defining a partial image in the specified area, {HEAD ~ the partial image} being composed of {TAIL ~ a target pixel} and peripheral pixels on a line in a specified direction in which the target pixel exists 
composed of
defining a partial image in the specified area , { HEAD ~ the partial image } being composed of { TAIL ~ a target pixel } and peripheral pixels on a line in a specified direction in which the target pixel exists
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH