The State of UHDTV

There's more to Ultra HD than 4K.

In the last 12 months 4K video has been a hot topic. There are now a range of cameras that can capture professional quality 4K video and there are various 4K monitors and TVs, the majority of which support the 3840×2160 flavor of 4K. You can even capture 4K video on smart phones and compact cameras.

Content creators need to remember that for consumers the next big thing is not only 4K but UHDTV and that means improved dynamic range and high frame rates. The increase in resolution in these three areas will really make consumers notice the improvement in quality that UHDTV offers and should make it compelling. Remember that it took a very long time for HD to be adopted so if industry wants Ultra HD to become standard then this is not the time to be ignoring what will soon be standard features for UHDTV.

Improved dynamic range is achieved via Wide Color Gamut (WCG) through adoption of the BT.2020 color standard and improved bit depth (10-12 bits per color channel). This allows a much wider range of colors to be reproduced at the display. However, the new hot topic is High Dynamic Range (HDR). The term High Dynamic Range is being used to mean something slightly different to WCG; in this case it refers to contrast and brightness.

LCDs traditionally find it difficult to display "black blacks" because of leaks and reflections from the backlight which is a global light source. OLED based displays, on the other hand, can output light at any location on the display but there is a limit to how bright each pixel can be. LCD's use of backlighting makes locally dark areas difficult to reproduce. The latest LCD TVs have segmented backlights allowing local adjustments to brightness and therefore the possibility to have darker regions on one side of the screen and brighter regions on the other.

A new certification from the UHD Alliance was announced at the start of 2016 called Ultra HD Premium. It sets a minimum specification for Ultra HD based on Wide Color Gamut (WCG) and High Dynamic Range (HDR) but does not mention High Frame Rate (HFR) or audio. Sony have already stated they will be using their own 4K HDR branding even though its higher end TVs would pass the criteria.


One of the reasons for this new certification is to avoid the potential "HDR ready" labelling on products that don't really display HDR but render SDR video from HDR data. Perhaps confusingly, UHD Premium defines two specifications for contrast designed for the two most popular TV display technologies (LCD and OLED).

Although there are several 4K TVs available now, only higher end models have HDR, HFR or even WCG support. The rest are simply 4K with 8 bit color primaries under good old BT.709; most UHDTVs from 2015 would not pass UHD Premium certification. It's easy to see why HDR is receiving more attention than WCG. Remember that TVs are RGB devices but video is typically coded using YCbCr at 4:2:0 so color resolution is already somewhat compromised. 4K is the eye popping spec because consumers will easily perceive strong differences between HD and UHD displays even without HDR or WCG.

There are two competing formats for HDR, Dolby Vision (DV) and HDR10. DV is 12 bit; HDR10 is 10 bit. DV requires use of a compatible TV but is graded on a scene by scene basis whereas HDR10 is graded once for the whole movie. DV is clearly the superior spec on paper but whether you notice it depends on the content type and capabilities of the TV you are viewing it on.

High Frame Rate (HFR) refers to 60Hz and higher frame rates but realistically it will only be 60Hz and perhaps some content at 48Hz. The main beneficiaries of HFR will probably be sport and live broadcast TV. People still associate film look with 24Hz so apart from The Hobbit, there probably won't be many HFR movies soon.

For full UHDTV we need to consider the classic content chain model otherwise we have the chicken and egg problem; we need the products but we also need the content.

1. TVs

Some high end TV models already support 4K, HDR/WCG and HFR. 60Hz TVs have been around the block for some time now aimed at improving the motion performance by interpolating new frames or double/quadruple scanning of frames. High end models include Samsung SUHD models, Sony XBR/XD and LG EF. At this time don't expect to see any models supporting UHD Premium at less than 55 inch. Expect many models to have disturbing artefacts when scaling up legacy content from HD to 4K, particularly around the edges of moving objects.

2. Content

H.265, also known as HEVC, is the next evolution of video codecs for delivery. Achieving better compression for higher resolutions than MPEG-4/H.264; it is fundamentally similar, with larger block sizes and improved intra prediction responsible for most of the compression improvement. Most of the adjustable parameters are the same so it will be easy for content producers to switch over to the new codec with little changes to their workflow. We can easily use H.265 in an MP4 container so most existing tools will continue to function.

Online

Streaming by Netflix at 4K uses H.265. HDR10 and Dolby Vision streams are now being served. Amazon Prime are currently supporting 4K HDR streaming with Samsung SUHD model TVs.

Disk

Ultra HD Blu-ray is 4K only; there will be 3 sizes of disk for 3 bit rates. 4K Blu-rays all use H.265, disk players have a built in codec so TVs won't need it. UHD Blu-ray players will play legacy BDs. WCG is supported via BD-HDR or Dolby Vision; all Blu-rays include HDR10 as the baseline HDR encoding.

The first BD players are being released now at premium prices, as you would expect. Initial prices are expected to be 2 to 3 times the cost of HD Blu-ray players. At CES2016 it was being said that disks will be a bit more expensive but are aimed at "comparable" cost. However, prices in the US are about 1.5 times the cost of HD Blu-ray disks and in the UK are twice the cost so we will have to wait and see how that changes as demand increases.

3. Interconnects

DisplayPort 1.3 supports 4K at 120Hz. DisplayPort 1.4 supports up to 8K HDR at 60Hz. DP 1.4 can be supported over Thunderbolt 2 and USB-C.

HDMI 2.0 supports 4K at 60Hz. All HDMI cables are the same so you don't need new or "faster" cables. HDMI 2.0a adds supports for HDR (DV doesn't need this but can make use of it); again there is no change to the cables.

4. Audio

Finally, we shouldn't forget that sound quality is also vital to the experience and video doesn't stand by itself. Blu-ray is supporting object-based immersive sound; 22.2 channel is already available on some HD Blu-ray disks.

 

The Final Word

If you're planning to buy a UHDTV, but not a high end model then wait a little longer and get a 4K, HDR, WCG, HFR model.