Examples/Statistics/ImageHistogram2.cxx

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 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
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// Software Guide : BeginLatex
//
// From the previous example you will have noticed that there is a significant
// number of operations to perform to compute the simple histogram of
// a scalar image. Given that this is a relatively common operation, it is
// convenient to encapsulate many of these operations in a single helper class.
//
// The \subdoxygen{Statistics}{ScalarImageToHistogramGenerator} is the result
// of such encapsulation.  This example illustrates how to compute the
// histogram of a scalar image using this helper class.
//
// Software Guide : EndLatex


// Software Guide : BeginLatex
//
// We should first include the header of the histogram generator and the image
// class.
//
// \index{itk::Statistics::Scalar\-Image\-To\-Histogram\-Generator!header}
//
// Software Guide : EndLatex

// Software Guide : BeginCodeSnippet
#include "itkScalarImageToHistogramGenerator.h"
#include "itkImage.h"
// Software Guide : EndCodeSnippet

#include "itkImageFileReader.h"

int main( int argc, char * argv [] )
{

  if( argc < 2 )
    {
    std::cerr << "Missing command line arguments" << std::endl;
    std::cerr << "Usage :  ImageHistogram1  inputImageFileName " << std::endl;
    return EXIT_FAILURE;
    }


  // Software Guide : BeginLatex
  //
  // The image type must be defined using the typical pair of pixel type and
  // dimension specification.
  //
  // Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet
  using PixelType = unsigned char;
  constexpr unsigned int Dimension = 2;

  using ImageType = itk::Image<PixelType, Dimension >;
  // Software Guide : EndCodeSnippet


  using ReaderType = itk::ImageFileReader< ImageType >;

  ReaderType::Pointer reader = ReaderType::New();

  reader->SetFileName( argv[1] );

  try
    {
    reader->Update();
    }
  catch( itk::ExceptionObject & excp )
    {
    std::cerr << "Problem reading image file : " << argv[1] << std::endl;
    std::cerr << excp << std::endl;
    return EXIT_FAILURE;
    }


  // Software Guide : BeginLatex
  //
  // We use now the image type in order to instantiate the type of the
  // corresponding histogram generator class, and invoke its \code{New()} method
  // in order to construct one.
  //
  // \index{itk::Statistics::Scalar\-Image\-To\-Histogram\-Generator!header}
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using HistogramGeneratorType =
    itk::Statistics::ScalarImageToHistogramGenerator<ImageType>;

  HistogramGeneratorType::Pointer histogramGenerator =
                                        HistogramGeneratorType::New();
  // Software Guide : EndCodeSnippet


  // Software Guide : BeginLatex
  //
  // The image to be passed as input to the histogram generator is taken in this
  // case from the output of an image reader.
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  histogramGenerator->SetInput(  reader->GetOutput() );
  // Software Guide : EndCodeSnippet


  // Software Guide : BeginLatex
  //
  // We define also the typical parameters that specify the characteristics of
  // the histogram to be computed.
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  histogramGenerator->SetNumberOfBins( 256 );
  histogramGenerator->SetMarginalScale( 10.0 );

  histogramGenerator->SetHistogramMin(  -0.5 );
  histogramGenerator->SetHistogramMax( 255.5 );
  // Software Guide : EndCodeSnippet


  // Software Guide : BeginLatex
  //
  // Finally we trigger the computation of the histogram by invoking the
  // \code{Compute()} method of the generator. Note again, that a generator is
  // not a pipeline object and therefore it is up to you to make sure that the
  // filters providing the input image have been updated.
  //
  // \index{itk::Statistics::Scalar\-Image\-To\-Histogram\-Generator!Compute()}
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  histogramGenerator->Compute();
  // Software Guide : EndCodeSnippet


  // Software Guide : BeginLatex
  //
  // The resulting histogram can be obtained from the generator by invoking its
  // \code{GetOutput()} method. It is also convenient to get the Histogram type
  // from the traits of the generator type itself as shown in the code below.
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using HistogramType = HistogramGeneratorType::HistogramType;

  const HistogramType * histogram = histogramGenerator->GetOutput();
  // Software Guide : EndCodeSnippet


  const unsigned int histogramSize = histogram->Size();

  std::cout << "Histogram size " << histogramSize << std::endl;

  unsigned int bin;
  for( bin=0; bin < histogramSize; bin++ )
    {
    std::cout << "bin = " << bin << " frequency = ";
    std::cout << histogram->GetFrequency( bin, 0 ) << std::endl;
    }


  // Software Guide : BeginLatex
  //
  // In this case we simply print out the frequency values of the histogram.
  // These values can be accessed by using iterators.
  //
  // \index{itk::Statistics::Histogram!Iterators}
  //
  // Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  HistogramType::ConstIterator itr = histogram->Begin();
  HistogramType::ConstIterator end = histogram->End();

  unsigned int binNumber = 0;
  while( itr != end )
    {
    std::cout << "bin = " << binNumber << " frequency = ";
    std::cout << itr.GetFrequency() << std::endl;
    ++itr;
    ++binNumber;
    }
  // Software Guide : EndCodeSnippet


  return EXIT_SUCCESS;

}