Video: Broadcast Fundamentals: High Dynamic Range

Update: Unfortunately CVP choose to take down this video within 12 hours of this article going live. But there’s good news if you’re interested in HDR. Firstly, you can find the outline and some of the basics of the talk explained below. Secondly, at The Broadcast Knowledge there are plenty of talks discussing HDR! Here’s hoping CVP bring the video back.

Why is High Dynamic Range is like getting a giraffe on a tube train? HDR continues its ascent. Super Bowl LIV was filmed in HDR this year, Sky in the UK has launched HDR and many of the big streaming services support it including Disney+, Prime and Netflix. So as it slowly takes its place, we look at what it is and how it’s achieved in the camera and in production.

Neil Thompson, an Sony Independent Certified Expert, takes a seat in the CVP Common Room to lead us through HDR from the start and explain how giraffes are part of the equation. Dynamic Range makes up two thirds of HDR, so he starts by explaining what it is with an analogy to audio. When you turn up the speakers so they start to distort, that’s the top of your range. The bottom is silence – or rather what you can hear over the quiet hiss that all audio systems have. Similarly in cameras, you can have bright pixels which are a different brightness to the next which represents the top of your range, and the dithering blacks which are the bottom of your range. In video, if you go too bright, all pixels become white even if the subject’s brightness varies which the equivalent of the audio distortion.

With the basic explanation out of the way, Neil moves on to describing the amount or size of dynamic range (DR) which can be done either in stops, contrast ratio or signal to noise ratio. He compares ‘stops’ to a bucket of water with some sludge at the bottom where the range is between the top of sludge and the rim of the bucket. One stop, he explains, is a halving of the range. With the bucket analogy, if you can go half way down the bucket and still hit clear water, you have 1 stop of dynamic range. If you can then go a quarter down with clean water, you have 2 stops. By the time you get to 1/32nd you have 5 stops. If going to 1/64 of the height of the bucket means you end up in the sludge, your system has 5 stops of dynamic range. Reducing the sludge so there’s clear water at 1/64th the height, which in cameras means reducing the noise in the blacks, is one way of increasing the dynamic range of your acquisition.

Update: Unfortunately CVP choose to take down this video within 12 hours of this article going live. But there’s good news if you’re interested in HDR. Firstly, you can find the outline and some of the basics of the talk explained below. Secondly, at The Broadcast Knowledge there are plenty of talks discussing HDR! Here’s hoping CVP bring the video back.

If you would like to know how lenses fit into the equation of gathering light, check out this talk from Cannon’s Larry Thorpe.

Neil looks next at the range of light that we see in real life from sunlight to looking at the stars at night. Our eye has 14 stops of range, though with our iris, we can see the equivalent of 24 stops. Similarly, cameras use an iris to regulate the light incoming which helps move the restricted dynamic range of the camera into the right range of brightness for our shot.

Of course, once you have gathered the light, you need to display it again. Displays’ ability to produce light is measured in ‘nits’, which is the amount of light per metre squared. Knowing how many nits a displays helps you understand the brightness it can show with 1000 nits, currently, being a typical HDR display. Of course, dynamic range is as much about the blacks as the brightness. OLED screens are fantastic at having low blacks, though their brightness can be quite low. LEDs, conversely, Neil explains, can go very bright but the blacks do suffer. You have to also take into account the location of a display device to understand what range it needs. In a dim gallery you can spend longer caring about the blacks, but many places are so bright, the top end is much more important than the blacks.

With the acquisition side explained, Neil moves on to transmission of HDR and it’s like getting a giraffe on a tube train. Neil relates the already familiar ‘log profiles’. There are two HDR curves, known as transfer functions, PQ from Dolby and HLG (Hybrig Log Gamma). Neil looks at which profiles are best for each part of the production workflow and then explains how PQ differs from HLG in terms of expressing brightness levels. In HLG, the brightest part of the signal tells the display device to output as brightly as it can. A PQ signal, however, reserves the brightest signal for 10,000 nits – far higher than displays available today. This means that we need to do some work to deal with the situation where your display isn’t as bright as the one used to master the signal. Neil discusses how we do that with metadata.

Finishing off the talk, Neil takes questions from the audience, but also walks through a long list of questions he brought along including discussing ‘how bright is too bright?’, what to look for in an engineering monitor, lighting for HDR and costs.

Watch now!
Speakers

Neil Thompson Neil Thompson
Freelance Engineer & Trainer

Video: 2019 What did I miss? HDR Formats and Trends

The second most popular video of 2019 looked at HDR. A long promised format which routinely wows spectators at conferences and shops a like is increasingly seen, albeit tentatively, in the wild. For instance, this Christmas UK viewers were able to watch HDR Premiership football in HDR with Amazon Prime, but only a third of the matches benefitted from the format. Whilst there are many reasons for this, many of them due to commercial and practical reasons rather than technical reasons, this is an important part of the story.

Brian Alvarez from Amazon Prime Video goes into detail on the background and practicalities of HDR in this talk given at the Video Tech Seattle meet up in August, part of the world-wide movement of streaming video engineers who meet to openly swap ideas and experiences in making streaming work. We are left with a not only understanding HDR better, but with a great insight into the state of the consumer market – who can watch HDR and in what format – as well as who’s transmitting HDR.

Read more about the video or just hit play below!

If you want to start from the beginning on HDR, check out the other videos on the topic. HDR relies on both the understanding of how people see, the way we describe colour and light, how we implement it and how theworkflows are modified to suit. Fortunately, you’re already at the one place that brings all this together! Explore, learn and enjoy.

Speaker

Brian Alvarez Brian Alvarez
Principal Product Manager,
Amazon Prime Video

Video: HDR Formats and Trends

As HDR continues its slow march into use, its different forms both in broadcast and streaming can be hard to keep track of and even differentiate. This talk from the Seattle Video Tech meetup aims to tease out these details. Whilst HDR has long been held up as a perfect example of ‘better pixels’ and many have said they would prefer to deploy HD video plus HDR rather than moving in to UHD at the same time as introducing HDR, few have followed through.

Brian Alvarez from Amazon Prime Video starts with a very brief look at how HDR has been created to sit on top of the existing distribution formats: HLS, DASH, HEVC, VP9, AV1, ATSC 3.0 and DVB. The way it does this is in a form based on either HLG or PQ.

Brian takes some time to discuss the differences between the two approaches to HDR. First off, he looks at HLG which is an ARIB standard freely available, though still with licencing. This standard is, technically, backwards compatible with SDR but most importantly doesn’t require metadata which is a big benefit in the live environment and simplifies broadcast. PQ is next, and we hear about the differences in approach from HLG with the suggestion that this gives better visual performance than HLG. In the PQ ecosystem, Brian works through the many standards explaining how they differ and we see that the main differences are in in colour space and bit-depth.

The next part of the talk looks at the, now famous, venn diagrams (by Yoeri Geutskens) showing which companies/products support each variant of HDR. This allows us to visualise and understand the adoption of HDR10 vs HLG for instance, to see how much broadcast TV is in PQ and HLG, to see how the film industry is producing exclusively in PQ and much more. Brian comments and gives context to each of the scenarios as he goes.

Finally a Q&A session talks about displays, end-to-end metadata flow, whether customers can tell the difference, the drive for HDR adoption and a discussion on monitors for grading HDR.

Watch now! / Download the Slides

Speaker

Brian Alvarez Brian Alvarez
Principal Product Manager,
Amazon Prime Video

Video: Content Production Technology on Hybrid Log-Gamma


‘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