itkLabelVotingImageFilter.h

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

  Program:   Insight Segmentation & Registration Toolkit
  Module:    itkLabelVotingImageFilter.h
  Language:  C++
  Date:      $Date$
  Version:   $Revision$

  Copyright (c) 2002 Insight 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 __itkLabelVotingImageFilter_h
#define __itkLabelVotingImageFilter_h

#include "itkImage.h"
#include "itkImageToImageFilter.h"

namespace itk
{
/** \class LabelVotingImageFilter
 *
 * \brief This filter performs pixelwise voting among an arbitrary number
 * of input images, where each of them represents a segmentation of the same
 * scene (i.e., image).
 *
 * Label voting is a simple method of classifier combination applied to
 * image segmentation. Typically, the accuracy of the combined segmentation
 * exceeds the accuracy of any of the input segmentations. Voting is therefore
 * commonly used as a way of boosting segmentation performance.
 *
 * The use of label voting for combination of multiple segmentations is
 * described in
 *
 * T. Rohlfing and C. R. Maurer, Jr., "Multi-classifier framework for 
 * atlas-based image segmentation," Pattern Recognition Letters, 2005.
 * 
 * \par INPUTS
 * All input volumes to this filter must be segmentations of an image,
 * that is, they must have discrete pixel values where each value represents
 * a different segmented object.
 *
 * Input volumes must all contain the same size RequestedRegions. Not all
 * input images must contain all possible labels, but all label values must
 * have the same meaning in all images.
 *
 * \par OUTPUTS
 * The voting filter produces a single output volume. Each output pixel
 * contains the label that occured most often among the labels assigned to
 * this pixel in all the input volumes, that is, the label that received the
 * maximum number of "votes" from the input pixels.. If the maximum number of 
 * votes is not unique, i.e., if more than one label have a maximum number of
 * votes, an "undecided" label is assigned to that output pixel.
 *
 * By default, the label used for undecided pixels is the maximum label value
 * used in the input images plus one. Since it is possible for an image with
 * 8 bit pixel values to use all 256 possible label values, it is permissible
 * to combine 8 bit (i.e., byte) images into a 16 bit (i.e., short) output
 * image.
 *
 * \par PARAMETERS
 * The label used for "undecided" labels can be set using 
 * SetLabelForUndecidedPixels. This functionality can be unset by calling
 * UnsetLabelForUndecidedPixels.
 *
 * \author Torsten Rohlfing, SRI International, Neuroscience Program
 *
 */
template <typename TInputImage, typename TOutputImage = TInputImage>
class ITK_EXPORT LabelVotingImageFilter :
    public ImageToImageFilter< TInputImage, TOutputImage >
{
public:
  /** Standard class typedefs. */
  typedef LabelVotingImageFilter Self;
  typedef ImageToImageFilter< TInputImage, TOutputImage > 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(LabelVotingImageFilter, ImageToImageFilter);
  
  /** Extract some information from the image types.  Dimensionality
   * of the two images is assumed to be the same. */
  typedef typename TOutputImage::PixelType OutputPixelType;
  typedef typename TInputImage::PixelType InputPixelType;

  /** Extract some information from the image types.  Dimensionality
   * of the two images is assumed to be the same. */
  itkStaticConstMacro(InputImageDimension, unsigned int,
                      TInputImage::ImageDimension );
  itkStaticConstMacro(ImageDimension, unsigned int,
                      TOutputImage::ImageDimension);
  
  /** Image typedef support */
  typedef TInputImage  InputImageType;
  typedef TOutputImage OutputImageType;
  typedef typename InputImageType::ConstPointer InputImagePointer;
  typedef typename OutputImageType::Pointer     OutputImagePointer;
  
  /** Superclass typedefs. */
  typedef typename Superclass::OutputImageRegionType OutputImageRegionType;

  /** Set label value for undecided pixels.
    */
  void SetLabelForUndecidedPixels( const OutputPixelType l )
  {
    this->m_LabelForUndecidedPixels = l;
    this->m_HasLabelForUndecidedPixels = true;
    this->Modified();
  }
  
  /** Get label value used for undecided pixels.
    * After updating the filter, this function returns the actual label value
    * used for undecided pixels in the current output. Note that this value
    * is overwritten when SetLabelForUndecidedPixels is called and the new
    * value only becomes effective upon the next filter update.
    */
  OutputPixelType GetLabelForUndecidedPixels() const
  {
    return this->m_LabelForUndecidedPixels;
  }
  
  /** Unset label value for undecided pixels and turn on automatic selection.
    */
  void UnsetLabelForUndecidedPixels()
  {
    if ( this->m_HasLabelForUndecidedPixels )
      {
      this->m_HasLabelForUndecidedPixels = false;
      this->Modified();
      }
  }

#ifdef ITK_USE_CONCEPT_CHECKING
  /** Begin concept checking */
  itkConceptMacro(InputConvertibleToOutputCheck,
    (Concept::Convertible<InputPixelType, OutputPixelType>));
  itkConceptMacro(IntConvertibleToInputCheck,
    (Concept::Convertible<int, InputPixelType>));
  itkConceptMacro(SameDimensionCheck,
    (Concept::SameDimension<InputImageDimension, ImageDimension>));
  itkConceptMacro(InputConvertibleToUnsignedIntCheck,
    (Concept::Convertible<InputPixelType, unsigned int>));
  itkConceptMacro(IntConvertibleToOutputPixelType,
    (Concept::Convertible<int, OutputPixelType>));
  itkConceptMacro(InputPlusIntCheck,
    (Concept::AdditiveOperators<InputPixelType, int>));
  itkConceptMacro(InputIncrementDecrementOperatorsCheck,
    (Concept::IncrementDecrementOperators<InputPixelType>));
  itkConceptMacro(OutputOStreamWritableCheck,
    (Concept::OStreamWritable<OutputPixelType>));
  /** End concept checking */
#endif

protected:
  LabelVotingImageFilter() { this->m_HasLabelForUndecidedPixels = false; }
  virtual ~LabelVotingImageFilter() {}  

  /** Determine maximum label value in all input images and initialize global data.*/
  void BeforeThreadedGenerateData ();
  void ThreadedGenerateData
  ( const OutputImageRegionType &outputRegionForThread, int threadId);
  
  void PrintSelf(std::ostream&, Indent) const;

  /** Determine maximum value among all input images' pixels */
  InputPixelType ComputeMaximumInputValue();

private:
  LabelVotingImageFilter(const Self&); //purposely not implemented
  void operator=(const Self&); //purposely not implemented

  OutputPixelType m_LabelForUndecidedPixels;
  bool m_HasLabelForUndecidedPixels;
  InputPixelType m_TotalLabelCount;
};
  
} // end namespace itk

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

#endif