Inter-View Direct Mode for Multiview Video Coding

Global disparity between views is usually caused by the displacement between cameras, which can be accurately represented by a global geometric transformation. In this paper, we first propose an inter-view motion model in terms of the global geometric transformation to represent the motion correlation between two adjacent views. Specifically, the motion vector of a pixel in one view may be directly derived from that in another view according to the inter-view motion model. Further, we propose an inter-view direct mode to signal the decoder that the motion of a macroblock (MB) can be achieved from the coded view without any coding bits. The proposed inter-view direct mode is further incorporated in the existing multiview video coding (MVC) schemes (i.e., AVC-based MVC and 4-D wavelet-based MVC), working together with the other classical coding modes. The mode selection at each MB is accomplished with the rate-distortion optimization technique. The proposed inter-view direct mode can significantly reduce bits to code motion vectors especially at low bit rates, thus improving the coding efficiency

I. Introduction

In modern video coding schemes, motion prediction is becoming more and more accurate for better coding efficiency. For example in MPEG-4 AVC/H.264 standard [1], a macroblock (MB) in P-picture may have up to 16 different motion vectors, while an MB in B-picture may even have up to 32 different motion vectors in the case of bidirectional prediction. However, it also implied that many bits have to be assigned to code these motion vectors. Although motion vectors are relatively efficiently coded considering that they are differentially coded compared to a motion vector predictor, taken as the median value of the motion vectors of the spatially adjacent blocks, MPEG-4 AVC/H.264 standard still introduces two direct modes: SKIP and DIRECT within P- and B-pictures respectively, for a further reduction to the amount of bits for coding motion vectors [2].