obtaining as a gray level ratio a ratio of calculation result of the left area to {HEAD ~ calculation result} of {TAIL ~ the right area} 
obtaining as a gray level ratio a ratio of calculation result of the left area to { HEAD ~ calculation result } of { TAIL ~ the right area }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL