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HDR in Cinema: Technology Projections and Predictions
BY JON SILBERG
HDR in home entertainment has received a lot of attention lately, but theatrical HDR? Not so much.
Dolby Cinema and IMAX each have offerings that exceed the maximum brightness levels for the DCI (Digital Cinema Initiative) SDR (standard dynamic range) projection of 48 nits, but the differences aren’t as pronounced as they can be in the home entertainment arena. The SMPTE-sponsored panel discussion about HDR in cinemas, a part of that organizations Future of Cinema track, kicked off on the first day of the 2023 NAB Show to allow attendees to hear from experts where theatrical HDR specifications might be headings.
Annie Chang, Universal Pictures VP of Creative Technologies, presented an update about the new DCI HDR D-Cinema Addendum. She reported on the DCI’s experiments showing groups of test audiences scenes from well-known films in forms of HDR that do not exist commercially but exceed the dynamic range of Dolby Vision with its 108-nit maximum white.
Chang reported that the tests involved both direct view, such as LED panels and projection technologies. They set up double-blind testing with a wide variety of test viewers, from members of AMPAS and NATO and other professional organizations to students and other non-pros, who were asked to rate the visual experiences.
The results indicated significantly higher ratings as they lowered black levels down towards .05 nits (five millinits) with a flattening of the curve below that level. In terms of highlights, the 108-nit Dolby Cinema spec was “marginally preferred over SDR’s 48-nit” standard, but ratings increased significantly at peak brightness levels up to 300 nits, and then flattened out with the experience of viewing 500- and 800-nit versions being rated roughly the same. While there’s a lot more to do before new standards are written, this testing suggested 300 nits maximum brightness and five millinits darkest black as a possible sweet spot.
Joaquim Zell, head of HDR Content Workflow at projector manufacturer Barco, began his presentation by announcing that he expects the “HDR” to come off his title soon “because HDR will be normal. Most TVs, most streaming services offer HDR,” and stating his belief that the number of HDR screens in theaters, whether the current Dolby Cinema standard or something else, is imminent.
Zell spoke about advantages of laser projectors vs. traditional light engines in terms of power consumption and heat dissipation, noting that lasers can offer more flexibility to emit the greater light output needed for HDR.
He discussed the transformation of DLP projection, groundbreaking tech when it was released in the first years of this century, but a system with issues his company has striven to address in the years since. The micromirror based system, he noted, is “on at all times and the mirrors’ position determines how much of that gets to the screen,” which he says is a waste of light and energy, not to mention that the resulting light scattering effect introduces an intrinsic limitation to the depth of blacks achievable.
He then touched on Barco’s “light steering” technology to “focus” light more specifically by moving light away from dark regions into bright areas of an image, offering greater efficiency and allowing certain portions of an image, specular highlights for example, to exceed the “maximum” brightness level, something DLP cannot do.
Zell also touched on the issue of how our eyes actually respond to light and why more nits doesn’t necessarily equate to a better experience. “When we watch a movie at 48 nits or 100 nits,” he said, “our irises stay open. When we’re looking at 150 nits, they start to close down and by 300 nits, they are really small. A screen at full white at 300 nits, makes viewers’ “heads jerk backwards, it makes them cover their eyes with their hands.”
And while there would be very few situations of pure white being projected on a screen for any significant length of time, he did suggest that if movies are to be shown at levels beyond 300 nits, editors and colorists will need to understand the fatigue and headache that can result when viewers’ irises are made to frequently open up and close down and to factor this into their work.
Bill Mandel, vice president of Samsung Research‘s Visual Solutions Lab, was less interested in the limits suggested by the previous speakers. He stated that he doesn’t think it’s time to close the door to any approach to HDR in theaters. He doesn’t think the industry knows yet if deepest black should be five millinits, suggesting one millinit, or even zero, might turn out to be attainable and preferable. He didn’t want to rule out peak white at 500 or 800 nits or more, either.
“I don’t want to block innovation,” he said.