 maintaining, by the motion coordinate calculator, {TAIL ~ the reference image} previously set in an X channel reference unit when it is determined at the step that {HEAD ~ the X axis motion vector} has a value of zero 
maintaining , by the motion coordinate calculator , { TAIL ~ the reference image } previously set in an X channel reference unit when it is determined at the step that { HEAD ~ the X axis motion vector } has a value of zero
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH