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