Posted by Andrew Cotton on , last updated
There is little doubt that, amongst the broadcast TV community, 2016 will be remembered as the year the industry delivered high dynamic range (HDR) television; and it makes us immensely proud to have played a key part in that. At the start of the year few people had heard about Hybrid Log-Gamma (HLG) HDR. But we end the year with a public trial of a selection of stunning “Planet Earth II” UHD HLG HDR clips on iPlayer, and some amazing audience feedback.
As some of you will have read, the Hybrid Log-Gamma HDR solution, jointly developed by the BBC and NHK, was specifically designed to allow a straightforward migration to HDR-TV production. But even if the technology is straightforward, developing the suite of standards necessary to allow HLG programme production, programme delivery and distribution to the home to become a reality, was anything but straightforward!
The new year started with us reporting the findings from a series of scientific experiments to the ITU-R’s Working Party 6C. These were designed to address the last remaining issues ahead of the inclusion of HLG in ITU-R BT.2100 – the worldwide standard for high dynamic range television production and programme exchange. On Friday 5th February, after one last week of intense discussion, negotiation and debate, and three years after the “kick-off” meeting that launched our research, Working Party 6C finally agreed the preliminary draft new recommendation which was to become ITU-R BT.2100 – approved and published on 5th July 2016. A summary of the findings from those key experiments was published in the ITU-R report BT.2390, and more details were presented in our IBC conference paper in September 2016.
Ordinarily, following the approval of an ITU-R recommendation, one might be able to sit back and relax for a short while to allow the industry to digest the new standard before the launch of any new services. Some of you may remember that ITU-R BT.709, the standard for HDTV, was first published in 1993 – but it was almost 13 years before HDTV services launched in the UK. The world has moved on since then. With HDR televisions already on sale, and growing interest from both programme makers and consumers in the new technology, it was essential to complete the remaining technical standards as quickly as possible to ensure the HDR televisions finding their way in to viewers’ homes are standards compliant, and can access HDR-TV content as services are launched.
After a mammoth effort, DVB (the organisation responsible for specifying the technical standards for television and set-top box receivers in Europe) published their “Blue Book” specification for both UHD HDR and UHD HFR (high frame rate) TV services in November. We are supporting a similar effort in North America’s ATSC, as it’s in all our interests to have as much commonality as possible in the standards that are used around the world.
The final piece of the jigsaw was completed earlier this month, when HDMI extended their 2.0b specification to support HLG.
But standards alone are not sufficient to ensure the successful adoption of a new system – particularly when, in the case of high dynamic range TV, there are two options to choose from in BT.2100: HLG and PQ (Perceptual Quantizer). So one of the most rewarding activities for the team has been working with the BBC’s Natural History Unit (NHU) in Bristol to trial and demonstrate HLG content at industry events throughout the year.
We are fortunate that the BBC’s Natural History programmes are popular around the world. So, just as they did for the launch of HD with the original Planet Earth series, BBC Worldwide were interested in providing the additional funding to allow Planet Earth II to be produced in UHD and HDR – protecting the long-term value of their investment.
So back in March of this year we helped the BBC Bristol post-production team learn how to grade their UHD camera rushes in HLG HDR. The results were spectacular. For the very first time we saw HLG content looking as stunning as PQ graded HDR movies. We knew that technically the picture quality of the two systems is pretty much identical, but until that point all we had seen were our own colour grades. It quickly become clear that as engineers we are better off sticking to designing the technology, and letting those with the craft skills use that technology to create spectacular looking programmes.
The HDR Planet Earth II test clips were first shown at MIPTV in Cannes in April, where they caused quite a stir. Off the back of the positive feedback from MIP, and a series of internal BBC and BBC Worldwide demonstrations, funding was confirmed to produce all six episodes of Planet Earth II in HLG HDR. It's those same MIPTV Rain and Jaguar clips that we are using in the iPlayer trial mentioned earlier.
But delivering an HDR production “eco-system” is more than just standards and content. We need to be able to convert content to and from the HLG production format. So in April of this year we presented a paper at the NAB conference in Las Vegas, illustrating how those mathematical format conversions should be performed – we are delighted to see those format conversions from BT.709 SDR to BT.2100 HLG HDR and between the HLG and PQ HDR production formats are now beginning to appear in products. We extended those mathematical conversions with further research, developing algorithms for SDR “up-conversion” and HDR “down-conversion”, each of which requires a degree of subjective optimisation. Both solutions were presented at the SMPTE Technical Conference in Hollywood in October. We also made HLG test content available under licence to allow others to develop HLG solutions of their own.
Transitioning to HDR-TV is the biggest change to television since the introduction of colour 50 years ago. So, in the space of a blog, it’s simply not possible to do justice to the hard work of all of the BBC R&D teams, our NHK colleagues and those in industry who have contributed to and supported our standardisation efforts. But we should not forget our colleagues in BBC R&D’s Video Coding Project who delivered the HEVC signalling that is used by DVB to identify HLG content, those in the File Based Delivery project who developed the DPP specification for the delivery of pre-recorded HDR programmes and the IP Studio project who are developing the standards for HDR live production over an IP-based infrastructure.
As I write this blog, in addition to the BBC iPlayer trial, there are four experimental UHD HDR TV services available on satellite in Europe, and they all use the HLG standard. The only commercial HDR-TV service that we are aware of, Sky Perfect Japan, also uses HLG. As we enter 2017, let’s hope that a few more of those HDR trials transform in to real services, and we can start enjoying at home, some of the spectacular HDR content we’ve seen in our research labs.
UHD Production Training and Skills from the BBC Academy including:
This post is part of the Broadcast and Connected Systems section