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Visualize a Static Dense 2D Level Set as Elevation Map

Synopsis

Convert a binary mask into a dense level-set function and write the function values as an image. Rendered as a height field, these values form an elevation map whose zero level is the contour. The mask comes from an Otsu threshold of the input image.

Results

Input image

Code

C++

#include "itkBinaryImageToLevelSetImageAdaptor.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkLevelSetDenseImage.h"
#include "itkOtsuMultipleThresholdsImageFilter.h"
#include "itkRescaleIntensityImageFilter.h"

int
main(int argc, char * argv[])
{
  if (argc != 3)
  {
    std::cerr << "Missing Arguments" << std::endl;
    std::cerr << argv[0] << std::endl;
    std::cerr << "<Input Image> <Output Image>" << std::endl;
    return EXIT_FAILURE;
  }

  constexpr unsigned int Dimension = 2;

  using InputPixelType = unsigned char;
  using InputImageType = itk::Image<InputPixelType, Dimension>;

  InputImageType::Pointer input = itk::ReadImage<InputImageType>(argv[1]);

  using LevelSetPixelType = float;
  using LevelSetImageType = itk::Image<LevelSetPixelType, Dimension>;
  using LevelSetType = itk::LevelSetDenseImage<LevelSetImageType>;

  // Generate a binary mask that will be used as initialization for the level
  // set.
  using OtsuFilterType = itk::OtsuMultipleThresholdsImageFilter<InputImageType, LevelSetImageType>;
  auto otsu = OtsuFilterType::New();
  otsu->SetInput(input);
  otsu->SetNumberOfHistogramBins(256);
  otsu->SetNumberOfThresholds(1);

  using RescaleType = itk::RescaleIntensityImageFilter<LevelSetImageType, LevelSetImageType>;
  auto rescaler = RescaleType::New();
  rescaler->SetInput(otsu->GetOutput());
  rescaler->SetOutputMinimum(0);
  rescaler->SetOutputMaximum(1);
  rescaler->Update();

  // Convert the binary mask to a level-set function
  using BinaryImageToLevelSetType = itk::BinaryImageToLevelSetImageAdaptor<LevelSetImageType, LevelSetType>;
  auto adaptor = BinaryImageToLevelSetType::New();
  adaptor->SetInputImage(rescaler->GetOutput());
  adaptor->Initialize();

  LevelSetType::Pointer levelSet = adaptor->GetModifiableLevelSet();

  try
  {
    itk::WriteImage(levelSet->GetImage(), argv[2]);
  }
  catch (const itk::ExceptionObject & error)
  {
    std::cerr << "Error: " << error << std::endl;
    return EXIT_FAILURE;
  }

  return EXIT_SUCCESS;
}

Classes demonstrated

template<typename TImage>
class LevelSetDenseImage : public itk::DiscreteLevelSetImage<TImage::PixelType, TImage::ImageDimension>

Base class for the “dense” representation of a level-set function on one image.

This representation is a “dense” level-set function, i.e. it defines a level-set function on a grid (more precisely the underlying structure is an Image).

Todo:

Think about using image iterators instead of GetPixel()

Template Parameters:

TImage – Input image type of the level set function

See itk::LevelSetDenseImage for additional documentation.