A black area measurement section measures a black area S by obtaining {HEAD ~ ratio} of the number of pixels satisfying {TAIL ~ Y≦Y0} in the screen 
A black area measurement section measures a black area S by obtaining { HEAD ~ ratio } of the number of pixels satisfying { TAIL ~ Y≦Y0 } in the screen
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH