New scaling technique for direct mode coding in B pictures
To leave the maximum flexibility in encoder to optimize the trade-off between coding performance and complexity, in video coding standards such as H.264 AVC, H.263 and MPEG-4 etc, any number of B pictures and any arrangement of P pictures within a group of pictures (GOP) of arbitrary length are permitted. In addition, multiple reference picture prediction is also permitted in some video coding systems such as H.264/AVC to achieve efficient coding by allowing the encoder to select reference pictures among a large number of coded pictures. Both of the above cases without fixing the temporal distance between forward and backward reference pictures require the division operation for deriving the motion vectors of direct mode, which can efficiently exploit the temporal correlation among pictures and does not require any bits for coding the motion vectors. However, the division is an expensive and undesired operation in video decoder hardware design. Although the H.264/AVC video standard has provided a scaling technique to tackle this problem, unfortunately, its performance is also deteriorated. This paper presents a new scaling technique to both remove the division operation for deriving direct mode motion vectors and efficiently improve the accuracy of derived direct mode motion vectors compared with the scaling technique in H.264/AVC.