 determining, by the motion coordinate calculator, whether {TAIL ~ or not a Y axis motion vector} corresponding to {HEAD ~ the calculated Y axis motion} has a value of zero 
determining , by the motion coordinate calculator , whether { TAIL ~ or not a Y axis motion vector } corresponding to { HEAD ~ the calculated Y axis motion } has a value of zero
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH