Enhanced prediction for motion estimation in Scalable Video Coding
In this paper, we present a temporal candidate generation scheme that can be applied to motion estimators in Scalable Video Codecs (SVCs). For bidirectional motion estimation, usually a test is made for each block to determine which motion compensation direction is preferred: forward, bidirectional or backward. Instead of simply using the last computed motion vector field (backward or forward), giving an asymmetry in the estimation, we involve both vector fields to generate a single candidate field for a more stable and improved prediction. This field is generated with the aid of mode decision information of the codec. This single field of motion vector candidates serves two purposes: (1) it initializes the next recursion and (2) it is the foundation for the succeeding scale in the scalable coding. We have implemented this improved candidate system for both HPPS as EPZS motion estimators in a scalable video codec. We have found that it reduces the errors caused by occlusion of moving objects or image boundaries. For EPZS, only a small improvement is observed compared to the simple candidate scheme. However, for HPPS improvements are more significant: when looking at individual levels, motion compensation performance improves by up to 0.84 dB and when implemented in SVC, HPPS slightly outperforms EPZS.