Means are provided for setting {HEAD ~ the value} of {TAIL ~ the local black/white reference point} for each detected constant area pixel to a calculated value for that pixel 
Means are provided for setting { HEAD ~ the value } of { TAIL ~ the local black / white reference point } for each detected constant area pixel to a calculated value for that pixel
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH