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

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkSobelOperator.h,v $
  Language:  C++
  Date:      $Date: 2003/09/10 14:29:26 $
  Version:   $Revision: 1.8 $

  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 __itkSobelOperator_h
#define __itkSobelOperator_h

#include "itkExceptionObject.h"
#include "itkNeighborhoodOperator.h"

namespace itk {

/**
 * \class SobelOperator
 *
 * \brief A NeighborhoodOperator for performing a directional Sobel
 * edge-detection operation * at a pixel location.
 * 
 * SobelOperator is a directional NeighborhoodOperator that should be
 * applied a NeighborhoodIterator using the NeighborhoodInnerProduct
 * method. To create the operator:
 * 
 * 1) Set the direction by calling  \code{SetDirection}
 * 2) call \code{CreateOperator()}
 * 3) You may optionally scale the coefficients of this operator using the
 * \code{ScaleCoefficients} method.  This is useful if you want to take the
 * spacing of the image into account when computing the edge strength.  Apply
 * the scaling only after calling to \code{CreateOperator}.
 *
 * The Sobel Operator in vertical direction for 2 dimensions is
 * \verbatim
 *             -1  -2  -1  
 *             0    0   0 
 *             1    2   1
 *
 * \endverbatim
 * The Sobel Operator in horizonal direction is for 2 dimensions is
 * \verbatim
 *             -1   0   1      
 *             -2   0   2 
 *             -1   0   1
 * \endverbatim
 *
 * The current implementation of the Sobel operator is for 2 and 3 dimensions only.
 * The ND version is planned for future releases.
 *
 * The extension to 3D is from the publication
 *  "Irwin Sobel. An Isotropic 3x3x3 Volume Gradient Operator.
 * Technical report, Hewlett-Packard Laboratories, April 1995."
 *
 * The Sobel operator in 3D has the kernel
 *
 * \verbatim
 * -1 -3 -1   0 0 0  1 3 1
 * -3 -6 -3   0 0 0  3 6 3 
 * -1 -3 -1   0 0 0  1 3 1
 *
 *    x-1       x     x+1
 * \endverbatim
 *
 * The \code{x} kernel is just rotated as required to obtain the kernel in the
 * \code{y} and \code{z} directions.
 * 
 * \sa NeighborhoodOperator
 * \sa Neighborhood
 * \sa ForwardDifferenceOperator
 * \sa BackwardDifferenceOperator
 * 
 * \ingroup Operators
 */
template<class TPixel, unsigned int VDimension=2,
  class TAllocator = NeighborhoodAllocator<TPixel> >
class ITK_EXPORT SobelOperator
  : public NeighborhoodOperator<TPixel, VDimension, TAllocator>
{
public:
  /** Standard typedefs */
  typedef SobelOperator Self;
  typedef NeighborhoodOperator<TPixel, VDimension, TAllocator>  Superclass;

  itkTypeMacro(SobelOperator, NeighborhoodOperator);
  
  SobelOperator() {}
  SobelOperator(const Self& other)
    : NeighborhoodOperator<TPixel, VDimension, TAllocator>(other) 
  {  }

  /** Creates the operator with length only in the specified direction.  For
   * the Sobel operator, this 
   * The radius of the operator will be 0 except along the axis on which
   * the operator will work.
   * \sa CreateToRadius \sa FillCenteredDirectional \sa SetDirection() \sa GetDirection() */
  virtual void CreateDirectional()
  {
    this->CreateToRadius(1);
  }
  
  /** Creates the operator with a specified radius ("square", same length
   * on each side). The spatial location of the coefficients within the
   * operator is defined by the subclass implementation of the Fill method.
   * \sa CreateDirectional \sa Fill */
  // virtual void CreateToRadius(const unsigned long);
  /**
   * Assignment operator
   */
  Self &operator=(const Self& other)
  {
    Superclass::operator=(other);
    return *this;
  }
  /**
   * Prints some debugging information
   */
  virtual void PrintSelf(std::ostream &os, Indent i) const  
  { 
    os << i << "SobelOperator { this=" << this  << "}" << std::endl;
    Superclass::PrintSelf(os, i.GetNextIndent());
  }

protected:
  /**
   * Typedef support for coefficient vector type.  Necessary to
   * work around compiler bug on VC++.
   */
  typedef typename Superclass::CoefficientVector CoefficientVector;
  typedef typename Superclass::PixelType PixelType;

  /**
   * Calculates operator coefficients.
   */
  CoefficientVector GenerateCoefficients();

  /**
   * Arranges coefficients spatially in the memory buffer.
   */
  void Fill(const CoefficientVector &c);

};

} // namespace itk

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

#endif


