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/*=========================================================================
Program: Insight Segmentation & Registration Toolkit
Module: itkNormalizedMutualInformationHistogramImageToImageMetric.txx
Language: C++
Date: $Date$
Version: $Revision$
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 __itkNormalizedMutualInformationHistogramImageToImageMetric_txx
#define __itkNormalizedMutualInformationHistogramImageToImageMetric_txx
#include "itkNormalizedMutualInformationHistogramImageToImageMetric.h"
#include "itkHistogram.h"
namespace itk
{
template <class TFixedImage, class TMovingImage>
typename NormalizedMutualInformationHistogramImageToImageMetric<TFixedImage, \
TMovingImage>::MeasureType
NormalizedMutualInformationHistogramImageToImageMetric<TFixedImage, \
TMovingImage>
::EvaluateMeasure(HistogramType& histogram) const
{
MeasureType entropyX = NumericTraits<MeasureType>::Zero;
MeasureType entropyY = NumericTraits<MeasureType>::Zero;
MeasureType jointEntropy = NumericTraits<MeasureType>::Zero;
typedef typename NumericTraits< HistogramFrequencyType >::RealType HistogramFrequencyRealType;
HistogramFrequencyRealType totalFreq =
static_cast< HistogramFrequencyRealType >( histogram.GetTotalFrequency() );
for (unsigned int i = 0; i < this->GetHistogramSize()[0]; i++)
{
HistogramFrequencyRealType freq =
static_cast< HistogramFrequencyRealType >( histogram.GetFrequency(i, 0) );
if (freq > 0)
{
entropyX += freq*vcl_log(freq);
}
}
entropyX = -entropyX/static_cast<MeasureType>(totalFreq) + vcl_log(totalFreq);
for (unsigned int i = 0; i < this->GetHistogramSize()[1]; i++)
{
HistogramFrequencyRealType freq =
static_cast< HistogramFrequencyRealType >( histogram.GetFrequency(i, 1) );
if (freq > 0)
{
entropyY += freq*vcl_log(freq);
}
}
entropyY = -entropyY/static_cast<MeasureType>(totalFreq) + vcl_log(totalFreq);
HistogramIteratorType it = histogram.Begin();
HistogramIteratorType end = histogram.End();
while (it != end)
{
HistogramFrequencyRealType freq =
static_cast< HistogramFrequencyRealType >( it.GetFrequency() );
if (freq > 0)
{
jointEntropy += freq*vcl_log(freq);
}
++it;
}
jointEntropy = -jointEntropy/static_cast<MeasureType>(totalFreq) +
vcl_log(totalFreq);
return (entropyX + entropyY)/jointEntropy;
}
} // End namespace itk
#endif // itkNormalizedMutualInformationHistogramImageToImageMetric_txx
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