Many have professed confusion about HDR formats, with a belief that there are large number of different formats that provide compatibility and capability issues. However it is not as confused as it may seem once the fundamentals of HDR technology are understood and clarified.
News coming from CES this week is particularly full of these references, with discussion about HDR10+, Dolby Vision and Advanced HDR (from Technicolor). They are seen as new and incompatible approaches to the display of HDR and this is seen as some as a fundamental war of video formats, reopening the wounds of the pre-standardisation PQ and HLG discussions. However these are not video formats as such. These are display rendering solutions based on the processing, creation and delivery of additional metadata alongside the video format. Dolby Vision, HDR10+ and Advanced HDR are based upon the SCTE 2094 series of standards for Dynamic Metadata. It is an important difference, particularly with regard to video distribution for an operator or broadcaster.
In reality there are two core HDR video formats for distribution, PQ and HLG (alongside SDR). Each has its better application depending on a variety of technical opinions and market situations, but regardless whether delivering video using PQ and/or HLG, it will be receivable and usable by almost all HDR TVs that have been produced since CES2016. PQ (or Perceptual Quantizer) based video provides a pure HDR display-only video solution, whilst HLG (Hybrid Log Gamma) provides a HDR video solution with an SDR ‘backwards compatibility’ that provides a more universal solution for mixed SDR/HDR UHD displays (except the very oldest early adopter displays that only support BT709 colour space).
Let us take the odd one out first – Technicolor Advanced HDR. This is a set of technologies and standards (notably SL-HDR1, SMPTE2094-20 and SMPTE2094-30) that allows you to deliver content to SDR and HDR displays. As its base, video is delivered as SDR for those that do not support Technicolor’s HDR technology and HDR for those that do. The base video format of this is BT.709 based SDR video, with the reconstructive metadata passed in parallel containing all the data required for Technicolor Advanced HDR capable displays and devices to recreate the HDR image according to the capabilities of the Technicolor enabled TV.
Then we come to Dolby Vision and HDR10+, that use the PQ video format combined with dynamic metadata that will allow better rendering of the delivered video. It is important to understand that the base video layer being PQ means that when Dolby Vision or HDR10+ based services are delivered to displays that do not support either format of dynamic metadata, then these displays see purely the PQ video format and deal with them as PQ only video. This means that they will render a great HDR video representation of the content, just without the additional processing and tone mapping that both Dolby Vision and HDR10+ do. In other words, Dolby Vision and HDR10+ are backwards compatible with HDR PQ displays. Displays that support them though will provide better rendering of the HDR video according to the capabilities of both of these technologies, This is a very critical point and underlines the view that there is no technology risk or issue with HDR video delivery today even with the use of Dolby Vision and HDR10+ – as any delivery of video of this type will play pretty well on all HDR displays albeit using only the TV’s rendering and tone mapping that it would apply to PQ content. This is an important issue as even with HDR10 (the static metadata oriented profile of PQ as used by Blu-Ray), the metadata provided with the content is not necessarily used by the TV display, and the use of metadata is entirely optional.
It is also important to note that many TVs make use of HDR enhanced processing without the use of metadata, in ways that are proprietary to the manufacturer of the TV and in many respects Dolby Vision and HDR10+ are in the same realm as those solutions, although each offers what the manufacturer of the TV sees as being their consumer product advantage. Dolby Vision and HDR10+ offer a more multi-vendor solution approach to that processing than the proprietary solutions.
I hope this clarifies HDR so when you see the confusion or Format War articles/comments coming from CES. This is just one aspect of HDR video delivery and if you are investigating the deployment of HDR platforms during 2018 do get in touch to discuss where we can help further from architecture to delivery.
Fairmile West is a Consulting company focused on working in the Consumer Device and Video arena. We work with clients on technology strategy and product delivery through key practices in Consumer Devices and Video Services. If you are interested in learning more about what we do, please do get in touch via our website – Contact us. You can also keep track with what interests us in the industry by following our Link blog at TV Tech News, and you can specifically follow news on Ultra HD via the following link – Ultra HD News.