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 "vnl/vnl_math.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 -1;
    }

  // 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
  typedef unsigned short              PixelType;
  typedef itk::Image< PixelType, 2 >  ImageType2D;
  typedef itk::Image< PixelType, 3 >  ImageType3D;
  // Software Guide : EndCodeSnippet

  // Software Guide : BeginLatex
  //
  //  A slice iterator type is defined to walk the input image.
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  typedef itk::ImageLinearIteratorWithIndex< ImageType2D > LinearIteratorType;
  typedef itk::ImageSliceConstIteratorWithIndex< ImageType3D
                                                          > SliceIteratorType;
  // Software Guide : EndCodeSnippet

  typedef itk::ImageFileReader< ImageType3D > ReaderType;
  typedef itk::ImageFileWriter< ImageType2D > WriterType;

  ImageType3D::ConstPointer inputImage;
  ReaderType::Pointer reader = ReaderType::New();
  reader->SetFileName( argv[1] );
  try
    {
    reader->Update();
    inputImage = reader->GetOutput();
    }
  catch ( itk::ExceptionObject &err)
    {
    std::cout << "ExceptionObject caught !" << std::endl;
    std::cout << err << std::endl;
    return -1;
    }

  // 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
  unsigned int projectionDirection =
    static_cast<unsigned int>( ::atoi( 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 );

  ImageType2D::Pointer 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( vnl_math_max( outputIt.Get(), inputIt.Get() ));
        ++inputIt;
        ++outputIt;
        }
      outputIt.NextLine();
      inputIt.NextLine();

      }
    outputIt.GoToBegin();
    inputIt.NextSlice();
    }
    // Software Guide : EndCodeSnippet

  WriterType::Pointer writer = WriterType::New();
  writer->SetFileName( argv[2] );
  writer->SetInput(outputImage);
  try
    {
    writer->Update();
    }
  catch ( itk::ExceptionObject &err)
    {
    std::cout << "ExceptionObject caught !" << std::endl;
    std::cout << err << std::endl;
    return -1;
    }

  // 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 0;
}