SMPTE Motion Imaging Journal: Update on 4K Ultra HD Blu-ray Production
By Prabhu Anbananthan and Seth Hallen
What? Another Physical Format?
Despite the recent attention and growth in streaming services, 10 years after the first Blu-ray discs were released to the market a new physical disc format made its debut. In early 2016, several major Hollywood studios including Sony, Warner and Fox announced plans to release their first 4K Ultra HD Blu-ray titles and manufacturers like Samsung, Philips and Panasonic announced the release of their various 4K Ultra HD Blu-ray players and HDR-enabled 4K displays. At the time of launch there were obviously high hopes by all stakeholders that this new format would perform well in the consumer market and of course, these hopes were met with plenty of skepticism. However, by the end of 4K Ultra HD Blu-ray’s launch year of 2016, according to the Blu-ray Disc Association, 20 million 4K Ultra HD Blu-ray discs were sold placing the new format at about three times the sales penetration of Blu-ray players at an equivalent time in the original launch of the format, and according to the DEG First Quarter 2017 Home Entertainment Report, there are nearly 4 million households with 4K Ultra HD Blu-ray playback devices. Currently, Sony, LG, Microsoft and Oppo have all joined the game with devices that play 4K Ultra HD Blu-ray discs and by the end of 2017 it is estimated there will be a total of 360 titles available from studios including Sony, Warner, Fox, Lionsgate, Universal and Paramount. The Studios and hardware manufacturers clearly believe that consumers are driven to embrace products that improve the home entertainment experience. So just like all previous format evolutions, the challenge was how hardware manufacturers, content owners and post production service providers could pull together and not only deliver something that works, but deliver a new and compelling consumer experience.
How Did We Get Here?
Around the turn of the millennium, flat panel televisions powered by technologies such as liquid crystal display and Plasma replaced cathode ray tube (CRT) based displays as the de facto fixture in the living room. Along with these newer technologies came the ability to surpass the limits set by prevalent image signal standards (in fact, a standard, namely, International Telecommunication Union (ITU) BT.1886¹ was created to emulate CRT characteristics in modern displays). However, it would take several more years for this capability to be experienced by the consumers because the entire content pipeline, starting from content capture all the way to distribution, had to be improved. Let us take a brief journey on how this ecosystem evolved over the years.
As manufacturing processes improved, Consumer Electronics Manufacturers were able to produce larger panels and these were marketed as premium, top-of-the-line displays. However, as the size increased, the viewing distance remained the same for many users since they did not typically reposition their home furniture when upgrading display sets. This resulted in a loss of image sharpness and large displays with HD resolution did not necessarily produce compelling images. To address this, the first image parameter that was expanded was image resolution. The 84 in. panels that appeared in the fourth quarter of 2012 improved the image resolution
to 3840 × 2160 and were able to produce significantly sharper images than HD displays of equivalent size.
While the increased resolution did improve the consumer experience in larger displays, the improvement was not obvious from a consumer perspective in relatively smaller displays. At this point, work was underway in standards bodies such as SMPTE² and ITU³ to define image and signal parameters for UHD TV. Movielabs defined requirements on behalf of major Hollywood studios4 as well. In addition to resolution, the parameters that were evaluated were Frame Rate, Color Gamut, Dynamic Range, and Bit Depth. There was a lot of debate relating to which of these parameters was more important from a consumer perspective. It soon became clear that Color Gamut, Dynamic Range, and Bit Depth when combined together produced the most significant improvement for consumers. Also, higher frame rates reduced judder and motion blur especially in fast action sequences and shots with rapid camera movements. These studies were considered in the drafting of the BD specifications for next generation video.
4K Ultra HD Blu-ray is Born
Ultra-High Definition Blu-ray specifications were ratified in August 2015. The specifications allowed a maximum resolution of 3840 × 2160, a maximum frame rate of 60p, a maximum peak luminance of 10,000 nits, and a maximum bit depth of 12 bits. The color gamut specified in Ref. 3 was much larger than the gamut of the legacy HD Blu-ray format. It also required the use of the High Efficiency Video Coding (HEVC)5 encoding standard, which is the state of the art compression standard published by ITU. The main 10 profile and high tier with level 5.1 was chosen and the peak bit rate was 100 Mbits/sec. The specification mandated the use of SMPTE 20846 as the electro optic transfer function for HDR video. There was some skepticism in the early stages of licensing the new format. The main concern was whether a physical media product was relevant in the age of high-speed internet and at a time where consumers have grown comfortable accessing content with the click of a button. However, because sustained internet speeds to most consumer homes was well below 4K Ultra HD Blu-ray bit rates and also well below the demands of optimal UHD quality, there was a compelling argument that physical media would be the optimal delivery mechanism for such an experience. Fox, Sony, and Warner were the first to support and announce 4K Ultra HD Blu-ray titles and Panasonic, Samsung, and Philips were among the first to announce 4K Ultra HD Blu-ray players in early 2016.
Color grading facilities had to be trained to master in HDR. This included the technical aspects such as using new tools, plugins, and settings as well as the creative aspects such as adjusting mid tones and the roll off point for highlights. Another challenge was the huge disparity in display capabilities (e.g., peak luminance varied substantially from 4000 to 1000 to 600 nits). These challenges had to be addressed in short timelines without affecting the standard dynamic range (SDR) mastering workflow.
The authoring process involved the development of new tools and workflows for authoring as well as encoding, graphics handling, verification, encryption, and disc image mastering. Early development required the experimentation with menu graphics and subtitle overlays from a creative and user experience standpoint. The specification initially allowed 4K Ultra HD Blu-ray players to optionally convert BD java graphics from SDR to HDR. However, early results demonstrated that this was not an effective methodology and the specification clause was eventually removed (requiring the conversion to be performed upstream within the disc authoring workflow). Handling the large video source files and encoding them took several days. This introduced several storage and timeline challenges as well.
