VESA Rolls Out Updated DisplayHDR Standard for OLED Displays: DisplayHDR True Blackby Ryan Smith on January 3, 2019 11:15 AM EST
This morning the VESA is rolling out an update to the standard body’s DisplayHDR monitor performance standard that’s focused on expanding the specification to cover OLED displays. Dubbed DisplayHDR True Black, the new performance tiers to the DisplayHDR standard are intended for OLED and other emissive displays, laying out the levels of display performance that the association believes are appropriate for consumer HDR displays.
This update comes just over a year after the original DisplayHDR standard was launched. Intended to simplify the market for HDR displays, DisplayHDR sets a number of tiers of increasing performance, with each higher tier requiring better monitor technology and delivering a better HDR experience as a result. At the time of DisplayHDR’s launch, the VESA opted to focus on LCDs, as these displays were already in the PC market and were what the association had the most experience with. The end result was the DisplayHDR 400, 600, and 1000 standards, which covered a range of monitor designs that essentially stretched from not-very-HDR to cutting-edge full array local dimming displays.
The DisplayHDR True Black update in turn adds two more tiers to the DisplayHDR standard: DisplayHDR 400 True Black, and DisplayHDR 500 True Black. Like the tiers for LCDs, the True Black tiers are divided up based on performance; though the gap isn’t quite as big as with the LCD tiers. The end result is that displays reaching these standards, besides meeting the DisplayHDR specification’s baseline requirements, can also hit a peak brightness of 400 nits and 500 nits respectively.
The need for separate tiers for OLEDs – and other future emissive technologies like microLEDs – is rooted in the fact that HDR itself is as much (or more) about dynamic range as it is absolute maximum and minimum brightness. While LCDs can offer the necessary contrast ratios with the right backlighting technology, they are still backlit displays, meaning that they can’t quite hit black since they’re always illuminated to a degree. OLEDs, on the other hands, can hit almost perfect black levels since the pixels can simply be turned off entirely – hence the True Black moniker – which means these displays need to be measured on a different scale. Conversely, while LCDs can sustain incredible 600+ nit brightness levels over the whole screen, OLED technology can only burst to these levels for short periods of time, so the maximum brightness offered by OLED displays isn’t quite in sync either with HDR LCDs.
Overall the DisplayHDR standard covers a number of performance requirements (the VESA’s full chart is below), however as OLED displays are currently a high-end solution, DisplayHDR True Black displays are primarily competing with DisplayHDR 1000 displays. So I’ve distilled the important points to the below.
|DisplayHDR Luminance Specification Comparison|
|DHDR 1000||DHDR 500 TB||DHDR 400 TB|
|White - 10% Center Patch
|1000 nits||500 nits||400 nits|
|White - Full Screen Flash
|1000 nits||300 nits||250 nits|
|White - Full Screen Sustained
|600 nits||300 nits||250 nits|
|Black - Corner
|0.05 nits||0.0005 nits||0.0005 nits|
In short, DispayHDR True Black mandates a maximum black level performance of 0.0005 nits, 1/100th the brightness of a DisplayHDR 1000 display. While technically not 0 for practical measurement reasons (measuring nothing is surprisingly hard), in practice the standard fully expects and exploits the fact that OLED displays can turn off individual pixels to achieve perfect blacks. Conversely, the standard calls for a maximum of 500 or 400 nits respectively for a 10% patch of full white, and only 300/250 nits for the full screen. This is around half of what a DisplayHDR 1000 display can offer, which is 1000 nits for everything short of a long-duration full screen image.
The net result is that the new tiers reflect what we already know about each technology: OLEDs can get very dark, but they can’t get super bright. Meanwhile LCDs can’t hit pitch black, but they can get incredibly bright. But both can offer extensive dynamic ranges – over 20,000:1 for LCDs and 1,000,000:1 for OLEDs – allowing both to deliver the “high” part of high dynamic range. And now the standard can express these differences while requiring both display types to offer appropriate contrast ratios.
Meanwhile it’s interesting to note that the DisplayHDR True Black tiers also leverage OLEDs in one other way: response times. The standard requires a black-to-white response time of 2 frames for OLEDs, as opposed to 8 frames for LCDs. This again reflects the technology: the LED backlights in an LCD unfortunately take some time to ramp up, whereas OLED is virtually instantaneous. So DisplayHDR True Black doesn’t hold back, and certified displays need to be able to ramp up with the kind of quick response rates that the tech is capable of.
Past the specific brightness and ramp-up requirements, the other aspects of DisplayHDR True Black 500 & 400 are identical to DisplayHDR 1000/600. All of these displays need to be able to cover at least 99% of the sRGB color gamut and 90% of the DCI-P3 65 color gamut. And all internal image processing must be done with 10bpc – though 8bpc is allowed for the pixel driver. So DisplayHDR True Black displays won’t necessarily have wider color gamuts or finer steps between colors than DisplayHDR 1000 displays, rather they’ll simply operate with different ranges of luminance requirements.
DisplayHDR 500 – A Little Lighter For Laptops
Finally, tucked in along with the new True Black tiers, VESA is also rolling out DisplayHDR 500. Not to be confused with DisplayHDR 500 True Black, DisplayHDR 500 is a new tier for LCDs. Specifically, it appears to be a compromise tier aimed primarily at laptop vendors. The quality requirements are functionally identical to DisplayHDR 600, however the maximum brightness levels have been reduced to 500 nits for short durations and 320 nits for long durations, down from 600/350 respectively for DisplayHDR 600.
VESA’s announcement notes that this was done particularly to accommodate thin notebooks, where the lower tier is useful for helping to better control thermals in these laptops (a thin screen implies limited thermal mass). Though the VESA notes that like all other DisplayHDR standards, this isn’t limited to one form factor of displays, and that any display – including desktop monitors – could be DisplayHDR 500 certified if an OEM desired.