[Update: Since this story was written, Dolby has admitted there is a bug with the way Dolby Vision works over HDMI. This is covered in this separate story. Also, Apple has rolled out tvOS 11.3, which introduces Dolby Vision compatibility with Sony TVs.]
While it may have arrived with some teething problems to sort out, the Apple TV 4K is in many ways a significant AV milestone. Basically, it’s the first time Apple has really taken AV quality seriously with an Apple TV.
Particularly eye-catching for AV fans is the Apple TV 4K’s support for Dolby Vision. This premium high dynamic range format adds a layer of extra information to its core HDR pictures that helps TVs optimize their HDR playback - and when done right it can deliver stunning results. [For more on this, check out my reviews of the 4K Blu-rays of Despicable Me 1&2, Spider-Man: Homecoming and Atomic Blonde].
Unfortunately, though, something isn’t quite working right with Dolby Vision on the Apple TV 4K - at least on LG’s OLED TVs.
The problem seems related to one I’ve noticed before when reviewing the Dolby Vision version of The Fate Of The Furious on 4K Blu-ray: raised black levels during some dark scenes.
What happens is that sometimes when watching Dolby Vision content on an LG OLED TV, certain dark scenes can suddenly cause a sharp rise in the picture’s baseline brightness. Then, when the action switches to a brighter scene, the screen’s black levels return to the sort of inky look you would expect from an OLED TV.
If you have an Apple TV 4K with a Dolby Vision OLED TV and want to see the problem for yourself, I know that Mindhunter and Godless on Netflix are definitely affected by it. For instance, if you fire up Mindhunter Episode 8 and start watching from around 8 minutes and 25 seconds in, you can clearly see big shifts in the image’s black levels as the picture shifts from the bright school interview to Holden sitting on a step outside his girlfriend’s flat.
There’s another big shift during a cut within this exterior night-time sequence too, and the black bars above and below the picture clearly drop back to their normal inky depths once the action cuts to the brighter interior of the girlfriend’s house.
The fact that the problem impacts the black bars above and below wide aspect ratio pictures makes it more distracting - and suggests that some instruction in the Dolby Vision metadata is pushing the OLED TV out of its brightness comfort zone. After all, as I’ve pointed out in my reviews of LG’s OLED TVs, you only have to nudge their brightness levels up a couple of points above their default ’50’ position before their previously imperious black levels start to descend quite dramatically into greyness.
Making the situation more confusing, though (and throwing the spotlight back onto the Apple TV 4K box rather than Dolby Vision, LG or Netflix) is the fact that if I watch the same Mindhunter clip in Dolby Vision using the Netflix app built into the LG TV, the shifting black levels don’t occur. Or at least they’re nowhere near as visible as they are via the Apple TV 4K.
You can greatly reduce the problem when watching the Apple TV 4K by activating the LG OLED TV’s Dolby Cinema preset rather than sticking with the default Dolby Cinema Home one. This substantially reduces the overall brightness of the image, and in doing so seems to return the OLED TV’s pictures back within their brightness ‘comfort zone’.
However, for me the Dolby Cinema setting’s pictures look too dark to really do HDR justice, so this is a far from ideal solution to what truly is an annoying problem that’s readily visible to anyone (we’re not talking about something only ‘trained eyes’ can see). You don’t have to activate the Dolby Cinema preset, by the way, to avoid raised black issues when viewing Dolby Vision on the LG TV’s own Netflix app.
I’m in contact with Dolby, Apple and LG over this issue, and will report back if anything useful - including, ideally, an at-source solution - is forthcoming.
I should also say that as I’m based in the UK, the pool of Dolby Vision TVs available to me to test with the Apple TV 4K is very limited right now. So if you have another brand of Dolby Vision TV running with an Apple TV 4K, please look for the issue described here and let me know via the Twitter account that appears at the bottom of this article if you see it on your TV too.
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