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