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