Extract Boundaries of Connected Regions in Binary Image#

Synopsis#

Extract the boundaries of connected regions in a binary image.

Results#

../../../../_images/ExtractBoundariesOfConnectedRegionsInBinaryImage.png — Output In VTK Window#

Code#

C++#

#include "itkImage.h"
#include "itkBinaryContourImageFilter.h"

#ifdef ENABLE_QUICKVIEW
#  include "QuickView.h"
#endif

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

static void
CreateImage(ImageType::Pointer image);

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

  using binaryContourImageFilterType = itk::BinaryContourImageFilter<ImageType, ImageType>;

  auto binaryContourFilter = binaryContourImageFilterType::New();
  binaryContourFilter->SetInput(image);

#ifdef ENABLE_QUICKVIEW
  QuickView viewer;
  viewer.AddImage<ImageType>(image);
  viewer.AddImage<ImageType>(binaryContourFilter->GetOutput());
  viewer.Visualize();
#endif
  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> class BinaryContourImageFilter : public itk::InPlaceImageFilter<TInputImage, TOutputImage>, protected itk::ScanlineFilterCommon<TInputImage, TOutputImage>

Labels the pixels on the border of the objects in a binary image.

BinaryContourImageFilter takes a binary image as input, where the pixels in the objects are the pixels with a value equal to ForegroundValue. Only the pixels on the contours of the objects are kept. The pixels not on the border are changed to BackgroundValue.

The connectivity can be changed to minimum or maximum connectivity with SetFullyConnected(). Full connectivity produces thicker contours.

https://www.insight-journal.org/browse/publication/217

Author

Gaetan Lehmann. Biologie du Developpement et de la Reproduction, INRA de Jouy-en-Josas, France.

See

LabelContourImageFilter BinaryErodeImageFilter SimpleContourExtractorImageFilter

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