ConnectedThresholdImageFilter.cxx

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 *  Licensed under the Apache License, Version 2.0 (the "License");
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//  Software Guide : BeginCommandLineArgs
//    INPUTS:  {BrainProtonDensitySlice.png}
//    OUTPUTS: {ConnectedThresholdOutput1.png}
//    ARGUMENTS:    60 116 150 180
//  Software Guide : EndCommandLineArgs
//  Software Guide : BeginCommandLineArgs
//    INPUTS:  {BrainProtonDensitySlice.png}
//    OUTPUTS: {ConnectedThresholdOutput2.png}
//    ARGUMENTS:    81 112 210 250
//  Software Guide : EndCommandLineArgs
//  Software Guide : BeginCommandLineArgs
//    INPUTS:  {BrainProtonDensitySlice.png}
//    OUTPUTS: {ConnectedThresholdOutput3.png}
//    ARGUMENTS:    107 69 180 210
//  Software Guide : EndCommandLineArgs

// Software Guide : BeginLatex
//
// The following example illustrates the use of the
// \doxygen{ConnectedThresholdImageFilter}. This filter uses the flood fill
// iterator. Most of the algorithmic complexity of a region growing method
// comes from visiting neighboring pixels. The flood fill iterator assumes
// this responsibility and greatly simplifies the implementation of the
// region growing algorithm. Thus the algorithm is left to establish a
// criterion to decide whether a particular pixel should be included in
// the current region or not.
//
// \index{itk::FloodFillIterator!In Region Growing}
// \index{itk::ConnectedThresholdImageFilter}
// \index{itk::ConnectedThresholdImageFilter!header}
//
// The criterion used by the \code{ConnectedThresholdImageFilter} is based on an
// interval of intensity values provided by the user. Lower and upper threshold
// values should be provided. The region-growing algorithm includes
// those pixels whose intensities are inside the interval.
//
// \begin{equation}
// I(\mathbf{X}) \in [ \mbox{lower}, \mbox{upper} ]
// \end{equation}
//
// Let's look at the minimal code required to use this algorithm. First, the
// following header defining the \code{ConnectedThresholdImageFilter} class
// must be included.
//
// Software Guide : EndLatex


// Software Guide : BeginCodeSnippet
#include "itkConnectedThresholdImageFilter.h"
// Software Guide : EndCodeSnippet


#include "itkImage.h"
#include "itkCastImageFilter.h"


//  Software Guide : BeginLatex
//
//  Noise present in the image can reduce the capacity of this filter to grow
//  large regions. When faced with noisy images, it is usually convenient to
//  pre-process the image by using an edge-preserving smoothing filter. Any of
//  the filters discussed in Section~\ref{sec:EdgePreservingSmoothingFilters}
//  could be used to this end. In this particular example we use the
//  \doxygen{CurvatureFlowImageFilter}, so we need to include its header
//  file.
//
//  Software Guide : EndLatex

// Software Guide : BeginCodeSnippet
#include "itkCurvatureFlowImageFilter.h"
// Software Guide : EndCodeSnippet


#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"


int
main(int argc, char * argv[])
{
  if (argc < 7)
  {
    std::cerr << "Missing Parameters " << std::endl;
    std::cerr << "Usage: " << argv[0];
    std::cerr << " inputImage  outputImage seedX seedY lowerThreshold upperThreshold"
              << std::endl;
    return EXIT_FAILURE;
  }


  //  Software Guide : BeginLatex
  //
  //  We declare the image type based on a particular pixel type and
  //  dimension. In this case the \code{float} type is used for the pixels
  //  due to the requirements of the smoothing filter.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using InternalPixelType = float;
  constexpr unsigned int Dimension = 2;
  using InternalImageType = itk::Image<InternalPixelType, Dimension>;
  // Software Guide : EndCodeSnippet


  using OutputPixelType = unsigned char;
  using OutputImageType = itk::Image<OutputPixelType, Dimension>;
  using CastingFilterType = itk::CastImageFilter<InternalImageType, OutputImageType>;
  CastingFilterType::Pointer caster = CastingFilterType::New();

  // We instantiate reader and writer types
  //
  using ReaderType = itk::ImageFileReader<InternalImageType>;
  using WriterType = itk::ImageFileWriter<OutputImageType>;

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

  reader->SetFileName(argv[1]);
  writer->SetFileName(argv[2]);


  //  Software Guide : BeginLatex
  //
  //
  //  The smoothing filter is instantiated using the image type as
  //  a template parameter.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using CurvatureFlowImageFilterType =
    itk::CurvatureFlowImageFilter<InternalImageType, InternalImageType>;
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Then the filter is created by invoking the \code{New()} method and
  //  assigning the result to a \doxygen{SmartPointer}.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  CurvatureFlowImageFilterType::Pointer smoothing = CurvatureFlowImageFilterType::New();
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  We now declare the type of the region growing filter. In this case it is
  //  the \code{ConnectedThresholdImageFilter}.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using ConnectedFilterType =
    itk::ConnectedThresholdImageFilter<InternalImageType, InternalImageType>;
  // Software Guide : EndCodeSnippet

  //  Software Guide : BeginLatex
  //
  //  Then we construct one filter of this class using the \code{New()}
  //  method.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  ConnectedFilterType::Pointer connectedThreshold = ConnectedFilterType::New();
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Now it is time to connect a simple, linear pipeline. A file reader is
  //  added at the beginning of the pipeline and a cast filter and writer
  //  are added at the end. The cast filter is required to convert
  //  \code{float} pixel types to integer types since only a few image file
  //  formats support \code{float} types.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  smoothing->SetInput(reader->GetOutput());
  connectedThreshold->SetInput(smoothing->GetOutput());
  caster->SetInput(connectedThreshold->GetOutput());
  writer->SetInput(caster->GetOutput());
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  \code{CurvatureFlowImageFilter} requires a couple of parameters.
  //  The following are typical values for $2D$ images. However, these
  //  values may have to be adjusted depending on the amount of noise present in
  //  the input image.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  smoothing->SetNumberOfIterations(5);
  smoothing->SetTimeStep(0.125);
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  We now set the lower and upper threshold values.  Any pixel whose value
  //  is between \code{lowerThreshold} and \code{upperThreshold} will be
  //  included in the region, and any pixel whose value is outside will be excluded.
  //  Setting these values too close together will be too restrictive
  //  for the region to grow; setting them too far apart will
  //  cause the region to engulf the image.
  //
  //  \index{itk::ConnectedThresholdImageFilter!SetUpper()}
  //  \index{itk::ConnectedThresholdImageFilter!SetLower()}
  //
  //  Software Guide : EndLatex

  const InternalPixelType lowerThreshold = std::stod(argv[5]);
  const InternalPixelType upperThreshold = std::stod(argv[6]);

  // Software Guide : BeginCodeSnippet
  connectedThreshold->SetLower(lowerThreshold);
  connectedThreshold->SetUpper(upperThreshold);
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  The output of this filter is a binary image with zero-value pixels
  //  everywhere except on the extracted region. The intensity value set
  //  inside the region is selected with the method \code{SetReplaceValue()}.
  //
  //  \index{itk::ConnectedThresholdImageFilter!SetReplaceValue()}
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  connectedThreshold->SetReplaceValue(255);
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  The algorithm must be initialized by setting a seed point (i.e., the
  //  \doxygen{Index} of the pixel from which the region will grow) using the
  //  \code{SetSeed()} method.  It is convenient to initialize with a point in a
  //  \emph{typical} region of the anatomical structure to be segmented.
  //
  //  \index{itk::ConnectedThresholdImageFilter!SetSeed()}
  //
  //  Software Guide : EndLatex

  InternalImageType::IndexType index;

  index[0] = std::stoi(argv[3]);
  index[1] = std::stoi(argv[4]);


  // Software Guide : BeginCodeSnippet
  connectedThreshold->SetSeed(index);
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Invocation of the \code{Update()} method on the writer triggers
  //  execution of the pipeline.  It is usually wise to put update calls in a
  //  \code{try/catch} block in case errors occur and exceptions are thrown.
  //
  //  Software Guide : EndLatex

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


  //  Software Guide : BeginLatex
  //
  //  Let's run this example using as input the image
  //  \code{BrainProtonDensitySlice.png} provided in the directory
  //  \code{Examples/Data}. We can easily segment the major anatomical
  //  structures by providing seeds in the appropriate locations and defining
  //  values for the lower and upper thresholds.
  //  Figure~\ref{fig:ConnectedThresholdOutput} illustrates several examples of
  //  segmentation. The parameters used are presented in
  //  Table~\ref{tab:ConnectedThresholdOutput}.
  //
  //  \begin{table}
  //  \begin{center}
  //  \begin{tabular}{|l|c|c|c|c|}
  //  \hline
  //  Structure & Seed Index & Lower & Upper & Output Image \\ \hline
  //  White matter & $(60,116)$ & 150 & 180 & Second from left in Figure
  //  \ref{fig:ConnectedThresholdOutput} \\ \hline Ventricle    & $(81,112)$ & 210 & 250
  //  & Third  from left in Figure \ref{fig:ConnectedThresholdOutput} \\ \hline Gray
  //  matter  & $(107,69)$ & 180 & 210 & Fourth from left in Figure
  //  \ref{fig:ConnectedThresholdOutput} \\ \hline \end{tabular} \end{center}
  //  \itkcaption[ConnectedThreshold example parameters]{Parameters used for
  //  segmenting some brain structures shown in
  //  Figure~\ref{fig:ConnectedThresholdOutput} with the filter
  //  \doxygen{ConnectedThresholdImageFilter}.\label{tab:ConnectedThresholdOutput}}
  //  \end{table}
  //
  // \begin{figure} \center
  // \includegraphics[width=0.24\textwidth]{BrainProtonDensitySlice}
  // \includegraphics[width=0.24\textwidth]{ConnectedThresholdOutput1}
  // \includegraphics[width=0.24\textwidth]{ConnectedThresholdOutput2}
  // \includegraphics[width=0.24\textwidth]{ConnectedThresholdOutput3}
  // \itkcaption[ConnectedThreshold segmentation results]{Segmentation results
  // for the ConnectedThreshold filter for various seed points.}
  // \label{fig:ConnectedThresholdOutput}
  // \end{figure}
  //
  //  Notice that the gray matter is not being completely segmented.  This
  //  illustrates the vulnerability of the region-growing methods when the
  //  anatomical structures to be segmented do not have a homogeneous
  //  statistical distribution over the image space. You may want to
  //  experiment with different values of the lower and upper thresholds to
  //  verify how the accepted region will extend.
  //
  //  Another option for segmenting regions is to take advantage of the
  //  functionality provided by the \code{ConnectedThresholdImageFilter} for
  //  managing multiple seeds. The seeds can be passed one-by-one to the
  //  filter using the \code{AddSeed()} method. You could imagine a user
  //  interface in which an operator clicks on multiple points of the object
  //  to be segmented and each selected point is passed as a seed to this
  //  filter.
  //
  //  Software Guide : EndLatex


  return EXIT_SUCCESS;
}