positioning said edge detection filter at {HEAD ~ an origin} of {TAIL ~ a first direction} and an origin of a second direction within said image 
of
positioning said edge detection filter at { HEAD ~ an origin } of { TAIL ~ a first direction } and an origin of a second direction within said image
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH