Examples/Statistics/ImageHistogram2.cxx

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 *
 *  Copyright NumFOCUS
 *
 *  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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 *         https://www.apache.org/licenses/LICENSE-2.0.txt
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 *  distributed under the License is distributed on an "AS IS" BASIS,
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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>;
 
  auto reader = ReaderType::New();
 
  reader->SetFileName(argv[1]);
 
  try
  {
    reader->Update();
  }
  catch (const 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>;
 
  auto 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();
  const 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;
}