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

  Program:   Insight Segmentation & Registration Toolkit
  Module:    itkOptMattesMutualInformationImageToImageMetric.h
  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 __itkOptMattesMutualInformationImageToImageMetric_h
#define __itkOptMattesMutualInformationImageToImageMetric_h

#include "itkOptImageToImageMetric.h"
#include "itkCovariantVector.h"
#include "itkPoint.h"
#include "itkIndex.h"
#include "itkBSplineKernelFunction.h"
#include "itkBSplineDerivativeKernelFunction.h"
#include "itkCentralDifferenceImageFunction.h"
#include "itkBSplineInterpolateImageFunction.h"
#include "itkBSplineDeformableTransform.h"
#include "itkArray2D.h"

#include "itkMultiThreader.h"

namespace itk
{

/** \class MattesMutualInformationImageToImageMetric
 * \brief Computes the mutual information between two images to be 
 * registered using the method of Mattes et al.
 *
 * MattesMutualInformationImageToImageMetric computes the mutual 
 * information between a fixed and moving image to be registered.
 *
 * This class is templated over the FixedImage type and the MovingImage 
 * type.
 *
 * The fixed and moving images are set via methods SetFixedImage() and
 * SetMovingImage(). This metric makes use of user specified Transform and
 * Interpolator. The Transform is used to map points from the fixed image to
 * the moving image domain. The Interpolator is used to evaluate the image
 * intensity at user specified geometric points in the moving image.
 * The Transform and Interpolator are set via methods SetTransform() and
 * SetInterpolator().
 *
 * If a BSplineInterpolationFunction is used, this class obtain
 * image derivatives from the BSpline interpolator. Otherwise, 
 * image derivatives are computed using central differencing.
 *
 * \warning This metric assumes that the moving image has already been
 * connected to the interpolator outside of this class. 
 *
 * The method GetValue() computes of the mutual information
 * while method GetValueAndDerivative() computes
 * both the mutual information and its derivatives with respect to the
 * transform parameters.
 *
 * The calculations are based on the method of Mattes et al [1,2]
 * where the probability density distribution are estimated using
 * Parzen histograms. Since the fixed image PDF does not contribute
 * to the derivatives, it does not need to be smooth. Hence, 
 * a zero order (box car) BSpline kernel is used
 * for the fixed image intensity PDF. On the other hand, to ensure
 * smoothness a third order BSpline kernel is used for the 
 * moving image intensity PDF.
 *
 * On Initialize(), the FixedImage is uniformly sampled within
 * the FixedImageRegion. The number of samples used can be set
 * via SetNumberOfSpatialSamples(). Typically, the number of
 * spatial samples used should increase with the image size.
 *
 * The option UseAllPixelOn() disables the random sampling and uses
 * all the pixels of the FixedImageRegion in order to estimate the 
 * joint intensity PDF.
 * 
 * During each call of GetValue(), GetDerivatives(),
 * GetValueAndDerivatives(), marginal and joint intensity PDF's
 * values are estimated at discrete position or bins. 
 * The number of bins used can be set via SetNumberOfHistogramBins().
 * To handle data with arbitray magnitude and dynamic range, 
 * the image intensity is scale such that any contribution to the
 * histogram will fall into a valid bin.
 *
 * One the PDF's have been contructed, the mutual information
 * is obtained by doubling summing over the discrete PDF values.
 *
 *
 * Notes: 
 * 1. This class returns the negative mutual information value.
 * 2. This class in not thread safe due the private data structures
 *     used to the store the sampled points and the marginal and joint pdfs.
 *
 * References:
 * [1] "Nonrigid multimodality image registration"
 *      D. Mattes, D. R. Haynor, H. Vesselle, T. Lewellen and W. Eubank
 *      Medical Imaging 2001: Image Processing, 2001, pp. 1609-1620.
 * [2] "PET-CT Image Registration in the Chest Using Free-form Deformations"
 *      D. Mattes, D. R. Haynor, H. Vesselle, T. Lewellen and W. Eubank
 *      IEEE Transactions in Medical Imaging. Vol.22, No.1, 
        January 2003. pp.120-128.
 * [3] "Optimization of Mutual Information for MultiResolution Image
 *      Registration"
 *      P. Thevenaz and M. Unser
 *      IEEE Transactions in Image Processing, 9(12) December 2000.
 *
 * \ingroup RegistrationMetrics
 */
template <class TFixedImage,class TMovingImage >
class ITK_EXPORT MattesMutualInformationImageToImageMetric :
    public ImageToImageMetric< TFixedImage, TMovingImage >
{
public:

  /** Standard class typedefs. */
  typedef MattesMutualInformationImageToImageMetric           Self;
  typedef ImageToImageMetric< 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(MattesMutualInformationImageToImageMetric,
               ImageToImageMetric);

  /** Types inherited from Superclass. */
  typedef typename Superclass::TransformType            TransformType;
  typedef typename Superclass::TransformPointer         TransformPointer;
  typedef typename Superclass::TransformJacobianType    TransformJacobianType;
  typedef typename Superclass::InterpolatorType         InterpolatorType;
  typedef typename Superclass::MeasureType              MeasureType;
  typedef typename Superclass::DerivativeType           DerivativeType;
  typedef typename Superclass::ParametersType           ParametersType;
  typedef typename Superclass::FixedImageType           FixedImageType;
  typedef typename Superclass::MovingImageType          MovingImageType;
  typedef typename Superclass::MovingImagePointType     MovingImagePointType;
  typedef typename Superclass::FixedImageConstPointer   FixedImageConstPointer;
  typedef typename Superclass::MovingImageConstPointer  MovingImageConstPointer;
  typedef typename Superclass::BSplineTransformWeightsType
                                                        BSplineTransformWeightsType;
  typedef typename Superclass::BSplineTransformIndexArrayType
                                                        BSplineTransformIndexArrayType;

  typedef typename Superclass::CoordinateRepresentationType
                                                   CoordinateRepresentationType;
  typedef typename Superclass::FixedImageSampleContainer   
                                                      FixedImageSampleContainer;
  typedef typename Superclass::ImageDerivativesType     ImageDerivativesType;
  typedef typename Superclass::WeightsValueType         WeightsValueType;
  typedef typename Superclass::IndexValueType           IndexValueType;

  typedef typename FixedImageType::OffsetValueType      OffsetValueType;

  /** The moving image dimension. */
  itkStaticConstMacro( MovingImageDimension, unsigned int,
                       MovingImageType::ImageDimension );

  /** 
   *  Initialize the Metric by 
   *  (1) making sure that all the components are present and plugged 
   *      together correctly,
   *  (2) uniformly select NumberOfSpatialSamples within
   *      the FixedImageRegion, and 
   *  (3) allocate memory for pdf data structures. */
  virtual void Initialize(void) throw ( ExceptionObject );

  /**  Get the value. */
  MeasureType GetValue( const ParametersType & parameters ) const;

  /** Get the derivatives of the match measure. */
  void GetDerivative( const ParametersType & parameters,
                      DerivativeType & Derivative ) const;

  /**  Get the value and derivatives for single valued optimizers. */
  void GetValueAndDerivative( const ParametersType & parameters, 
                              MeasureType & Value,
                              DerivativeType & Derivative ) const;

  /** Number of bins to used in the histogram. Typical value is
   * 50. The minimum value is 5 due to the padding required by the Parzen
   * windowing with a cubic-BSpline kernel. Note that even if the metric
   * is used on binary images, the number of bins should at least be
   * equal to five. */
  itkSetClampMacro( NumberOfHistogramBins, unsigned long,
                    5, NumericTraits<unsigned long>::max() );
  itkGetConstReferenceMacro( NumberOfHistogramBins, unsigned long);   

  /** This variable selects the method to be used for computing the Metric
   * derivatives with respect to the Transform parameters. Two modes of
   * computation are available. The choice between one and the other is a
   * trade-off between computation speed and memory allocations. The two modes
   * are described in detail below: 
   *
   * UseExplicitPDFDerivatives = True 
   * will compute the Metric derivative by first calculating the derivatives of
   * each one of the Joint PDF bins with respect to each one of the Transform
   * parameters and then accumulating these contributions in the final metric
   * derivative array by using a bin-specific weight.  The memory required for
   * storing the intermediate derivatives is a 3D array of doubles with size
   * equals to the product of (number of histogram bins)^2 times number of
   * transform parameters. This method is well suited for Transform with a small
   * number of parameters.
   *
   * UseExplicitPDFDerivatives = False will compute the Metric derivative by
   * first computing the weights for each one of the Joint PDF bins and caching
   * them into an array. Then it will revisit each one of the PDF bins for
   * computing its weighted contribution to the full derivative array. In this
   * method an extra 2D array is used for storing the weights of each one of
   * the PDF bins. This is an array of doubles with size equals to (number of
   * histogram bins)^2. This method is well suited for Transforms with a large
   * number of parameters, such as, BSplineDeformableTransforms. */
  itkSetMacro(UseExplicitPDFDerivatives,bool);
  itkGetConstReferenceMacro(UseExplicitPDFDerivatives,bool);
  itkBooleanMacro(UseExplicitPDFDerivatives);

protected:

  MattesMutualInformationImageToImageMetric();
  virtual ~MattesMutualInformationImageToImageMetric();
  void PrintSelf(std::ostream& os, Indent indent) const;

private:

  //purposely not implemented
  MattesMutualInformationImageToImageMetric(const Self &); 
  //purposely not implemented
  void operator=(const Self &); 


  /** The marginal PDFs are stored as std::vector. */
  typedef float                       PDFValueType;
  typedef float *                     MarginalPDFType;

  mutable MarginalPDFType             m_FixedImageMarginalPDF;

  /** The moving image marginal PDF. */
  mutable MarginalPDFType             m_MovingImageMarginalPDF;

  /** Helper array for storing the values of the JointPDF ratios. */
  typedef double                      PRatioType;
  typedef Array2D< PRatioType >       PRatioArrayType;
  mutable PRatioArrayType             m_PRatioArray;

  /** Helper variable for accumulating the derivative of the metric. */
  mutable DerivativeType              m_MetricDerivative;
  mutable DerivativeType            * m_ThreaderMetricDerivative;

  /** Typedef for the joint PDF and PDF derivatives are stored as ITK Images. */
  typedef Image<PDFValueType,2>                 JointPDFType;
  typedef Image<PDFValueType,3>                 JointPDFDerivativesType;
  typedef JointPDFType::IndexType               JointPDFIndexType;
  typedef JointPDFType::PixelType               JointPDFValueType;
  typedef JointPDFType::RegionType              JointPDFRegionType;
  typedef JointPDFType::SizeType                JointPDFSizeType;
  typedef JointPDFDerivativesType::IndexType    JointPDFDerivativesIndexType;
  typedef JointPDFDerivativesType::PixelType    JointPDFDerivativesValueType;
  typedef JointPDFDerivativesType::RegionType   JointPDFDerivativesRegionType;
  typedef JointPDFDerivativesType::SizeType     JointPDFDerivativesSizeType;

  /** The joint PDF and PDF derivatives. */
  typename JointPDFType::Pointer                m_JointPDF;
  unsigned long                                 m_JointPDFBufferSize;
  typename JointPDFDerivativesType::Pointer     m_JointPDFDerivatives;
  unsigned long                                 m_JointPDFDerivativesBufferSize;

  /** Variables to define the marginal and joint histograms. */
  unsigned long  m_NumberOfHistogramBins;
  double         m_MovingImageNormalizedMin;
  double         m_FixedImageNormalizedMin;
  double         m_FixedImageTrueMin;
  double         m_FixedImageTrueMax;
  double         m_MovingImageTrueMin;
  double         m_MovingImageTrueMax;
  double         m_FixedImageBinSize;
  double         m_MovingImageBinSize;

  /** Typedefs for BSpline kernel and derivative functions. */
  typedef BSplineKernelFunction<3>           CubicBSplineFunctionType;
  typedef BSplineDerivativeKernelFunction<3> CubicBSplineDerivativeFunctionType;

  /** Cubic BSpline kernel for computing Parzen histograms. */
  typename CubicBSplineFunctionType::Pointer   m_CubicBSplineKernel;
  typename CubicBSplineDerivativeFunctionType::Pointer   
                                               m_CubicBSplineDerivativeKernel;

  /** Precompute fixed image parzen window indices. */
  virtual void ComputeFixedImageParzenWindowIndices( 
                                         FixedImageSampleContainer & samples );

  /** Compute PDF derivative contribution for each parameter. */
  virtual void ComputePDFDerivatives( unsigned int threadID,
                                      unsigned int sampleNumber,
                                      int movingImageParzenWindowIndex,
                                      const ImageDerivativesType
                                              &  movingImageGradientValue,
                                      double cubicBSplineDerivativeValue 
                                      ) const;

  PDFValueType                                * m_ThreaderFixedImageMarginalPDF;
  typename JointPDFType::Pointer              * m_ThreaderJointPDF;
  typename JointPDFDerivativesType::Pointer   * m_ThreaderJointPDFDerivatives;
  int                                         * m_ThreaderJointPDFStartBin;
  int                                         * m_ThreaderJointPDFEndBin;
  mutable double                              * m_ThreaderJointPDFSum;
  mutable double                                m_JointPDFSum;

  bool                                          m_UseExplicitPDFDerivatives;
  mutable bool                                  m_ImplicitDerivativesSecondPass;


  virtual inline void GetValueThreadPreProcess( unsigned int threadID,
                                        bool withinSampleThread ) const;
  virtual inline bool GetValueThreadProcessSample( unsigned int threadID,
                                       unsigned long fixedImageSample,
                                       const MovingImagePointType & mappedPoint,
                                       double movingImageValue ) const;
  virtual inline void GetValueThreadPostProcess( unsigned int threadID,
                                        bool withinSampleThread ) const;

  virtual inline void GetValueAndDerivativeThreadPreProcess( 
                                       unsigned int threadID,
                                       bool withinSampleThread ) const;
  virtual inline bool GetValueAndDerivativeThreadProcessSample( unsigned int threadID,
                                       unsigned long fixedImageSample,
                                       const MovingImagePointType & mappedPoint,
                                       double movingImageValue,
                                       const ImageDerivativesType &
                                               movingImageGradientValue ) const;
  virtual inline void GetValueAndDerivativeThreadPostProcess( 
                                       unsigned int threadID,
                                       bool withinSampleThread ) const;

};

} // end namespace itk

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

#endif