itkHistogramToEntropyImageFilter.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 itkHistogramToEntropyImageFilter_h
#define itkHistogramToEntropyImageFilter_h
 
#include "itkHistogramToImageFilter.h"
 
namespace itk
{
namespace Function
{
template <typename TInput, typename TOutput = double>
class HistogramEntropyFunction
{
public:
  // Probability function = Number of occurrences in each bin /
  //   Total Number of occurrences.
  //
  // Returns pixels of float..
  using OutputPixelType = TOutput;
 
  HistogramEntropyFunction() = default;
 
  ~HistogramEntropyFunction() = default;
 
  inline OutputPixelType
  operator()(const TInput & A) const
  {
    if (A)
    {
      const double p = static_cast<OutputPixelType>(A) / static_cast<OutputPixelType>(m_TotalFrequency);
      return static_cast<OutputPixelType>((-1) * p * std::log(p) / std::log(2.0));
    }
    else
    {
      const double p = static_cast<OutputPixelType>(A + 1) / static_cast<OutputPixelType>(m_TotalFrequency);
      return static_cast<OutputPixelType>((-1) * p * std::log(p) / std::log(2.0));
    }
  }
 
  void
  SetTotalFrequency(const SizeValueType n)
  {
    m_TotalFrequency = n;
  }
 
  SizeValueType
  GetTotalFrequency() const
  {
    return m_TotalFrequency;
  }
 
private:
  SizeValueType m_TotalFrequency{ 1 };
};
} // namespace Function
 
template <typename THistogram, typename TImage = Image<double, 3>>
class HistogramToEntropyImageFilter
  : public HistogramToImageFilter<THistogram,
                                  TImage,
                                  Function::HistogramEntropyFunction<SizeValueType, typename TImage::PixelType>>
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(HistogramToEntropyImageFilter);
 
  using Self = HistogramToEntropyImageFilter;
 
  using Superclass =
    HistogramToImageFilter<THistogram,
                           TImage,
                           Function::HistogramEntropyFunction<SizeValueType, typename TImage::PixelType>>;
 
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;
 
  itkOverrideGetNameOfClassMacro(HistogramToEntropyImageFilter);
 
  itkNewMacro(Self);
 
protected:
  HistogramToEntropyImageFilter() = default;
  ~HistogramToEntropyImageFilter() override = default;
};
} // end namespace itk
 
#endif