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