defining {HEAD ~ a left area} and {TAIL ~ a right area} respectively positioned on left and right sides of the target pixel on the line in the specified direction 
defining { HEAD ~ a left area } and { TAIL ~ a right area } respectively positioned on left and right sides of the target pixel on the line in the specified direction
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH