Examples/Statistics/ImageHistogram1.cxx

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// Software Guide : BeginLatex
//
// This example shows how to compute the histogram of a scalar image.  Since
// the statistics framework classes operate on Samples and
// ListOfSamples, we need to introduce a class that will make the image look
// like a list of samples. This class is the
// \subdoxygen{Statistics}{ImageToListSampleAdaptor}.  Once we have connected
// this adaptor to an image, we can proceed to use the
// \subdoxygen{Statistics}{SampleToHistogramFilter} in order to compute
// the histogram of the image.
//
// First, we need to include the headers for the
// \subdoxygen{Statistics}{ImageToListSampleAdaptor} and the \doxygen{Image}
// classes.
//
// \index{itk::Statistics::Scalar\-Image\-To\-List\-Adaptor!header}
// \index{Statistics!Images}
//
// Software Guide : EndLatex
 
// Software Guide : BeginCodeSnippet
#include "itkImageToListSampleAdaptor.h"
#include "itkImage.h"
// Software Guide : EndCodeSnippet
 
// Software Guide : BeginLatex
//
// Now we include the headers for the \code{Histogram}, the
// \code{SampleToHistogramFilter}, and the reader that we will use for
// reading the image from a file.
//
// \index{itk::Statistics::List\-Sample\-To\-Histogram\-Generator!header}
//
// Software Guide : EndLatex
 
// Software Guide : BeginCodeSnippet
#include "itkImageFileReader.h"
#include "itkHistogram.h"
#include "itkSampleToHistogramFilter.h"
// Software Guide : EndCodeSnippet
 
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
 
  // Software Guide : BeginLatex
  //
  // Using the same image type we instantiate the type of the image reader
  // that will provide the image source for our example.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using ReaderType = itk::ImageFileReader<ImageType>;
 
  auto reader = ReaderType::New();
 
  reader->SetFileName(argv[1]);
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // Now we introduce the central piece of this example, which is the use of
  // the adaptor that will present the \doxygen{Image} as if it was a list of
  // samples. We instantiate the type of the adaptor by using the actual image
  // type. Then construct the adaptor by invoking its \code{New()} method and
  // assigning the result to the corresponding smart pointer. Finally we
  // connect the output of the image reader to the input of the adaptor.
  //
  // \index{itk::Statistics::Scalar\-Image\-To\-List\-Adaptor!instantiation}
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using AdaptorType = itk::Statistics::ImageToListSampleAdaptor<ImageType>;
 
  auto adaptor = AdaptorType::New();
 
  adaptor->SetImage(reader->GetOutput());
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // You must keep in mind that adaptors are not pipeline objects. This means
  // that they do not propagate update calls. It is therefore your
  // responsibility to make sure that you invoke the \code{Update()} method of
  // the reader before you attempt to use the output of the adaptor. As usual,
  // this must be done inside a try/catch block because the read operation can
  // potentially throw exceptions.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  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 : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // At this point, we are ready for instantiating the type of the histogram
  // filter. We must first declare the type of histogram we wish to use.
  // The adaptor type is also used as template parameter of the filter.
  // Having instantiated this type, we proceed to create one filter
  // by invoking its \code{New()} method.
  //
  // \index{itk::Statistics::Sample\-To\-Histogram\-Filter!instantiation}
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using HistogramMeasurementType = PixelType;
  using HistogramType = itk::Statistics::Histogram<HistogramMeasurementType>;
  using FilterType =
    itk::Statistics::SampleToHistogramFilter<AdaptorType, HistogramType>;
 
  auto filter = FilterType::New();
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // We define now the characteristics of the Histogram that we want to
  // compute. This typically includes the size of each one of the component,
  // but given that in this simple example we are dealing with a scalar image,
  // then our histogram will have a single component. For the sake of
  // generality, however, we use the \code{HistogramType} as defined inside of
  // the Generator type. We define also the marginal scale factor that will
  // control the precision used when assigning values to histogram bins.
  // Finally we invoke the \code{Update()} method in the filter.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  constexpr unsigned int  numberOfComponents = 1;
  HistogramType::SizeType size(numberOfComponents);
  size.Fill(255);
 
  filter->SetInput(adaptor);
  filter->SetHistogramSize(size);
  filter->SetMarginalScale(10);
 
  HistogramType::MeasurementVectorType min(numberOfComponents);
  HistogramType::MeasurementVectorType max(numberOfComponents);
 
  min.Fill(0);
  max.Fill(255);
 
  filter->SetHistogramBinMinimum(min);
  filter->SetHistogramBinMaximum(max);
 
  filter->Update();
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // Now we are ready for using the image histogram for any further
  // processing. The histogram is obtained from the filter by invoking the
  // \code{GetOutput()} method.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  const HistogramType::ConstPointer histogram = filter->GetOutput();
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // In this current example we simply print out the frequency values of all
  // the bins in the image histogram.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  const unsigned int histogramSize = histogram->Size();
 
  std::cout << "Histogram size " << histogramSize << std::endl;
 
  for (unsigned int bin = 0; bin < histogramSize; ++bin)
  {
    std::cout << "bin = " << bin << " frequency = ";
    std::cout << histogram->GetFrequency(bin, 0) << std::endl;
  }
  // Software Guide : EndCodeSnippet
 
  return EXIT_SUCCESS;
}