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