Modern VideoFilm's senior digital colourist Bryan McMahan talks here aboutcreating, grading and displaying HDR video, and its future role in media and
entertainment.
Colourist Bryan McMahan Talks on HDR Video and Creating Better Pixels |
High dynamic range videowas one of topics that interested vendors and visitors most at the IBC2015 exhibition – how to create, display and broadcast it, and its effect on viewers’ reception of content.Modern VideoFilmpost production participated in a 4K/HDR panel discussion in August 2015, shortly before IBC, titled ‘The Future of Post: 4K and HDR’, sponsored by Sony and KeyCode Media and moderated by Larry Jordan. The panel included Modern Video Film's award winning senior digital colouristBryan McMahan, known most recently for ‘Knight of Cups’ and ‘The End of the Tour’, as well as Michael Cioni, president of Light Iron post studio, and Michael Whipple, executive director of post-production technologies at Sony Pictures Entertainment. |
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Capturing HDRBased on these experiences, Bryan now feels that HDR creates a new visual palette for DPs and colourists to work with.Digital Media Worldhad a chance to ask Bryan some questions regarding the colourist’s point of view on this topic, including how HDR recording might affect the relationship of colourists with DPs. Both will have access to more options for fine-tuning looks as digital cameras become more sophisticated and capable of capturing a wider colour gamut or range of colours, and a higher dynamic range - the ratio between the maximum and minimum measurable light intensities within which a sensor can record detail. Traditionally, when using standard dynamic range cameras, the aim is to present a range of luminance similar to what we see in everyday life through our own eyes, which continuously adjust to the broad changes in dynamic range that occur naturally in the environment. Your brain continuously interprets this information so that you can see in a wide range of light conditions. Until recently, most digital camera sensors haven’t been able do this very effectively, and HDR images were produced by capturing and merging in post two or more different, narrower-range exposures of the same subject. |
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This image comes from anarticlebyJoseph Eckerttitled 'High Dynamic Range Without that HDR Look', discussing images produced both by merging bracketed exposures and from singles images captured with a digital camera with a large dynamic range. |
Contrast ratios, and therefore dynamic ranges, are increasing in new cameras. The RED Raven, introduced at IBC, claims a range of over 16.5 f-stops. Regardinggrading softwareto work with this kind of imagery, Bryan said, “As cameras become more sophisticated so will colour correction systems, but this has always been the case. Because HDR display requires access to the most range the camera can give us, the software in the colour correctors needs to give us the ability to use all of those bits.” Role of the ColouristIn some ways, Bryan expects HDR capture to extend the role of the colourist further into production-side activities, similar to the effect that creating and using on-set LUTs had on their role. “I think the situation will be very similar, but the one difference is that the monitors used on set most likely won't have the same range in luminance or in bit depth as the HDR mastering monitors or HDR projectors have. I believe this fact will create a closer relationship and greater trust between the cinematographer in the field and the colourist he or she will be working with on the final result.” |
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This illustration from Dolby Laboratories shows that in this ordinary flower, brightness ranges from 145 nits for the background all the way to 14,700 nits (unit of measure for brightness) for the yellow part of the petal. The current TV and Blu-ray standards limit maximum brightness to 100 nits and minimum brightness to 0.117 nits, while also limiting the range of colours, or gamut, that can be displayed. |
“The information that a camera captures, whether it's a digital camera or especially a film camera, is much greater than the displays or projectors that are currently on the market,” he said. “Home monitors, whether standard definition or high definition, are in the Rec 709 colour space, which can’t reproduce all of the colour that has been recorded. Therefore, colour must be manipulated to work within the limitations of the display. Bending Colour to Fit“However, because HDR displays are closer to P3 colour space, which is a larger colour gamut, I don't have bend the colour to fit. The same goes for the luminance of the image. With HDR I don't need to spend as much time worrying about clipping skies, hot spots on buildings, windows, cars, faces and so on. Also we finally have good blacks in the picture that are rich but let you see into them. I don't have to crush the blacks to get good contrast. “P3 is also the colour space for digital cinema so I don't need to convert colour space from the DI process to the home version, but even with that large colour gamut, the luminance is still limited compared to what the HDR can produce. Having this luminance to work with means I spend less time trying to fit a large peg into a small hole. |
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Illustration: Dolby Laboratories |
“But as always, the most important point is the communication between the cinematographer, the director and storyteller as to how their story should be seen. Just because my car will go 200 mph doesn't mean I have to drive it that way all the time.” New Starting PointBryan is uncertain about how much specialized training most colourists will need to feel competent at working with and taking advantage of HDR content. It takes him a few days to get used to the HDR image, and after that a few days to go back and re-do what he started. He said, “My base setting or starting point will most likely change and evolve as I become more familiar with the HDR workflow. So far, there are still very few home displays on the market and as others start to appear we will need to figure out what the conversion process is to all of these other displays.” Regarding monitoring, the luminance output of available HDR capable monitors, which are still very expensive, varies considerably and depends on whether the displays are LED or OLED. “As the manufacturers improve their products, specifications become a moving target. This is going to be a big challenge and means that collaboration between the on-set crew and the post production team producing the final product is imperative,” Bryan noted. |
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Illustration: Dolby Laboratories |
Visual ChangeBryan feels distributors are facing a similar visual change as they did when they went from standard definition to high-definition. Viewers subjectively see more detail in a HDR image, even if the number of pixels is the same, and once they have seen HDR imagery, it will hard to turn back to SDR programming. When describing their Dolby Vision system for displays, Dolby Laboratories maintains that while 4K televisions have more pixels and the new UHD TV standards include high frame rates, neither of these two standards makes each pixel better able to represent the full range of brightness people see in reality. This kind of improvement comes from more dynamic range and wider colour gamut. “But for viewing, it's really not that big a change on the equipment side apart from the display,” Bryan reflected. “As far as production goes, camera crews will need more storage because a 16-bit file is preferred and the workflow may be 12-bit rather than 10-bit, but the cameras are the same. HDR does not define resolution so what you are currently working in, other than your display, should not have to change drastically.” www.mvf.com |