{HEAD ~ Each grey level signal} causes a particular proportion of {TAIL ~ pixels} to be illuminated, in order to produce a particular grey level 
{ HEAD ~ Each grey level signal } causes a particular proportion of { TAIL ~ pixels } to be illuminated , in order to produce a particular grey level
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH