Examples/Filtering/WarpImageFilter1.cxx

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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.
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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 to use the WarpImageFilter and a
//  deformation field for resampling an image. This is typically done
//  as the last step of a deformable registration algorithm.
//
//  \index{itk::WarpImageFilter}
//
//  Software Guide : EndLatex
 
 
#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
 
 
// Software Guide : BeginCodeSnippet
#include "itkWarpImageFilter.h"
// Software Guide : EndCodeSnippet
 
 
int
main(int argc, char * argv[])
{
  if (argc < 4)
  {
    std::cerr << "Usage: " << std::endl;
    std::cerr << argv[0]
              << "  inputImageFile  inputDisplacementField  outputImageFile"
              << std::endl;
    return EXIT_FAILURE;
  }
 
  constexpr unsigned int Dimension = 2;
 
  // Software Guide : BeginLatex
  //
  // The deformation field is represented as an image of vector pixel types.
  // The dimension of the vectors is the same as the dimension of the input
  // image. Each vector in the deformation field represents the distance
  // between a geometric point in the input space and a point in the output
  // space such that: \begin{equation} p_{in} = p_{out} + \text{distance}
  // \end{equation}
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using VectorComponentType = float;
  using VectorPixelType = itk::Vector<VectorComponentType, Dimension>;
  using DisplacementFieldType = itk::Image<VectorPixelType, Dimension>;
 
  using PixelType = unsigned char;
  using ImageType = itk::Image<PixelType, Dimension>;
  // Software Guide : EndCodeSnippet
 
 
  using ReaderType = itk::ImageFileReader<ImageType>;
  using WriterType = itk::ImageFileWriter<ImageType>;
 
  // Software Guide : BeginLatex
  //
  // The field is read from a file, through a reader instantiated over the
  // vector pixel types.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using FieldReaderType = itk::ImageFileReader<DisplacementFieldType>;
  // Software Guide : EndCodeSnippet
 
  auto reader = ReaderType::New();
  auto writer = WriterType::New();
 
  reader->SetFileName(argv[1]);
  writer->SetFileName(argv[3]);
 
  // Software Guide : BeginCodeSnippet
  auto fieldReader = FieldReaderType::New();
  fieldReader->SetFileName(argv[2]);
  fieldReader->Update();
 
  DisplacementFieldType::ConstPointer deformationField =
    fieldReader->GetOutput();
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // The \doxygen{WarpImageFilter} is templated over the input image type,
  // output image type and the deformation field type.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using FilterType =
    itk::WarpImageFilter<ImageType, ImageType, DisplacementFieldType>;
 
  auto filter = FilterType::New();
  // Software Guide : EndCodeSnippet
 
  // Software Guide : BeginLatex
  //
  // Typically the mapped position does not correspond to an integer pixel
  // position in the input image. Interpolation via an image function is used
  // to compute values at non-integer positions. This is done via the
  // \code{SetInterpolator()} method.
  // \index{itk::Warp\-Image\-Filter!SetInterpolator()}
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  using InterpolatorType =
    itk::LinearInterpolateImageFunction<ImageType, double>;
 
  auto interpolator = InterpolatorType::New();
 
  filter->SetInterpolator(interpolator);
  // Software Guide : EndCodeSnippet
 
  // SoftwareGuide : BeginLatex
  //
  // The output image spacing and origin may be set via SetOutputSpacing(),
  // SetOutputOrigin(). This is taken from the deformation field.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  filter->SetOutputSpacing(deformationField->GetSpacing());
  filter->SetOutputOrigin(deformationField->GetOrigin());
  filter->SetOutputDirection(deformationField->GetDirection());
 
  filter->SetDisplacementField(deformationField);
  // Software Guide : EndCodeSnippet
 
  filter->SetInput(reader->GetOutput());
  writer->SetInput(filter->GetOutput());
 
  try
  {
    writer->Update();
  }
  catch (const itk::ExceptionObject & excp)
  {
    std::cerr << "Exception thrown " << std::endl;
    std::cerr << excp << std::endl;
  }
 
  return EXIT_SUCCESS;
}