Examples/Iterators/ImageRandomConstIteratorWithIndex.cxx

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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 ( 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;
}