HDR is the new black

TVB Europe

High Dynamic Range is touted by some as the best thing since the introduction of colour but will all HDR versions of it be equal? 

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The potential to offer High Dynamic Range (HDR) is considered by many broadcasters and OTT players to as a key value proposition in the move to upgrade viewers from HD. Both Netflix and Amazon Prime are offering UHD HDR remastered videos and shooting original content in the format. For little to no additional bandwidth, viewers can see a difference over normal HD at any viewing distance. There can be few if any manufacturers with a stake in Ultra HD not also offering a means of getting HDR through the chain. As Simon Fell, EBU director of technology and innovation neatly put it: "HDR is the new Black”. 

While the average TV today has a brightness range of around 100 candela per square metre (known as nits), HDR displays could offer 1,000 nits, 1,500 nits or more. That’s still far less bright than some things you might see in real life, but the increased luminosity will still mean a far more realistic picture. The difference is immediately apparent when looking at images of water, or of clouds, for example. 

The introduction of HDR also ramps up the colour. HDTV is based on an 8-bit system, meaning there are up to 256 shades of each colour available (in theory – in practice around 220, for historical technical reasons). But with HDR, a 10-bit system allows an increase in the colour gamut to 1,024 shades of each colour. Combine increased luminosity and richer colour with the greater resolution 4K can provide and HDR could be as important an experience as the introduction of colour was 80 years ago.

“It's hard to believe unless you experience it,” claimed Dominic Glynn, Pixar's senior scientist who guided the HDR finish for Inside Out. “We can show the audience colours they've never seen before.”

But any mainstream TV industry shift towards HDR will be delayed as technical standards are agreed. “How you create that HDR data chain is a question that needs a lot more attention,” said Sean McCarthy, engineering fellow at Arris. “It’s not as interesting as the pretty colours and stuff, but it is important.” 

“HDR is the area with the least agreement across the board for a single standard,” notes Rowan de Pomerai, senior technical manager, Digital Production Partnership which wants to design a single UHD HDR specification for programme delivery.

SMPTE will publish a Study Group report on the current state of the HDR ecosystem for content mastering and broadcast shortly. It has already published two HDR standards related to content mastering: ST-2084, for the Electrical Optical Transfer Function (EOTF); and ST-2086, to define static metadata. SMPTE is now working on a standard for dynamic metadata needed to support SDR and HDR content at the same time. 

Dolby helped deliver SMPTE 2984 implemented in its own Dolby Vision system – this SMPE standard has been adopted in the Blu Ray Disc Association. Content owners including most of the studios are starting to remaster older content for HDR-compatible UHD Blu-Ray. 

However broadcasters BBC and NHK have expressed concerns that this standard is not ideal for the workflow of live TV where a single broadcast version needs to deliver acceptable quality on both HDR and standard dynamic range (SDR) displays, minimising additional bandwidth. This is a different challenge to on-demand content or packaged media, where different versions can be created to optimise the quality for both SDR and HDR, and selected for playback appropriately. 

So NHK and BBC have created the Hybrid Log-Gamma HDR solution to try and solve this issue. It intends to ensure that an UHD HDR signal can be displayed not only by HDR-enabled devices but in the vast majority of household sets with the SDR range of HD. It is one of a number of options being considered by the ITU for standardisation, but even then it then needs to be implemented into TV sets. 

Which brings us around to the consumer messaging: TVs are already being marketed as supporting HDR, but which standards are they supporting? How ‘High’ is the dynamic range, with brightness levels of displays varying from 400 NITs to over 1,000 NITs and giving dramatically different experiences for the viewer. 

“Currently, the clearest proposition is the BDA, with Ultra HD Blu-rays reportedly launching before the end of the year,” says DTG chief technology officer Simon Gauntlett. “The HDMI specification was updated to 2.0a, to deliver the metadata to the displays to enable SMPTE 2084 presentation. This suggests that if the display supports HDMI 2.0a it should decode HDR content correctly . However the message to consumers is far from clear.” 

Peter White, CEO and co-founder, Rethink Technology Research, agrees: “HDR is being seen by many TV manufacturers as something that they will introduce after 4K. That’s the wrong approach, but the TV manufacturers hold a lot of sway. In the US, manufacturers are selling ‘4K’ devices that are not UHD. The fight to differentiate among those players is pushing ‘4K’ rather than UHD, in the same way that they tried to push 3D when no-one was ready for it.” 

The UHD Alliance which includes members of the consumer electronics community and Netflix is also trying to specify UHD, which will include HDR requirements. All eyes will be on the CES show in Las Vegas in January where the next crucial stage of the UHD HDR debate will be played out. 

Live HDR 

For live broadcasting the issue is more complex. The main outside broadcasters including Visions, Telegenic and Arena, are testing live HDR (UHD and HD chains) for clients including BT Sports. Delia Bushell, managing director at BT TV said at IBC that the company is looking to add HDR capabilities to its Ultra HD 4K channel within two years.

How might live HDR broadcasting be handled? Technicolor has a new server-based version of its Intelligent Tone Management software that scales standard dynamic range source material (such as 4K 60p) for HDR use. The aim is to allow sports or live event productions to continue use current cameras and infrastructure at a venue with the upscaling occurring on the final output mix.

Importantly, the upscaled signal is routed through an Elemental encoder which spits out a single stream which can be received in HDR and SDR which for a broadcaster reaching the mass of households with plane old SDR screens is a must.

“You can't justify the cost of running two infrastructures so the distribution system needs to be combined,” says Mark Turner VP, Business Development & Relationships. “The cheapest way of implementing HDR live is for the mix to happen as normal with the final mix upscaled. OB engineers can adjust the settings in realtime or apply different HDR settings to different sports.”

Dolby offers an alternate route to HDR. It has worked with Grass Valley to introduce a process for individual camera feeds. Grass Valley has a XDR software-upgrade option for all LDX 86 Series cameras working in single-speed formats (HD/3G/4K). This is claimed to deliver 15 F-stops of sensitivity to the home with a suitably equipped HDR set. At IBC the feed was encoded along with the HDR information by a Muse Live encoder in from Envivio (now an Ericsson company). A licence upgrade from Grass Valley is required to unlock it on all LDX series, plus you need a monitor to view it on – and Dolby has those.

Sony pledged its commitment to incorporate HDR capabilities into more of its production equipment. It has trialled 4K HDR capture with Dorna Sports using HDC-4300’s at the 2015 British Grand Prix MotoGP.

Michael Harrit, Marketing Director, Sony Europe, said, “We have built HDR into leading production tools to create an HDR end to end production workflow from acquisition to delivery to the living room.”

RED Digital Cinema also has a live HDR output solution allowing users to simultaneously monitor both the standard dynamic range and HDR images of the same shot on-set, in real-time. That will allow users to see more of what the sensors on their cameras are capturing – from the deep shadows to bright highlights. Like Dolby, the RED solution meets the SMPTE 2084 standard.

Creatively, what can HDR do?

There are also some obvious ways in which HDR could enhance specific types of programming like sports: it means you can actually see a flying golf ball against the sky; or watch a football match in a stadium half in and half out of bright sunlight without experiencing that clunky moment when the camera has to jump through five or six stops as the play moves in or out of light or shade. 

Pixar's Rick Sayre says that on Tomorrowland, on which he was Digital Imaging Consultant, the HDR “revealed a gleam in the eyes of the actors which it has not been possible to show before.”

“The eye tends to be drawn to the highlights which can pull a viewer out of the story,” says cinematographer Steven Poster. “We may see some gimmicky HDR that has nothing to do with storytelling. Just because we can now see through a brightly lit window exterior doesn't mean that we should.”

“As time goes on, filmmakers will take advantage of the expanded colour space offered by the use of laser light source technology to bring colours and contrast never seen before on a cinema screen,” says Stuart Bowling, Director, Content and Creative Relations at Dolby.

“Animation is an amazing way to apply wider colour gamut to audiences,” he adds, highlighting a scene in Inside Out which exploited Dolby Vision’s wider colour gamut capabilities. This is when Joy and Sadness enter the Subconscious and the production design called for the look of a black-light room— glowing, colourful, and highly saturated.