calculating an evaluation function by {TAIL ~ means} of the gray level ratio by repeating the gray level ratio calculating {HEAD ~ step} in the specified area 
calculating an evaluation function by { TAIL ~ means } of the gray level ratio by repeating the gray level ratio calculating { HEAD ~ step } in the specified area
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH