Distortion-Aware Loop Filtering of Intra 360^o Video Coding with Equirectangular Projection

TL;DR

This paper introduces a distortion-aware loop filtering method for intra coding of 360° videos in equirectangular projection, enhancing quality and reducing bitrate by adaptively processing content based on distortion analysis.

Contribution

It proposes a novel distortion-aware filtering model with content analysis, partial convolution, and residual attention modules, improving intra coding efficiency for 360° videos.

Findings

Achieves around 8-9% bitrate reduction compared to baseline.

Improves local and global image quality in 360° video coding.

Demonstrates significant performance gains in experimental results.

Abstract

In this paper, we propose a distortion-aware loop filtering model to improve the performance of intra coding for 360$^o$ videos projected via equirectangular projection (ERP) format. To enable the awareness of distortion, our proposed module analyzes content characteristics based on a coding unit (CU) partition mask and processes them through partial convolution to activate the specified area. The feature recalibration module, which leverages cascaded residual channel-wise attention blocks (RCABs) to adjust the inter-channel and intra-channel features automatically, is capable of adapting with different quality levels. The perceptual geometry optimization combining with weighted mean squared error (WMSE) and the perceptual loss guarantees both the local field of view (FoV) and global image reconstruction with high quality. Extensive experimental results show that our proposed scheme achieves significant bitrate savings compared with the anchor (HM + 360Lib), leading to 8.9%, 9.0%, 7.1% and 7.4% on average bit rate reductions in terms of PSNR, WPSNR, and PSNR of two viewports for luminance component of 360^o videos, respectively.