The local reference point is also adjusted as {HEAD ~ a function} of {TAIL ~ the value} of each local extremum or nonextremum pixel after it is detected 
The local reference point is also adjusted as { HEAD ~ a function } of { TAIL ~ the value } of each local extremum or nonextremum pixel after it is detected
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH