Do We Need 10 Bits? Assessing HEVC Encoders for Energy-efficient HDR Video Streaming

High-dynamic range (HDR) video content has gained popularity due to its enhanced color depth and luminance range, but it also presents new challenges in terms of compression efficiency and energy consumption. In this paper, we present an in-depth study of the compression performance and energy efficiency of HDR video encoding using High-Efficiency Video Coding (HEVC). In addition to using a native 10-bit HDR encoding configuration as a reference, we explore whether applying tone mapping to an 8-bit representation before encoding can result in additional bitrate and energy savings without compromising visual quality. The main contributions of this work are as follows: 1) a detailed evaluation of four HDR video encoding configurations, three of which leverage tone mapping techniques, 2) a comprehensive experimental setup involving over 15,000 individual encodings across three open-source HEVC encoders (Kvazaar, x265, and SVT-HEVC) and multiple presets, 3) the use of two advanced perception-based metrics for BD-rate calculations, one of which is specifically tailored to capture colour distortions and 4) an open-source dataset consisting of all experimental results for further research. Among the three tone-mapping configurations tested, our findings show that a simple bit-shifting approach can achieves significant reductions in both bitrate and energy consumption compared to the native 10-bit HDR encoding configuration. This research aims to lay an initial foundation for understanding the balance between coding efficiency and energy consumption in HDR video encoding, offering valuable insights to guide future advancements in the field.