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