Label Binary Regions and Get Properties#

Synopsis#

Label binary regions in an image and get their properties.

Results#

image.png#

Output:

There are 1 objects.
Object 0 has bounding box ImageRegion (0x7ff924a4e558)
Dimension: 2
Index: [6, 6]
Size: [4, 4]

Code#

C++#

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

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

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

  using BinaryImageToShapeLabelMapFilterType = itk::BinaryImageToShapeLabelMapFilter<ImageType>;
  BinaryImageToShapeLabelMapFilterType::Pointer binaryImageToShapeLabelMapFilter =
    BinaryImageToShapeLabelMapFilterType::New();
  binaryImageToShapeLabelMapFilter->SetInput(image);
  binaryImageToShapeLabelMapFilter->Update();

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

  // Loop over all of the blobs
  for (unsigned int i = 0; i < binaryImageToShapeLabelMapFilter->GetOutput()->GetNumberOfLabelObjects(); ++i)
  {
    BinaryImageToShapeLabelMapFilterType::OutputImageType::LabelObjectType * labelObject =
      binaryImageToShapeLabelMapFilter->GetOutput()->GetNthLabelObject(i);
    // Output the bounding box (an example of one possible property) of the ith region
#if ITK_VERSION_MAJOR >= 4
    std::cout << "Object " << i << " has bounding box " << labelObject->GetBoundingBox() << std::endl;
#else
    std::cout << "Object " << i << " has region " << labelObject->GetRegion() << std::endl;
#endif
  }

  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;
  }

  itk::WriteImage(image, "image.png");
}

Classes demonstrated#

template<typename TInputImage, typename TOutputImage = LabelMap<ShapeLabelObject<SizeValueType, TInputImage::ImageDimension>>> class BinaryImageToShapeLabelMapFilter : public itk::ImageToImageFilter<TInputImage, TOutputImage>

Converts a binary image to a label map and valuate the shape attributes.

A convenient class that converts a binary image to a label map and valuates the shape attributes at once.

The GetOutput() function returns an itk::ShapeLabelMap. A typical use would be to iterate over the ShapeLabelObjects in the map, using something like this:

for(unsigned int i = 0; i < filter->GetOutput()->GetNumberOfLabelObjects(); ++i)
  {
  FilterType::OutputImageType::LabelObjectType* shapeLabelObject =
    filter->GetOutput()->GetLabelObject(i);
  // Here you can get properties of the ShapeLabelObject
  std::cout << "Bounding box: " << shapeLabelObject->GetBoundingBox();
  }