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