distanceTransform.h

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#ifndef TIL_DISTANCE_TRANSFORM_H
#define TIL_DISTANCE_TRANSFORM_H

// Local includes
#include "til/til_common.h"

namespace til
{

        // NB: both foreground and background are needed, since it might be that
        // other objects are present inside the image, inside which the distance
        // is not computed. However they are important, since the geodesics
        // goes around these objects.

        template < typename TImage >
        void
        cityBlock(TImage &seg,                          
        typename TImage::value_type foreground, 
        typename TImage::value_type background  
        )
        {
                {
                typename TImage::LinearIterator iSeg(seg);
                
                const TImage::value_type INFINITY               = std::numerical_limits<T>::max() - 1;
                const TImage::value_type OTHER_OBJECT   = std::numerical_limits<T>::max();

                // Initialize seg for distance map
                for (; !iSeg.isAtEnd(); ++iSeg)
                {
                        // Object has a distance of zero
                        if (*iSeg == foreground)                *iSeg = 0;
                        // Background has an initial distance of as close as infinity we can get
                        else if (*iSeg == background)   *iSeg = INFINITY;
                        // Other objects have a special value
                        else                                                    *iSeg = OTHER_OBJECT;
                }
                

                {                       
                        // forward loop
                        typename TImage::LinearIterator iSeg(seg);
                        for(; !iSeg.isAtEnd(); ++iSeg)
                        {
                                if (*iSeg == OTHER_OBJECT) continue;
                                *iSeg = min(*iSeg, min(min(min(iSeg.getValue<-1,0,0>(), iSeg.getValue<0,-1,0>()), iSeg.getValue<0,0,-1>) + T(1), INFINITY)));
                        }
                }
                {                       
                        // backward loop
                        typename TImage::LinearIterator iSeg(seg);
                        for(; !iSeg.isAtEnd(); --iSeg)
                        {
                                if (*iSeg == OTHER_OBJECT) continue;
                                *iSeg = min(*iSeg, min(min(min(iSeg.getValue<+1,0,0>(), iSeg.getValue<0,+1,0>()), iSeg.getValue<0,0,+1>) + T(1), INFINITY)));
                        }
                }
        }


} // namespace

#endif