Each of {HEAD ~ these bits} in a given line is compared with a dither coded second stream of bits generated in response to the background illumination along {TAIL ~ a line} immediately adjacent to the line being scanned 
Each of { HEAD ~ these bits } in a given line is compared with a dither coded second stream of bits generated in response to the background illumination along { TAIL ~ a line } immediately adjacent to the line being scanned
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH 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 OTH OTH OTH OTH OTH OTH OTH