Want to enjoy your HDR videos in a bright viewing environment? Shoot HLG!

“With both PQ and HLG, if video content is displayed at the same brightness and in the same viewing conditions as those in which it was produced, it will look the same as it did on the production monitor. The creative intent will be maintained. Indeed, under these conditions PQ and HLG deliver identical looking pictures. However, content will not usually be consumed under the same conditions as it was produced… In order to maintain creative intent under different viewing conditions, and on different displays, content should look perceptually the same, but the pixels don’t necessarily need to have the same absolute luminance. After all, a photograph has the same creative intent whether it is viewed in bright daylight or in dim artificial light, even though the absolute brightness is very different. It is well-known that the relative luminance levels in a scene are much more important in perceptual judgements than the absolute luminance levels… When viewing in a brighter environment it is more comfortable, and easier to see dark details, if the image is reproduced at a higher luminance than during production… With HLG, luminance levels are implicitly scaled by the display, maintaining the relative luminance between pixels… This design for HLG means that the picture looks perceptually the same over a wide range of display brightnesses, and there is no need to specify a single “reference” display brightness… PQ is a display-referred approach to HDR, where the signal corresponds directly to the absolute displayed pixel luminance levels on the mastering display. This is like the approach taken for movies, where the final image is crafted in a cinema environment, the same brightness and environment in which the movie will be presented… Display-referred signals, such as PQ, work well when the production and viewing environments are the same, but are not ideal when they differ. Scene-referred signals, such as HLG, are a more natural choice when the viewing conditions vary.”

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