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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
*
* 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
{
/** \class HistogramToEntropyImageFilter
* \brief The class takes a histogram as an input and gives the entropy
* image as the output. A pixel, at position I, in the output image is given by
*
* \f[
* f(I) = -p \log_2 p
* \f]
*
* where
* \f[
* p = \frac{q_I}{\sum_{i \in I} q_I}
* \f]
* where \f$q_I\f$ is the frequency of measurement vector, I.
*
* \f$p\f$ is the frequency of a measurement vector by the sum of all frequencies =
* Probability of the the measurement vector
*
* The output image is of type double.
*
* This is useful in plotting the joint histograms during registration.
*
* \sa HistogramToImageFilter, HistogramToLogProbabilityImageFilter,
* HistogramToIntensityImageFilter, HistogramToProbabilityImageFilter
*
* \ingroup ITKStatistics
*/
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..
typedef TOutput OutputPixelType;
HistogramEntropyFunction():
m_TotalFrequency(1) {}
~HistogramEntropyFunction() {}
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;
};
}
template< typename THistogram, typename TImage=Image< double, 3> >
class HistogramToEntropyImageFilter:
public HistogramToImageFilter< THistogram, TImage,
Function::HistogramEntropyFunction< SizeValueType, typename TImage::PixelType > >
{
public:
/** Standard class typedefs. */
typedef HistogramToEntropyImageFilter Self;
/** Standard "Superclass" typedef. */
typedef HistogramToImageFilter< THistogram, TImage,
Function::HistogramEntropyFunction< SizeValueType, typename TImage::PixelType > >
Superclass;
typedef SmartPointer< Self > Pointer;
typedef SmartPointer< const Self > ConstPointer;
/** Run-time type information (and related methods). */
itkTypeMacro(HistogramToEntropyImageFilter, HistogramToImageFilter);
/** Method for creation through the object factory. */
itkNewMacro(Self);
protected:
HistogramToEntropyImageFilter() {}
virtual ~HistogramToEntropyImageFilter() ITK_OVERRIDE {}
private:
ITK_DISALLOW_COPY_AND_ASSIGN(HistogramToEntropyImageFilter);
};
} // end namespace itk
#endif
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