HLG, Advanced HDR and the long road ahead for HDR broadcasts in the U.S.

While many trials have taken place, and improvements and updates are being made to formats like HDR10 and Dolby Vision, it’s still not clear which format will win (or if any one format really needs to win). Image: LG

HDR may be the brightest star among the Ultra HD suite of features but the imaging technology has a ways to go before it can brighten broadcast television content in the U.S.

The current narrative places HDR (or high dynamic range) ahead of 4K resolution in terms of improving picture quality for the average viewer. HDR, in a nutshell, enables brighter colors and deeper contrast, making video more vivid. Separate but often associated with HDR is the expanded color range is known as wide color gamut, or Rec. 2020 within the UHD standard, which is ahead of the Rec. 709 achievable with HD.

4K, meanwhile, significantly boosts the pixels per square inch, but fails to make much of a difference to viewers using TVs smaller than 60 inches that are placed more than 6.5 feet away.

Still, 4K UHD TV panels, many with HDR, are becoming ubiquitous. IHS predicted that 4K TV shipments in North America will reach 25.9 million in 2020. But it’s really HDR, which often goes hand-in-hand with 4K or UHD TV sets, that’s attracting the most attention.

Streaming services like Amazon and Netflix have been pushing HDR content. Netflix recently announced it was re-releasing its Marvel original series in HDR, and the service hasn’t tried to hide the fact that HDR is a higher priority than 4K.

"It's less about packing more pixels on the screen like the move from HD to ultra-HD 4K was, it's about extending the total range of those pixels ... what that means is there's a much more photo realistic image that you're watching which is much more representative of the total range that your eye can see when you're just looking around in real life," said Chris Jaffe, VP of user interface innovation for Netflix, during last year’s Mobile World Congress in Barcelona.

Of course, broadcasters in the U.S. are also keen to set their transmissions in HDR, but the process won’t be as simple for them. As Techradar pointed out, the screen to screen logistics for broadcasters are much more difficult than for streaming services, and broadcasters have a tougher time addressing issues of metadata (which is required by HDR formats like HDR10 and Dolby Vision) and backward compatibility.

For broadcasters and programmers, it will be important to know about all the varying HDR formats so they can navigate that ecosystem and pick the best option that fits with their production workflow and reaches the most consumers.

As the ATSC 3.0 standards for next-generation broadcast television near finalization and undergo the public rulemaking process at the FCC, HDR is a primary consideration.

The video group within ATSC—the organization advancing development of the 3.0 standards—has agreed on the use of the HEVC video codec, Main-10 profile, Main Tier, and that HDR solutions will need to be 10-bit and compatible with the ATSC 3.0 video specification. ATSC President Mark Richer said the ATSC 3.0 A/341 standard supports use of HLG EOTF, PQ EOTF, and PQ EOTF with optional static metadata sometimes referred to as HDR10, and that the group does not recommend use of one over the other.

“We believe the inclusion of HDR capabilities in ATSC is very important. It will facilitate broadcast transmission of stunning images to the consumer,” Richer said.

Meanwhile, Dolby is working with camera manufacturers and broadcasters to create equipment that will allow producers to create Dolby Vision PQ (perceptual quantizer) signals that can be transmitted and optionally have the emission encoder include content metadata, according to a recent white paper.

But there are other newer formats of HDR that could help advance HDR broadcast content. In particular, HLG (hybrid log gamma) and Advanced HDR propose interesting options.

HLG

HLG is an HDR format developed jointly by the BBC and Japanese broadcaster NHK. The companies decided to pursue HLG development in order to create an HDR format that fits in with their current 10 bit infrastructure and to overcome the burden of metadata.

“We concluded that any approach couldn't rely on end-to-end metadata as metadata often gets lost or becomes out-of-sync with the content as it passes through the production chain and that standard presentation techniques such as mixing video sources become overly complex with metadata,” the BBC wrote on its website.

Thus far, HLG hasn’t made too many inroads in the U.S. but the format did factor heavily into an HDR broadcast trial that PBS’s Advanced Format Center organized last September.

Renard Jenkins, vice president of operations at PBS, described the work PBS did in coordination with DTS and DPA Microphones and why PBS selected HLG for the trial. “We wanted to test HLG because the primary focus in North America has been on PQ and we wanted to see what HLG could do,” Jenkins told FierceBroadcasting, adding that PBS wanted a format that was relatively simple to pull off.

“The ease of processing was one of the things that drew us to [HLG] and how easily we could give the specifications to [the processor] and have them return a product to us ready to go,” Jenkins said, careful to point out that PBS’s goal was not to prove HLG as viable for use in the North American market.

The trial took place in a 10,000 square-foot warehouse near Washington, D.C., and featured professional drummer Dennis Chambers and some local musicians. The trial was meant to test not only the visual capacity of HLG but also immersive sound aspects. Deluxe was brought in to process the live-to-memory visuals in HLG and other firms were asked to help process the audio. Once PBS had a finished product, it worked with SES to perform a live transmission through a Maryland-based uplink on a continuous loop to PBS affiliate stations in the St. Paul, Minnesota and Jackson, Mississippi.

Ericsson provided the 8200 IRD which was used for the satellite downlink and ViXS provided the decoder set-top box.

In Mississippi, the receiving set could accept the HLG-transcoded HDR video and only sound bar-quality audio. In St. Paul, the receiving set could only accept down-converted SDR, but accepted the full 11.1 array for audio.

Jenkins said the utilization of HLG was relatively straightforward. He said HLG is “almost there but not quite,” based on what he saw during PBS’s trial last summer. He said the SDR downconverted version seemed to “lack a little punch” and said that the brighter luminants of HLG seemed a “little washed” to eyes accustomed to the 709 color space. But he added that HLG was able to produce the intense blacks needed for the better contrast associated with HDR.

Indeed, Dolby said that HLG’s backward compatibility is only for SDR UHD televisions that natively understand Rec. 2020 color, representing a fairly small portion of TV sets currently in the market.

“I don’t see North America adopting HLG in the very near future. But I personally believe that there is merit in what the BBC and NHK have attempted to do with HLG. The idea of having something that is backwards compatible to an SDR television set is a really good thing. But it needs to be done very, very well to be successful. The SDR has to feel like it is within the 709 color space, and individuals have to feel like they’re not losing anything with the downconvert,” Jenkins said.

Advanced HDR

Advanced HDR is another option under development for delivering HDR content via broadcast.

Advanced HDR is designed to be a distribution platform that can take in any form of content and ensure that it is accurately received by the backend device. That means it can take in HDR10, PQ or SDR, and all of it will get normalized.

Josh Limor, vice president of technology, ecosystem and development at Technicolor, said that Advanced HDR has two ways of deploying SDR upconversion: It can either be a part of the headend distribution and/or it can be part of the silicon itself. Broadcasters interested in a more consistent experience for both SDR and HDR would do the upconversion on the silicon, whereas broadcasters who only want to send out HDR content would do the upconversion at the headend.

Technicolor has been seeking content partners to use upconversion to get to live HDR in a quicker and less expensive way, particular in terms of sports where switching out all the equipment in a stadium or arena would be a costly undertaking.

In September 2016, Technicolor partnered with Time Warner Cable to broadcast an MLB game in HDR by upconverting the SDR signal. Technicolor’s upconversion technology was also used for NBCUniversal’s 2016 Summer Olympics coverage available on VOD.

Technicolor said Advanced HDR is completely compatible with distribution platforms including cable, satellite, OTT and ATSC 3.0 broadcast.

“Our desire is to see everything native HDR at some point in the ecosystem, but right now we have to fill the gap. As we saw with the transition to 4K, the lack of content was one of the biggest limiters to deployment. Having high-quality upconversion allows the deployment to start now,” Limor told FierceBroadcasting, adding that HDR won’t likely get off the runway if content creators hold off for the perfect “10,000 nit” version of the technology that could be 10 years down the road.

When LG announced its new TV sets at CES in January, the company said that those devices would be ready to support Advanced HDR. Limor didn’t mention any other OEMs by name, but said there are about 14 SoCs for deployment and circuit boards for TVs and streaming devices that already include Technicolor’s technology.

Limor said that speeding HDR content to market is one part of technologies like Advanced HDR, but another point is addressing growing HDR interoperability concerns in a divided device ecosystem. HLG broadcasts might be received by PQ devices, while SDR devices are still in the ecosystem, trying to remain at a cheap price point and need to do tone mapping.

“All of these are flawed concepts as far as what the consumer electronics mentality is,” Limor said.

The road ahead for HDR

While many trials have taken place, and improvements and updates are being made to formats like HDR10 and Dolby Vision, it’s still not clear which format will win (or if any one format really needs to win).  As the Verge pointed out, HDR10, Dolby Vision, HLG and Advanced HDR could be largely cross compatible. And it could be that the first steps for HDR broadcast in the U.S. won’t be beholden to the UHD standards.

In terms HDR broadcast’s future in the U.S., Jenkins believes the first step will be HD HDR.

“I think that’s an easier lift for the U.S. to deal with. We’ve got a lot of HD infrastructure here and to change and to move things into the UHD world along with high frame rate, HDR and wide color gamut. That’s so much of a heavy lift. So I think it will be a phased approach that the U.S. takes,” Jenkins said. “I really don’t see that resolution change happening until two to three years from now.”

That said, Jenkins said that ATSC 3.0 seems to be pointing toward HDR10 or Dolby Vision PQ. With the ATSC 3.0 finalization timeline coming up, the next-gen standards will soon become clearer in terms of HDR. And with ample options out there for HDR formats, there’s hope the HDR—be it HD or 4K UHD—can make its way into enough live broadcast content to the format relevant for consumers.

This article was updated to clarify that HDR and WCG are independent of one another.