SphinxExamples/src/Core/Common/UseParallelizeImageRegion/Code.cxx

/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
 
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkWatershedImageFilter.h"
#include "itkImageRegionIterator.h"
 
constexpr unsigned int Dimension = 2;
using InputPixelType = unsigned char;
using InputImageType = itk::Image<InputPixelType, Dimension>;
using OutputPixelType = itk::RGBAPixel<unsigned char>;
using OutputImageType = itk::Image<OutputPixelType, Dimension>;
using LabeledImageType = itk::Image<itk::IdentifierType, Dimension>;
 
OutputImageType::Pointer
segmentationAndCustomColorization(InputImageType::Pointer inImage)
{
  using WatershedFilterType = itk::WatershedImageFilter<InputImageType>;
  auto watershed = WatershedFilterType::New();
  watershed->SetThreshold(0.05);
  watershed->SetLevel(0.3);
  watershed->SetInput(inImage);
  watershed->Update();
 
  LabeledImageType::Pointer image = watershed->GetOutput();
  image->DisconnectPipeline();
 
  auto outImage = OutputImageType::New();
  outImage->CopyInformation(image);
  outImage->SetRegions(image->GetBufferedRegion());
  outImage->Allocate(true);
 
  itk::MultiThreaderBase::Pointer mt = itk::MultiThreaderBase::New();
  // ParallelizeImageRegion invokes the provided lambda function in parallel
  // each invocation will contain a piece of the overall region
  mt->ParallelizeImageRegion<Dimension>(
    image->GetBufferedRegion(),
    // the lambda will have access to outer variables 'image' and 'outImage'
    // it will have parameter 'region', which needs to be processed
    [image, outImage](const LabeledImageType::RegionType & region) {
      itk::ImageRegionConstIterator<LabeledImageType> iIt(image, region);
      itk::ImageRegionIterator<OutputImageType>       oIt(outImage, region);
      for (; !iIt.IsAtEnd(); ++iIt, ++oIt)
      {
        LabeledImageType::IndexType ind = iIt.GetIndex();
        OutputPixelType             p;
        p.SetAlpha(iIt.Get());
        static_assert(Dimension <= 3, "Dimension has to be 2 or 3");
        for (unsigned d = 0; d < Dimension; ++d)
        {
          p.SetElement(d, ind[d]);
        }
        oIt.Set(p);
      }
    },
    nullptr); // we don't have a filter whose progress needs to be updated
 
  return outImage;
}
 
int
main(int argc, char * argv[])
{
  if (argc != 3)
  {
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0];
    std::cerr << " <InputFileName>";
    std::cerr << " <OutputFileName>" << std::endl;
    return EXIT_FAILURE;
  }
 
  const auto input = itk::ReadImage<InputImageType>(argv[1]);
 
  try
  {
    OutputImageType::Pointer outImage = segmentationAndCustomColorization(input);
    itk::WriteImage(outImage, argv[2], true); // compression
  }
  catch (const itk::ExceptionObject & error)
  {
    std::cerr << "Error: " << error << std::endl;
    return EXIT_FAILURE;
  }
 
  return EXIT_SUCCESS;
}