Thus, the value {TAIL ~ Δe} is used as {HEAD ~ a threshold} to check whether an extremum is an edge or an error 
Thus , the value { TAIL ~ Δe } is used as { HEAD ~ a threshold } to check whether an extremum is an edge or an error
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH