Context-based 2D-VLC for video coding

It is well observed that usually the run-length of successive zero coefficients becomes longer and the magnitude of non-zero coefficients gets smaller while the DCT subband frequency increases. So the probability distributions of level/run combinations should be different at different DCT positions. Based on this observation, an efficient context based 2D-VLC entropy coder, especially designed for 8×8 DCT, is proposed in this paper to exploit this context characteristic. The key element of the proposed coder is to design multiple 2D-VLC tables and each can be used context-adaptively to better match different level/run combination probability distributions. Another key element is the usage of Exponential-Golomb codes, which keep the multiple tables with low memory requirement. In terms of coding efficiency, the experimental results show that the proposed method can gain up to 0.23dB when compared to one-table-for-one-block coding method.