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

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkCorrelationCoefficientHistogramImageToImageMetric.h,v $
  Language:  C++
  Date:      $Date: 2009-05-02 05:43:54 $
  Version:   $Revision: 1.5 $

  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 __itkCorrelationCoefficientHistogramImageToImageMetric_h
#define __itkCorrelationCoefficientHistogramImageToImageMetric_h

#include "itkHistogramImageToImageMetric.h"

namespace itk
{
/** \class CorrelationCoefficientHistogramImageToImageMetric
    \brief Computes correlation coefficient similarity measure between two
    images to be registered.

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

    This metric computes the similarity measure between pixels in the
    moving image and pixels in the fixed images using a histogram.

    \ingroup RegistrationMetrics */
template <class TFixedImage, class TMovingImage>
class ITK_EXPORT CorrelationCoefficientHistogramImageToImageMetric :
public HistogramImageToImageMetric<TFixedImage, TMovingImage>
{
public:
  /** Standard class typedefs. */
  typedef CorrelationCoefficientHistogramImageToImageMetric      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(CorrelationCoefficientHistogramImageToImageMetric,
    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;

#ifdef ITK_USE_REVIEW_STATISTICS
  typedef typename HistogramType::AbsoluteFrequencyType HistogramAbsoluteFrequencyType;
#else
  typedef typename HistogramType::FrequencyType         HistogramAbsoluteFrequencyType;
#endif
  typedef HistogramAbsoluteFrequencyType                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. */
  CorrelationCoefficientHistogramImageToImageMetric(){}
  virtual ~CorrelationCoefficientHistogramImageToImageMetric(){}
  
  /** Evaluates the sum of squared differences from the histogram. */
  virtual MeasureType EvaluateMeasure(HistogramType& histogram) const;

private:
  /** Returns the mean in the x-direction. */
  MeasureType MeanX(HistogramType& histogram) const;

  /** Returns the mean in the y-direction. */
  MeasureType MeanY(HistogramType& histogram) const;

  /** Returns the variance in the x-direction. */
  MeasureType VarianceX(HistogramType& histogram) const;

  /** Returns the variance in the y-direction. */
  MeasureType VarianceY(HistogramType& histogram) const;

  /** Returns the variance. */
  MeasureType Covariance(HistogramType& histogram) const;

  // Purposely not implemented.
  CorrelationCoefficientHistogramImageToImageMetric(Self const&); 
  void operator=(Self const&); // Purposely not implemented.
};

} // End namespace itk.

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

#endif // __itkCorrelationCoefficientHistogramImageToImageMetric_h
