WikiExamples/ImageProcessing/BinaryImageToLabelMapFilter.cxx

#include "itkImage.h"
#include "itkImageFileWriter.h"
#include "itkImageRegionIterator.h"
#include "itkBinaryImageToLabelMapFilter.h"

using ImageType = itk::Image<unsigned char, 2>;
static void CreateImage(ImageType::Pointer image);

int main(int, char *[])
{
  ImageType::Pointer image = ImageType::New();
  CreateImage(image);

  using BinaryImageToLabelMapFilterType = itk::BinaryImageToLabelMapFilter<ImageType>;
  BinaryImageToLabelMapFilterType::Pointer binaryImageToLabelMapFilter = BinaryImageToLabelMapFilterType::New();
  binaryImageToLabelMapFilter->SetInput(image);
  binaryImageToLabelMapFilter->Update();

  // The output of this filter is an itk::LabelMap, which contains itk::LabelObject's
  std::cout << "There are " << binaryImageToLabelMapFilter->GetOutput()->GetNumberOfLabelObjects() << " objects." << std::endl;

  // Loop over each region
  for(unsigned int i = 0; i < binaryImageToLabelMapFilter->GetOutput()->GetNumberOfLabelObjects(); i++)
    {
    // Get the ith region
    BinaryImageToLabelMapFilterType::OutputImageType::LabelObjectType* labelObject = binaryImageToLabelMapFilter->GetOutput()->GetNthLabelObject(i);

    // Output the pixels composing the region
    for(unsigned int pixelId = 0; pixelId < labelObject->Size(); pixelId++)
      {
      std::cout << "Object " << i << " contains pixel " << labelObject->GetIndex(pixelId) << std::endl;
      }
    }

  return EXIT_SUCCESS;
}

void CreateImage(ImageType::Pointer image)
{
  // Create a black image with a white square
  ImageType::IndexType start;
  start.Fill(0);

  ImageType::SizeType size;
  size.Fill(20);

  ImageType::RegionType region;
  region.SetSize(size);
  region.SetIndex(start);
  image->SetRegions(region);
  image->Allocate();

  itk::ImageRegionIterator<ImageType> imageIterator(image,image->GetLargestPossibleRegion());

  // Make a square
  while(!imageIterator.IsAtEnd())
    {
    if((imageIterator.GetIndex()[0] > 5 && imageIterator.GetIndex()[0] < 10) &&
      (imageIterator.GetIndex()[1] > 5 && imageIterator.GetIndex()[1] < 10) )
        {
        imageIterator.Set(255);
        }
      else
        {
        imageIterator.Set(0);
        }

    ++imageIterator;
    }

  using WriterType = itk::ImageFileWriter< ImageType  >;
  WriterType::Pointer writer = WriterType::New();
  writer->SetFileName("image.png");
  writer->SetInput(image);
  writer->Update();
}