, G, and B components;

- vtkImageMagnitude does a simple sum-of-squares computation of the components (i.e. the Euclidean norm -- not the quadratic mean!), and is meant for vector data.

For an example of usage of the vtkImageMagnitude filter, see ImageMagnitude.

### Code

ImageLuminance.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageLuminance.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkRenderer.h>
    #include <vtkImageActor.h>

    int main(int, char *[])
    {
      // Create an image of a rectangle
      vtkSmartPointer<vtkImageCanvasSource2D> source =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      source->SetScalarTypeToUnsignedChar();
      source->SetNumberOfScalarComponents(3);
      source->SetExtent(0, 200, 0, 200, 0, 0);

      // Clear the image
      source->SetDrawColor(0,0,0);
      source->FillBox(0,200,0,200);

      // Draw a red box
      source->SetDrawColor(255,0,0);
      source->FillBox(100,120,100,120);
      source->Update();

      vtkSmartPointer<vtkImageLuminance> luminanceFilter =
          vtkSmartPointer<vtkImageLuminance>::New();
      luminanceFilter->SetInputConnection(source->GetOutputPort());
      luminanceFilter->Update();

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

      vtkSmartPointer<vtkImageActor> luminanceActor =
        vtkSmartPointer<vtkImageActor>::New();
      luminanceActor->GetMapper()->SetInputConnection(
        luminanceFilter->GetOutputPort());

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
      double luminanceViewport[4] = {0.5, 0.0, 1.0, 1.0};

      // Setup renderers
      vtkSmartPointer<vtkRenderer> originalRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      originalRenderer->SetViewport(originalViewport);
      originalRenderer->AddActor(originalActor);
      originalRenderer->ResetCamera();
      originalRenderer->SetBackground(.4, .5, .6);

      vtkSmartPointer<vtkRenderer> luminanceRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      luminanceRenderer->SetViewport(luminanceViewport);
      luminanceRenderer->AddActor(luminanceActor);
      luminanceRenderer->ResetCamera();
      luminanceRenderer->SetBackground(.4, .5, .7);

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(600, 300);
      renderWindow->AddRenderer(originalRenderer);
      renderWindow->AddRenderer(luminanceRenderer);

      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      vtkSmartPointer<vtkInteractorStyleImage> style =
        vtkSmartPointer<vtkInteractorStyleImage>::New();

      renderWindowInteractor->SetInteractorStyle(style);

      renderWindowInteractor->SetRenderWindow(renderWindow);
      renderWindow->Render();
      renderWindowInteractor->Initialize();

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ImageLuminance)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkImagingColor
      vtkImagingSources
      vtkInteractionStyle
      vtkRenderingContextOpenGL2
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingGL2PSOpenGL2
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping ImageLuminance: ${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(ImageLuminance MACOSX_BUNDLE ImageLuminance.cxx )
      target_link_libraries(ImageLuminance PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(ImageLuminance MACOSX_BUNDLE ImageLuminance.cxx )
      target_link_libraries(ImageLuminance PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS ImageLuminance
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build ImageLuminance

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

    cd ImageLuminance/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:

    ./ImageLuminance

WINDOWS USERS

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