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