# ImageAccumulateGreyscale

VTKExamples/Cxx/Images/ImageAccumulateGreyscale

### Code

ImageAccumulateGreyscale.cxx

    #include <vtkActor.h>
    #include <vtkBarChartActor.h>
    #include <vtkFieldData.h>
    #include <vtkImageAccumulate.h>
    #include <vtkImageData.h>
    #include <vtkImageExtractComponents.h>
    #include <vtkIntArray.h>
    #include <vtkJPEGReader.h>
    #include <vtkLegendBoxActor.h>
    #include <vtkProperty2D.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkSmartPointer.h>
    #include <vtkImageMagnitude.h>

    int main( int argc, char *argv[] )
    {
      // Handle the arguments
      if( argc < 2 )
      {
        std::cout << "Required arguments: filename.jpg" << std::endl;
        return EXIT_FAILURE;
      }

      // Read a jpeg image
      vtkSmartPointer<vtkJPEGReader> reader =
        vtkSmartPointer<vtkJPEGReader>::New();
      reader->SetFileName( argv[1] );
      reader->Update();

      vtkSmartPointer<vtkImageMagnitude> magnitude =
        vtkSmartPointer<vtkImageMagnitude>::New();
      magnitude->SetInputConnection(reader->GetOutputPort());
      magnitude->Update();

      double red[3] = {1, 0, 0 };

      vtkSmartPointer<vtkIntArray> frequencies =
        vtkSmartPointer<vtkIntArray>::New();

      vtkSmartPointer<vtkImageAccumulate> histogram =
        vtkSmartPointer<vtkImageAccumulate>::New();
      histogram->SetInputConnection(magnitude->GetOutputPort());
      histogram->SetComponentExtent(0,255,0,0,0,0);
      histogram->SetComponentOrigin(0,0,0);
      histogram->SetComponentSpacing(1,0,0);
      histogram->IgnoreZeroOn();
      histogram->Update();

      frequencies->SetNumberOfComponents(1);
      frequencies->SetNumberOfTuples(256);
      int* output = static_cast<int*>(histogram->GetOutput()->GetScalarPointer());

      for(int j = 0; j < 256; ++j)
      {
        frequencies->SetTuple1(j, *output++);
      }

      vtkSmartPointer<vtkDataObject> dataObject =
        vtkSmartPointer<vtkDataObject>::New();

      dataObject->GetFieldData()->AddArray( frequencies );

      // Create a vtkBarChartActor
      vtkSmartPointer<vtkBarChartActor> barChart =
        vtkSmartPointer<vtkBarChartActor>::New();

      barChart->SetInput(dataObject);
      barChart->SetTitle("Histogram");
      barChart->GetPositionCoordinate()->SetValue(0.05,0.05,0.0);
      barChart->GetPosition2Coordinate()->SetValue(0.95,0.85,0.0);
      barChart->GetProperty()->SetColor(1,1,1);

      barChart->GetLegendActor()->SetNumberOfEntries(dataObject->GetFieldData()->GetArray(0)->GetNumberOfTuples());
      barChart->LegendVisibilityOff();
      barChart->LabelVisibilityOff();

      int count = 0;
      for(int i = 0; i < 256; ++i)
      {
        barChart->SetBarColor( count++, red );
      }

      // Visualize the histogram
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->AddActor(barChart);

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      renderWindow->SetSize(640, 480);

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

      // Initialize the event loop and then start it
      interactor->Initialize();
      interactor->Start();

      return  EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ImageAccumulateGreyscale)

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

    add_executable(ImageAccumulateGreyscale MACOSX_BUNDLE ImageAccumulateGreyscale.cxx)

    target_link_libraries(ImageAccumulateGreyscale ${VTK_LIBRARIES})

### Download and Build ImageAccumulateGreyscale

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

    cd ImageAccumulateGreyscale/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:

    ./ImageAccumulateGreyscale

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.