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# MedianComparison

VTKEx/Cxx/ImageProcessing/MedianComparison

### Description

Comparison of Gaussian and Median smoothing for reducing low-probability high-amplitude noise.

Info

See this figure in Chapter 10 the VTK Textbook.

Other languages

See (Python)

Question

If you have a simple question about this example contact us at VTKExProject If your question is more complex and may require extended discussion, please use the VTK Discourse Forum

### Code

MedianComparison.cxx

    #include <vtkDataArray.h>
    #include <vtkImageActor.h>
    #include <vtkImageCast.h>
    #include <vtkImageData.h>
    #include <vtkImageGaussianSmooth.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageMathematics.h>
    #include <vtkImageMedian3D.h>
    #include <vtkImageNoiseSource.h>
    #include <vtkImageProperty.h>
    #include <vtkImageReader2.h>
    #include <vtkImageReader2Factory.h>
    #include <vtkImageThreshold.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkPointData.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkSmartPointer.h>

    #include <vector>

    namespace
    {
    void AddShotNoise(vtkSmartPointer<vtkImageData> &inputImage,
                      vtkSmartPointer<vtkImageData> &outputImage,
                      double amplitude,
                      double noiseFraction,
                      int extent[6]);
    }
    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;
      reader.TakeReference(
        readerFactory->CreateImageReader2(argv[1]));
      reader->SetFileName(argv[1]);
      reader->Update();

      int scalarRange[2];
      scalarRange[0] =
        reader->GetOutput()->GetPointData()->GetScalars()->GetRange()[0];
      scalarRange[1] =
        reader->GetOutput()->GetPointData()->GetScalars()->GetRange()[1];
      std::cout << "Range: "
                << scalarRange[0] << ", " << scalarRange[1]
                << std::endl;
      int middleSlice = (reader->GetOutput()->GetExtent()[5] -
                         reader->GetOutput()->GetExtent()[4]) / 2;

      // Work with double images
      vtkSmartPointer<vtkImageCast> cast =
        vtkSmartPointer<vtkImageCast>::New();
      cast->SetInputConnection(reader->GetOutputPort());
      cast->SetOutputScalarTypeToDouble();
      cast->Update();

      vtkSmartPointer<vtkImageData> originalData =
        vtkSmartPointer<vtkImageData>::New();
      originalData->DeepCopy(cast->GetOutput());

      vtkSmartPointer<vtkImageData> noisyData =
        vtkSmartPointer<vtkImageData>::New();

      AddShotNoise(originalData, noisyData,
                   2000.0, .1, reader->GetOutput()->GetExtent());
      vtkSmartPointer<vtkImageMedian3D> median =
        vtkSmartPointer<vtkImageMedian3D>::New();
      median->SetInputData(noisyData);
      median->SetKernelSize(5, 5, 1);

      vtkSmartPointer<vtkImageGaussianSmooth> gaussian =
        vtkSmartPointer<vtkImageGaussianSmooth>::New();
      gaussian->SetDimensionality(2);
      gaussian->SetInputData(noisyData);
      gaussian->SetStandardDeviations(2.0, 2.0);
      gaussian->SetRadiusFactors(2.0, 2.0);

      int colorWindow = (scalarRange[1] - scalarRange[0]) * .8;
      int colorLevel = colorWindow / 2;
      vtkSmartPointer<vtkImageActor> originalActor =
        vtkSmartPointer<vtkImageActor>::New();
      originalActor->GetMapper()->SetInputData(originalData);
      originalActor->GetProperty()->SetColorWindow(colorWindow);
      originalActor->GetProperty()->SetColorLevel(colorLevel);
      originalActor->GetProperty()->SetInterpolationTypeToNearest();
      originalActor->SetZSlice(middleSlice);

      vtkSmartPointer<vtkImageActor> noisyActor =
        vtkSmartPointer<vtkImageActor>::New();
      noisyActor->GetMapper()->SetInputData(noisyData);
      noisyActor->GetProperty()->SetColorWindow(colorWindow);
      noisyActor->GetProperty()->SetColorLevel(colorLevel);
      noisyActor->GetProperty()->SetInterpolationTypeToNearest();
      noisyActor->SetZSlice(middleSlice);

      vtkSmartPointer<vtkImageActor> gaussianActor =
        vtkSmartPointer<vtkImageActor>::New();
      gaussianActor->GetMapper()->SetInputConnection(gaussian->GetOutputPort());
      gaussianActor->GetProperty()->SetColorWindow(colorWindow);
      gaussianActor->GetProperty()->SetColorLevel(colorLevel);
      gaussianActor->GetProperty()->SetInterpolationTypeToNearest();
      gaussianActor->SetZSlice(middleSlice);

      vtkSmartPointer<vtkImageActor> medianActor =
        vtkSmartPointer<vtkImageActor>::New();
      medianActor->GetMapper()->SetInputConnection(median->GetOutputPort());
      medianActor->GetProperty()->SetColorWindow(colorWindow);
      medianActor->GetProperty()->SetColorLevel(colorLevel);
      medianActor->GetProperty()->SetInterpolationTypeToNearest();
      medianActor->SetZSlice(middleSlice);

