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Are we HDR ready?

Matthew Goldman, SVP Technology, MediaKind
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The media industry has long championed the merits of Ultra-High Definition (UHD) with High Dynamic Range (HDR) and without doubt, it offers the unprecedented ‘wow’ factor that delivers the all-important immersive, next generation viewing experience that consumers are demanding. According to a May 2018 Futuresource Consulting report, more than 100 million 4K UHD televisions will be sold worldwide this year, with around “60 percent of 4K UHD sets sold this year [including] HDR.” 

The more people see of HDR, the more they want it – and it’s a view held by broadcasters, content owners, service providers and consumers alike. However, while there is a desire to provide, deliver and receive content in this format, there are still a number of technical challenges to overcome before we see widespread adoption.

For clarity, HDR as a system refers to the combination of HDR transfer function, Wide Color Gamut (WCG), and 10 bit sample (quantization) depth.

Too many formats

While significant strides have been made this year, the main issue is that there are still too many HDR formats in existence. This has caused industry confusion about how to proceed and delays in deployment.

HDR10 was the first major format, initially championed by the Blu-ray Disc Association and the Consumer Technology Association, and it is the mostly widely used HDR format for motion picture and TV episodic productions. This format uses the perceptual quantization (PQ) transfer function (originally developed by Dolby Labs and later standardized as SMPTE ST 2084 and Rec. ITU-R BT.2100) along with static mastering display color volume metadata (SMPTE ST 2086 plus additions), which provide descriptive information about the color primaries, white point, and minimum/maximum luminance.

Another popular HDR format is Dolby Vision, which uses the PQ HDR transfer function along with dynamic content-dependent metadata (SMPTE ST 2094-10) that could change on a frame-by-frame basis. Dolby Vision is claimed to have superior operating characteristics and to deliver a richer consumer experience versus the other HDR formats. However, some manufacturers have balked at the per device license fee, especially at the lower end of the consumer electronics market.

HDR10+, another PQ-based system with dynamic metadata (SMPTE ST 2094-40), was subsequently introduced by Samsung and has since garnered support from Panasonic. Content producers and distributors such as Amazon, Warner Brothers and 20th Century Fox have also shown their commitment.

Hybrid Log-Gamma (HLG), an alternative HDR transfer function that also happens to be royalty free, was jointly developed by the BBC and NHK, the national broadcasters in the UK and Japan, and later also standardized in Rec. ITU-R BT.2100. HLG10 has emerged as an early favorite among the HDR formats for live TV production, partially because it does not use metadata and therefore none of the complications around maintaining metadata exist. Time will tell if this trend will continue.

The situation today

The above four HDR systems, along with the baseline system PQ10 (PQ HDR transfer function, WCG, 10 bit, without metadata) and Philips/Technicolor SL-HDR1 are the six most common HDR systems being discussed in the industry. In many cases, most – if not all – of these systems have been (or will soon be) specified by the major regional industry associations, including the ATSC, DVB, and SCTE/ISBE.

So here we are: six different HDR systems. While the Ultra HD Forum has worked diligently to create and publish guidelines on how to implement these systems, having six major options for HDR has created industry confusion nonetheless and, in fact, has delayed HDR deployments. Which format is the best to use for the use case being considered? Which format will survive in the long run? Which format produces the most compelling HDR quality? Or are they all relatively the same? Questions like these abound even if a single ‘house format’ is selected to simplify the workflow. Moreover, the live mixing of content in standard dynamic range (SDR) – what we now call the dynamic range of all the legacy displays, and TV and movie studio production systems prior to the introduction of the new HDR technologies –with content produced in the various HDR systems, seriously complicates live production.

Live production and delivery challenges

Another primary challenge involves increasing the availability of 4K content. Without doing so, it will prove extremely difficult to achieve widespread, mainstream adoption of 4K. While indications show pre-produced content in 4K is already increasing in availability, this is not the case for live events. Live content requires everything to work flawlessly in real-time – there is no possibility for a ‘let’s do it again’ retransmission.

In addition to the obvious bandwidth challenge with producing and delivering 4K (3840×2160 resolution @ 50 or 60 frames/s progressive requires eight times the bandwidth of standard 1920×180 HD resolution at 50 or 60 frames/s interlaced in baseband or three to four times more bandwidth when compressed), the situation is exacerbated if HDR is included. This is due to not only the number of different formats available, but also because of the issues around mixing live with pre-produced content that has been produced with different light levels. The carriage of HDR metadata through the live plant has some complications as well – although if the HLG10 or PQ10 formats are used, no metadata is used.

Ready for adoption?

However, there are a number of solutions entering the market to help solve some of these challenges. For example, live real-time ‘color volume’ mapping is emerging, converting SDR to HDR (inverse tone mapping), HDR to SDR and between different light levels of HDR. Tone mapping (inverse or forward) can be used to mix live and pre-produced content, enabling the industry to deliver it in UHD, end-to-end. Content producers can determine the native format, while broadcasters are able to perform conversion as necessary. This removes many of the barriers caused by having multiple formats by converting all content to a common house format.

Earlier this year, the Ultra HD Forum released its UHD Phase B Guidelines (1.0), which aim to help the industry address some of the remaining challenges that still exist, including the addition of dynamic HDR metadata systems and high frame rate (HFR) systems. In the near term, however, it is likely that both 4K (2160p50/60) and full HD (1080p50/60) with the more basic HDR systems (HLG10, PQ10 or HDR10) will continue to dominate as broadcasters, service providers and operators need to offer services that deliver the most immersive viewing experiences for end-users, with the simplest implementation.

Yet, while technical challenges remain, HDR can be monetized successfully because the impact on the viewing experience is very noticeable, often more so than the difference between 1080p and 2160p (4K) spatial resolution. We already are seeing how some broadcasters are delivering content in 1080p50/60 HDR. 4K displays do a wonderful job of upconverting this to 2160p, and assuming the 4K display supports HDR, we can enable the ‘wow’ factor that in many consumer viewing environments is very close to native 4K HDR viewing. By greatly reducing the bandwidth requirements and offering this richer, more lifelike picture quality over standard HD SDR, the industry can leverage 1080p HDR, a format that I dub “the best bang for the bit.”

What next?

To simplify matters, the next step should be to define a small number of ‘universal’ profiles. This hasn’t happened yet, partly due to the newness of the technology, but also through a lack of clarity and universal agreement over the best methodology to use. As more UHD/HDR services come to market, this understanding will increase and in turn will lead the industry towards best practices and recommendations. In doing so, we can finally draw closer to realizing the full potential of HDR and deliver next generation immersive viewing experiences for everyone, everywhere.

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