Patent ID: 7769087

Claim:
A method of encoding an image sequence having a plurality of pictures, wherein at least one of said plurality of pictures is a current picture to be encoded as a bi-predictive coded (B) picture, comprising: at an encoder: selectively encoding at least one of said plurality of pictures in a frame coding mode; selectively encoding at least one of said plurality of pictures in a field coding mode; wherein if said current picture is in frame coding, dividing said current picture into a plurality of macroblocks, where said macroblock is divided into at least one block comprising at least one of 16×16 pixels, 16×8 pixels, 8×16 pixels, 8×8 pixels, 8×4 pixels, 4×8 pixels, and 4×4 pixels; wherein if said current picture comprising a pair of current fields is in field coding, dividing each current field of said current picture into a plurality of macroblocks, where said macroblock is divided into at least one block comprising at least one of 16×16 pixels, 16×8 pixels, 8×16 pixels, 8×8 pixels, 8×4 pixels, 4×8 pixels, and 4×4 pixels; and computing at least two motion vectors and deriving two associated reference pictures or fields pointed by said two motion vectors for at least one current block of said macroblocks, wherein each of said two associated reference pictures or fields is a forward or a backward reference picture or field.