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