A preliminary version called Phase A has been brought out now to ensure that forthcoming UHD deployments this year are on the right track and well placed to incorporate further tweaks in the standard, as well as tackling the complex issue of backwards compatibility.

The Forum also needed to demonstrate its alignment with other key emerging standards, especially the sister body the UHD Alliance, which published its first guidelines at CES 2016 in January. The two bodies have some common members such as Dolby and LG and collaborate closely but have remained separate to focus on the two key aspects of the whole UHD value chain. The Ultra HD Forum focuses on the UHD ecosystem from camera to consumer device as well as the delivery infrastructure in between, while the UHD Alliance is more engaged with the content creation and playback issues.

To some extent the Alliance is looking ahead to how UHD services should become while the Forum is doing the dirty work and heavy lifting associated with ensuring that UHD can slot into existing infrastructures and be backwards compatible with display devices and other components already installed. This distinction is reflected in the memberships even if these are converging somewhat, with the Alliance comprising content producers, distributors and device manufacturers, which have coalesced to define the “Ultra HD Premium” brand of standards. These standards impose minimum specifications and technological benchmarks that have to be met for content development, production, streaming, replay and the display devices themselves.

The Forum is more dominated by the big infrastructure players like Harmonic, Ericsson and Technicolor, as well as pay TV operators such as Comcast and AT&T’s DirecTV seeking to deploy UHD services in the real world. There is of course considerable overlap in the activities, with both particularly engaged with HDR since that emerged as a major ingredient of the overall next generation immersive experience that the whole UHD standards group is supposed to usher in.

Thierry Fautier, President of the Ultra HD Forum, emphasized that the guidelines were a combined effort “synthesizing contributions from content providers, broadcasters, service providers, professional equipment manufacturers, technology solution providers, CDNs, chip-makers and device manufacturers.” He added, “this would not have been possible without close collaboration with our colleagues at MPEG, DVB, DASH-IF, ATSC, SCTE, SMPTE, CableLabs, NAB and the UHD Alliance, with whom strong liaisons are being built.”

The point here is that the other bodies were responsible for actual development of the standards, while the Forum and the Alliance are charged with selection, alignment, compatibility and implementation. So naturally the respective guidelines published by the Alliance and Forum are compatible, but with the difference that the latter has to embrace some legacy standards.

Both therefore include display resolution at the 3840 x 2160 pixels associated with 4K, color bit depth of 10 bits, color palette with Wide Color Gamut (WGC), and signal input based on the BT.2020 color representation and 3 color spectrum. The use of 10 bits for color depth allows 1024 shades of each color rather than the 256 currently with 8 bits. The BT.2020 color representation with a display reproduction comprising more than 90% of DCI-P3 colors is essentially the standard developed by the US Film Industry to come closer to the color spectrum perceived by humans with normal vision.

When it comes to HDR the Alliance specified two options to cater for the starkly different display characteristics of LED and OLED displays. It selected the SMPTE ST2084 EOTF version for both cases, but with a contrast performance either a minimum 1000 nits peak brightness and less than 0.05 nits black level or minimum 540 nits peak brightness and less than 0.0005 nits black level. The first of these is for LED displays, which are capable of reaching higher luminance levels but weaker blacks and so can do better on the former while requiring a less strict standard for the latter. OLED can go significantly deeper on black levels, enabling display of more realistic darker scenes, but cannot go as bright.

There are other contending versions of HDR, including HDR10 adopted for Blu-ray disks and already backed by many studios as well as Samsung and Sony. Dolby has its own format for OTT services called HDR, while Hybrid Log-Gamma (HLG) has gained some ground with the ITU-R as well as having been adopted by the Japanese Association of Radio Industries and Businesses (ARIB).

Indeed HDR could become the next major format battlefront for video, which both the Forum and the Alliance are anxious to avoid. But the Forum has to contend to a greater extent with legacy and so unlike the Alliance includes SDR as an option within its guidelines, so that UHD services will work with existing displays.

Another difference is that the Forum includes 1080p as an option as well as 3840 x 2160 for the resolution. But this is only for services that also incorporate WCG and HDR, in which case they can be deemed to be next generation and probably actual yield a superior viewing experience to say full UHD 3840x2160 resolution with just SDR. The Forum stressed that 1080p without either WGC or HDR is considered to be only an HD rather than UHD format and indicated that 1080p would be dropped from the next Phase B guidelines due out later this year or early 2017.