The pattern of {TAIL ~ illuminated pixels} changes smoothly with {HEAD ~ time} to produce the required uniform high quality grey level 
The pattern of { TAIL ~ illuminated pixels } changes smoothly with { HEAD ~ time } to produce the required uniform high quality grey level
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH