Comparison of HDR quality metrics in Per-Clip Lagrangian multiplier optimisation with AV1

TL;DR

This study evaluates HDR quality metrics in AV1 rate-distortion optimization, demonstrating their impact on compression efficiency and highlighting the importance of chroma information in quality assessment.

Contribution

It provides a comparative analysis of HDR metrics in per-clip AV1 optimization and shows how chroma inclusion affects rate-distortion performance.

Findings

HDR metrics improve BD-Rate by up to 7.253%

Chroma information significantly influences optimization results

Per-clip optimization with HDR metrics enhances compression efficiency

Abstract

The complexity of modern codecs along with the increased need of delivering high-quality videos at low bitrates has reinforced the idea of a per-clip tailoring of parameters for optimised rate-distortion performance. While the objective quality metrics used for Standard Dynamic Range (SDR) videos have been well studied, the transitioning of consumer displays to support High Dynamic Range (HDR) videos, poses a new challenge to rate-distortion optimisation. In this paper, we review the popular HDR metrics DeltaE100 (DE100), PSNRL100, wPSNR, and HDR-VQM. We measure the impact of employing these metrics in per-clip direct search optimisation of the rate-distortion Lagrange multiplier in AV1. We report, on 35 HDR videos, average Bjontegaard Delta Rate (BD-Rate) gains of 4.675%, 2.226%, and 7.253% in terms of DE100, PSNRL100, and HDR-VQM. We also show that the inclusion of chroma in the quality metrics has a significant impact on optimisation, which can only be partially addressed by the use of chroma offsets.