GEAR | HDR
ABOVE This graphic illustrates Mission Digital’s colour pipeline for on-set SDR and HDR monitoring using Dolby Vision. The various transforms (IDT, RRT, ODT and LMT) are all part of the ACES workflow, which works to maintain a linear colour space through non-linear devices
would be at the display’s max – 1000 nits or higher. In SDR, those values might be 95 nits and 100 nits, so only a 5% difference. Thinking like that, you can easily see the separation that exists in HDR,” he says. “So, who’s going to benefit most from HDR monitoring on set?” he continues. “The camera department will benefit, though HDR can be a little less forgiving than SDR, as much as it gives. Clipping, for example, will appear at the peak luminance of the monitor, which isn’t pleasant – and once that data is lost it’s hard to rebuild in post. More so than the camera, I’d say HDR benefits the art and makeup departments most. To see that
and chromaticity,” Soriano says. “With HDR, we also need to consider the third dimensionality of light, which is how colourful it can be.” Much like the specifics of contrast ratio, what gamut and what percentage of it that needs to be covered vary. Dolby Vision requires a monitor that can cover almost the full Rec. 2020 colour space. Though this aspect of HDR has some catching up to do – and that’s if it ever gets there. “The HDR television mastering is usually created for a 1000 nit display, but the Rec. 2020 colour space isn’t always used, simply because most consumer displays don’t even come close to that
“When we’re talking about displays, viewing environment is extremely critical. The brightness of a Dolby Vision HDR projection in the cinema is only around 130 nits, but that’s because you’re in a very dark environment. If a cinema screen were 1000 nits, it would be unbearable. In colour science, there’s a branch that covers ‘perceptual engines’. These algorithms try to preserve creative intent, adapting the picture to different viewing environments. Providers like Dolby and Colorfront are working hard here.” There’s another perceptual element at play in HDR, too, and it’s down to all of us. It seems an obvious point, but all viewing technology can only be related to the human eye. “There’s a concept known as 18% grey, often called mid grey. It’s what humans perceive to be the middle point between black and white, though it only reflects 18% of the light that hits it, not 50%,” Soriano explains. “We see most of our information between 0% and 18% if we consider it in a measure of a camera’s stops, with each stop doubling the amount of light over the previous one. At base ISO, a camera behaves the same way as our brain, using around half the tonal data for that 0-18% range. “The overall contrast ratio is just as much about those darkest parts as it is the brightest parts, and that’s where monitors are becoming much better. I’d also say most of the beauty of HDR is in those better blacks, too, and it all links to our evolutionary perception.” Dynamic range is just one part of HDR displays, though. Another is colour space. “Light is two things: it’s intensity
standard. With Rec. 2020, the top corner of that colour space triangle (at the luminance it should be) would essentially be a green laser. I consider no display will ever get there.” “The vast majority of natural reflective colours are contained within the DCI-P3 gamut, you don’t need Rec. 2020 for those. Within the extra range of 2020, you’re talking only about a high-vis vest perhaps, or the fluorescent wings of a butterfly, or a lightsaber,” Soriano explains. Certainly, there’s joy to be had from a wider gamut and the dynamic range, both for a viewer and those in all departments. “Viewed in HDR, a piece of paper may be 250 nits, while something that reflects 100% of the light
16 DEF I N I T ION | JANUARY 202 1
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