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