标题: | 用于HEVC编码单元之快速决策演算法 与 结合移动向量与DCT之H.264编码器优化 Fast HEVC Coding Unit Decision Algorithm and Combined MV and DCT Optimization for H.264/AVC Codec |
作者: | 许维哲 Hsu, Wei-Jhe 杭学鸣 Hang, Hsueh-Ming 电子研究所 |
关键字: | 高效率视讯编码;编码单元;时间节省;进阶视讯编码;移动估计;位元率-失真最佳化;HEVC;Coding unit (CU);Time reduction;H.264/AVC;Motion Estimation (ME);Rate-Distortion (R-D) Optimization |
公开日期: | 2011 |
摘要: | 由于高解析度影像应用的需求,视讯编码在3C产品中是不可或缺的技术,例如行动电话、高画质电视、蓝光光碟机。进阶视讯编码(Advanced Video Coding, AVC/H.264)是目前商业产品中,广泛采用的压缩标准格式。为了达到更高的编码效率,国际组织JCT-VC正在进行下一代标准的制定,即高效率视讯编码(High Efficiency Video Coding, HEVC) 。 相较于进阶视讯编码,虽然高效率视讯编码的复杂度提升许多,但是在相似的影像品质下,可以增加近一倍的压缩效率。 此论文包含两个研究主题:第一个主题是改善进阶视讯编码中,整数精确度的移动估测以增进编码效能;第二个主题是关于高效率视讯编码的编码单元(Coding Unit, CU)大小的快速决策,以达到降低编码器复杂度的目标。在进阶视讯编码中,整数移动估测的失真项,是以区块之绝对误差总和(The Sum of the Absolute Distortion, SAD)来计算,但是此方法并不能完全反应最后结果的失真。为了在相似的画面品质下,进一步节省位元率,我们提出迭代的位元率-失真(Rate-Distortion, R-D)计算方式,以选择较佳的移动向量。我们将此演算法实现于JM18.0,用许多组MPEG测试影像来检验此方法的效能,并将执行结果和原始JM做法的结果进行比较。虽然JM18.0是发展已久的优化编码器,我们仍可从中节省1.1%至4.2%的位元率,但代价是增加45%的运算复杂度。 另一方面,高效率视讯编码在传统的编码流程中,增加了编码单元四元分割树的构造。弹性的编码单元设计提升了编码效率,但相较于进阶视讯编码传统的巨区块(Macroblock, MB)结构而言,编码复杂度提升不少。因此我们设计快速演算法以有效率地建造出编码单元四元分割树,其中演算法包括分裂决策、终止决策。这些快速编码单元大小决策参考周遭相关的编码单元之切割资讯以进行判断。此外,我们设计额外的工具以增进我们提出的演算法效能,其中包含画面层级加速控制和跳过决策后的快速预测单元判断。最后,我们分析提出的快速演算法,并和HM5.0中的两种快速演算法进行比较,以找出有效率的结合方法。相较于HM5.0的原始设定,我们提出的快速演算法,经过多组高解析度的影像测试,可以节省高达49%的整体编码时间,但平均损失0.06dB的峰值信噪比(PSNR)。 With the growing demand for high resolution video applications, video coding is an indispensable element in many 3C products, such as mobile phone, DTV, and BD player. Today, Advanced Video coding (AVC/H.264) is one of the most popular video formats in commercial applications. Aiming at higher compression efficiency, the international JCT-VC is currently developing the next generation standard, High Efficiency Video Coding (HEVC). With a much higher encoder complexity, HEVC is able to achieve a 50% bitrate reduction compared to H.264/AVC. This thesis has two topics, one is the enhanced motion estimation (ME) for AVC/H.264 and the other is the fast coding unit (CU) decision for HEVC. In H.264, the sum of the absolute difference (SAD) is used as the distortion term in ME, but it does not reflect the final coding distortion. To achieve further bitrate reduction, we propose an enhanced motion vector selection method based on the iterative R-D calculation. We compare the proposed method with the original H.264/AVC JM18.0 reference software on several MPEG test sequences. Although JM18.0 is a highly optimized scheme, we can still obtain a BD-rate improvement from 1.1% to 4.2% but with additional 45% complexity increase. In HEVC, the CU quadtree structure is added to the traditional fixed size macroblock. With flexible CU size selection, the coding efficiency increases but the complexity of HEVC becomes much higher than that of AVC/H.264 fixed macroblock (MB) structure. To reduce computational complexity, we propose a fast algorithm, which includes the splitting decision and the termination decision, in building the CU quadtree. The fast CU size decision of the current CU makes use of the size information of its neighboring CUs. Furthermore, we design the additional tools to enhance the performance of the proposed algorithm. The additional tools include the frame level acceleration and the fast PU size decision after the splitting decision. At the end, we compare it with the existing fast algorithms in HM5.0 and find an efficient way to blend them together. In comparison to the original HM5.0, our method saves the overall encoding time up to 49% with 0.06 dB average PSNR drop. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT079911617 http://hdl.handle.net/11536/49153 |
显示于类别: | Thesis |
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