Ultra HD 4K and beyond: Rec. 2020 glimpses the future of TVs

The ITU Radiocommunication Assembly has put out new recommended standards for Ultra HD TVs. What do they mean to you?

The inner, solid triangle, is the current Rec. 709. All colors recorded in the current TV system lay inside this triangle. The outer, dotted triangle, is the proposed Rec. 2020 color gamut. Geoffrey Morrison/CNET (triangles); Sakurambo (base chart)
The International Telecommunications Union is the regulatory body that establishes the parameters by which all TVs and their related paraphernalia (cameras, etc.) work. Without them, every TV show would look different on every TV.

To help with the adoption of Ultra HD, otherwise known as "4K," they've put out the sexy sounding Recommendation ITU-R BT.2020. What does it mean for you?

Well, not much. Wait! Keep reading! True, these standards are for Ultra HD TVs, but they tell a lot about where the ITU expects and hopes televisions to go. Keep in mind, the current HDTV standard Rec. 709, was developed and finalized in the mid-to-late 1990s. Televisions and technology have come a long way since then. We have the technology ("we can rebuild him"), to do far more than what Rec. 709 specifies.

Let's start with the basic stuff you probably already know from the various Ultra HD coverage recently. Rec. 2020 specifies two resolutions, both with a 16:9 aspect ratio: 3,840x2,160 (what everyone calls "4K") and 7,680x4,320 ("8K"). All the same frame rates are included, from 24 to 60 just like now -- but a higher frame rate, 120 Hz, is also mentioned. This is interesting, as the maximum frame rate currently available is 60, and that's not even available on Blu-ray. Check out What is Refresh Rate? and What is the "Soap Opera Effect"? for more info on frame rates.

Unlike Rec. 709, there's no more interlaced, only progressive.


Perhaps the most interesting recommendation in Rec. 2020 is the significantly better color. Currently, Rec. 709 specifies the following x/y coordinates for red, green, and blue:
(R) 0.640, 0.330
(G) 0.300, 0.600
(B) 0.150, 0.060

These are the specific values for the locations of those colors, as shown on the smaller triangle in the chart above. These colors are "OK" but certainly not as realistic as what we see in the real world. Anything outside that triangle is not captured by the camera, encoded on the disc, or accurately shown on your television.

Rec. 2020's color recommendations are insane (in a good way):
(R) 0.708, 0.292
(G) 0.170, 0.797
(B) 0.131, 0.046

These are massively deeper colors than what's possible now. Of all the aspects of Rec. 2020, this is the part I fear is most likely not to be implemented. These colors are so radically different (that is, better) than what we have now, it's going to take a lot to get current technologies to be able to produce them. Most TVs today are capable of a wider color gamut than Rec. 709, but not this wide. According to sources I spoke to, no current TVs can produce these color points. So this is likely a more difficult technological hurdle than upping the resolution to 4K. Maybe OLED or quantum dots can help.

The reference white, or color temperature, stays the same at 0.3127, 0.329 (D65, or D6500). Why mess with what's already right?

Wide-gamut TVs today

It's worth noting that implementing Rec. 2020 colors, or anything beyond Rec. 709 colors, isn't a great idea in current TVs. The entire television system, from the camera all the way to your TV, needs standards to work correctly. If there weren't standards, as I mentioned above, every TV program would look differently than every other program, on every TV. It would be chaos. Like, fire and brimstone coming down from the skies. Rivers and seas boiling. Forty years of darkness. Earthquakes, volcanoes... eh, you get the point.

As it's set now -- or at least, how it's supposed to work -- the TV system itself doesn't add or take away anything from the camera to your TV, presuming the TV is calibrated. So you're seeing exactly what was shot by the camera, plus any flourishes desired and added by the filmmakers or TV producers.

Extended or wider color gamuts, or wildly oversaturated colors, are added by the TV, manipulating the correct image supplied by the Blu-ray or cable/satellite box. Worse, there are serious issues trying to get accurate colors if the TV itself starts with oversaturated color points. Specifically, if the TV is capable of crazy oversaturated colors, getting it to mellow out and create accurate colors is processing intensive and extremely difficult. So the wider the color gamut is from being accurate, the less accurate the TV can ever be. I'll dig further into this in a future article.

If you like oversaturated, hyper-realistic color, that's your prerogative, but it isn't accurate. And it isn't what the directors intended for you to see.

Bit depth
The other side of the color conversation is bit depth, or how many shades of each color there are. The current TV system is 8 bits per color: 256 shades, minus some margin on either end. This means that Rec. 709 is capable of a maximum of 16.78 million colors (256 red x 256 green x 256 blue).

Rec. 2020 stipulates 10 or 12 bits. With 10-bit, this means a possible 1,073,741,824 colors (1,024x1,024x1,024). Yowzers. With 12-bit (4,096x4,096x4,096), it's even crazier: 68,719,476,736!!! 68 billion colors. Beat that, Skittles.

This is exciting as well, meaning finer shades of colors, smoother transitions from light to dark, and so on.

I've gotten some flak by being skeptical of Ultra HD in small screen sizes, as it's beyond what your eye can see from where most people sit. While no specific sizes are mentioned in Rec 2020 (obviously), there is this note: "Both 3,840 x 2,160 and 7,680 x 4,320 systems of UHDTV will find their main applications for the delivery of television programming to the home where they will provide viewers with an increased sense of "being there" and increased sense of realness by using displays with a screen diagonal of the order of 1.5 metres or more and for large screen (LSDI) presentations in theatres, halls and other venues such as sports venues or theme parks." That's 59-inches or more. Just sayin'.

Bottom line

Personally, I think the resolution increase from 1080i/p to 4K/8K is the least interesting part of Rec. 2020. Better color and bit depth? Sign me up. Unfortunately, it's hard to say what of the current version of Rec. 2020 will survive to future revisions, and when, if ever, any of these revisions may come to fruition. The first version of Recommendation BT.709 was approved in November of 1993. Obviously, a lot changed between then and the most recent change (April 2002), and now. With Rec. 2020 the ITU wants to establish a direction and guidelines for the next generation of televisions. Will it be 10 years before we see TVs and content matching this standard? Will the standard change? We shall see. It is, for now, a fascinating and hopeful direction.

If you want to read the full Recommendation, the ITU has it as a free download on their Web site.

Got a question for Geoff? First, check out all the other articles he's written on topics like HDMI cables, LED LCD vs. plasma, Active vs Passive 3D, and more. Still have a question? Send him an e-mail! He won't tell you what TV to buy, but he might use your letter in a future article. You can also send him a message on Twitter: @TechWriterGeoff.

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