HDR Is Here—But Don't Rush Out to Buy a New TV Just Yet
HDR, which stands for High Dynamic Range, is here. Is that good news, or bad news? The answer to that question depends on who you ask.
That is, if you were the kind of person who enjoyed the Blu-ray vs. HD-DVD standards war, you’ll love HDR in spades. If you’re the type who thinks that consumer electronics manufacturers should get their standards together before they offer new products to the masses, well, you’ll be shaking your head in disgust, particularly if you actually bought a soon-to-be-obsolete 4K TV in the last twelve months. Oh well, you can’t say we didn’t warn you.
Here’s the backstory. We’ve heard about 4K/UHD for years now, but as you probably know, unless the TV is really, really big, or you’re sitting extraordinarily close to it, the perceptible image is similar to 1080p. For this reason, many Hollywood studios sitting on film or similar stock that could be converted to 4K have resisted.
HDR is different. Briefly, HDR expands the range between the brightest and the darkest pixels in a TV set, expanding the contrast to look more like film than video. Many TVs that support HDR will also expand the color space from Rec 709 to Rec 2020 (discussed in our earlier article), so the colors will look richer and deeper. So unlike Plain Jane 4K, the difference doesn’t depend upon how close you sit to the TV, or how big the set is. The difference will be very noticeable even on similarly sized sets viewed from the same distance. So unlike 4K, which has been a pretty big "meh" for most consumers without too much money on their hands, everyone who sees HDR will want it.
A simulated HDR comparison from 4K Ultra HD Review
The problem is that there are too many competing standards, and no matter where you are in the digital video food chain, that’s a pretty chilling concept. In the short term, the biggest impact will be felt by content owners and distributors that encode for TV viewing, whether via STB, OTT, or smart TVs, all of which will likely be forced to support multiple HDR standards so their videos will play on a broad base of consumer TV and playback devices. Encoding vendors that support the OTT/STB/smart TV market will have to support multiple HDR technologies in their encoding tools. In contrast, if the bulk of the video files that you produce are viewed on computers and mobile devices, HDR won’t likely be a factor for at least several years.
Of course, we’re all consumers, and unless you enjoy the concept of having to buy separate 4K TVs to watch HDR videos from Netflix, Amazon, and M-Go, these dueling standards will do nothing but convince you to delay your new TV purchase until a more cohesive approach coalesces.
How is HDR Implemented?
Let’s take a high-level look at how HDR is implemented to help frame the related technical and distribute issues. Briefly, the increased contrast delivered by HDR, along with the expansion of the color gamut from Rec 709 to Rec 2020, means that each compressed pixel in a stream will require much more data to define. Some of that data will be included with the compressed video, and some will be in an accompanying metadata file, which according to some estimates will add about 20% in file size.
In a streaming distribution environment, the size of the metadata will make it difficult to stream a single package that supports multiple standards, not to mention a stream that supports both legacy and HDR TVs.
According to discussions that I had with a contact at Elemental Technologies, the basic compressed stream for most HDR standards will be similar, but the metadata will all be different. From an interface perspective, the various standards will likely be selected via a simple check-box or drop-down list. It’s very simple from a user perspective, but the development effort required to support the different standards will be substantial.
Then there’s the issue of supporting legacy devices. Here, there are two basic approaches, but even that is evolving. Initially, there was a concept of a single-layer and dual-layer approach, like that implemented by Dolby. Under this schema, a single layer would deliver the full HDR experience to compatible TVs, but wouldn’t be backwards compatible to older sets. However, a second layer of data, transmitted with the initial layer, could enable backwards compatibility.
While most viewers don't yet have a TV that can display high dynamic range content, YouTube is taking an early position in supporting the rich color technology.