itkFrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex.h

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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.
 *  You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0.txt
 *
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 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef itkFrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex_h
#define itkFrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex_h

#include "itkImageRegionConstIteratorWithIndex.h"

namespace itk
{
template< typename TImage >
class FrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex:
  public ImageRegionConstIteratorWithIndex< TImage >
{
public:
  using Self = FrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex;
  using Superclass = ImageRegionConstIteratorWithIndex< TImage >;

  using IndexType = typename Superclass::IndexType;
  using SizeType = typename Superclass::SizeType;
  using OffsetType = typename Superclass::OffsetType;
  using RegionType = typename Superclass::RegionType;
  using ImageType = typename Superclass::ImageType;
  using PixelContainer = typename Superclass::PixelContainer;
  using PixelContainerPointer = typename Superclass::PixelContainerPointer;
  using InternalPixelType = typename Superclass::InternalPixelType;
  using PixelType = typename Superclass::PixelType;
  using AccessorType = typename Superclass::AccessorType;

  using FrequencyType = typename ImageType::SpacingType;
  using FrequencyValueType = typename ImageType::SpacingValueType;
  FrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex() :
    ImageRegionConstIteratorWithIndex< TImage >()
  {
    this->Init();
  }

  FrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex(const TImage *ptr, const RegionType & region) :
    ImageRegionConstIteratorWithIndex< TImage >(ptr, region)
  {
    this->Init();
  }

  explicit FrequencyShiftedFFTLayoutImageRegionConstIteratorWithIndex(const Superclass & it) :
    ImageRegionConstIteratorWithIndex< TImage >(it)
  {
    this->Init();
  }

  /*
   * Image Index [0, N - 1] returns [-N/2 + 1, -1] (negative) union [0 to N/2] (positive). So index N/2 + 1 returns the bin 0.
   * It is a shift by -N/2 + 1, from [0, N-1] to [-N/2 + 1, N/2]
   * If first index of the image is not zero, it stills returns values in the same range.
   */
  IndexType GetFrequencyBin() const
  {
    IndexType freqInd;

    freqInd.Fill(0);
    for (unsigned int dim = 0; dim < TImage::ImageDimension; dim++)
      {
        freqInd[dim] = this->m_PositionIndex[dim] - this->m_ZeroFrequencyIndex[dim];
      }
    return freqInd;
  }

  FrequencyType GetFrequency() const
  {
    FrequencyType freq;
    IndexType     freqInd = this->GetFrequencyBin();

    for (unsigned int dim = 0; dim < TImage::ImageDimension; dim++)
      {
      freq[dim] = this->m_FrequencyOrigin[dim]
        + this->m_FrequencySpacing[dim] * freqInd[dim];
      }
    return freq;
  }

  FrequencyValueType GetFrequencyModuloSquare() const
  {
    FrequencyValueType w2(0);
    FrequencyType      w( this->GetFrequency() );

    for (unsigned int dim = 0; dim < TImage::ImageDimension; dim++)
      {
      w2 += w[dim] * w[dim];
      }
    return w2;
  }

  itkGetConstReferenceMacro(ZeroFrequencyIndex, IndexType);

  itkGetConstReferenceMacro(FrequencyOrigin, FrequencyType);

  itkGetConstReferenceMacro(FrequencySpacing, FrequencyType);

  void SetActualXDimensionIsOdd(bool value)
    {
    this->m_ActualXDimensionIsOdd = value;
    };
  itkGetMacro(ActualXDimensionIsOdd, bool);
  itkBooleanMacro(ActualXDimensionIsOdd);

private:
  void Init()
  {
    IndexType minIndex =
      this->m_Image->GetLargestPossibleRegion().GetIndex();
    SizeType sizeImage =
      this->m_Image->GetLargestPossibleRegion().GetSize();
    for (unsigned int dim = 0; dim < ImageType::ImageDimension; dim++)
      {
      this->m_ZeroFrequencyIndex[dim] = static_cast<FrequencyValueType>(
          minIndex[dim] + std::floor( sizeImage[dim] / 2.0 ));
      // Set frequency metadata.
      // Origin of frequencies is zero in the standard layout of a FFT output.
      this->m_FrequencyOrigin[dim] = 0.0;
      // SamplingFrequency = 1.0 / SpatialImageSpacing
      // Freq_BinSize = SamplingFrequency / Size
      this->m_FrequencySpacing[dim] = 1.0 / (this->m_Image->GetSpacing()[dim] * sizeImage[dim]);
      }
  }

  IndexType     m_ZeroFrequencyIndex;
  FrequencyType m_FrequencyOrigin;
  FrequencyType m_FrequencySpacing;
  bool          m_ActualXDimensionIsOdd;
};
} // end namespace itk
#endif