Examples/Iterators/ImageRandomConstIteratorWithIndex.cxx

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 *  Copyright NumFOCUS
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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
//
// \doxygen{ImageRandomConstIteratorWithIndex} was developed to randomly
// sample pixel values.  When incremented or decremented, it jumps to a random
// location in its image region.
//
// \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!sample size}
// \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!begin and end
// positions}
//
// The user must specify a sample size when creating this iterator. The sample
// size, rather than a specific image index, defines the end position for the
// iterator.  \code{IsAtEnd()} returns
// \code{true} when the current sample number equals the sample size.
// \code{IsAtBegin()} returns \code{true} when the current sample number
// equals zero.  An important difference from other image iterators is that
// ImageRandomConstIteratorWithIndex may visit the same pixel
//  more than once.
//
// \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!example of using|(}
// \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!and statistics}
// Let's use the random iterator to estimate some simple image statistics. The
// next example calculates an estimate of the arithmetic mean of pixel values.
//
// First, include the appropriate header and declare pixel and image types.
//
// Software Guide : EndLatex
 
#include "itkImage.h"
// Software Guide : BeginCodeSnippet
#include "itkImageRandomConstIteratorWithIndex.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 < 3)
  {
    std::cerr << "Missing parameters. " << std::endl;
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0] << " inputImageFile numberOfSamples" << std::endl;
    return EXIT_FAILURE;
  }
 
  // Software Guide : BeginCodeSnippet
  constexpr unsigned int Dimension = 2;
 
  using PixelType = unsigned short;
  using ImageType = itk::Image<PixelType, Dimension>;
  using ConstIteratorType = itk::ImageRandomConstIteratorWithIndex<ImageType>;
  // Software Guide : EndCodeSnippet
 
  using ReaderType = itk::ImageFileReader<ImageType>;
 
  ImageType::ConstPointer inputImage;
  ReaderType::Pointer     reader = ReaderType::New();
  reader->SetFileName(argv[1]);
  try
  {
    reader->Update();
    inputImage = reader->GetOutput();
  }
  catch (const itk::ExceptionObject & err)
  {
    std::cerr << "ExceptionObject caught !" << std::endl;
    std::cerr << err << std::endl;
    return EXIT_FAILURE;
  }
 
  // Software Guide : BeginLatex
  //
  // The input image has been read as \code{inputImage}.  We now create an
  // iterator with a number of samples set by command line argument. The call
  // to \code{ReinitializeSeed} seeds the random number generator.  The
  // iterator is initialized over the entire valid image region.
  //
  //  \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!SetNumberOfSamples()}
  //  \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!ReinitializeSeed()}
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  ConstIteratorType inputIt(inputImage, inputImage->GetRequestedRegion());
  inputIt.SetNumberOfSamples(::std::stoi(argv[2]));
  inputIt.ReinitializeSeed();
  // Software Guide : EndCodeSnippet
 
  // Software Guide: BeginLatex
  //
  // Now take the specified number of samples and calculate their average
  // value.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  float mean = 0.0f;
  for (inputIt.GoToBegin(); !inputIt.IsAtEnd(); ++inputIt)
  {
    mean += static_cast<float>(inputIt.Get());
  }
  mean = mean / ::std::stod(argv[2]);
 
  // Software Guide : EndCodeSnippet
  std::cout << "Mean estimate with " << argv[2] << " samples is " << mean
            << std::endl;
 
  // Software Guide : BeginLatex
  //
  /*
   The following table shows the results
   of running this example on several of the data files from
   \code{Examples/Data} with a range of sample sizes.
 
   \begin{table}
   \begin{center}
   \begin{tabular}[]{rc|c|c|c}
   & \multicolumn{4}{c}{\emph{Sample Size}} \\  & \code{\textbf{10}} &
   \code{\textbf{100}} & \code{\textbf{1000}} & \code{\textbf{10000}} \\
   \cline{2-5} \code{RatLungSlice1.mha} & 50.5 & 52.4 & 53.0 & 52.4 \\
   \code{RatLungSlice2.mha} & 46.7 & 47.5 & 47.4 & 47.6  \\
   \code{BrainT1Slice.png} & 47.2 & 64.1 & 68.0 & 67.8  \\ \end{tabular}
   \itkcaption[ImageRandomConstIteratorWithIndex usage]{Estimates of mean
   image pixel value using the ImageRandomConstIteratorWithIndex at
   different sample sizes.} \end{center}
   \label{tab:ImageRandomConstIteratorWithIndexExample}
   \end{table}
 
   \index{itk::Image\-Random\-Const\-Iterator\-With\-Index!example of
   using|)}
  */
  // Software Guide : EndLatex
 
  return EXIT_SUCCESS;
}