{HEAD ~ The value} of each local extremum pixel is modified as a function of {TAIL ~ the current local reference point} 
{ HEAD ~ The value } of each local extremum pixel is modified as a function of { TAIL ~ the current local reference point }
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL