Abstract
Simplified Fast Motion Estimation: Simplified and Unified Multi-Hexagon Search (SUMH) with Context Adaptive Lagrange Multiplier (CALM)
Abstract: Fast motion estimations are especially important to speed up the time-consuming encoding processes for H.264 video encoding. In this talk, we first present our simplified fast motion estimation method, called Simplified and Unified Multi-Hexagon Search (SUMH), that produces a significant speed-up as compared with today's fast motion estimations, yet encounters only a small PSNR degradation when compared to that of full search. In addition, we present a novel method to refine the Lagrange multiplier, called Context Adaptive Lagrange Multiplier (CALM), for rate-constrained motion estimation. Both our methods were recently adopted into the H.264/MPEG-4 AVC video coding international standard (including the text document and the JM reference software).
Our SUMH is based on two principles, partial distortion search (PDS) and dual-halfway-stop (DHS) algorithms. PDS generally produces less video quality degradation of the predicted images than those of conventional fast block matching algorithms (BMAs). However, the speedup gain of PDS algorithms is usually limited. In this talk, we present an enhancement over a normalized PDS (NPDS) algorithm to further reduce block matching motion estimation complexity and improve video fidelity. The novelty of our algorithm is that, in addition to the halfway-stop technique in NPDS, a dual-halfway-stop (DHS) method, which is based on a dynamic threshold, is proposed so that block matching is not performed against all searching points. The dynamic threshold is obtained via a linear model utilizing already computed distortion statistics. An adaptive search range mechanism based on inter block distortion further constrains the searching process. Experimental results show that our proposed method reduces the encoding time by about 55% on the average when compared to those of the state-of-the-art methods, with similar rate-distortion performances. Our SUMH algorithm, making use of DHS-NPDS, consists of two parts, an integer-pel fast search and a sub-pel fast search.
To extend motion estimation further, we propose a new simple and efficient method to adjust Lagrange multipliers based on the context (CALM), which improves the accuracy for the detection of true motion vectors as well as the most efficient encoding modes for luma, which are used for deriving the motion vectors and modes for chroma. Simulation results show that the chroma bit rates can be reduced by 4.36% and 4.80% (on the average) for U- and V- chroma components, respectively, when compared with that of the recent JM reference software. In addition, the coding efficiency improvement is comparable to the more complicated rate-distortion optimized (RDO) mode decision techniques.