summing the negative of pixel values of image pixels corresponding to each of columns 2M+1 to M+2 in a row of {TAIL ~ the edge detection filter} and adding the pixel values of image pixels corresponding to each of columns M to 1 in said row of the edge detection filter to calculate a row value for {HEAD ~ said row} 
summing the negative of pixel values of image pixels corresponding to each of columns 2M+1 to M+2 in a row of { TAIL ~ the edge detection filter } and adding the pixel values of image pixels corresponding to each of columns M to 1 in said row of the edge detection filter to calculate a row value for { HEAD ~ said row }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD