Convert itk::Image With Labels to Label Map#

Synopsis#

Convert an itk::Image consisting of labeled regions to a LabelMap.

Results#

Output:

There are 2 objects.

Code#

C++#

#include "itkImage.h"
#include "itkLabelImageToLabelMapFilter.h"
#include "itkConnectedComponentImageFilter.h"

using ImageType = itk::Image<unsigned char, 2>;

static void
CreateImage(ImageType::Pointer image);

int
main()
{
  auto image = ImageType::New();
  CreateImage(image);

  using ConnectedComponentImageFilterType = itk::ConnectedComponentImageFilter<ImageType, ImageType>;
  auto connectedComponentImageFilter = ConnectedComponentImageFilterType::New();
  connectedComponentImageFilter->SetInput(image);
  connectedComponentImageFilter->Update();

  using LabelImageToLabelMapFilterType = itk::LabelImageToLabelMapFilter<ImageType>;
  auto labelImageToLabelMapFilter = LabelImageToLabelMapFilterType::New();
  labelImageToLabelMapFilter->SetInput(connectedComponentImageFilter->GetOutput());
  labelImageToLabelMapFilter->Update();

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

  return EXIT_SUCCESS;
}

void
CreateImage(ImageType::Pointer image)
{
  // Create an image with 2 connected components
  ImageType::RegionType region;
  ImageType::IndexType  start;
  start[0] = 0;
  start[1] = 0;

  ImageType::SizeType size;
  unsigned int        NumRows = 200;
  unsigned int        NumCols = 300;
  size[0] = NumRows;
  size[1] = NumCols;

  region.SetSize(size);
  region.SetIndex(start);

  image->SetRegions(region);
  image->Allocate();

  // Make a square
  for (unsigned int r = 20; r < 80; ++r)
  {
    for (unsigned int c = 30; c < 100; ++c)
    {
      ImageType::IndexType pixelIndex;
      pixelIndex[0] = r;
      pixelIndex[1] = c;

      image->SetPixel(pixelIndex, 255);
    }
  }

  // Make another square
  for (unsigned int r = 100; r < 130; ++r)
  {
    for (unsigned int c = 115; c < 160; ++c)
    {
      ImageType::IndexType pixelIndex;
      pixelIndex[0] = r;
      pixelIndex[1] = c;

      image->SetPixel(pixelIndex, 255);
    }
  }
}

Classes demonstrated#

template<typename TInputImage, typename TOutputImage = LabelMap<LabelObject<typename TInputImage::PixelType, TInputImage::ImageDimension>>> class LabelImageToLabelMapFilter : public itk::ImageToImageFilter<TInputImage, TOutputImage>