“The PQ system was developed by Dolby, a company whose main focus is on the cinema while the HLG system was developed jointly by BBC and NHK, two organizations whose main focus is on television… Television is probably better served by the HLG system that was designed from the ground up by television engineers for the special requirements of television on multiple display platforms.”
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There’s no denying that’s it’s super annoying not being able to share HDR10 videos with friends during daytime hours, so we thought we’d try grading and uploading an HLG HDR video to YouTube to see what that’s like. HLG HDR is mastered to 1,000 nits, doesn’t require any metadata, and is monitored at video levels, not full data levels. If the HLG HDR badge didn’t appear in the upper right-hand corner of the TV, no one would know whether the YouTube video was PQ or HLG, except that it can be enjoyed in either daytime or evening viewing conditions. However, unlike HDR10, when grading HLG in DaVinci Resolve on a MacBook Pro (late 2021), the viewer looks wrong – but the picture on the LG CX connected via an UltraStudio 4K Mini, the exported QuickTime file played back on the Mac and YouTube playback on both the Mac and on the LG CX all look pretty much alike – which is to say, no different from PQ. Unfortunately, our LG 32EP950 doesn’t support HLG. Nevertheless, back in 2017, Alistair Chapman cautioned against grading HLG footage, writing:
My advice – don’t try to grade HLG footage. There are three problems. The first is that the gamma is very different in the low/mid range compared to the highlights. This means that in post the shadows and mid range will respond to corrections and adjustments very differently to the high range. That makes grading tricky as you need to apply separate correction to the midrange and highlights.
The second problem is that the is a very large highlight range squeezed into a very small recording range. It should look OK when viewed directly with no adjustment. But if you try stretching that out to make the highlights brighter (remember they never reach 100% as recorded) or to make them more contrasty, there is a higher probability of seeing banding artefacts than with any other gamma in the camera.
The third issue is simply that the limited recording range means you have fewer code values per stop than regular Rec-709, the cinegammas or S-Log2. HLG is the least best choice for grading in the FS5.
RED Komodo 6K Sample Footage (downloadable file in video description)
Diffuse White vs. Specular Highlights
There’s been a lot of nonsense online arguing that movies and episodic television with no highlights can still be considered HDR, simply because they have been mastered in PQ. The Digital Cinema Initiative’s (DCI) study of 157 individuals, including both experts and laypersons, conclusively determined that an increase of just one stop (108 nits) was incapable of providing a sufficiently differentiated experience from traditional 48-nit theatrical projection. Dolby Laboratories’ own study of viewer preferences found that participants wanted much brighter highlights than is possible with today’s consumer televisions. SMPTE has written that, “A High Dynamic Range System (HDR System) is specified and designed for capturing, processing, and reproducing a scene, conveying the full range of perceptible shadow and highlight detail, with sufficient precision and acceptable artifacts, including sufficient separation of diffuse white and specular highlights.” [italics added] Specular highlights need to be around 3-5X the nit value of diffuse white in order to provide adequate separation. In the video below, highlights touch around 479 nits, but more would have been desirable.
The Daejeon Chronicles 
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