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/*=========================================================================
Program: Insight Segmentation & Registration Toolkit
Module: $RCSfile: itkHistogramToEntropyImageFilter.h,v $
Language: C++
Date: $Date: 2009-04-01 14:36:37 $
Version: $Revision: 1.10 $
Copyright (c) Insight Software Consortium. All rights reserved.
See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notices for more information.
=========================================================================*/
#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
*
*/
namespace Function {
template< class TInput, class TOutput=double >
class HistogramEntropyFunction
{
public:
//Probability function = Number of occurances in each bin /
// Total Number of occurances.
//
// 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 * vcl_log(p) / vcl_log(2.0));
}
else
{
const double p = static_cast<OutputPixelType>(A+1) /
static_cast<OutputPixelType>(m_TotalFrequency);
return static_cast<OutputPixelType>( (-1) * p * vcl_log(p) / vcl_log(2.0));
}
}
void SetTotalFrequency( const unsigned long n )
{
m_TotalFrequency = n;
}
unsigned long GetTotalFrequency() const
{
return m_TotalFrequency;
}
private:
unsigned long m_TotalFrequency;
};
}
template <class THistogram, class TOutputPixel=double >
class ITK_EXPORT HistogramToEntropyImageFilter :
public HistogramToImageFilter< THistogram,
Function::HistogramEntropyFunction< unsigned long, TOutputPixel > >
{
public:
/** Standard class typedefs. */
typedef HistogramToEntropyImageFilter Self;
/** Standard "Superclass" typedef. */
typedef HistogramToImageFilter< THistogram,
Function::HistogramEntropyFunction< unsigned long, TOutputPixel > >
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() {}
private:
HistogramToEntropyImageFilter(const Self&); //purposely not implemented
void operator=(const Self&); //purposely not implemented
};
} // end namespace itk
#endif
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