Direct Mode Coding for B Pictures using Virtual Reference Picture
The direct mode used in the bi-predictive pictures (B-pictures) can efficiently improve the coding performance of B pictures, because it has small overhead and obtains a predictive picture from two reference pictures. The traditional temporal direct mode (TDM) derives the motion vector of the current block by scaling the motion vector of the co-located block in the backward reference picture. However, when the current block and its co-located block in backward reference picture belong to different objects with different motion directions, the prediction efficiency of TDM is drastically reduced. In this paper, we propose an improved direct mode prediction method. In the method, a virtual reference picture is generated using the pixel projection technique. Then the virtual reference picture is used to predict the direct mode blocks in B pictures. The proposed method can enhance the prediction performance of the direct mode blocks and achieve a higher coding efficiency.