Examples/Iterators/ImageSliceIteratorWithIndex.cxx

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// Software Guide : BeginLatex
//
// \index{Iterators!and image slices}
//
// The \doxygen{ImageSliceIteratorWithIndex} class is an extension of
// \doxygen{ImageLinearIteratorWithIndex} from iteration along lines to
// iteration along both lines \emph{and planes} in an image.
// A \emph{slice} is a 2D
// plane spanned by two vectors pointing along orthogonal coordinate axes. The
// slice orientation of the slice iterator is defined by specifying its two
// spanning axes.
//
// \begin{itemize}
// \index{itk::Image\-Slice\-Iterator\-With\-Index!SetFirstDirection()}
// \item \textbf{\code{SetFirstDirection()}}
// Specifies the first coordinate axis
// direction of the slice plane.
//
// \index{itk::Image\-Slice\-Iterator\-With\-Index!SetSecondDirection()}
// \item \textbf{\code{SetSecondDirection()}}
// Specifies the second coordinate axis
// direction of the slice plane.
// \end{itemize}
//
// Several new methods control movement from slice to slice.
//
// \begin{itemize}
//
// \index{itk::Image\-Slice\-Iterator\-With\-Index!NextSlice()}
// \item \textbf{\code{NextSlice()}} Moves the iterator to the beginning pixel
// location of the next slice in the image.  The origin of the next slice is
// calculated by incrementing the current origin index along the fastest
// increasing dimension of the image subspace which excludes the first and
// second dimensions of the iterator.
//
// \index{itk::Image\-Slice\-Iterator\-With\-Index!PreviousSlice()}
// \item \textbf{\code{PreviousSlice()}} Moves the iterator to the \emph{last
// valid pixel location} in the previous slice.  The origin of the previous
// slice is calculated by decrementing the current origin index along the
// fastest increasing dimension of the image subspace which excludes the first
// and second dimensions of the iterator.
//
// \index{itk::Image\-Slice\-Iterator\-With\-Index!IsAtReverseEndOfSlice()}
// \item \textbf{\code{IsAtReverseEndOfSlice()}} Returns true if the iterator
// points to \emph{one position before} the beginning pixel of the current
// slice.
//
// \index{itk::Image\-Slice\-Iterator\-With\-Index!IsAtEndOfSlice()}
// \item \textbf{\code{IsAtEndOfSlice()}} Returns true if the iterator points
// to \emph{one position past} the last valid pixel of the current slice.
//
// \end{itemize}
//
// The slice iterator moves line by line using \code{NextLine()} and
// \code{PreviousLine()}.  The line direction is parallel to the \emph{second}
// coordinate axis direction of the slice plane (see also
// Section~\ref{sec:itkImageLinearIteratorWithIndex}).
//
// \index{itk::Image\-Slice\-Iterator\-With\-Index!example of using|(}
// The next code example calculates the maximum intensity projection along one
// of the coordinate axes of an image volume.  The algorithm is
// straightforward using ImageSliceIteratorWithIndex because we can coordinate
// movement through a slice of the 3D input image with movement through the 2D
// planar output.
//
// Here is how the algorithm works.  For each 2D slice of the input, iterate
// through all the pixels line by line. Copy a pixel value to the
// corresponding position in the 2D output image if it is larger than the
// value already contained there.  When all slices have been processed, the
// output image is the desired maximum intensity projection.
//
// We include a header for the const version of the slice iterator. For
// writing values to the 2D projection image, we use the linear iterator from
// the previous section.  The linear iterator is chosen because it can be set
// to follow the same path in its underlying 2D image that the slice iterator
// follows over each slice of the 3D image.
//
// Software Guide : EndLatex
 
#include "itkImage.h"
#include "itkMath.h"
 
// Software Guide : BeginCodeSnippet
#include "itkImageSliceConstIteratorWithIndex.h"
#include "itkImageLinearIteratorWithIndex.h"
// Software Guide : EndCodeSnippet
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
 
int
main(int argc, char * argv[])
{
  //   Verify the number of parameters on the command line.
  if (argc < 4)
  {
    std::cerr << "Missing parameters. " << std::endl;
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0]
              << " inputImageFile outputImageFile projectionDirection"
              << std::endl;
    return EXIT_FAILURE;
  }
 
  // Software Guide : BeginLatex
  //
  // The pixel type is defined as \code{unsigned short}.  For this
  // application, we need two image types, a 3D image for the input, and a 2D
  // image for the intensity projection.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using PixelType = unsigned short;
  using ImageType2D = itk::Image<PixelType, 2>;
  using ImageType3D = itk::Image<PixelType, 3>;
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  //  A slice iterator type is defined to walk the input image.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using LinearIteratorType = itk::ImageLinearIteratorWithIndex<ImageType2D>;
  using SliceIteratorType =
    itk::ImageSliceConstIteratorWithIndex<ImageType3D>;
  // Software Guide : EndCodeSnippet
 
  ImageType3D::ConstPointer inputImage;
  try
  {
    inputImage = itk::ReadImage<ImageType3D>(argv[1]);
  }
  catch (const itk::ExceptionObject & err)
  {
    std::cerr << "ExceptionObject caught !" << std::endl;
    std::cerr << err << std::endl;
    return EXIT_FAILURE;
  }
 
