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