text: /*=========================================================================
   *
   *  Copyright Insight Software Consortium
   *
   *  Licensed under the Apache License, Version 2.0 (the "License");
   *  you may not use this file except in compliance with the License.
   *  You may obtain a copy of the License at
   *
   *         http://www.apache.org/licenses/LICENSE-2.0.txt
   *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS,
   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   *
   *=========================================================================*/
  #ifndef itkSymmetricForcesDemonsRegistrationFilter_h
  #define itkSymmetricForcesDemonsRegistrationFilter_h
  
  #include "itkPDEDeformableRegistrationFilter.h"
  #include "itkSymmetricForcesDemonsRegistrationFunction.h"
  
  namespace itk
  {
  /** \class SymmetricForcesDemonsRegistrationFilter
   * \brief Deformably register two images using the demons algorithm.
   *
   * This class was contributed by Corinne Mattmann, ETH Zurich, Switzerland.
   * based on a variation of the DemonsRegistrationFilter. The basic modification
   * is to use equation (5) from Thirion's paper along with the modification for
   * avoiding large deformations when gradients have small values.
   *
   * SymmetricForcesDemonsRegistrationFilter implements the demons deformable algorithm that
   * register two images by computing the deformation field which will map a
   * moving image onto a fixed image.
   *
   * A deformation field is represented as a image whose pixel type is some
   * vector type with at least N elements, where N is the dimension of
   * the fixed image. The vector type must support element access via operator
   * []. It is assumed that the vector elements behave like floating point
   * scalars.
   *
   * This class is templated over the fixed image type, moving image type
   * and the deformation field type.
   *
   * The input fixed and moving images are set via methods SetFixedImage
   * and SetMovingImage respectively. An initial deformation field maybe set via
   * SetInitialDisplacementField or SetInput. If no initial field is set,
   * a zero field is used as the initial condition.
   *
   * The algorithm has one parameters: the number of iteration to be performed.
   *
   * The output deformation field can be obtained via methods GetOutput
   * or GetDisplacementField.
   *
   * This class make use of the finite difference solver hierarchy. Update
   * for each iteration is computed in DemonsRegistrationFunction.
   *
   * \warning This filter assumes that the fixed image type, moving image type
   * and deformation field type all have the same number of dimensions.
   *
   * \sa SymmetricForcesDemonsRegistrationFunction
   * \sa DemonsRegistrationFilter
   * \sa DemonsRegistrationFunction
   * \ingroup DeformableImageRegistration MultiThreaded
   * \ingroup ITKPDEDeformableRegistration
   */
  template< typename TFixedImage, typename TMovingImage, typename TDisplacementField >
  class ITK_TEMPLATE_EXPORT SymmetricForcesDemonsRegistrationFilter:
    public PDEDeformableRegistrationFilter< TFixedImage, TMovingImage,
                                            TDisplacementField >
  {
  public:
    /** Standard class typedefs. */
    typedef SymmetricForcesDemonsRegistrationFilter                                         Self;
    typedef PDEDeformableRegistrationFilter< TFixedImage, TMovingImage, TDisplacementField > 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(SymmetricForcesDemonsRegistrationFilter,
                 PDEDeformableRegistrationFilter);
  
    /** FixedImage image type. */
    typedef typename Superclass::FixedImageType    FixedImageType;
    typedef typename Superclass::FixedImagePointer FixedImagePointer;
  
    /** MovingImage image type. */
    typedef typename Superclass::MovingImageType    MovingImageType;
    typedef typename Superclass::MovingImagePointer MovingImagePointer;
  
    /** Deformation field type. */
    typedef typename Superclass::DisplacementFieldType
    DisplacementFieldType;
    typedef typename Superclass::DisplacementFieldPointer
    DisplacementFieldPointer;
  
    /** FiniteDifferenceFunction type. */
    typedef typename Superclass::FiniteDifferenceFunctionType
    FiniteDifferenceFunctionType;
  
    /** Take timestep type from the FiniteDifferenceFunction. */
    typedef typename FiniteDifferenceFunctionType::TimeStepType TimeStepType;
  
    /** DemonsRegistrationFilterFunction type. */
    typedef SymmetricForcesDemonsRegistrationFunction< FixedImageType, MovingImageType,
                                                       DisplacementFieldType >  DemonsRegistrationFunctionType;
  
    /** Get the metric value. The metric value is the mean square difference
     * in intensity between the fixed image and transforming moving image
     * computed over the the overlapping region between the two images.
     * This value is calculated for the current iteration */
    virtual double GetMetric() const;
  
    virtual const double & GetRMSChange() const ITK_OVERRIDE;
  
    /** Set/Get the threshold below which the absolute difference of
     * intensity yields a match. When the intensities match between a
     * moving and fixed image pixel, the update vector (for that
     * iteration) will be the zero vector. Default is 0.001. */
    virtual void SetIntensityDifferenceThreshold(double);
  
    virtual double GetIntensityDifferenceThreshold() const;
  
  protected:
    SymmetricForcesDemonsRegistrationFilter();
    ~SymmetricForcesDemonsRegistrationFilter() ITK_OVERRIDE {}
    void PrintSelf(std::ostream & os, Indent indent) const ITK_OVERRIDE;
  
    /** Initialize the state of filter and equation before each iteration. */
    virtual void InitializeIteration() ITK_OVERRIDE;
  
    /** Apply update. */
    virtual void ApplyUpdate(const TimeStepType& dt) ITK_OVERRIDE;
  
  private:
    ITK_DISALLOW_COPY_AND_ASSIGN(SymmetricForcesDemonsRegistrationFilter);
  };
  } // end namespace itk
  
  #ifndef ITK_MANUAL_INSTANTIATION
  #include "itkSymmetricForcesDemonsRegistrationFilter.hxx"
  #endif
  
  #endif
  