Performance evaluation of objective quality metrics on HLG-based HDR image coding

Abstract

We evaluate the performance of objective quality metrics for high dynamic range (HDR) image coding that uses the transfer function (TF) of the Hybrid Log-Gamma (HLG) method. Previous evaluations of objective metrics for HDR image coding have studied which of them are reliable predictors of perceived quality; however, in those tests, all the non-linear transforms used both for encoding and by the best-performing metrics are essentially very similar and based on visual perception data of detection thresholds for lightness variations. The HLG non-linearity on the other hand is very different, as it is designed for backward compatibility with standard dynamic range (SDR) displays. We test a variety of options for objective metrics, including HLG-based. Our results show that the ranking of metrics for HDR coding changes drastically depending on the TF used for compression.