The limited availability of playback devices and consumer monitors at the time of format launch also contributed to scheduling challenges. As with any format launch, there was a significant effort involved in debugging the authoring tool chain as well as playback devices and displays. Other bumps in the road included the requirement for special HDR display mode settings as well as High-Definition Multimedia Interface cables that were incapable of the high speeds required for handling UHD signals.
However, the final results delivered stunning imagery and soon skeptics and enthusiasts alike were able to appreciate the substantial benefits of the 4K Ultra HD Blu-ray format.
While the format specifies a wide color gamut3 and a peak luminance of 10,000 nits, there are no current displays able to achieve these characteristics. Therefore, the displays must perform a tone map based on their native color primaries and peak luminance capabilities. The Blu-ray format allows for static and dynamic metadata to be included in the video stream to help displays perform this tone map. For example, Dolby Vision dynamic metadata is being delivered to consumer displays at present, which enables the displays to tone map to the reference trims performed during mastering.
Now that more and more content providers are choosing to perform an HDR grade, some of the earlier mastering challenges, such as training and turnaround time, have improved. The creation of a mezzanine file for interchange is still a challenge due to the lack of support tools in the traditional color grading workflow as well as time constraints. The good news is that the Interoperable Master Format has emerged as the de facto standard for HDR mezzanines and it is only a matter of time before the tool chains improve. Until mezzanine based interchange becomes prevalent, ancillary data including source image characteristics and static/dynamic metadata must be exchanged as a sidecar.
Early adopters and enthusiasts have acknowledged that 4K Ultra HD Blu-ray provides a significantly improved consumer experience over all existing formats and their reviews have been positive overall. For example, a recent Forbes review stated, “From start to finish, Planet Earth II’s 4K/HDR/wide color presentation feels like a five hour demo reel for the future of television.”
4K Ultra HD Blu-ray format specifications allow for significantly improved picture quality that far surpasses legacy Blu-ray. The bar set by the specification is much higher than the capabilities of current displays. As the industry evolves and display technology improvements make their way into the professional and consumer market, the consumer experience will only get better. Also, several other shortcomings with today’s commercial panels, such as viewing angle in light emitting diode (LED) based displays and lifespan in Organic LED displays, will disappear with the next round of panel innovation.
Content providers typically use a mastering workflow that incorporates reference displays with the largest color volume available at the time. However, two key challenges will continue to persist, namely consistency in the depiction of the video signal and future proofing of the mastering and distribution process. With continuous improvement in display technologies, there will always be a variety of displays in active use in the marketplace with differing dynamic range capabilities and these displays should produce the best image possible with the provided video stream in a manner consistent with creative intent. The challenge from a mastering and distribution standpoint is to identify the process and tools that can be used to make sure the content continues to take advantage of future developments.
At the end of the day, shrinking timelines between the theatrical and home video launch will challenge the industry to continuously evolve and increase efficiency of the mastering and production processes for 4K Ultra HD Blu-ray. Content providers, post-production houses and other ecosystem partners will need to collaborate closer with each other as well as with hardware manufacturers to continue bringing the magic of superlative imagery to the consumer for years to come.
About the Authors
Prabhu Anbananthan is the vice president of technology at Pixelogic Media, where he is working on the global technology roadmap for media distribution and localization services. Prior to Pixelogic’s acquisition of Sony DADC New Media Solutions Creative Services business unit, he held various technology leadership positions in post-production and digital media operations at Sony over the past 15 years. He has worked on optimizing image quality for various mastering and consumer formats and continues to study advances in display and encoding technology. He has been active in the standardization efforts of the various profiles of BD format. Anbananthan received a Master’s degree in computer science from Loyola Marymount University.
Seth Hallen is a senior vice president of global business development and strategy at Pixelogic Media and president of the Hollywood Professional Association. With a proven ability to lead teams toward the successful tactical execution of strategies designed to capitalize on emerging trends and opportunities, he has been building profitable, innovative and market dominant companies for over 25 years. Prior to Pixelogic, he was a senior vice president of global creative services at Sony DADC New Media Solutions, the chief executive officer of Testronic Labs, a vice president of North American Operations for Lightworks, and the producer of the Emmy Award-winning TalkShow. TV. Seth is president of the Hollywood Professional Association (HPA) and serves as governor-at-large of the Society of Motion Picture and Television Engineers (SMPTE). He holds a BA degree in radio, television, and film from the University of Maryland.
- International Telecommunication Union-Radiocommunication (ITU-R), Recommendation BT.1886-0, “Reference Electro-Optical Transfer Function for Flat Panel Displays Used in HDTV Studio Production,” 03/2011.
- SMPTE, ST 2036-1:2013, “Ultra High Definition Television— Image Parameter Values for Program Production.”
- International Telecommunication Union-Radiocommunication (ITU-R), Recommendation BT.2020-1, “Parameter Values for Ultra-High Definition Television Systems for Production and International Programme Exchange,” 06/2014.
- MovieLabs Specification for Next Generation Video—Version 1.0
- International Telecommunication Union-Telecommunication (ITU-T), Recommendation H.265, “High Efficiency Video Coding,” International Telecommunication Union, 1: 2015.
- SMPTE, ST 2084:2014, “High Dynamic Range Electro- Optical Transfer Function of Mastering Reference Displays.”
A Contribution received June 2017. Copyright © 2017 by SMPTE.