A Question of Standards
Probably the biggest challenge for anyone interested in HDR is knowing what to buy. At best, HDR is an umbrella term that covers a range of technologies and features. However, some standards are emerging that should make buying easier.
Currently, the two best established standards are HDR10 and Dolby Vision. The most obvious difference between the two is color depth. As its name suggests, HDR-10 requires 10-bit per channel color capability, while Dolby Vision ups the ante to 12-bit. How much difference that will make in practice remains to be seen, but on paper, Dolby Vision is superior in that regard.
The other major difference is support for brightness. HDR-10 supports up to 1,000cd/m2 of brightness for LCD displays, while Dolby Vision goes up to 4,000cd/m2, with plans to support 10,000cd/m2 in the future. Again, Dolby Vision is superior, and it is likewise much more expensive.
What’s not clear is whether PC monitor manufacturers will adopt either of these standards. Making matters even more complicated is the fact that a monitor may have some HDR capabilities without being marketed as an HDR display. That’s especially true of any OLED PC display. OLED panels have very high contrast capabilities. Indeed, an OLED display is only required to generate around half the brightness of an LCD display to comply with the HDR10 standard for that very reason.
Complicating things even further, the UHD Premium standard adopts HDR-10 as a subsection of its requirements. So it’s another label you may see attached to a display, even if it’s not a separate HDR standard in a strict sense. Ultimately, it’s early days for HDR displays, and it’s not clear which standard (or standards) will become the norm on the PC. would be capable of infinite contrast if the pixels were fully switchable, as per OLED. Thus HDR doesn’t just deal with relative values of brightness, but also absolutes. Again, by way of example, UHD Premium stipulates a maximum brightness of at least 1,000cd/m2 for an LCD screen—roughly three times brighter than a typical LCD.
BACKLIGHT OR BLACK
As for how that’s achieved with existing LCD tech, obviously a more powerful backlight is needed. But, very likely, a backlight composed of subpixels (though not as many as the LCD panel), and thus capable of local dimming, is required. A single, big, dumb backlight cranking out massive brightness would enable greater brightness, but it would also guarantee that the black levels are very poor in some scenarios.
For an idea of what this combination of huge contrast and extreme brightness will enable, imagine the powerful flash of light as a car passes on a really bright day, and the glass momentarily reflects the sun directly into your eyes. Even an HDR screen won’t put out real-world levels of light for such events. But the effect of simulating them on screen will be far, far more realistic.
Displays that capture much or all of these new color, contrast, and brightness capabilities already exist. HDR is the latest big thing in HDTVs, and using an HDR HDTV as a monitor is an option for PC enthusiasts. HDR is also a new feature in the latest refresh of games consoles from Microsoft and Sony. But that same technology is coming to screens designed to be used with PCs. The downside is that it will likely come in many confusing forms. Already, there are inconsistencies with terminology, such as “4K” and “UHD,” which are used virtually interchangeably but are not the same.
Then there’s the likelihood that some monitors will support certain aspects of what’s known as HDR, but not others. For instance, you could argue that, for PC gaming, what matters is the contrast and brightness aspects of HDR, along with speed, in terms of pixel response. So you might not want a more expensive and slower LCD panel that’s required to deliver
the wider color gamuts. You might want what amounts to an HDR backlight with local dimming, combined with a TN panel with relatively limited colors. But would that be an HDR monitor? Or something else? Tricky. Other displays may take up the broader color gamut, and leave off the local dimming. It’s very early days, and it will probably take a few years to shake out, especially when you factor in the likely coming transition from LCD tech to OLED.
Speaking of that transition, it’s yet to be seen how PC monitor manufacturers will achieve HDR capabilities. If LCD tech is used, a backlight with local dimming is required to achieve the extreme contrast ratios. Quantum dot tech can also be used to bolster the range of colors on offer in combination with a 10-bit or 12-bit LCD panel. But arguably, any attempt to achieve HDR visuals via LCD tech is a bit of a kludge.
Instead, OLED displays with pixels that are their own light source are a much more efficient way to do things. What’s more, OLED technology lends itself better, in cost terms, to more compact PC displays than massive HDTVs. It’s a similar rationale that has seen OLED become common in smartphones. Very likely, therefore, HDR LCD monitors will be at best a stopgap before OLED becomes the dominant solution. With that in mind, it might make sense to consider a cheap HDR LCD TV as your own stopgap solution, while we wait for OLED HDR monitors to become affordable.
CAN YOU HAVE IT ALL?
Things get even more complicated with the technologies needed to achieve UHD color depths beyond the screen itself. With all those colors and ranges of intensity, HDR is seriously bandwidth hungry. HDMI 2.0, for instance, can’t do the full 12-bit per channel at 60fps and 4K resolution—for that you need HDMI 2.0a. Upping the refresh rate to 120Hz and beyond only makes the bandwidth limitation worse. In other words, a display that does it all—120Hz-plus, adaptive-sync, HDR, the lot—isn’t coming any time soon. Even when it does, your existing video card almost certainly won’t cope when gaming.
You’ll also require a compliant video card to enable HDR visuals. For Nvidia GPUs, that’s Maxwell or Pascal families (GTX 960, GTX 980, GTX 1070, GTX 1080, and so on). For AMD, its Radeon R9 300 Series can do HDR at 60Hz up to 2560x1600. For full 4K 60Hz HDR output, only the latest Polaris boards, such as the RX 480, can pull it off.
Then there’s the question of content. In terms of video, there’s very little out there. It was only in 2014 that the Blu-ray standard was updated to support 10-bit per channel color. HDR photos are in more plentiful supply. Even most smartphones support HDR image capture, achieved by capturing the same image multiple times with a range of exposures, then combining the results into a single image. In theory, HDR video capture works the same way, it’s just harder to achieve because of the need to process so much data in real time. As for games, much of the early HDR content on the PC will likely be driven by the parallel emergence of HDR tech on games consoles (see boxout above).
HDR is one hell of a complicated technology: Currently, it’s not clear when the first dedicated HDR monitors will go on sale, which standards they will conform to, or how much they will cost. But HDR is coming. So we’d better get ready.