Hybrid Variable Length Coding in Video Compression using Variable Breakpoint

Hybrid variable length coding (HVLC) was recently proposed as a novel entropy coding scheme for block-based image and video compression, in observation of the inefficiency of the conventional run-level variable length coding scheme in coding consecutive nonzero transform coefficients. In HVLC, each transform block is partitioned into low-frequency and high-frequency regions, and the coefficients in the two regions are coded separately by different schemes. The partition of the transform block was performed based on a predefined, constant breakpoint. In this paper, we propose to partition the transform block using a variable breakpoint that is adaptive to the local context. We present a method to find one optimal breakpoint per transform block or per multi-block partition efficiently, and we show that by using variable breakpoint, the efficiency of HVLC can be improved considerably compared to the constant breakpoint case.