A few notes on DolbyPQ & the new 4k AppleTV and TV High Dynamic Range.

STOP PRESS! 27th Sept. 2017 Update;

So it turns out that the new AppleTV does support HLG.

- Why did it take somebody hacking around with a firmware update to discover it; perhaps big corporations (Apple and Dolby) talk and would rather not highlight the fact?


HDR is half my life at the moment; the distinction between "Display Referred" and "Scene Referred" video is lost on most people, but is pretty central to understanding why the BBC/NHK "Hybrid Log Gamma" system is ten times more appropriate for television (non-theatrical video) vs anything based on the SMPTE 2084 (AKA Dolby/HDR10 etc) curve.

For my presentation on "intro to HDR for TV" download here.

1. Display Referred HDR makes no sense for TV (when I say TV I mean all non theatrical video). DolbyPQ makes video dimensioned (so code values actually represent light levels) which makes a lot of sense when you have complete control over the environment you're viewing in - a theatre. To define where black and white sit (and actually assign light-levels to them) is problematic for TV workflows. Remember, you have to give the colourist/racks-engineer/domestic-viewer the liberty to set black according to the room. Although BT.1886 is commonly accepted to mean 100Cdm^-2 peak white a lot of colourists drive their rooms at 80Cdm^-2 and at least one film guy I know prefers to work at 60Cdm^-2. Also - what happens in three years when everyone is selling TVs with specular highlights that can hit 2,000Cdm^-2 and people can see the difference between PQ content mastered with peaks at 1,000Cdm^-2 ( the current standard) and new content? The same will be true all the way up to Dolby's max light level of 10,000Cdm^-2. Dolby at least has the benefit of dynamic metadata to allow or this, but HDR10 is static metadata and so has all the problems of display-referred HDR with none of the DolbyPQ benefits.
2. BBC/NHK HLG is a much more pragmatic solution as it doesn't assign code-value to light-levels (when has that ever been a thing in TV?!) and allows HDR content to look good on all devices capable of displaying it; tablets, TVs, laptops etc. It also allows the broadcasters to make a gradual change to HDR. None of the broadcasters I've spoken to have any appetite for having Dolby CMUs all over the place to manage the metadata (which, being a licensed format, they would be obliged to have). HLG also tracks 1886 for most of the curve (to around 65%) which means conversion to/from is easier and even when you get it wrong the pictures look OK. It's why scene-referred video makes sense for TV.
3. Having seen the same SLog3 (so camera HDR gamma) played out from Transkoder in both DolbyPQ (mastered at 1,000Cdm^-2) next to the same machine converting to HLG with two Sony X300 monitors set for the appropriate gamma curves and the same Rec.2020 colour calibration you could not tell them apart in a blind viewing. 
4. It's typical Dolby - they are trying to dominate the domestic space by shoe-horning their theatrical format into TVs. Broadcasters get hobbled with licensing costs, onerous upgrade requirements and pictures that are locked to whatever version of PQ/HDR10/HDR10+ they were mastered for rather than allowing the display to make the best of what it's given; scene referred pictures.
5. The good thing about HLG is that rec.2100 ratifies it, the DVB have too. It's also trivial to upgrade HDR10-capable sets to support it (unlike PQ). I imagine it'll be the case that broadcasters will deliver HDR (for the reasons mentioned) and either you have to upgrade your TV (but pretty much all the current ones support it out of the box) OR your STB will do the conversion.

Which is why the new 4k AppleTV is a damp-squib...