itkStandardDeviationProjectionImageFilter.h

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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
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  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 itkStandardDeviationProjectionImageFilter_h
#define itkStandardDeviationProjectionImageFilter_h
 
#include "itkProjectionImageFilter.h"
#include "itkConceptChecking.h"
 
namespace itk
{
 
namespace Functor
{
template <typename TInputPixel, typename TAccumulate>
class StandardDeviationAccumulator
{
public:
  using RealType = typename NumericTraits<TInputPixel>::RealType;
 
  StandardDeviationAccumulator(SizeValueType size)
  {
    m_Size = size;
    m_Values.reserve(size);
  }
 
  ~StandardDeviationAccumulator() = default;
 
  inline void
  Initialize()
  {
    m_Sum = TAccumulate{};
    m_Values.clear();
  }
 
  inline void
  operator()(const TInputPixel & input)
  {
    m_Sum = m_Sum + input;
    m_Values.push_back(input);
  }
 
  inline RealType
  GetValue()
  {
    // to avoid division by zero
    if (m_Size <= 1)
    {
      return RealType{};
    }
 
    const typename NumericTraits<TInputPixel>::RealType mean = ((RealType)m_Sum) / m_Size;
    typename std::vector<TInputPixel>::iterator         it;
    RealType                                            squaredSum{};
    for (it = m_Values.begin(); it != m_Values.end(); ++it)
    {
      squaredSum += itk::Math::sqr(*it - mean);
    }
    return std::sqrt(squaredSum / (m_Size - 1));
  }
 
  TAccumulate              m_Sum;
  SizeValueType            m_Size;
  std::vector<TInputPixel> m_Values;
};
} // namespace Functor
 
template <typename TInputImage,
          typename TOutputImage,
          typename TAccumulate = typename NumericTraits<typename TOutputImage::PixelType>::AccumulateType>
class StandardDeviationProjectionImageFilter
  : public ProjectionImageFilter<TInputImage,
                                 TOutputImage,
                                 Functor::StandardDeviationAccumulator<typename TInputImage::PixelType, TAccumulate>>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(StandardDeviationProjectionImageFilter);
 
  using Self = StandardDeviationProjectionImageFilter;
 
  using Superclass =
    ProjectionImageFilter<TInputImage,
                          TOutputImage,
                          Functor::StandardDeviationAccumulator<typename TInputImage::PixelType, TAccumulate>>;
 
  using InputImageType = TInputImage;
  using InputPixelType = typename InputImageType::PixelType;
 
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  itkOverrideGetNameOfClassMacro(StandardDeviationProjectionImageFilter);

  itkNewMacro(Self);
 
  itkConceptMacro(InputPixelToOutputPixelTypeGreaterAdditiveOperatorCheck,
                  (Concept::AdditiveOperators<TAccumulate, InputPixelType, TAccumulate>));
  itkConceptMacro(InputHasNumericTraitsCheck, (Concept::HasNumericTraits<InputPixelType>));
 
  itkConceptMacro(AccumulateHasNumericTraitsCheck, (Concept::HasNumericTraits<TAccumulate>));
 
protected:
  StandardDeviationProjectionImageFilter() = default;
  ~StandardDeviationProjectionImageFilter() override = default;
}; // end StandardDeviationProjectionImageFilter
} // end namespace itk
 
#endif