WikiExamples/ImageProcessing/ExtractImageFilter.cxx

// This is different from CropImageFilter only in the way
// that the region to crop is specified.
#include "itkImage.h"
#include <itkImageFileReader.h>
#include <itkExtractImageFilter.h>

int main(int, char *[])
{
  using ImageType = itk::Image<unsigned char, 2>;

  ImageType::IndexType start;
  start.Fill(0);

  ImageType::SizeType size;
  size.Fill(10);

  ImageType::RegionType region(start, size);
  
  ImageType::Pointer image = ImageType::New();
  image->SetRegions(region);
  image->Allocate();
  image->FillBuffer(5);

  std::cout << "Image largest region: " << image->GetLargestPossibleRegion() << std::endl;

  ImageType::IndexType desiredStart;
  desiredStart.Fill(3);

  ImageType::SizeType desiredSize;
  desiredSize.Fill(4);

  ImageType::RegionType desiredRegion(desiredStart, desiredSize);

  std::cout << "desiredRegion: " << desiredRegion << std::endl;
  
  using FilterType = itk::ExtractImageFilter< ImageType, ImageType >;
  FilterType::Pointer filter = FilterType::New();
  filter->SetExtractionRegion(desiredRegion);
  filter->SetInput(image);
#if ITK_VERSION_MAJOR >= 4
  filter->SetDirectionCollapseToIdentity(); // This is required.
#endif
  filter->Update();
  
  ImageType::Pointer output = filter->GetOutput();
  output->DisconnectPipeline();
  output->FillBuffer(2);

  itk::Index<2> index;
  index.Fill(5);

  std::cout << "new largest region: " << output->GetLargestPossibleRegion() << std::endl;
  std::cout << "new: " << (int)output->GetPixel(index) << std::endl;
  std::cout << "Original: " << (int)image->GetPixel(index) << std::endl;

  return EXIT_SUCCESS;
}