Practical Use Suggests a Re-evaluation of HDR Objective Quality Metrics

Full-reference objective quality metrics for high dynamic range (HDR) images must be validated in terms of their consistency with subjective evaluation results, and previous studies have found a number of metrics that appear to correlate well with the preference of observers. However, those conclusions were based on experiments that do not correspond to the practical use of a current day HDR professional production scenario. In this work, we carry out subjective evaluation experiments for the popular HDR standards of perceptual quantization (PQ) and Hybrid Log-Gamma (HLG), with a state-of-the-art HDR reference monitor used in broadcasting and post-production, and where all the observers participating in the tests are video experts. We find that the ranking of HDR metrics is now substantially different from what was reported earlier, and also that a simple standard dynamic range (SDR) metric can be applied directly to PQ or HLG encoded signals providing excellent results that surpass those of HDR metrics.