Examples/Filtering/FFTDirectInverse.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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//
// This example was originally contributed by Stephan in the users list
//
//     https://public.kitware.com/pipermail/insight-users/2005-June/013482.html
//
//
 
// Software Guide : BeginLatex
//
// This example illustrates how to compute the direct Fourier transform
// followed by the inverse Fourier transform in order to recover the original
// data.
//
// Software Guide : EndLatex
 
#include "itkImage.h"
#include "itkImageFileReader.h"
#include "itkImageFileWriter.h"
#include "itkResampleImageFilter.h"
#include "itkVnlForwardFFTImageFilter.h"
#include "itkVnlInverseFFTImageFilter.h"
 
int
main(int argc, char * argv[])
{
  if (argc != 3)
  {
    std::cerr << "Usage: " << argv[0] << " input output" << std::endl;
    return EXIT_FAILURE;
  }
 
  // Software Guide : BeginLatex
  //
  // First we set up the types of the input and output images.
  //
  // Software Guide : EndLatex
 
  // Software Guide : BeginCodeSnippet
  constexpr unsigned int Dimension = 2;
  using IOPixelType = unsigned short;
  using WorkPixelType = float;
 
  using IOImageType = itk::Image<IOPixelType, Dimension>;
  using WorkImageType = itk::Image<WorkPixelType, Dimension>;
  // Software Guide : EndCodeSnippet
 
  // File handling
  using ReaderType = itk::ImageFileReader<IOImageType>;
  using WriterType = itk::ImageFileWriter<IOImageType>;
 
  auto inputreader = ReaderType::New();
  auto writer = WriterType::New();
 
  inputreader->SetFileName(argv[1]);
  writer->SetFileName(argv[2]);
 
  // Handle padding of the image with resampling
  using ResamplerType = itk::ResampleImageFilter<IOImageType, WorkImageType>;
 
  auto inputresampler = ResamplerType::New();
  inputresampler->SetDefaultPixelValue(0);
 
  // Read the image and get its size
  inputreader->Update();
 
  IOImageType::SizeType inputsize;
  IOImageType::SizeType worksize;
 
  inputsize = inputreader->GetOutput()->GetLargestPossibleRegion().GetSize();
 
  // worksize is the nearest multiple of 2 larger than the input
  for (unsigned int i = 0; i < 2; ++i)
  {
    unsigned int n = 0;
    worksize[i] = inputsize[i];
    while (worksize[i] >>= 1)
    {
      n++;
    }
    worksize[i] = static_cast<IOImageType::SizeValueType>(1)
                  << static_cast<IOImageType::SizeValueType>(n + 1);
 
    std::cout << "inputsize[" << i << "]=" << inputsize[i] << std::endl;
    std::cout << "worksize[" << i << "]=" << worksize[i] << std::endl;
  }
 
  inputresampler->SetSize(worksize);
  inputresampler->SetInput(inputreader->GetOutput());
 
  // Forward FFT filter
  using FFTFilterType = itk::VnlForwardFFTImageFilter<WorkImageType>;
  auto fftinput = FFTFilterType::New();
  fftinput->SetInput(inputresampler->GetOutput());
 
  // This is the output type from the FFT filters
  using ComplexImageType = FFTFilterType::OutputImageType;
 
  // Do the inverse transform = forward transform / num voxels
  using invFFTFilterType = itk::VnlInverseFFTImageFilter<ComplexImageType>;
  auto fftoutput = invFFTFilterType::New();
  fftoutput->SetInput(
    fftinput->GetOutput()); // try to recover the input image
 
  // undo the padding
  using ResampleOutType =
    itk::ResampleImageFilter<WorkImageType, IOImageType>;
  auto outputResampler = ResampleOutType::New();
  outputResampler->SetDefaultPixelValue(0);
  outputResampler->SetSize(inputsize);
  outputResampler->SetInput(fftoutput->GetOutput());
 
  // Write the output
  writer->SetInput(outputResampler->GetOutput());
  writer->Update();
 
  return EXIT_SUCCESS;
}