Dolby Vision is one or the highest image quality standards in cinemas. It’s so demanding there are just a handful of Dolby Vision screens across the world. They’re not cheap to make—each screen uses two 4K laser-light projectors, rather than bog standard DLP—but with high brightness and 12-bit HDR colour they look superb.
At MWC 2017 LG and Dolby announced that the new LG G6 supports Dolby Vision, once again raising the question of how Dolby has diluted one of its audiovisual cinema techs this time. After all, Dolby Vision is a standard that ostensibly supports brightness levels up to 10,000 nits, where the brightest phones top out at 600-700.
In much the same way that Dolby Atmos, originally a multi-speaker cinema technology, is now available on mobile devices, Dolby is risking the credibility of Dolby Vision by bringing it to the LG G6, and presumably other phones and laptops soon. Thankfully, I can report that it’s more than a branding exercise—though only just.
Dolby’s vice president of interactive imaging Taeho Oh explained to us how it works. “All Dolby Vision devices look as close as possible to the reference monitor,” he says, the “reference monitor” being, for example, the display a Hollywood colourist would use when grading not-best-movie-Oscar-winner La La Land.
He explained the process. “Manufacturers work with LCD manufacturers, and they then select an LCD panel. We work based on that. We tune the device to that LCD, to what works best with our reference.”
Dolby Vision in a phone doesn’t mean a device has reached a certain minimum standard for colour gamut coverage, brightness, or contrast, but that Dolby has tweaked the screen to appear as good as is possible. “Our colourist actually tunes [the screen] so it maps with the displays used by content creators.”
We should note that this Dolby Vision colour profile isn’t used 24/7: it’s only enabled when the LG G6 is fed Dolby Vision-encoded content. Netflix and Amazon Video have announced they will provide mobile video content with Dolby Vision, although right now we’re not sure if the library will match that of Dolby Vision-certified TVs.
There are limits to how far clever calibration can get you, though. Dolby Vision content uses the Rec 2020 colour gamut, an incredibly wide standard that encompasses 67 percent of the colours our eyes and brains can perceive (the CIE standard). For some context, the traditional display standard, sRGB, only covers 34 percent, and most cheaper phones today struggle to cover all of sRGB.
We haven’t tested the LG G6 with a colorimeter, but we’ll give it the benefit of the doubt and assume it can cover 100 percent of sRGB. But it probably can’t cover 100 percent of Adobe RGB or DCI P3, both of which are far narrower than Rec 2020.
We saw a little of the effect of this in the Dolby Vision demo Dolby showed us, where the colour contrast in a bright red flower began to bottom out in its most reddy bits. Crucially, though, it didn’t simply blow out the red colour channel, the colour version of overexposure, leaving the LG G6 with a flat plane of red. It’s here we see the benefits of an expert’s touch.
As Taeho Oh says, “we make a lower-performing screen closer to reference.” The colour began to plateau at, we assume, the native abilities of the panel, but without making the LG G6’s screen limitations glaringly obvious.