Hybrid Variable Length Coding for Image and Video Compression

The conventional run-level variable length coding (RL-VLC), commonly adopted in block-based image and video compression to code quantized transform coefficients, is not efficient in coding consecutive nonzero coefficients. To overcome the deficiency, hybrid variable length coding (HVLC) is proposed in this paper. HVLC takes advantage of the clustered nature of nonzero transform coefficients in the low-frequency (LF) region and the scattered nature of nonzero transform coefficients in the high-frequency (HF) region by employing two types of VLC schemes. A novel two-dimensional position and one-dimensional amplitude coding scheme is proposed to code the LF coefficients while RL-VLC or an equivalent VLC scheme is retained to code the HF coefficients. Experimental results show that HVLC greatly favors the coding of high-resolution, high-complexity scenes, while it preserves low computational complexity.