Examples/IO/CovariantVectorImageRead.cxx

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//  Software Guide : BeginLatex
//
//  This example illustrates how to read an image whose pixel type is
//  \code{CovariantVector}. For practical purposes this example is applicable
//  to images of pixel type \doxygen{Vector}, \doxygen{Point} and
//  \doxygen{FixedArray}. These pixel types are similar in that they are all
//  arrays of fixed size in which the components have the same representation
//  type.
//
//  In this example we are reading a gradient image from a file (written in
//  the previous example) and computing its magnitude using the
//  \doxygen{VectorMagnitudeImageFilter}. Note that this filter is
//  different from the \doxygen{GradientMagnitudeImageFilter} which actually
//  takes a scalar image as input and computes the magnitude of its gradient.
//  The VectorMagnitudeImageFilter class takes an image of vector
//  pixel type as input and computes pixel-wise the magnitude of each vector.
//
//  Let's start by including the relevant header files.
//
//  \index{ImageFileRead!Vector images}
//  \index{VectorMagnitudeImageFilter!header}
//
//  Software Guide : EndLatex

// Software Guide : BeginCodeSnippet
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkVectorMagnitudeImageFilter.h"
#include "itkRescaleIntensityImageFilter.h"
// Software Guide : EndCodeSnippet


#include "itkImage.h"


int main( int argc, char ** argv )
{
  // Verify the number of parameters in the command line
  if( argc < 3 )
    {
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0] << " inputImageFile  outputVectorImageFile " << std::endl;
    return EXIT_FAILURE;
    }


  //  Software Guide : BeginLatex
  //
  //  We read an image of \doxygen{CovariantVector} pixels and compute pixel
  //  magnitude to produce an image where each pixel is of type
  //  \code{unsigned short}. The components of the CovariantVector
  //  are selected to be \code{float} here. Notice that a renormalization is
  //  required in order to map the dynamic range of the magnitude values into
  //  the range of the output pixel type.  The
  //  \doxygen{RescaleIntensityImageFilter} is used to achieve this.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using ComponentType = float;
  constexpr unsigned int Dimension = 2;

  using InputPixelType = itk::CovariantVector< ComponentType,
                                    Dimension  >;

  using MagnitudePixelType = float;
  using OutputPixelType = unsigned short;

  using InputImageType = itk::Image< InputPixelType,      Dimension >;
  using MagnitudeImageType = itk::Image< MagnitudePixelType,  Dimension >;
  using OutputImageType = itk::Image< OutputPixelType,     Dimension >;
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  The \doxygen{ImageFileReader} and \doxygen{ImageFileWriter}
  //  are instantiated using the image types.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using ReaderType = itk::ImageFileReader< InputImageType  >;
  using WriterType = itk::ImageFileWriter< OutputImageType >;
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  The VectorMagnitudeImageFilter is instantiated using the
  //  input and output image types. A filter object is created with the
  //  \code{New()} method and assigned to a \doxygen{SmartPointer}.
  //
  //  \index{VectorMagnitudeImageFilter!Instantiation}
  //  \index{VectorMagnitudeImageFilter!New()}
  //  \index{VectorMagnitudeImageFilter!Pointer}
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using FilterType = itk::VectorMagnitudeImageFilter<
                                          InputImageType,
                                          MagnitudeImageType    >;

  FilterType::Pointer filter = FilterType::New();
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  The RescaleIntensityImageFilter class is instantiated next.
  //
  //  \index{RescaleIntensityImageFilter!Instantiation}
  //  \index{RescaleIntensityImageFilter!New()}
  //  \index{RescaleIntensityImageFilter!Pointer}
  //
  //  Software Guide : EndLatex

  //  Software Guide : BeginCodeSnippet
  using RescaleFilterType = itk::RescaleIntensityImageFilter<
                                  MagnitudeImageType,
                                  OutputImageType >;

  RescaleFilterType::Pointer  rescaler = RescaleFilterType::New();
  //  Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  In the following the minimum and maximum values for the output image
  //  are specified. Note the use of the \doxygen{NumericTraits} class which
  //  allows us to define a number of type-related constants in a generic
  //  way. The use of traits is a fundamental characteristic of generic
  //  programming~\cite{Austern1999,Alexandrescu2001}.
  //
  //  \index{RescaleIntensityImageFilter!SetOutputMinimum()}
  //  \index{RescaleIntensityImageFilter!SetOutputMaximum()}
  //
  //  Software Guide : EndLatex

  //  Software Guide : BeginCodeSnippet
  rescaler->SetOutputMinimum( itk::NumericTraits< OutputPixelType >::min() );
  rescaler->SetOutputMaximum( itk::NumericTraits< OutputPixelType >::max() );
  //  Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Below, we create the reader and writer using the \code{New()} method and
  //  assign the result to a \doxygen{SmartPointer}.
  //
  //  \index{itk::ImageFileReader!New()}
  //  \index{itk::ImageFileWriter!New()}
  //  \index{itk::ImageFileReader!SmartPointer}
  //  \index{itk::ImageFileWriter!SmartPointer}
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  ReaderType::Pointer reader = ReaderType::New();
  WriterType::Pointer writer = WriterType::New();
  // Software Guide : EndCodeSnippet


  // Here we recover the file names from the command line arguments
  //
  const char * inputFilename  = argv[1];
  const char * outputFilename = argv[2];


  //  Software Guide : BeginLatex
  //
  //  The name of the file to be read or written is passed with the
  //  \code{SetFileName()} method.
  //
  //  \index{itk::ImageFileReader!SetFileName()}
  //  \index{itk::ImageFileWriter!SetFileName()}
  //  \index{SetFileName()!itk::ImageFileReader}
  //  \index{SetFileName()!itk::ImageFileWriter}
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  reader->SetFileName( inputFilename  );
  writer->SetFileName( outputFilename );
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Below we connect the reader, filter and writer to form the data
  //  processing pipeline.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  filter->SetInput( reader->GetOutput() );
  rescaler->SetInput( filter->GetOutput() );
  writer->SetInput( rescaler->GetOutput() );
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Finally we execute the pipeline by invoking \code{Update()} on the
  //  writer. The call is placed in a \code{try/catch} block in case exceptions
  //  are thrown.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  try
    {
    writer->Update();
    }
  catch( itk::ExceptionObject & err )
    {
    std::cerr << "ExceptionObject caught !" << std::endl;
    std::cerr << err << std::endl;
    return EXIT_FAILURE;
    }
  // Software Guide : EndCodeSnippet

  return EXIT_SUCCESS;
}