# ImageGradientMagnitude

VTKExamples/Cxx/Images/ImageGradientMagnitude

### Code

ImageGradientMagnitude.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageGradientMagnitude.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkRenderer.h>
    #include <vtkJPEGReader.h>
    #include <vtkImageActor.h>
    #include <vtkImageEllipsoidSource.h>
    #include <vtkImageCast.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageEllipsoidSource> source =
        vtkSmartPointer<vtkImageEllipsoidSource>::New();
      source->SetWholeExtent(0, 20, 0, 20, 0, 0);
      source->SetCenter(10,10,0);
      source->SetRadius(3,4,0);
      source->Update();

      vtkSmartPointer<vtkImageGradientMagnitude> gradientMagnitudeFilter =
          vtkSmartPointer<vtkImageGradientMagnitude>::New();
      gradientMagnitudeFilter->SetInputConnection(source->GetOutputPort());
      gradientMagnitudeFilter->Update();

      vtkSmartPointer<vtkImageCast> gradientMagnitudeCastFilter =
        vtkSmartPointer<vtkImageCast>::New();
      gradientMagnitudeCastFilter->SetInputConnection(gradientMagnitudeFilter->GetOutputPort());
      gradientMagnitudeCastFilter->SetOutputScalarTypeToUnsignedChar();
      gradientMagnitudeCastFilter->Update();

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

      vtkSmartPointer<vtkImageActor> gradientMagnitudeActor =
        vtkSmartPointer<vtkImageActor>::New();
      gradientMagnitudeActor->GetMapper()->SetInputConnection(
        gradientMagnitudeCastFilter->GetOutputPort());

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

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

      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(ImageGradientMagnitude)

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

    add_executable(ImageGradientMagnitude MACOSX_BUNDLE ImageGradientMagnitude.cxx)

    target_link_libraries(ImageGradientMagnitude ${VTK_LIBRARIES})

### Download and Build ImageGradientMagnitude

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

    cd ImageGradientMagnitude/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:

    ./ImageGradientMagnitude

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.