Example usage:

./ImageRegionIteratorWithIndex Input/ROI_QB_MUL_2.tif Output/ImageRegionIteratorWithIndexOutput.jpg

Example source code (ImageRegionIteratorWithIndex.cxx):

// \index{Iterators!speed}
// The ``WithIndex'' family of iterators was designed for algorithms that
// use both the value and the location of image pixels in calculations.  Unlike
// \doxygen{itk}{ImageRegionIterator}, which calculates an index only when
// asked for, \doxygen{itk}{ImageRegionIteratorWithIndex} maintains its
// index location as a member variable that is updated during the increment or
// decrement process. Iteration speed is penalized, but the index queries are
// more efficient.
// \index{itk::ImageRegionIteratorWithIndex!example of using|(}
// The following example illustrates the use of
// ImageRegionIteratorWithIndex.  The algorithm mirrors
// a 2D image across its $x$-axis (see \doxygen{itk}{FlipImageFilter} for an ND
// version).  The algorithm makes extensive use of the \code{GetIndex()}
// method.
// We start by including the proper header file.

#include "otbImage.h"
#include "itkRGBPixel.h"
#include "itkImageRegionIteratorWithIndex.h"
#include "otbImageFileReader.h"
#include "otbImageFileWriter.h"

int main(int argc, char* argv[])
  // Verify the number of parameters on the command line.
  if (argc < 3)
    std::cerr << "Missing parameters. " << std::endl;
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0] << " inputImageFile outputImageFile" << std::endl;
    return -1;

  // For this example, we will use an RGB pixel type so that we can process color
  // images. Like most other ITK image iterator,
  // ImageRegionIteratorWithIndex class expects the image type as its
  // single template parameter.

  const unsigned int Dimension = 2;

  using RGBPixelType = itk::RGBPixel<unsigned char>;
  using ImageType    = otb::Image<RGBPixelType, Dimension>;

  using IteratorType = itk::ImageRegionIteratorWithIndex<ImageType>;

  using ReaderType = otb::ImageFileReader<ImageType>;
  using WriterType = otb::ImageFileWriter<ImageType>;

  ImageType::ConstPointer inputImage;
  ReaderType::Pointer     reader = ReaderType::New();
    inputImage = reader->GetOutput();
  catch (itk::ExceptionObject& err)
    std::cout << "ExceptionObject caught !" << std::endl;
    std::cout << err << std::endl;
    return -1;

  // An \code{ImageType} smart pointer called \code{inputImage} points to the
  // output of the image reader.  After updating the image reader, we can
  // allocate an output image of the same size, spacing, and origin as the
  // input image.

  ImageType::Pointer outputImage = ImageType::New();

  // Next we create the iterator that walks the output image.  This algorithm
  // requires no iterator for the input image.

  IteratorType outputIt(outputImage, outputImage->GetRequestedRegion());

  // This axis flipping algorithm works by iterating through the output image,
  // querying the iterator for its index, and copying the value from the input
  // at an index mirrored across the $x$-axis.

  ImageType::IndexType requestedIndex = outputImage->GetRequestedRegion().GetIndex();
  ImageType::SizeType  requestedSize  = outputImage->GetRequestedRegion().GetSize();

  for (outputIt.GoToBegin(); !outputIt.IsAtEnd(); ++outputIt)
    ImageType::IndexType idx = outputIt.GetIndex();
    idx[0]                   = requestedIndex[0] + requestedSize[0] - 1 - idx[0];

  WriterType::Pointer writer = WriterType::New();
  catch (itk::ExceptionObject& err)
    std::cout << "ExceptionObject caught !" << std::endl;
    std::cout << err << std::endl;
    return -1;

  // Let's run this example on the image \code{ROI\_QB\_MUL\_2.tif} found in
  // the \code{Examples/Data} directory.
  // Figure~\ref{fig:ImageRegionIteratorWithIndexExample} shows how the original
  // image has been mirrored across its $x$-axis in the output.
  // \begin{figure} \center
  // \includegraphics[width=0.44\textwidth]{ROI_QB_MUL_2.eps}
  // \includegraphics[width=0.44\textwidth]{ImageRegionIteratorWithIndexOutput.eps}
  // \itkcaption[Using the ImageRegionIteratorWithIndex]{Results of using
  // ImageRegionIteratorWithIndex to mirror an image across an axis. The original
  // image is shown at left.  The mirrored output is shown at right.}
  // \label{fig:ImageRegionIteratorWithIndexExample}
  // \end{figure}
  // \index{itk::ImageRegionIteratorWithIndex!example of using|)}

  return EXIT_SUCCESS;