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