High dynamic range (HDR) displays are all the rage. HDR systems do a much better job than their predecessors of presenting details in the darkest shadows and brightest highlights of an image, and also maintain cleaner separation of details in highly saturated portions of the picture. The difference might not be quite as big as the step up from SDTV to high-definition, but it's pretty impressive. And many observers say HDR is a more important and fundamental improvement on HDTV than the increased resolution of 4K by itself.
But the roll-out of HDR-capable TV sets has been a little confusing. At an event at Sony's New York headquarters last month, the company said that five of its 4K TVs had been firmware-upgraded to support HDR. (That's the top-of-the-line $7,000 X940C, with its contrast-enhancing backlight plate, above). Further, it said HDR content from Sony Pictures Home Entertainment would stream to the TV via Amazon Video. But the picture wasn't entirely clear. For example, a journalist asked if the TVs would support HDR content encoded using Dolby Vision — by far the most ballyhooed new HDR system (and one that's already supported by TVs from Vizio). The answer was no. And the images Sony showed to reporters in a darkened demo room were undeniably impressive, but raised more questions. For example, all of the TVs support HDR, but the two high-end models feature something Sony calls "X-tended Dynamic Range" to make the pictures look even better. (Think of it as Even Higher Dynamic Range.) So you might reasonably wonder: if you're grading a picture for home viewing, which of those screens are you grading for? It's starting to look like HDR is a moving target.
For the last 12 months, SMPTE has been working on identifying the biggest issues raised by emerging HDR technology, with a study group considering the big questions and generating a series of recommendations. The report was published today, in conjunction with the SMPTE 2015 Annual Technical Conference & Exhibition taking place this week at the Loews Hollywood Hotel. Here's our take on some of the issues identified and what they mean to overall adoption of HDR technology inside and outside the industry.
1) HDR Compliance Is Not a Yes/No Question
Manufacturers have started advertising their high-end sets as HDR-compatible, but it's unclear exactly what that means. There are as yet no agreed-upon standards, and even different models of HDR-ready TV sets will display a visibly different range of color and luminance. As the SMPTE report notes, key specifications for peak luminance and black levels have not been set. In fact, the study group writes, such capabilities "are largely considered an optimization issue for display makers, who must evaluate issues such as panel capability, image quality, color gamut, cost, power consumption, manufacturing, etc…. It is expected that deployment of HDR will occur through gradual improvement and a migration over time to enhanced consumer equipment." That means the HDR set you buy for home viewing this year is far from future-proof. In fact, it may well be superseded next year by a new HDR set with even better dynamic range.
2) The Viewing Environment Is More Important Than Ever
For creating HDR content, as well as for viewing it, the ambient lighting in the environment where the display is placed will have a greater impact on how brightness is perceived — especially in the darkest parts of the image. "Ambient and surround light have a large effect on perceived blacks and contrast, and can change the choices in grading content to better reproduce images within a particular viewing environment," the study group writes. "This becomes even more pronounced when working with HDR content." The study group suggested testing is needed to define correct lighting levels for mastering in HDR, and said automatic brightness control on a display might be "essential" in order to match a display's calibration to a range of room lighting environments, suggesting such research "might be a useful SMPTE effort."
3) Nobody's Sure How Much New Metadata We Will Need
The study group said existing systems, including the ASC's CDL, will become even more important in order to keep acquisition, dailies and editorial speaking in a common color language. But more metadata may be needed. For example, the report highlights some uncertainty about whether new dynamic, content-driven metadata will be required to allow better interoperability between HDR content and SDR-only displays, or whether standard, pre-defined conversion techniques will maintain acceptable quality. Of course, standards will have to be created for carrying that metadata over SDI and IP infrastructure, as well as in file and code stream wrappers.
4) HDR Adds Complexity to the Filmmaking Process
The co-existence of HDR and SDR displays will raise some new issues in production and post, the study group noted. For example, do editors need to cut HDR pictures, or will SDR images suffice? Do multiple deliverables need to be created so that dailies can be viewed on displays with different characteristics? Does grading on set take on new importance if cinematographers will be able to hold onto more dynamic range through delivery?
5) It's Hard to Even Test HDR Worflows
A filmmaking A team including director Howard Lukk (formerly of Disney and Pixar) and DP Daryn Okada, ASC, tried out an HDR worfklow on the 13-minute short "Emma," shot last year on the ARRI Alexa XT. The Academy's ACES color-encoding method was a great help, but Lukk noted that the lack of HDR support in projection display devices prevented the production from doing a full theatrical grade, and the lack of appropriate lighting environments for on-set monitoring in HDR meant lighting choices were made "in the blind" — just like in the old days of shooting film. "Lack of standards for HDR display devices and its ecosystem is probably the biggest issue facing filmmakers at this moment," Lukk wrote in January of this year. "Without standards, one must provide a separate, color-corrected version for each HDR ecosystem."
6) A Good Old-Fashioned Format War Is Brewing
The study's Appendix A outlines differing approaches to providing HDR signals from rivals in the broadcast and consumer electronics technology industries. The BBC and NHK have a combined proposal. Dolby is aggressively promoting Dolby Vision. And Technicolor, Philips and Samsung all have their own approaches. The study group warns that these multiple, competing schemes would make the HDR roll-out a vastly more complicated proposition. "Such fragmentation will introduce complications to HDR workflow, and may lead to requirements for multiple HDR deliverables. This, in turn, could lead to a delay or even a barrier in adoption of HDR technologies by content creators and users." The study group is urging SMPTE to create a standard before conflicting proposals — and the ensuing consumer confusion — derail HDR entirely.
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