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