Context-based adaptive variable length coding (CAVLC) is an entropy coding scheme employed in H.264/AVC for transform coefficient compression. The CAVLC encodes levels of nonzero-valued coefficients. Then indicates their positions with run_before which is number of zeros preceding each nonzero coefficient in scan order. In H.264, the run_before is coded using lookup tables depending on number of zero-valued coefficients that have not been coded. This paper presents an improved run_before coding method which encodes run_before using tables taking both zero-valued and nonzero-valued coefficients into consideration. Simulation results report that the proposed method yields an average of 4.40 bit rate reduction for run_before coding over H.264 baseline profile with intra-only coding structure. It corresponds to 0.52 bit rate saving over total bit rate on average.
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