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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.
 *  You may obtain a copy of the License at
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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
//
// This example illustrates how the \doxygen{ImageAdaptor} can be used to cast
// an image from one pixel type to another. In particular, we will
// \emph{adapt} an \code{unsigned char} image to make it appear as an image of
// pixel type \code{float}.
//
// \index{itk::ImageAdaptor!Instantiation}
// \index{itk::ImageAdaptor!Header}
//
// We begin by including the relevant headers.
//
// Software Guide : EndLatex

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


#include "itkImageRegionIteratorWithIndex.h"
#include "itkImageFileReader.h"


//  Software Guide : BeginLatex
//
// First, we need to define a \emph{pixel accessor} class that does the actual
// conversion. Note that in general, the only valid operations for pixel
// accessors are those that only require the value of the input pixel. As
// such, neighborhood type operations are not possible. A pixel accessor must
// provide methods \code{Set()} and \code{Get()}, and define the types of
// \code{InternalPixelType} and \code{ExternalPixelType}. The
// \code{InternalPixelType} corresponds to the pixel type of the image to be
// adapted (\code{unsigned char} in this example). The
// \code{ExternalPixelType} corresponds to the pixel type we wish to emulate
// with the ImageAdaptor
// (\code{float} in this case).
//
//  Software Guide : EndLatex


// Software Guide : BeginCodeSnippet
class CastPixelAccessor
{
public:
  using InternalType = unsigned char;
  using ExternalType = float;

  static void
  Set(InternalType & output, const ExternalType & input)
  {
    output = static_cast<InternalType>(input);
  }

  static ExternalType
  Get(const InternalType & input)
  {
    return static_cast<ExternalType>(input);
  }
};
// Software Guide : EndCodeSnippet


//-------------------------
//
//   Main code
//
//-------------------------

int
main(int argc, char * argv[])
{
  if (argc < 2)
  {
    std::cerr << "Usage: " << std::endl;
    std::cerr << "ImageAdaptor1   inputFileName" << std::endl;
    return EXIT_FAILURE;
  }


  //  Software Guide : BeginLatex
  //
  //  The CastPixelAccessor class simply applies a
  //  \code{static\_cast} to the pixel values. We now use this pixel accessor
  //  to define the image adaptor type and create an instance using
  //  the standard \code{New()} method.
  //
  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet
  using InputPixelType = unsigned char;
  constexpr unsigned int Dimension = 2;
  using ImageType = itk::Image<InputPixelType, Dimension>;

  using ImageAdaptorType = itk::ImageAdaptor<ImageType, CastPixelAccessor>;
  auto adaptor = ImageAdaptorType::New();
  // Software Guide : EndCodeSnippet

  // Software Guide : BeginLatex
  //
  // We also create an image reader templated over the input image type and
  // read the input image from file.
  //
  // Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet
  using ReaderType = itk::ImageFileReader<ImageType>;
  auto reader = ReaderType::New();
  // Software Guide : EndCodeSnippet


  reader->SetFileName(argv[1]);
  reader->Update();


  //  Software Guide : BeginLatex
  //
  //  The output of the reader is then connected as the input to the image
  //  adaptor.
  //
  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet
  adaptor->SetImage(reader->GetOutput());
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  In the following code, we visit the image using an iterator
  //  instantiated using the adapted image type and compute the
  //  sum of the pixel values.
  //
  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet
  using IteratorType = itk::ImageRegionIteratorWithIndex<ImageAdaptorType>;
  IteratorType it(adaptor, adaptor->GetBufferedRegion());

  double sum = 0.0;
  it.GoToBegin();
  while (!it.IsAtEnd())
  {
    float value = it.Get();
    sum += value;
    ++it;
  }
  // Software Guide : EndCodeSnippet


  std::cout << "Sum of pixels is: " << sum << std::endl;


  //  Software Guide : BeginLatex
  //
  // Although in this example, we are just performing a simple summation, the
  // key concept is that access to pixels is performed as if the pixel is of
  // type
  //  \code{float}. Additionally, it should be noted that the adaptor is used
  // as if it was an actual image and not as a filter. ImageAdaptors conform
  // to the same API as the  \doxygen{Image} class.
  //
  //  Software Guide : EndLatex

  return EXIT_SUCCESS;
}
