优化VVC标准中的自适应环路滤波，大幅降低内存访问和计算时间。
Optimized Adaptive Loop Filter in Versatile Video Coding
- 并行处理GALF与CCALF，减少冗余数据访问。
- 仅需1次缓冲区访问，比原方案减少99%内存读写。
- 适合视频编码器软硬件实现，兼顾性能与效率。
在通用视频编码（VVC）标准中，自适应环路滤波（ALF），包括基于几何变换的ALF（GALF）和跨分量ALF（CCALF），对减少压缩伪影起关键作用。然而，其编码复杂度高，且在编码器中需多次访问图像缓冲区，增加外部内存访问，不利于软硬件设计。为此，本文提出一种优化的ALF框架，包含GALF与CCALF的并行设计、GALF参数的自适应决策，以及通过有效估计滤波失真实现的一次遍历CCALF方案。相比VTM-8.0，所提方法将图像缓冲区访问从152次降至1次，在RA配置下使ALF模块耗时减少约25%，编码性能几乎无损失。部分方法已被纳入VVC参考软件。
原文摘要 · Abstract (English)
In the Versatile Video Coding~(VVC) standard, adaptive loop filter~(ALF), including Geometry transformation-based Adaptive Loop Filter~(GALF) and Cross Component Adaptive Loop Filter~(CCALF), plays an essential role in reducing compression artifacts. However, it also has high coding complexity and requires many picture buffer accesses in the encoder that will increase external memory access and is unfriendly to the software and hardware design. Therefore, we propose an optimized ALF framework, including the parallel design of GALF and CCALF, the adaptive parameter decision of GALF, and one-pass CCALF scheme by effectively estimating the CCALF filtering distortion without conducting filter operation. Compared to VTM-8.0, the proposed method can reduce the picture buffer access from 152 to 1 and achieve roughly 25\% time-savings of the ALF module with negligible coding performance change under RA configuration. Some of the proposed methods have been adopted in the VVC reference software.
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