Bearded Bandwidth: HDR Explained
Welcome to Edition Number One of Purple Pages, our revamped, quarterly newsletter designed to provide helpful, accurate, information and insight into solving the technological obstacles you face daily in delivering world class video images for your clients.
Recently, Murideo has completed updating our test gear for 8K output resolution, meeting HDMI 2.1 specifications, incorporated into the reference-level Seven G, the calibrator’s favorite 8K Six-G and 8K Six-A Field Test Suite, and remarkably, also including the industry’s most essential, affordable, and popular commercial and custom integrator digital tool kit, the Fox & Hound analyzer and generator testing kit. Examine how these important tools effortlessly streamline installation hours, eliminating guesswork and confirming system performance, and please contact Murideo with any questions or for additional information.
Question of the Quarter: What HDR technologies exist and how do they differ?
High Dynamic Range (HDR) has been wholly embraced by television and projector manufacturers for nearly eight years. To adequately convey depth of field with highlighted accents provided by HDR content, projectors require a prodigious amount of light, usually supplied by machines in the S-Class price range (perhaps a discussion for a later edition) so let’s limit this to the variety of flat panel displays in today’s marketplace. At HDR’s introduction, television manufacturers were in a recession-draining period, seeking to introduce appealing new features to a public that rejected 3D. An industry no stranger to more-is-better knew precisely what to do. The push for higher resolution (1080P up to UHD) began just as now, 8K is making headway, despite any predictable content.
Hollywood was of a different mindset however, as the pursuit was not more pixels, but belief the need was for better pixels. A better contrast ratio – the difference between the highest amount of light a display could produce against its darkest backdrop, dynamic range – with a wider array of colors to command the eye’s attention, was felt to be the natural progression in display development and content enhancement. In other words, be more like the observable world and less a compressed rendering of it.
HDR 10 and HLG
HDR10 was jointly developed by the UHD Alliance, a consortium of manufacturers and content developers ranging from Amazon to Warner Bros., along with the Consumer Electronics Association. It is license free and to date has been the most used form of HDR. More recently, some Hollywood entities have dictated content be mastered in Dolby Vision. Netflix, as an example, specifies its original programming be delivered in the Dolby Vision Interoperable Master Format, from which they will derive Dolby Vision, HDR10, and SDR accordingly.
Metadata, that invisible code that informs you of a myriad of things in your digital life such as the song title and album cover art for SiriusXM in your car, is used for communication between video content sources and display devices. Data exchanged over HDMI informs the source what limitations, if any, a display might have, such as total light output capability, color bit depth, and resolution.
In HDR10, metadata sets the dynamic range per the content holder’s stipulation, and this is fixed for the entirety of the content. A movie might be designated as having 1,000 nits peak brightness, to which the display will adjust its tone mapping based upon that information, establishing an average picture level, with appropriate headroom for specular highlights.
Hybrid Log Gamma (HLG and HLG10) little seen so far, is a joint development by the United Kingdom’s BBC and Japan’s NHK. Primarily of benefit when ATSC 3.0 broadcasting commences for live events, it has been used by Direct Broadcast Satellite systems worldwide. “Hybrid” defines two partner signal values of a non-linear optical-electrical transfer function where signal values in the lower half use a gamma curve while upper half signals are comprised of a logarithmic curve. Beneficial when bandwidth is at a premium, the lack of metadata coupled with backwards compatibility to SDR-UHD displays (pre-HDR sets) provides an efficient signal with more detail in darker image areas. HLG is most often generated at the camera during broadcast, emulating the response of the human eye in the observable world.
HDR10+ and HDR10+ Adaptive
Differing from HDR10 by increasing mastering output to 4000 nits (though HDR10 can master up to 10,000 by design) HDR10+ crosses the threshold into a licensed format with dynamic metadata that enables content creators to render brightness and color changes at the scene level or even by a single frame. Primarily driven by Samsung, Panasonic continues as an active partner though recently they have also adopted Dolby Vision. Hisense and Vizio support HDR10+.
HDR10+ Adaptive utilizes the room light sensor many displays have to adjust changes in ambient light in real time. Professional calibrators defeat this function.
Dolby Vision and Dolby Vision IQ
The alternative licensed format to HDR10+ is Dolby Vision. As with HDR10+, Dolby Vision is a dynamic metadata format which also enables scene by scene, frame by frame and even individual pixels. Additionally, Dolby Vision is considered future proof, with 8K resolution,12 bit color depth (HDR10 is 10 bit…what the 10 implies) and a workflow system for Hollywood that only relies on one master for Dolby Vision, HDR10, or SDR. Dolby’s objective is to achieve images mastered to 10,000 nits, thus setting the target for display manufacturers. While HDR10 was created with 10,000 nits in mind, little has been done to further that development.
Dolby Vision IQ functions like HDR10+ Adaptive, utilizing a display’s light sensor to real time adjust image parameters. The image “pumps” with these light changes in some applications which most people find annoying. As mentioned, professional calibrators defeat this function.
Advanced HDR by Technicolor
More a suite of application formats than one entity, the Technicolor HDR format was briefly supported by LG but as of 2020 seems to have quietly disappeared. It is still part of the ATSC 3.0 specifications so at this juncture how it may be implemented is unknown.
Murideo generators and analyzers are invaluable tools in your rack building / burn-in room and equally on site. Many displays auto-HDR10/+ or auto-Dolby when the appropriate signal is present. Frequently integrators are finalizing system installations prior to clients establishing services. Using a Murideo generator to provide these signals and correctly adjusting the display’s parameters can eliminate an additional site visit. You can also log these settings (cell phone pics are handy) and when service is established for streaming apps, these settings can be entered to duplicate the HDMI inputs.
Pro Tip: Don’t forget to enter settings on all available HDMI inputs (and especially for all apps, as they may have individual settings instead of global). You never know what might happen months down the line and if every input is properly adjusted, you may easily be saving a truck roll.
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