The EBU (European Broadcasting Union) has made test content available for assessing different varieties of UHD based on footage shot at last year’s European Athletics Championships in Zurich, Switzerland in August. The idea is to provide broadcasters and operators with a common set of clips shot at a wide range of resolutions, frame rates and other parameters to allow comparative testing by different laboratories with exchange of results. The goal is then to come up with recommendations for what the EBU refers to as UHD Phase 2, incorporating specifications for all relevant parameters, including frame rate and color depth in particular.
There is another critical parameter, dynamic range, for which there are currently a wide range of options deployed in the various UHD trials. For that reason defining a common specification for HDR (High Dynamic Range) is the first priority for the newly formed Ultra HD Alliance comprising 10 companies, mostly Hollywood studios, but also with Netflix and DirecTV representing service providers. At almost the same time another group called the Ultra HD Forum was formed by around 40 technology companies such as Harmonic, focusing on interoperability at the infrastructure level across the whole UHD ecosystem. The two groups have been in discussions to ensure their activities are aligned and that they do not overlap. The EBU will be offering both groups its test sets and be involved in discussions over development of this UHD 2.0.
The point about HDR is that it is not just a display parameter but has to be deployed across the ecosystem and requires compliant cameras, which is why the Ultra HD Alliance has made it top priority. The human eye has the ability to detect a vast span of brightness from objects illuminated just by starlight to the full glare of an overhead tropical sun, representing a range of around 1 billion. But the eye cannot perceive objects at both ends of this spectrum at the same time, since it adjusts by expanding and contracting the iris to adjust light intake. Currently TVs cannot replicate this effect, so that the viewing experience is much poorer than reality, both for dark scenes and in bright sunlight, or even under floodlights. HDR aims to fake reality by exaggerating the contrast among dark and light pixels even though the iris of the viewer is not actually responding as it would under natural conditions.
The other parameters also ripple through the ecosystem, but are easier to cater for, so that for example cameras can readily film at a variety of frame rates. The point of the EBU’s test content is that the quality impact of different parameters can be assessed by many different labs on a large scale to obtain clear results. This entailed taking a large number of different 10 second clips at frame rates of 50, 100, 120, 150, 200, 300 and even 1000. There were just two resolutions, full HD at 1920 x 1080 and UHD at 3840 x 2160, also with several data formats for color. The main point is to compare all these different frame rates for fast moving sport, with the value of the test sets being that they were shot at an actual event that was widely broadcast.
The EBU is able to make these test sets available on a commercial basis because its broadcasting arm, Euronet, owned full rights to the European Athletics Championships and so was under no constraints over which formats it could film or distribute. There has been growing demand for high quality comparative test sets for UHD, given the realization that it will require higher frame rates, but with no consensus over what they should be. The problem is that the optimum set of parameters will depend on the nature of the content, with sports quite likely requiring at least 60 fps and perhaps 120 fps, while slow moving shots will be fine at 30 fps or even 24 fps.
It may well be that while there is a common resolution and HDR specification, as well as color depth, frame rates will vary, so that a sports channel might get more and say an arts channel less.