{HEAD ~ Second means} are provided for modifying an input value of each detected edge area pixel as a function of the local black/white reference point for {TAIL ~ the detected edge area pixel} 
{ HEAD ~ Second means } are provided for modifying an input value of each detected edge area pixel as a function of the local black / white reference point for { TAIL ~ the detected edge area pixel }
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL