# GaussianSmooth

VTKExamples/Cxx/ImageProcessing/GaussianSmooth

### Description

Low-pass filters can be implemented as convolution with a Gaussian kernel. The Gaussian kernel displayed on top has been magnified for this figure.

Info

See this figure in Chapter 10 the VTK Textbook.

Other Languages

See (Python)

### Code

GaussianSmooth.cxx

    #include <vtkImageActor.h>
    #include <vtkImageCast.h>
    #include <vtkImageData.h>
    #include <vtkImageGaussianSmooth.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageNoiseSource.h>
    #include <vtkImageReader2.h>
    #include <vtkImageReader2Factory.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkNamedColors.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkSmartPointer.h>

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

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

      // Process the image
      vtkSmartPointer<vtkImageCast> cast =
        vtkSmartPointer<vtkImageCast>::New();
      cast->SetInputConnection(reader->GetOutputPort());
      cast->SetOutputScalarTypeToFloat();

      vtkSmartPointer<vtkImageGaussianSmooth> filter =
        vtkSmartPointer<vtkImageGaussianSmooth>::New();
      filter->SetDimensionality(2);
      filter->SetInputConnection(cast->GetOutputPort());
      filter->SetStandardDeviations(4.0, 4.0);
      filter->SetRadiusFactors(2.0, 2.0);

      // Create actors
      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      vtkSmartPointer<vtkImageActor> originalActor =
        vtkSmartPointer<vtkImageActor>::New();
      originalActor->GetMapper()->SetInputConnection(
        reader->GetOutputPort());

      vtkSmartPointer<vtkImageActor> filteredActor =
        vtkSmartPointer<vtkImageActor>::New();
      filteredActor->GetMapper()->SetInputConnection(
        filter->GetOutputPort());

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
      double filteredViewport[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(colors->GetColor3d("SlateGray").GetData());

      vtkSmartPointer<vtkRenderer> filteredRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      filteredRenderer->SetViewport(filteredViewport);
      filteredRenderer->AddActor(filteredActor);
      filteredRenderer->ResetCamera();
      filteredRenderer->SetBackground(colors->GetColor3d("LightSlateGray").GetData());

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

      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(GaussianSmooth)

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

### Download and Build GaussianSmooth

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

    cd GaussianSmooth/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:

    ./GaussianSmooth

WINDOWS USERS

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