Fast Quantization Method With Simplified Rate–Distortion Optimized Quantization for an HEVC Encoder

While the rate-distortion optimized quantization (RDOQ) technique provides nontrivial coding gain in High Efficiency Video Coding (HEVC), it also involves considerable computations, whereby the complexity of quantization is significantly increased. In this paper, two schemes (the RDOQ bypass decision and the simplified level adjustment) are investigated to reduce the complexity of the quantization process in HEVC with RDOQ. The RDOQ bypass decision method initially selects the transform blocks for which the RDOQ is expected to give less/or no coding gain and enables the conventional uniform scalar quantization to be applied to these transform blocks instead of the RDOQ. The simplified level adjustment method only estimates the difference in rate-distortion costs among the candidate quantization levels to enable the encoder to select an optimal quantization level at a much reduced computational cost. Furthermore, the proposed simplified level adjustment scheme is designed so that it can be implemented in lookup tables. Experimental results show that the proposed fast method achieves 14.3% quantization complexity reduction in all intra main conditions, 15.2% in the random access main condition, and 14.9% in the low delay main condition on average with virtually no coding loss compared with the conventional quantization process with the RDOQ.