The race for what forms the next generation Ultra-High Definition (UHD) TV format focuses on many aspects. While the industry initially concentrated on resolution, it is now apparent that the next generation user experience needs to provide more than just resolution. This article outlines the current issues in the debate. By Hans Hoffmann, European Broadcasting Union (EBU)
For the display manufacturing industry it was relatively easy to upgrade the manufacturing lines to create panels with four times resolution but leaving dynamic range, frame rate and colorimetry untouched. A resolution increase can only be appreciated at short viewing distance (the optimum distance being 1.5 picture heights for a 4K display).
However, most viewers in the home are actually sitting at a much wider distance than 1.5 picture heights, making the benefit of resolution increase marginal. As a result, it became obvious for the industry that further technological developments were required in order to generate the ‘WOW’ effect for consumers and to make UHD a success.
Various industry parties conducted formal subjective tests (ie. EBU, 4EVER, NHK) and it became evident that 4K (‘UHD Phase 1’ in DVB terms) was only the starting point for a kind of full UHD or what we call ‘UHDTV Phase II’ in DVB terms. This phase consists of parameters which create a clearly perceptible improvement in image quality by using (in addition to resolution increase) higher dynamic range (HDR), wider colour gamut (WCG) and higher frame rates (HFR).
The International Telecommunications Union (ITU-R BT.2020) and the Society for Motion Picture & Television Engineers (SMPTE 2036) have standardised the baseband format for UHDTV with higher resolution, higher bit-depth and dynamic range, wider colour gamut and frame rates up to 120Hz.
Dynamic range rather than frame rate?
‘Talking heads’ will not be the driver for UHDTV and all experts are sure about this. Great stories are required to make UHDTV content attractive and increase consumer demand. It is also important that creatives become familiar with the different technical options offered by full UHDTV.
There is debate as to why some industry groups are focusing on the extended dynamic range discussion instead of treating the HFR parameter with similar importance. HFR is a must-have parameter for sports, but challenging to implement due to the enormous bit-rates in the uncompressed domain, and for early UHDTV decoders in the home.
However, it has a high gain in entropy during compression, and viewers simply appreciate HFR sports. Extended or HDR provides an added value to static as well as dynamic pictures, so it is well suited for multiple genres. In addition, movie producers see HDR as the added value for their particular content genre.
Over-the-top content (OTT) providers sell movies as their primary content. Consequently, they also opt for having HDR as their most important parameter (maybe followed by HFR later). From the production grammar perspective, HDR and HFR provide new shooting opportunities and new ways of creative expression. The CE display industry still struggles with the power consumption regulations particular for dynamic range, however, first models with 800 cd/m2 and higher are available.
Camera technologies have met the HDR requirements for some time. From the standards perspective the situation on HDR is somewhat difficult since several HDR systems are proposed and debated in ITU. SMPTE defined one particular HDR system that is backed by at least one manufacturer in the distribution chain.
Other industry partners, such as BBC and NHK (jointly), and others also proposed particular HDR ‘curves’ to the ITU-R meeting which took place in July 2015 (no clear direction was taken). Further work on the harmonisation of standards will be required.
Breaking the single format rule
With all former TV standards the camera and production raster has been similar to the distribution raster. UHDTV will clearly break the rule, and will serve as a master format in production for a variety of distribution formats at different resolutions, frame rates and dynamic range.
Theoretically, the optimum situation would be a system which would adapt the best parameters of UHDTV to the needs of a certain content genre and the capabilities of the distribution chain and the end device. For OTT providers in particular this would mean reducing resolution in situations where bandwidth is reduced (ie. from 4K to 1080p) while maintaining extended dynamic range and frame rates, for example.
UHDTV will need new infrastructures
One of the crucial aspects in the production chain is the need for new high bitrate realtime interfaces that support the various UHDTV parameter sets. SMPTE has defined a whole set of new SDI-based standards and at the NAB 2015 a number of implementations of the 12G SDI were shown. 12G is, however, not enough as a single link when we consider features such as HFR (and UHD-1).
In this case, multilink solutions will still be required (which are not mainstream solutions). On the other hand, the trend for full IP-based infrastructure production systems has also reached out to UHDTV. Several demonstrations have shown 4K over IP, uncompressed or compressed, with a mezzanine compression format.
IP will allow scalability and new workflows, but certainly requires a more complex network management than SDI links and more developments still have to be done (See the current work of the Joint EBU-SMPTE-VSF Task Force on Networked Media for more).
OTT and HBBTV 2.0 with 4K
One of the key questions in the future will be how broadcasters can deliver their content in whatever flavour of UHD they chose to the home. The internet offers a new alternative to satellite for experimenting and delivering test productions or events to the consumer in the home.
Well-known OTT providers such as Netflix and Amazon have already started on this. Broadcasters also have a unique possibility to provide UHDTV to consumers using the new HBBTV 2.0 standard that supports HEVC as a compression system and at least 4K (‘UHD Phase 1’).
Immersive audio: an integral part of the experience
Since the beginning of discussing UHDTV, the requirement for an immersive sound experience was defined. The industry responded with different technologies such as channel-based systems
(e.g. NHK’s 22.2), scene-based audio (Ambisonics) or object-based audio (e.g. MPEG-H, Atmos, etc.).
The primary purpose of these sound systems is to provide a significant better sound experience to the listener. But, there are many more advantages which particularly object-based systems can provide.
UHDTV will not have the same destiny as stereoscopic 3D. It will become a success, but when will it come, with what features and how many compromises in standards will have to be accepted?
A phased approach that introduces a 4K system with dynamic range (a kind of ‘Phase 1 plus HDR’) bears the risk that the industry will stabilise around such a system and introducing a full Phase 2 system (with HDR and HFR) will be significantly delayed. In standards the debate around the various options for extended dynamic range was dragging on already for too long, making it difficult for the industry to come up with implementations – and likely more than one HDR system will be used.
A secret for success for UHDTV will be to engage now with the creative communities and to produce content with the various features that UHDTV supports, such as extended dynamic range as well as higher frame rates and to demonstrate to the public the benefit of the next generation TV experience. The EBU and its activities will support and foster this dialogue, on the one hand by driving for open technical standards, and on the other hand, by demonstrating the benefit of UHDTV with extended dynamic range and higher frame rates to the public.
Join us at EBU Stand 10.F20 to find out more.