The label knows better: The impact of labeling effects on perceived quality of HD and UHD video streaming

There is an ongoing debate in the research community over the improved visual quality of UHD video in comparison to the still widely-deployed HD standard. It is the inspiration of many scientific studies, yet UHD displays and services are continuously spreading on the consumer market. This paper presents the results of a subjective paired-comparison test with both upscaled HD and UHD video sequences, investigating the primary research question of whether UHD can offer a significant improvement over HD for common viewing conditions. In our study, subjects rated their visual preference on video-only clips without lossy encoding. In addition we studied cognitive biases, by presenting a label of what users were about to see (HD or UHD) before the sequence, purposely manipulating the labels in some conditions to suggest different resolutions than actually shown. Finally, we investigated the impact of different rating scales on the precision of the results. Our studies show that HD clips appear indistinguishable from UHD clips when the rating scale chosen is not fine-grained enough. We also found that the labeling effect has a significant impact on the perceived quality, overriding the actual visual perception. Even with a precise scale, users cannot detect major improvements of UHD compared to HD, which may let us question the added value offered by UHD.