The sphere-to-plane projection of 360-degree video introduces substantial stretched redundant data, which is discarded when reprojected to the 3D sphere for display. Consequently, encoding and transmitting such redundant data is unnecessary. Highly redundant blocks can be referred to as all-zero blocks (AZBs). Detecting these AZBs in advance can reduce computational and transmission resource consumption. However, this cannot be achieved by existing AZB detection techniques due to the unawareness of the stretching redundancy. In this paper, we first derive a latitude-adaptive redundancy detection (LARD) approach to adaptively detect coefficients carrying redundancy in transformed blocks by modeling the dependency between valid frequency range and the stretching degree based on spectrum analysis. Utilizing LARD, a latitude-redundancy-aware AZB detection scheme tailored for fast 360-degree video coding (LRAS) is proposed to accelerate the encoding process. LRAS consists of three sequential stages: latitude-adaptive AZB (L-AZB) detection, latitude-adaptive genuine-AZB (LG-AZB) detection and latitude-adaptive pseudo-AZB (LP-AZB) detection. Specifically, L-AZB refers to the AZB introduced by projection. LARD is used to detect L-AZB directly. LG-AZB refers to the AZB after hard-decision quantization and zeroing redundant coefficients. A novel latitude-adaptive sum of absolute difference estimation model is built to derive the threshold for LG-AZB detection. LP-AZB refers to the AZB in terms of rate-distortion optimization considering redundancy. A latitude-adaptive rate-distortion model is established for LP-AZB detection. Experimental results show that LRAS can achieve an average total encoding time reduction of 25.85% and 20.38% under low-delay and random access configurations compared to the original HEVC encoder, with only 0.16% and 0.13% BDBR increases and 0.01dB BDPSNR loss, respectively. The transform and quantization time savings are 60.13% and 59.94% on average.

中文翻译：

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纬度冗余感知全零块检测，实现快速 360 度视频编码


360 度视频的球体到平面投影引入了大量拉伸冗余数据，这些数据在重新投影到 3D 球体进行显示时将被丢弃。因此，无需对此类冗余数据进行编码和传输。高度冗余的块可以称为全零块 （AZB）。提前检测这些 AZB 可以减少计算和传输资源的消耗。然而，由于没有意识到拉伸冗余，现有的 AZB 检测技术无法实现这一点。在本文中，我们首先推导了一种纬度自适应冗余检测 （LARD） 方法，通过基于频谱分析对有效频率范围与拉伸程度之间的依赖关系进行建模，自适应地检测变换块中携带冗余的系数。利用 LARD，提出了一种为快速 360 度视频编码 （LRAS） 量身定制的纬度冗余感知 AZB 检测方案，以加速编码过程。LRAS 由三个连续阶段组成：纬度自适应 AZB （L-AZB） 检测、纬度自适应真 AZB （LG-AZB） 检测和纬度自适应伪 AZB （LP-AZB） 检测。具体来说，L-AZB 是指投影引入的 AZB。LARD 用于直接检测 L-AZB。LG-AZB 是指经过硬决策量化和将冗余系数归零后的 AZB。该文构建了一种新的纬度自适应绝对差值和估计模型，以推导 LG-AZB 检测的阈值。LP-AZB 是指考虑冗余的速率失真优化 AZB。建立了用于 LP-AZB 检测的纬度自适应速率失真模型。实验结果表明，LRAS 可以实现平均总编码时间减少 25.85% 和 20。与原来的 HEVC 编码器相比，在低延迟和随机访问配置下，性能提高了 38%，BDBR 增加率分别仅为 0.16% 和 0.13%，BDPSNR 损失仅为 0.01dB。转换和量化时间平均节省 60.13% 和 59.94%。