In one embodiment, the method includes determining a reference field picture from a reference picture list composed of reference frames using index information for a reference field and index information for a reference frame. The determined reference field picture has a same parity as the current macroblock or a different parity from the current macroblock based on whether the index information for the reference field is an even number or a odd number. The determined reference field picture has a same parity as the current macroblock if the index information for the reference field is an even number. The determined reference field picture has a different parity from the current macroblock if the index information for the reference field is a odd number.