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.

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Speakers

Neil Thompson Neil Thompson
Freelance Engineer & Trainer

Webinar: HDR Dynamic Mapping

HDR broadcast is on the rise, as we saw from the increased number of ways to watch this week’s Super Bowl in HDR, but SDR will be with us for a long time. Not only will services have to move seamlessly between SDR and HDR services, but there is a technique that allows HDR itself to be dynamically adjusted to better match the display its on.

Introduced in July 2019, content can now be more accurately represented on any specific display, particularly lower end TVs. Dynamic Mapping (DM), is applies to PQ-10 which is the 10-bit version of Dolby’s Perceptual Quantizer HDR format standardised under SMPTE ST-2084. Because HLG (ARIB STV-B67) works differently, it doesn’t need dynamic mapping. Dynamic Metadata to support this function is defined as SMPTE ST 2094-10, -40 and also as part of ETSI TS 103 433-2.

Stitching all of this together and helping us navigate delivering the best HDR is Dolby’s Jason Power and Virginie Drugeon from Panasonic in this webinar organised by DVB.

Register now!
Speakers

Virginie Drugeon Virginie Drugeon
Senior Engineer for Digital TV Standardisation, Panasonic
Chair, DVB TM-AVC Group
Jason Power Jason Power
Senior Director, Commercial Partnerships and Standards, Dolby Laboratories
Chair, DVB CM-AVC Group

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: User-Generated HDR is Still Too Hard

HDR and wide colour gamuts are difficult enough in professional settings – how can YouTube get it right with user-generated content?

Steven Robertson from Google explains the difficulties that YouTube has faced in dealing with HDR in both its original productions but also in terms of user generated content (UGC). These difficulties stem from the Dolby PQ way of looking at the world with fixed brightnesses and the ability to go all the way up to 10,000 nits of brightness and also from the world of wider colour gamuts with Display P3 and BT.2020 (WCG).

Viewing conditions have been a challenge right from the beginning of TV but ever more so now with screens of many different shapes and sizes being available with very varied abilities to show brightness and colour. Steven spends some time discussing the difficulty of finding a display suitable for colour grading and previewing your work on – particularly for individual users who are without a large production budget.

Interestingly, we then see that one of the biggest difficulties is in visual perception which makes colours you see after having seen bad colours look much better. HDR can deliver extremely bright and extremely wrong colours. Steven shows real examples from YouTube of where the brain has been tricked into thinking colour and brightness are correct but they clearly are not.

Whilst it’s long been known that HDR and WCG are inextricably linked with human vision, this is a great insight into tackling this at scale and the research that has gone on to bring this under automated control.

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Free registration required

This talk is from Streaming Tech Sweden, an annual conference run by Eyevinn Technology. Videos from the event are available to paid attendees but are released free of charge after several months. As with all videos on The Broadcast Knowledge, this is available free of charge after registering on the site.

Speaker

Steven Robertson Steven Robertson
Software Engineer, YouTube Player Infrastructure
Google