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Frontiers of Information Technology & Electronic Engineering
ISSN 2095-9184 (print), ISSN 2095-9230 (online)
2015 Vol.16 No.10 P.883-891
A reversibility-gain model for integer Karhunen-Loève transform design in video coding
Abstract: Karhunen-Loève transform (KLT) is the optimal transform that minimizes distortion at a given bit allocation for Gaussian source. As a KLT matrix usually contains non-integers, integer-KLT design is a classical problem. In this paper, a joint reversibility-gain (R-G) model is proposed for integer-KLT design in video coding. Specifically, the ‘reversibility’ is modeled according to distortion analysis in using forward and inverse integer transform without quantization. It not only measures how invertible a transform is, but also bounds the distortion introduced by the non-orthonormal integer transform process. The ‘gain’ means transform coding gain (TCG), which is a widely used criterion for transform design in video coding. Since KLT maximizes the TCG under some assumptions, here we define the TCG loss ratio (LR) to measure how much coding gain an integer-KLT loses when compared with the original KLT. Thus, the R-G model can be explained as follows: subject to a certain TCG LR, an integer-KLT with the best reversibility is the optimal integer transform for a given non-integer-KLT. Experimental results show that the R-G model can guide the design of integer-KLTs with good performance.
Key words: Integer transform, Karhunen-Loève transform (KLT), Integer-KLT, Transform coding, Video coding
创新点:综合考虑KLT在视频压缩中所起作用,分别对整数KLT矩阵的可逆程度和其变换编码增益(TCG)进行建模,并形成可逆-增益模型。用该模型进行KLT的整数化设计,得到的整数KLT矩阵在视频压缩效率上都高于其他整数化方法得到的矩阵。
方法:首先,充分考虑KLT的正交性,分析无量化情形下整数变换编码过程中失真的来源及其与整数变换核矩阵的解析关系,并利用此解析关系为整数KLT矩阵的可逆程度进行建模(式15)。然后,由于KLT可以最大化TCG,我们对KLT在整数化过程中的TCG损失率进行建模(式16),并分析整数余弦变换的TCG损失率(表1),以作为参考。最后,联合变换的可逆程度和TCG损失率,形成一个指导整数KLT设计的可逆-增益模型(式18):在给定TCG损失率约束下,具有最佳可逆程度的整数KLT即是对给定KLT进行整数化的最优结果。
结论:在视频压缩中,给定任意KLT矩阵和倍乘因子下,利用本文提出的可逆-增益模型指导该KLT的整数化,能得到在压缩效率上最优的整数KLT矩阵。
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DOI:
10.1631/FITEE.1500071
CLC number:
TN919.8
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On-line Access:
2015-10-08
Received:
2015-03-09
Revision Accepted:
2015-07-31
Crosschecked:
2015-09-09