  // Software Guide : BeginLatex
  //
  // The projection direction is read from the command line. The projection
  // image will be the size of the 2D plane orthogonal to the projection
  // direction. Its spanning vectors are the two remaining coordinate axes in
  // the volume. These axes are recorded in the \code{direction} array.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  auto projectionDirection = static_cast<unsigned int>(std::stoi(argv[3]));
 
  unsigned int i, j;
  unsigned int direction[2];
  for (i = 0, j = 0; i < 3; ++i)
  {
    if (i != projectionDirection)
    {
      direction[j] = i;
      j++;
    }
  }
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // The \code{direction} array is now used to define the projection image
  // size based on the input image size.  The output image is created so that
  // its common dimension(s) with the input image are the same size.  For
  // example, if we project along the $x$ axis of the input, the size and
  // origin of the $y$ axes of the input and output will match.  This makes
  // the code slightly more complicated, but prevents a counter-intuitive
  // rotation of the output.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  ImageType2D::RegionType            region;
  ImageType2D::RegionType::SizeType  size;
  ImageType2D::RegionType::IndexType index;
 
  ImageType3D::RegionType requestedRegion = inputImage->GetRequestedRegion();
 
  index[direction[0]] = requestedRegion.GetIndex()[direction[0]];
  index[1 - direction[0]] = requestedRegion.GetIndex()[direction[1]];
  size[direction[0]] = requestedRegion.GetSize()[direction[0]];
  size[1 - direction[0]] = requestedRegion.GetSize()[direction[1]];
 
  region.SetSize(size);
  region.SetIndex(index);
 
  auto outputImage = ImageType2D::New();
 
  outputImage->SetRegions(region);
  outputImage->Allocate();
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // Next we create the necessary iterators.  The const slice iterator walks
  // the 3D input image, and the non-const linear iterator walks the 2D output
  // image. The iterators are initialized to walk the same linear path through
  // a slice.  Remember that the \emph{second} direction of the slice iterator
  // defines the direction that linear iteration walks within a slice.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  SliceIteratorType  inputIt(inputImage, inputImage->GetRequestedRegion());
  LinearIteratorType outputIt(outputImage, outputImage->GetRequestedRegion());
 
  inputIt.SetFirstDirection(direction[1]);
  inputIt.SetSecondDirection(direction[0]);
 
  outputIt.SetDirection(1 - direction[0]);
  // Software Guide : EndCodeSnippet
 
  // Software Guide: BeginLatex
  //
  // Now we are ready to compute the projection.  The first step is to
  // initialize all of the projection values to their nonpositive minimum
  // value.  The projection values are then updated row by row from the first
  // slice of the input.  At the end of the first slice, the input iterator
  // steps to the first row in the next slice, while the output iterator,
  // whose underlying image consists of only one slice, rewinds to its first
  // row.  The process repeats until the last slice of the input is processed.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  outputIt.GoToBegin();
  while (!outputIt.IsAtEnd())
  {
    while (!outputIt.IsAtEndOfLine())
    {
      outputIt.Set(itk::NumericTraits<unsigned short>::NonpositiveMin());
      ++outputIt;
    }
    outputIt.NextLine();
  }
 
  inputIt.GoToBegin();
  outputIt.GoToBegin();
 
  while (!inputIt.IsAtEnd())
  {
    while (!inputIt.IsAtEndOfSlice())
    {
      while (!inputIt.IsAtEndOfLine())
      {
        outputIt.Set(std::max(outputIt.Get(), inputIt.Get()));
        ++inputIt;
        ++outputIt;
      }
      outputIt.NextLine();
      inputIt.NextLine();
    }
    outputIt.GoToBegin();
    inputIt.NextSlice();
  }
  // Software Guide : EndCodeSnippet
 
  try
  {
    itk::WriteImage(outputImage, argv[2]);
  }
  catch (const itk::ExceptionObject & err)
  {
    std::cerr << "ExceptionObject caught !" << std::endl;
    std::cerr << err << std::endl;
    return EXIT_FAILURE;
  }
 
  // Software Guide : BeginLatex
  //
  // Running this example code on the 3D image
  // \code{Examples/Data/BrainProtonDensity3Slices.mha} using the $z$-axis as
  // the axis of projection gives the image shown in
  // Figure~\ref{fig:ImageSliceIteratorWithIndexOutput}.
  //
  // \begin{figure}
  // \centering
  // \includegraphics[width=0.4\textwidth]{ImageSliceIteratorWithIndexOutput}
  // \itkcaption[Maximum intensity projection using
  // ImageSliceIteratorWithIndex]{The maximum intensity projection through
  // three slices of a volume.}
  // \protect\label{fig:ImageSliceIteratorWithIndexOutput}
  // \end{figure}
  //
  //
  // \index{itk::Image\-Slice\-Iterator\-With\-Index!example of using|)}
  //
  // Software Guide : EndLatex
 
  return EXIT_SUCCESS;
}