# ImageMagnitude

VTKExamples/Cxx/Images/ImageMagnitude

### Description

There are two ways to convert images to greyscale: {{class|vtkImageLuminance}} uses the [(video)|luminance equation]]([wikipedia:Luma) for properly weighting the R, G, and B components; {{class|vtkImageMagnitude}} does a simple sum-of-squares computation of the components (i.e. the [(mathematics)#Euclidean vector space|Euclidean norm]] -- not the [wikipedia:Root mean square|quadratic mean]!), and is meant for vector data.

For an example of usage of the vtkImageLuminance filter, see .

### Code

ImageMagnitude.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageMagnitude.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkRenderer.h>
    #include <vtkJPEGReader.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<vtkImageMagnitude> magnitudeFilter =
          vtkSmartPointer<vtkImageMagnitude>::New();
      magnitudeFilter->SetInputConnection(source->GetOutputPort());
      magnitudeFilter->Update();

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

      vtkSmartPointer<vtkImageActor> magnitudeActor =
        vtkSmartPointer<vtkImageActor>::New();
      magnitudeActor->GetMapper()->SetInputConnection(
        magnitudeFilter->GetOutputPort());

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
      double magnitudeViewport[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> magnitudeRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      magnitudeRenderer->SetViewport(magnitudeViewport);
      magnitudeRenderer->AddActor(magnitudeActor);
      magnitudeRenderer->ResetCamera();
      magnitudeRenderer->SetBackground(.4, .5, .7);

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

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

      renderWindowInteractor->SetInteractorStyle(style);

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

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ImageMagnitude)

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

    add_executable(ImageMagnitude MACOSX_BUNDLE ImageMagnitude.cxx)

    target_link_libraries(ImageMagnitude ${VTK_LIBRARIES})

### Download and Build ImageMagnitude

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

    cd ImageMagnitude/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:

    ./ImageMagnitude

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.