Examples/Filtering/FFTDirectInverse.cxx

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 *
 *  Copyright Insight Software Consortium
 *
 *  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
//
//     http://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 >;

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

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

  // Handle padding of the image with resampling
  using ResamplerType = itk::ResampleImageFilter<
                              IOImageType,
                              WorkImageType >;

  ResamplerType::Pointer 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 >;
  FFTFilterType::Pointer 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 >;
  invFFTFilterType::Pointer fftoutput = invFFTFilterType::New();
  fftoutput->SetInput(fftinput->GetOutput()); // try to recover the input image

  // undo the padding
  using ResampleOutType = itk::ResampleImageFilter<WorkImageType, IOImageType>;
  ResampleOutType::Pointer 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;
}