Televisions and other equipment are now appearing with an 'Ultra HD Premium' logo. What does this mean, and is it worth having? For once, this is a marketing tag that seems to make sense, as Derek Powell explains.  
 
In the early days of digital photography, the specification everyone talked about was resolution. In some ways, it still is — it’s always the top figure quoted. But it has taken a long time for consumers to understand that characteristics like colour rendition, contrast handling, sensitivity and so on are even more important once past a certain basic level of resolution.
 
It’s turning out to be the same story with televisions. You can certainly see the difference that UHD resolution makes, but other factors also go into a making a better viewing experience. UHD TVs are flying off the shelves — but because each set has the same 4K resolution, manufacturers are finding consumers have difficulty in differentiating competing brands and understanding the premium features. Despite the numbers sold, manufacturers are realising that they need to do more to promote benefits other than that UHD resolution to the public.
 
Enter (stage left): Ultra HD Premium.
 
To earn the right to display the spiral rainbow ‘Ultra HD Premium’ logo, a TV or display system has to be able to demonstrate that it meets certain quality criteria in addition to displaying pictures in 2160p resolution. 
 
The main requirements are that the set must be able to display pictures with a Wide Colour Gamut (or WCG) and High Dynamic Range (HDR). Sadly though, many people’s understanding of exactly what these mean is more than a little hazy too. Let’s try to penetrate the fog a little.
 
The quest for realism
At the risk of oversimplifying a complex subject, there are three basic qualities that determine how “realistic” or true-to-life a displayed image seems: 
- how detailed the picture is (resolution); 
- how bright the brightest parts of the picture appear and how much detail you can still see in the shadows (dynamic range); and 
- how many of the possible colours that your eye can see can actually be reproduced (colour gamut).
 
HDR is big news at the moment, so we’ll start there. Readers of Sound+Image may recall that we first introduced the concept of HDR back in July 2009 when we reported on Dolby’s proposal for Dolby Vision, which sought to standardise a way of delivering and reproducing HDR video. We followed that up in April 2011 with a detailed article on the concept of HDR in photography and video; then the next year we looked at first piece of HDR hardware — a $40,000 reference display built by Dolby. 
 
Dolby Vision has been adopted by Warner Brothers and Sony Pictures but there are now a few other competing standards for encoding HDR. The most widely supported currently is HDR10 and support for this is the minimum requirement to gain Ultra HD Premium certification (though some sets can also reproduce Dolby Vision). 
 
The first thing to notice is that the Ultra HD Premium HDR criteria immediately branch into two different sets of requirements. A set can pass the test either by producing an extreme peak level of brightness (more than 1000 nits) and a not-so-extreme black level of less than 0.05 nits (or less than 0.03 nits if it is to be qualified as a mastering display), or by producing a less extreme peak brightness of only 540 nits along with a much more extreme black level of 0.0005 nits. 
 
Why two sets of benchmarks? This clearly comes down to the current state-of-the-art in OLED and LCD display technology. 
 
As it stands, OLED displays can produce much blacker blacks than LCD displays, but can’t produce the extremes of brightness. Practically, this means that that both can produce a wide dynamic range, though to see the full range of detail in the shadows, OLED displays need to be viewed in an environment with quite low ambient light (a dedicated home cinema room is ideal). The lower black level and less extreme ultimate brightness set of standards (0.0005 nits to 540 nits) allows OLED-based displays to qualify.
 
By contrast (pun intended), LCD sets can produce more than 1000 nits of peak brightness but cannot differentiate the extremely low black levels of OLED. This means that LCDs can be used in situations with significantly more ambient lighting and still exhibit a wide dynamic range. LCD panels therefore can more easily qualify using the 0.05 to 1000 nits branch of the Ultra HD Premium regulations. 
 
Living colour
The third set of yardsticks for Ultra HD Premium concerns wide colour gamut (WCG) – and that takes a little more explaining. 
 
There is a jumble of colour standards that are important to display manufacturers, but only a few really matter for this discussion. Back in 1931, the full set of colours (referred to as the colour gamut) that the human eye can perceive was defined and mapped for the first time, on the CIE colour space chromaticity diagram. For the first time, this diagram made it possible to define every visible shade in terms of relatively simple coordinates that relate to Red, Green and Blue primary colours. Despite dating back 85 years it’s still incredibly useful, because every practical colour standard that relates to displays can be mapped on the CIE diagram. 
 
No display currently made can display every visible colour. So each colour standard defined for displays over the years can be mapped as a triangle within the CIE diagram (the outer horseshoe shape in these colour plots).
 
The more of the colours in the CIE diagram that a TV can display the better, since it can recreate more of the colours that our eyes can see in the real world. 
 
Since 1990, all televisions have been made to conform to the standard known as ITU Rec.709, created to set out the standards for digital TV broadcasting, as well as DVDs and subsequently Blu-ray. It covers only 34% of the full gamut of CIE colours (first colour triangle) — less than the previous PAL broadcast standards, so hardly a step forward in TV colour! Nonetheless it remains the most important standard because it allows broadcast programs, DVDs and Blu-rays to look the same (at least as far as colour is concerned) on any brand of TV. 
 
Now, finally, there are new standards emerging that will allow broadcasters to record and transmit a wider gamut of colours.
 
The standard everyone is most excited about is IEC Rec.2020 (second colour triangle, right). This covers many elements but importantly here it covers about twice as many colours as Rec.709, allowing the reproduction of almost 70% of the colour gamut that we can see. (We should point out that this doesn’t mean that anyone has invented any new colours, it means that we can now display deeper, more detailed and more lifelike blues, greens, reds, yellows and so on.)
 
But we’re not there yet! No manufacturer has yet been able to build a consumer-grade display that can reproduce all the colours defined by Rec.2020. So the Ultra HD premium tag sets a much lower bar. 
 
Instead of meeting Rec.2020, TVs with the Ultra HD Premium tag need only be capable of reproducing 90% of the colours in the less demanding DCI-P3 colour standard (see third triangle). 
 
DCI-P3 is the standard used in the Digital Cinema industry and covers just 43% of the full CIE gamut. It’s better than the 34% of colours in Rec.709 (the current digital TV and DVD standard) but nowhere near as demanding as the 69% in Rec.2020.
 
Still, it is a good step forward. In fact most sets using OLED or quantum dots are getting to 99% of P3 colours — much better than the minimum Ultra HD Premium spec. Importantly, digital cinema producers are already creating content that contains the wider colour gamut of DCI-P3 colours, while no commercial producers are yet making content with the full Rec.2020 gamut.
 
So there we have it. If you are keen to buy a 4K set now, it does make sense to look for one that sports the spiral rainbow logo. While nothing is completely futureproof, it is a worthwhile step up to buy a TV that’s at least able to display content that has a wide(r) colour gamut and high(er) dynamic range. Oh, and look for the same logo on Blu-rays and other content — that’ll means they carry pictures that are encoded in HDR and WCG. Derek Powell