/*=========================================================================

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkNormalizedMutualInformationHistogramImageToImageMetric.h,v $
  Language:  C++
  Date:      $Date: 2004/07/13 18:56:40 $
  Version:   $Revision: 1.4 $

  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_h
#define __itkNormalizedMutualInformationHistogramImageToImageMetric_h

#include "itkHistogramImageToImageMetric.h"

namespace itk
{
  /** \class NormalizedMutualInformationHistogramImageToImageMetric
      \brief Computes normalized mutual information between two images to
      be registered using the histograms of the intensities in the images.

      The type of Normalize Mutual Information implemented in this class
      is given by the equation

      \f[  \frac{ H(A) + H(B) }{ H(A,B) }  \f]

      Where \$ H(A) \$ is the entropy of image \$ A \$, 
            \$ H(B) \$ is the entropy of image \$ B \$,  and
            \$ H(A,B) \$ is the joing entropy of images \$ A \$ and \$ B \$.  

      Details of this implementation can be found in the book 

      "Medical Image Registration" by Hajnal, Hill and Hawkes. 

      The book is available online at

               http://www-ipg.umds.ac.uk/d.hill/hhh/ 

      The implementation of this class corresponds to equation (30) in
      Chapter 3 of this book. Note that by slightly changing this class
      it will be trivial to compute the Normalized Mutual Information
      measures defined in equations (28) and (29) of the same book.


      This class is templated over the type of the fixed and moving
      images to be compared.

      \ingroup RegistrationMetrics */
template <class TFixedImage, class TMovingImage>
class ITK_EXPORT NormalizedMutualInformationHistogramImageToImageMetric :
public HistogramImageToImageMetric<TFixedImage, TMovingImage>
{
 public:
  /** Standard class typedefs. */
  typedef NormalizedMutualInformationHistogramImageToImageMetric Self;
  typedef HistogramImageToImageMetric<TFixedImage, TMovingImage> Superclass;
  typedef SmartPointer<Self>                                     Pointer;
  typedef SmartPointer<const Self>                               ConstPointer;

  /** Method for creation through the object factory. */
  itkNewMacro(Self);

  /** Run-time type information (and related methods). */
  itkTypeMacro(NormalizedMutualInformationHistogramImageToImageMetric,
    HistogramImageToImageMetric);

  /** Types transferred from the base class */
  typedef typename Superclass::RealType                 RealType;
  typedef typename Superclass::TransformType            TransformType;
  typedef typename Superclass::TransformPointer         TransformPointer;
  typedef typename Superclass::TransformParametersType
    TransformParametersType;
  typedef typename Superclass::TransformJacobianType    TransformJacobianType;
  typedef typename Superclass::GradientPixelType        GradientPixelType;

  typedef typename Superclass::MeasureType              MeasureType;
  typedef typename Superclass::DerivativeType           DerivativeType;
  typedef typename Superclass::FixedImageType           FixedImageType;
  typedef typename Superclass::MovingImageType          MovingImageType;
  typedef typename Superclass::FixedImageConstPointer   FixedImageConstPointer;
  typedef typename Superclass::MovingImageConstPointer
    MovingImageConstPointer;

  typedef typename Superclass::HistogramType            HistogramType;
  typedef typename HistogramType::FrequencyType         HistogramFrequencyType;
  typedef typename HistogramType::Iterator              HistogramIteratorType;
  typedef typename HistogramType::MeasurementVectorType
    HistogramMeasurementVectorType;

protected:
  /** Constructor is protected to ensure that \c New() function is used to
      create instances. */
  NormalizedMutualInformationHistogramImageToImageMetric(){}
  virtual ~NormalizedMutualInformationHistogramImageToImageMetric(){}

  /** Evaluates the normalized mutual information from the histogram. */
  virtual MeasureType EvaluateMeasure(HistogramType& histogram) const;

private:
  // Purposely not implemented.
  NormalizedMutualInformationHistogramImageToImageMetric(Self const&);
  void operator=(Self const&); // Purposely not implemented.
};

} // End namespace itk.

#ifndef ITK_MANUAL_INSTANTIATION
#include "itkNormalizedMutualInformationHistogramImageToImageMetric.txx"
#endif

#endif // __itkNormalizedMutualInformationHistogramImageToImageMetric_h
