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