SDR

Video: The Future of Live HDR Production

Posted on by Russell Trafford-Jones

HDR has long been hailed as the best way to improve the image delivered to viewers because it packs a punch whatever the resolution. Usually combined with a wider colour gamut, it brings brighter highlights, more colours with the ability to be more saturated. Whilst the technology has been in TVs for a long time now, it’s continued to evolve and it turns out doing a full, top tier production in HDR isn’t trivial so broadcasters have been working for a number of years now to understand the best way to deliver HDR material for live sports.

Leader has brought together a panel of people who have all cut their teeth implementing HDR in their own productions and ‘writing the book’ on HDR production. The conversation starts with the feeling that HDR’s ‘there’ now and is now much more routinely than before doing massive shows as well as consistent weekly matches in HDR.
 

 
Pablo Garcia Soriano from CORMORAMA introduces us to light theory talking about our eyes’ non-linear perception of brightness. This leads to a discussion of what ‘Scene referred’ vs ‘Display referred’ HDR means which is a way of saying whether you interpret the video as describing the brightness your display should be generating or the brightness of the light going into the camera. For more on colour theory, check out this detailed video from CVP or this one from SMPTE.

Pablo finishes by explaining that when you have four different deliverables including SDR, Slog-3, HLG and PQ, the only way to make this work, in his opinion, is by using scene-referred video.

Next to present is Prin Boon from PHABRIX who relates his experiences in 2019 working on live football and rugby. These shows had 2160p50 HDR and 1080i25 SDR deliverables for the main BT Programme and the world feed. Plus there were feeds for 3rd parties like the jumbotron, VAR, BT Sport’s studio and the EPL.

2019, Prin explains, was a good year for HDR as TVs and tablets were properly available in the market and behind the scenes, Stedicam now had compatible HDR rigs and radio links could now be 10-bit. Replay servers, as well, ran in 10bit. In order to produce an HDR programme, it’s important to look at all the elements and if only your main stadium cameras are HDR, you soon find that much of the programme is actually SDR originated. It’s vital to get HDR into each camera and replay machine.

Prin found that ‘closed-loop SDR shading’ was the only workable way of working that allowed them to produce a top-quality SDR product which, as Kevin Salvidge reminds us is the one that earns the most money still. Prin explains what this looks like, but in summary, all monitoring is done in SDR even though it’s based on the HDR video.

In terms of tips and tricks, Prin warns about being careful with nomenclature not only in your own operation but also in vendor specified products giving the example of ‘gain’ which can be applied either as a percentage or as dB in either the light or code space, all permutations giving different results. Additionally, he cautions that multiple trips to and from HDR/SDR will lead to quantisation artefacts and should be avoided when not necessary.
 

 
The last presentation is from Chris Seeger and Michael Drazin from NBC Universal talk about the upcoming Tokyo Olympics where they’re taking the view that SDR should look the ‘same’ as HDR. To this end, they’ve done a lot of work creating some LUTs (Look Up Tables) which allow conversion between formats. Created in collaboration with the BBC and other organisations, these LUTs are now being made available to the industry at large.

They use HLG as their interchange format with camera inputs being scene referenced but delivery to the home is display-referenced PQ. They explain that this actually allows them to maintain more than 1000 NITs of HDR detail. Their shaders work with HDR, unlike the UK-based work discussed earlier. NBC found that the HDR and SDR out of the CCU didn’t match so the HDR is converted using the NBC LUTs to SDR. They caution to watch out for the different primaries of BT 709 and BT 2020. Some software doesn’t change the primaries and therefore the colours are shifted.

NBC Universal put a lot of time into creating their own objective visualisation and measurement system to be able to fully analyse the colours of the video as part of their goal to preserve colour intent even going as far as to create their own test card.

The video ends with an extensive Q&A session.

Watch now!
Speakers

Chris Seeger Chris Seeger
Office of the CTO, Director, Advanced Content Production Technology
NBC Universal
Michael Drazin Michael Drazin
Director Production Engineering and Technology,
NBC Olympics
Pablo Garcia Soriano Pablo Garcia Soriano
Colour Supervisor, Managing Director
CROMORAMA
Prinyar Boon Prinyar Boon
Product Manager, SMPTE Fellow
PHABRIX
Ken Kerschbaumer Moderator: Ken Kerschbaumer
Editorial Director,
Sports Video Group
Kevin Salvidge
European Regional Development Manager,
Leader

Video: Quantitative Evaluation and Attribute of Overall Brightness in a HDR World

Posted on by Russell Trafford-Jones

HDR has long being heralded as a highly compelling and effective technology as high dynamic range can improve video of any resolution and much better mimics the natural world. HDR continues its relatively slow growth into real-world use, but continues to show progress.

HDR is so compelling because it can feed our senses more light and it’s no secret that TV shops know we like nice, bright pictures on our TV sets. But the reality of production in HDR is that you have to contend with human eyes which have a great ability to see dark and bright images – but not at the same time. The total ability of the eye to simultaneously distinguish brightness is about 12 stops, which is only two thirds of its non-simultaneous total range.
 

 
The fact that our eyes constantly adapt and, let’s face it, interpret what they see, makes understanding brightness in videos tricky. There are dependencies on overall brightness of a picture at any one moment, the previous recent brightness, the brightness of local adjacent parts of the image, the ambient background and much more to consider.

Selios Ploumis steps into this world of varying brightness to creat a ways of quantitatively evaluating brightness for HDR. The starting place is the Average Picture Level (APL) which is what the SDR world uses to indicate brightness. With the greater dynamic range in HDR and the way this is implemented, it’s not clear that APL is up to the job.

Stelios explains his work in analysing APL in SDR and HDR and shows the times that simply taking the average of a picture can trick you into seeing two images as practically the same, whereas the brain clearly sees one as more ‘bright’ than the other. On the same track, he also explains ways in which we can work to differentiate signals better, for instance taking in to account the spread of the brightness values as opposed to APL’s normalised average of all pixels’ values.

The talk wraps up with a description of how the testing was carried out and a summary of the proposals to improve the quantitive analysis of HDR video.

Watch now!
Speakers

Stelios Ploumis Stelios Ploumis
PhD Research Candidate
MTT Innovation Inc.

Video: Content Production Technology on Hybrid Log-Gamma

Posted on by Russell Trafford-Jones


‘Better Pixels’ is the continuing refrain from the large number of people who are dissatisfied with simply increasing resolution to 4K or even 8K. Why can’t we have a higher frame-rate instead? Why not give us a wider colour gamut (WCG)? And why not give us a higher dynamic range (HDR)? Often, they would prefer any of these 3 options over higher resolution.

Watch this video explain more, now.

Dynamic Range is the word given to describe how much of a difference there is between the smallest possible signal and the strongest possible signal. In audio, what’s the quietest things that can be heard verses the loudest thing that can be heard (without distortion). In video, what’s the difference between black and white – after all, can your TV fully simulate the brightness and power of our sun? No, what about your car’s headlights? Probably not. Can your TV go as bright as your phone flashlight – well, now that’s realistic.

So let’s say your TV can go from a very dark black to being as bright as a medium-power flashlight, what about the video that you send your TV? When there’s a white frame, do you want your TV blasting as bright as it can? HDR allows producers to control the brightness of your display device so that something that is genuinely very bright, like star, a bright light, an explosion can be represented very brightly, whereas something which is simply white, can have the right colour, but also be medium brightness. With video which is Standard Dynamic Range (SDR), there isn’t this level of control.

For films, HDR is extremely useful, but for sports too – who’s not seen a football game where the sun leaves half the pitch in shadow and half in bright sunlight? With SDR, there’s no choice but to have one half either very dark or very bright (mostly white) so you can’t actually see the game there. HDR enabled the production crew to let HDR TVs show detail in both areas of the pitch.

HLG, which stands for Hybrid Log-Gamma is the name of a way of delivering HDR video. It’s been pioneered, famously, by Japan’s NHK with the UK’s BBC and has been standardised as ARIB STV-B67. In this talk, NHK’s Yuji Nagata helps us navigate working with multiple formats; HDR HLG -> SDR, plus converting from HLG to Dolby’s HDR format called PQ.

The reality of broadcasting is that anyone who is producing a programme in HDR will have to create an SDR version at some point. The question is how to do that and when. For live, some broadcasters may need to fully automate this. In this talk, we look at a semi-automated way of doing this.

HDR is usually delivered in a Wide Colour Gamut signal such as the ITU’s BT.2020. Converting between this colour space and the more common BT.709 colour space which is part of the HD video standards, is also needed on top of the dynamic range conversion. So listen to Yugi Nagata’s talk to find out NHK’s approach to this.

NHK has pushed very hard for many years to make 8K broadcasts feasible and has in recent times focussed on tooling up in time for the the 2020 Olympics. This talk was given at the SMPTE 2017 technical conference, but is all the more relevant now as NHK up the number of 8K broadcasts approaching the opening ceremony. This work on HDR and WCG is part of making sure that the 8K format really delivers an impressive and immersive experience for those that are lucky enough to experience it. This work on the video goes hand in hand with their tireless work with audio which can deliver 22.2 multichannel surround.

Watch now!

Speaker

Yuji Nagata Yuji Nagata
Broadcast Engineer,
NHK