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