# CannyEdgeDetector

VTKExamples/Cxx/Images/CannyEdgeDetector

### Code

CannyEdgeDetector.cxx

    #include <vtkVersion.h>
    #include <vtkRenderer.h>
    #include <vtkImageActor.h>
    #include <vtkStructuredPoints.h>
    #include <vtkSmartPointer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkPNGReader.h>
    #include <vtkImageLuminance.h>
    #include <vtkProperty.h>
    #include <vtkImageGaussianSmooth.h>
    #include <vtkImageCast.h>
    #include <vtkImageGradient.h>
    #include <vtkImageMagnitude.h>
    #include <vtkImageNonMaximumSuppression.h>
    #include <vtkImageConstantPad.h>
    #include <vtkImageToStructuredPoints.h>
    #include <vtkLinkEdgels.h>
    #include <vtkThreshold.h>
    #include <vtkGeometryFilter.h>
    #include <vtkSubPixelPositionEdgels.h>
    #include <vtkStripper.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkCamera.h>

    int main(int argc, char* argv[])
    {
      if(argc != 2)
      {
        std::cerr << "Required args: filename.png" << std::endl;
        return EXIT_FAILURE;
      }

      std::string filename = argv[1];

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

      vtkSmartPointer<vtkRenderer> originalRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      originalRenderer->SetViewport(originalViewport);
      vtkSmartPointer<vtkRenderer> edgeRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      edgeRenderer->SetViewport(edgeViewport);

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(600,300);
      renderWindow->SetMultiSamples(0);
      renderWindow->AddRenderer(originalRenderer);
      renderWindow->AddRenderer(edgeRenderer);

      vtkSmartPointer<vtkRenderWindowInteractor> interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);

      vtkSmartPointer<vtkPNGReader> imageIn =
        vtkSmartPointer<vtkPNGReader>::New();
      imageIn->SetFileName(filename.c_str());
      imageIn->Update();

      vtkSmartPointer<vtkImageActor> imageActor =
        vtkSmartPointer<vtkImageActor>::New();
    #if VTK_MAJOR_VERSION <= 5
      imageActor->SetInput(imageIn->GetOutput());
    #else
      imageActor->SetInputData(imageIn->GetOutput());
    #endif
      originalRenderer->AddActor(imageActor);

      vtkSmartPointer<vtkImageLuminance> il =
        vtkSmartPointer<vtkImageLuminance>::New();
      il->SetInputConnection(imageIn->GetOutputPort());

      vtkSmartPointer<vtkImageCast> ic =
        vtkSmartPointer<vtkImageCast>::New();
      ic->SetOutputScalarTypeToFloat();
      ic->SetInputConnection(il->GetOutputPort());

      // Smooth the image
      vtkSmartPointer<vtkImageGaussianSmooth> gs =
        vtkSmartPointer<vtkImageGaussianSmooth>::New();
      gs->SetInputConnection(ic->GetOutputPort());
      gs->SetDimensionality(2);
      gs->SetRadiusFactors(1, 1, 0);

      // Gradient the image
      vtkSmartPointer<vtkImageGradient> imgGradient =
        vtkSmartPointer<vtkImageGradient>::New();
      imgGradient->SetInputConnection(gs->GetOutputPort());
      imgGradient->SetDimensionality(2);

      vtkSmartPointer<vtkImageMagnitude> imgMagnitude =
        vtkSmartPointer<vtkImageMagnitude>::New();
      imgMagnitude->SetInputConnection(imgGradient->GetOutputPort());

      // Non maximum suppression
      vtkSmartPointer<vtkImageNonMaximumSuppression> nonMax =
        vtkSmartPointer<vtkImageNonMaximumSuppression>::New();
    #if VTK_MAJOR_VERSION <= 5
      nonMax->SetMagnitudeInput(imgMagnitude->GetOutput());
      nonMax->SetVectorInput(imgGradient->GetOutput());
    #else
      imgMagnitude->Update();
      nonMax->SetMagnitudeInputData(imgMagnitude->GetOutput());
      imgGradient->Update();
      nonMax->SetVectorInputData(imgGradient->GetOutput());
    #endif
      nonMax->SetDimensionality(2);

      vtkSmartPointer<vtkImageConstantPad> pad =
        vtkSmartPointer<vtkImageConstantPad>::New();
      pad->SetInputConnection(imgGradient->GetOutputPort());
      pad->SetOutputNumberOfScalarComponents(3);
      pad->SetConstant(0);

      vtkSmartPointer<vtkImageToStructuredPoints> i2sp1 =
        vtkSmartPointer<vtkImageToStructuredPoints>::New();
      i2sp1->SetInputConnection(nonMax->GetOutputPort());
    #if VTK_MAJOR_VERSION <= 5
      i2sp1->SetVectorInput(pad->GetOutput());
    #else
      pad->Update();
     i2sp1->SetVectorInputData(pad->GetOutput());
    #endif

      // Link edgles
      vtkSmartPointer<vtkLinkEdgels> imgLink =
        vtkSmartPointer<vtkLinkEdgels>::New();
      imgLink->SetInputConnection(i2sp1->GetOutputPort());
      imgLink->SetGradientThreshold(2);

      // Threshold links
      vtkSmartPointer<vtkThreshold> thresholdEdgels =
        vtkSmartPointer<vtkThreshold>::New();
      thresholdEdgels->SetInputConnection(imgLink->GetOutputPort());
      thresholdEdgels->ThresholdByUpper(10);
      thresholdEdgels->AllScalarsOff();

      vtkSmartPointer<vtkGeometryFilter> gf =
        vtkSmartPointer<vtkGeometryFilter>::New();
      gf->SetInputConnection(thresholdEdgels->GetOutputPort());

      vtkSmartPointer<vtkImageToStructuredPoints> i2sp =
        vtkSmartPointer<vtkImageToStructuredPoints>::New();
      i2sp->SetInputConnection(imgMagnitude->GetOutputPort());
    #if VTK_MAJOR_VERSION <= 5
      i2sp->SetVectorInput(pad->GetOutput());
    #else
      pad->Update();
      i2sp->SetVectorInputData(pad->GetOutput());
    #endif

      // Subpixel them
      vtkSmartPointer<vtkSubPixelPositionEdgels> spe =
        vtkSmartPointer<vtkSubPixelPositionEdgels>::New();
      spe->SetInputConnection(gf->GetOutputPort());
    #if VTK_MAJOR_VERSION <= 5
      spe->SetGradMaps(i2sp->GetStructuredPointsOutput());
    #else
      i2sp->Update();
      spe->SetGradMapsData(i2sp->GetStructuredPointsOutput());
    #endif

      vtkSmartPointer<vtkStripper> strip =
        vtkSmartPointer<vtkStripper>::New();
      strip->SetInputConnection(spe->GetOutputPort());

      vtkSmartPointer<vtkPolyDataMapper> dsm =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      dsm->SetInputConnection(strip->GetOutputPort());
      dsm->ScalarVisibilityOff();

      vtkSmartPointer<vtkActor> planeActor =
        vtkSmartPointer<vtkActor>::New();
      planeActor->SetMapper(dsm);
      planeActor->GetProperty()->SetAmbient(1.0);
      planeActor->GetProperty()->SetDiffuse(0.0);

      // Add the actors to the renderer, set the background and size
      edgeRenderer->AddActor(planeActor);

      // Render the image
      interactor->Initialize();
      renderWindow->Render();
      renderWindow->Render();

      interactor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(CannyEdgeDetector)

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

    add_executable(CannyEdgeDetector MACOSX_BUNDLE CannyEdgeDetector.cxx )

    target_link_libraries(CannyEdgeDetector ${VTK_LIBRARIES})

### Download and Build CannyEdgeDetector

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

    cd CannyEdgeDetector/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:

    ./CannyEdgeDetector

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.