      // Setup renderers
      vtkSmartPointer<vtkRenderer> originalRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      originalRenderer->AddActor(originalActor);
      vtkSmartPointer<vtkRenderer> noisyRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      noisyRenderer->AddActor(noisyActor);
      vtkSmartPointer<vtkRenderer> gaussRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      gaussRenderer->AddActor(gaussianActor);
      vtkSmartPointer<vtkRenderer> medianRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      medianRenderer->AddActor(medianActor);

      std::vector<vtkSmartPointer<vtkRenderer> > renderers;
      renderers.push_back(originalRenderer);
      renderers.push_back(noisyRenderer);
      renderers.push_back(gaussRenderer);
      renderers.push_back(medianRenderer);

      // Setup viewports for the renderers
      int rendererSize = 400;
      unsigned int xGridDimensions = 2;
      unsigned int yGridDimensions = 2;

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(
        rendererSize * xGridDimensions, rendererSize * yGridDimensions);
      for (int row = 0; row < static_cast<int>(yGridDimensions); row++)
      {
        for (int col = 0; col < static_cast<int>(xGridDimensions); col++)
        {
          int index = row * xGridDimensions + col;
          // (xmin, ymin, xmax, ymax)
          double viewport[4] = {
            static_cast<double>(col) / xGridDimensions,
            static_cast<double>(yGridDimensions - (row + 1)) / yGridDimensions,
            static_cast<double>(col + 1) / xGridDimensions,
            static_cast<double>(yGridDimensions - row) / yGridDimensions};
          renderers[index]->SetViewport(viewport);
          renderWindow->AddRenderer(renderers[index]);
        }
      }

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

      renderWindowInteractor->SetInteractorStyle(style);
      renderWindowInteractor->SetRenderWindow(renderWindow);

      // Renderers share one camera
      renderWindow->Render();
      for (size_t r = 1; r < renderers.size(); ++r)
      {
        renderers[r]->SetActiveCamera(renderers[0]->GetActiveCamera());
      }
      renderWindowInteractor->Initialize();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }
    namespace
    {
    void AddShotNoise(vtkSmartPointer<vtkImageData> &inputImage,
                      vtkSmartPointer<vtkImageData> &outputImage,
                      double noiseAmplitude,
                      double noiseFraction,
                      int extent[6])
    {
      vtkSmartPointer<vtkImageNoiseSource> shotNoiseSource =
        vtkSmartPointer<vtkImageNoiseSource>::New();
      shotNoiseSource->SetWholeExtent(extent);
      shotNoiseSource->SetMinimum(0.0);
      shotNoiseSource->SetMaximum(1.0);

      vtkSmartPointer<vtkImageThreshold> shotNoiseThresh1 =
        vtkSmartPointer<vtkImageThreshold>::New();
      shotNoiseThresh1->SetInputConnection(shotNoiseSource->GetOutputPort());
      shotNoiseThresh1->ThresholdByLower(1.0 - noiseFraction);
      shotNoiseThresh1->SetInValue(0);
      shotNoiseThresh1->SetOutValue(noiseAmplitude);

      vtkSmartPointer<vtkImageThreshold> shotNoiseThresh2 =
        vtkSmartPointer<vtkImageThreshold>::New();
      shotNoiseThresh2->SetInputConnection(shotNoiseSource->GetOutputPort());
      shotNoiseThresh2->ThresholdByLower(noiseFraction);
      shotNoiseThresh2->SetInValue(1.0 - noiseAmplitude);
      shotNoiseThresh2->SetOutValue(0.0);

      vtkSmartPointer<vtkImageMathematics> shotNoise =
        vtkSmartPointer<vtkImageMathematics>::New();
      shotNoise->SetInputConnection(0, shotNoiseThresh1->GetOutputPort());
      shotNoise->SetInputConnection(1, shotNoiseThresh2->GetOutputPort());
      shotNoise->SetOperationToAdd();

      vtkSmartPointer<vtkImageMathematics> add =
        vtkSmartPointer<vtkImageMathematics>::New();
      add->SetInputData(0, inputImage);
      add->SetInputConnection(1, shotNoise->GetOutputPort());
      add->SetOperationToAdd();
      add->Update();
      outputImage->DeepCopy(add->GetOutput());
    }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(MedianComparison)

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

### Download and Build MedianComparison

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

    cd MedianComparison/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:

    ./MedianComparison

WINDOWS USERS

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