Three-dimensional position and amplitude VLC coding in H.264/AVC

Hybrid variable length coding (HVLC) was recently proposed as a novel entropy coding scheme for block-based image and video compression, which divides each transform block into low frequency (LF) region and high frequency (HF) region and codes them differently. To take advantage of the clustered nature of the nonzero coefficients in the LF region, a two-dimensional position and one- dimensional amplitude coding scheme (2DP1DA) was also proposed, which codes the 2D position information, i.e., run of consecutive zero-valued coefficients and run of consecutive nonzero coefficients, jointly by a 2D code table. To further improve the coding efficiency, joint position and amplitude coding is desirable. In this paper, we propose a three-dimensional position and amplitude coding scheme (3DPA) to jointly code the position and amplitude information for each nonzero cluster by a 3D code table. The experimental results show that HVLC with 3DPA for coding LF region achieves about 3.2%~3.7% bit rate reduction for a wide range of quantization parameters (QP) compared with CAVLC in H.264. Moreover, the 3DPA scheme is a compact way to realize the joint position and amplitude coding and it is very suitable for context-adaptive HVLC design.