Stranger HDR Things

High Dynamic range, or HDR, is perhaps the most exciting of the trio of improvements that Ultra HD brings to the table, the others being a wider color gamut and higher resolution. The images from a flat screen set pop off the screen in a way that the dimensional but often too dim 3D never could. And you don’t need special glasses to see it.

A flat screen set, capable of peak brightness levels of over 1000 nits (just under 300 foot-lamberts) can make the most of an HDR source. HDR program material is mastered for a peak output of either 1000 nits or 4000 nits, with most of that luminance reserved for bright highlights.

But not all displays can hit 1000 nits, and we know of no consumer products capable of anything beyond 2000. And not all displays can reach even 1000 nits; OLEDs, for example, generally top out at under 700, and cheaper 4K LCD/LED designs can’t even get to that.

There’s no tone mapping standard. We can tell you that tone mapping is almost universal, but not how it’s done.

If an HDR-capable set with, say, 500 nits of available peak luminance sees a scene that peaks at 1000 nits, what does it do with it? Absent any other processing it would simply clip all of the information above 500 nits. But to preserve at least the sense of that information, the set then “tone maps” it. How is this done? That’s where the fun begins, because the actual tone mapping process is up to the TV maker. There’s no tone mapping standard. We can tell you that tone mapping is almost universal, but not how it’s done—which in any case might require a Mensa membership to fully comprehend. If all sets were limited to a fixed peak brightness of, say, 1000 nits, and all sources limited to the same 1000 nits, tone mapping would never be needed. But with the wide range of product prices and performance on the market, that was never possible. So tone-mapping is with us and likely always will be until the peak brightness of our displays matches the peak brightness that can be mastered onto the source.

But the fun doesn’t stop there. HDR in projectors adds another whole layer of complexity to the mix. In fact, HDR was developed with consumer televisions in mind, not projectors. A home theater projector is unlikely to offer a peak brightness output of more than 150 nits, though the Epson 4000 I recently reviewed topped out at a “searing” 174 nits in Bright Cinema mode. But even that’s a hair on the dog of a good flat screen set’s peak output. That means that the tone mapping on a projector needs to begin at a far lower source level, and be far more aggressive. This makes a projector far trickier to set up and optimize in HDR than a flat screen set.

Ideally we’d have special “projection only” versions of HDR releases, mastered at a peak level of 150-200 nits. But that’s not happening. And there are other variables as well with projectors, including the size and gain of the screen. The only way to standardize for that would be to specify not only the capabilities of the projector but also everything else in the system. That’s unlikely to happen either. The only place you’ll find it is in one of the Dolby Cinema theaters, with about 100 of them scattered in multiplexes around the country. Dolby Cinema is a closed system; each piece of the puzzle, from content mastering to the screen, is fixed and known. No tone mapping needed there. But in our crazy world of ad hoc home theater, there are few such standards. HDR from a projector, for now, is the Forest Gump’s Box of Chocolates of the home theater world. You never know exactly what you’re going to get…but it usually tastes good.

drny's picture

Personally I am not wowed by OLED displays. At least not at 65" size display viewed in a living room with ambient light.
The main reason is that OLED black level excellence requires a true home theater room. That is to say a dark viewing room to maximize its contrast prowess.
HDR tone mapping on an OLED display looks impressive if viewed in a darken room. But the same can be said of a JVC-DLA faux 4k projector.
Under ideal circumstances, 10 feet away from the screen the image on a 100+ projector screen will be far more impressive than the 65"OLED at the same distance. Technically the OLED is far superior in reproducing detail and contrast of the HDR tone mapping, but optically our human eye will be capture by the larger image.
You doubt my assertions.
Please go to the nearest Dolby Vision Cinema Theater and see Blade Runner 2049. It is a fantastic sensory experience.
When the UHD is release the HDR tone mapping will far exceed that of the one in the Dolby Vsion Theater. Go ahead purchase an OLED and view the same movie 7 feet away from the screen.
You will be amazed but the experience won't match the Dolby Vision theater, or that of a true 4k or very decent faux 4k home projector.

johnty's picture

Enough with the HDR is 3D comparison. "The images from a flat screen set pop off the screen in a way that the dimensional but often too dim 3D never could." Nonsense. My passive 3D LCD TV displays Dolby Vision 4K HDR which is indeed stunning. My 3D movies are only 2K and will never have HDR but, with the proper settings, are just as bright as 2D programs. They also have incredible depth and "pop off the screen" visuals that 4k HDR can only dream about.

Too many writers love to use the HDR is 3D analogy. Too many writers are wrong.

DavidH's picture

johnty is right. HDR and 3D are different creatures. When I first heard of 3D for the home I was a sceptic. Who would wear glasses to watch TV? But 3D on LG's OLEDs has changed my mind. This is an exceptional experience; as good (or better) than many theaters can give.

HDR, on the other hand, is a very mixed bag. Great for capture, but so-so for home displays. I have seen one or two good examples - and many bad. Wide color gamut is terrific, but who needs 1,000 nits blasting from their TV? Maybe for a tiny highlight, but not for large expanses of the screen - that is downright unpleasant. And to "show off" HDR we are being given scenes with actors sitting in front of large windows at peak brightness. Where are my sunglasses?

HDR is being sold as the next coming, but I'm not on the bandwagon.

WildGuy's picture

i didn't really know or thought about tv with hdr and tone mapping for sets that is under 1,000 nits until i read this topic. a nice read. quite informative.

To DavidH, i believe most 4k hdr sets won't be able to output 1,000 nits in 100% of the screen, maybe like 10% to 20% of the screen area. So, like you said maybe for tiny highlight, so we shouldn't worry too much about it.:)