October 2012

 
  4 October 2012
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NW1Hot Button Discussion

Color Gamut Gains  

By Michael Goldman 

 

SMPTE Newswatch last examined the topic of expanding color gamut in projectors and displays a little over a year ago. Since then, there have been no fundamental shifts on the landscape regarding how best to achieve that expansion. On the cinema projection side of the equation, the best path to achieving wider gamut remains linked to improving light sources, brightness capabilities, and contrast--traits industry experts are optimistic will eventually become possible by evolving laser projection systems when they become practical and widely affordable to the industry. That is an important distinction because the technology is not yet where it needs to be for cinemas to consider converting from existing Xenon-based projection systems on a large scale. Until that changes, SMPTE ST431-1, or the P3 gamut range of the DCI specification, will remain dominant for theatrical exhibition.

 

On the broadcast side, strides in this area continue to come from manufacturers such as Sharp Corporation, which have developed multiple primary color (MPC) LCD displays--technology built on the notion of adding extra colors to the matrix beyond traditional RGB. Since 2010, Sharp has been offering four primary colors with the addition of yellow, in its so-called Quattron quad pixel display systems in the quest for a wider color gamut experience. As noted in that same SMPTE Newswatch article, that Sharp continues to research consumer display technology that would feature five primary colors with the addition of both yellow and cyan to the traditional RGB approach. Thus, high-end consumer displays are now well on the way to surpassing the Rec. 709 gamut threshold that has been in place for years.

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As these developments illustrate, wider color gamut that can be effectively displayed to audiences, on both large and small monitors, is inexorably linked to wider image capture and display developments generally--brightness, contrast levels, color fidelity, and so on. Indeed, Glenn Kennel, President/CEO of Arri Inc., also a SMPTE Fellow, points out that the pace and level of ongoing camera filter development to improve gamut capture and other such entities in the latest generation of digital motion picture camera systems are directly connected to what is happening on the display side. After all, if an acquisition improvement can't be seen by anyone, it doesn't end up being much of an improvement.

 

"Speaking in terms of Arri, when we look at camera design, we define and select the color filters on our sensor very carefully, and we try to have the color response of our system allow us to capture as wide a gamut, and maybe a little wider a gamut, than can currently be displayed on standard TV or digital cinema displays," Kennel says. "On the other hand, just pushing to wider gamut on the camera is not meaningful if you can't display it. You don't want to go too far beyond what today's displays can do. The tradeoff if you did that would be sensitivity--you can lose sensitivity of the camera if you widen the gamut too much. In other words, you would need to add light or increase your exposure."

 

As laser projection light sources improve and become practical for cinemas, permitting brighter pictures and wider contrast on screen, Kennel suggests camera manufacturers will follow by expanding gamut capabilities of their camera systems. "Until that happens, there is no utility in capturing much wider gamut right now," he says. 

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"Our focus is more on what the cinematographer needs most anyway--parameters like dynamic range from highlights to shadows and depth of field and color fidelity. Those are more important on the capture side than gamut. Creatively, most users are more concerned with desaturating and pulling in colors, rather than pushing them out. Having more impact and more vivid colors is nice, but typically, the creative tendency is toward muting the colors and focusing attention on a particular subject, person, or object in a scene. So, we tend not to push color too hard from a creative standpoint [in production] anyway. That is something that will work itself out in post, usually if the display is able to show that wide range of colors. That is a generalization, and certainly computer animation relies heavily on more vivid colors as a significant part of the story creatively. This more or less why our advances [on the camera side] are not as important as advances with displays in this area."

 

"The other thing to remember, from the camera perspective, is that most camera manufacturers, focus more on flesh tones and color fidelity within a certain range. We also focus on what we call 'memory colors'--apples, oranges--things you can touch or eat, or are real familiar with. If a camera reproduces colors in that zone, in a pleasant and natural way, that is more important than reproducing an extremely bright, pink neon, for example. The neon is so bright that the brain won't care much whether it is 90 or 100% perfectly reproduced. The brain will know instantly if a face tone isn't right, so we spend a lot of our development time in this area optimizing color responses to those flesh tones. We think a lot about the kind of illumination in which we are photographing people. We have tungsten, fluorescent, and now LED and other things, so the camera has to respond consistently across all those illuminants, and in mixed lighting situations. Color fidelity, skin tones, and memory colors are most important [on the camera development side]."

 

In terms of cinematic projection, Kennel is impressed with the laser demonstrations he has seen in recent months from various manufacturers. He predicts that even under the best economic circumstances--and the industry is far from that right now--it will be three to five years before they start becoming commercially available in cinemas across the country.

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"The cost of those systems has to come down a little bit, and at the same time, [manufacturers] need to demonstrate they are able to make small, bundled light sources out of them to retrofit into existing projector footprints in a standard theater," he explains. "So the idea, as I understand it, is to work toward an upgrade path so that people do not have to replace existing projection equipment right now. They want to be able to pull out a Xenon lamp and replace it with a laser source for the projector."

 

In any case, projection systems new or old are, by definition, limited to showing the best of what goes into the projector from original mastered content. Thus, original mastered color gamut--essentially the same P3 color gamut seen today with Xenon projection systems--is what viewers will see unless content is graded or re-graded for something more substantial than what today's projection systems are capable of displaying.

 

Therefore, "today's master on tomorrow's laser projector will need to be re-graded to fully take advantage of the ability to display wider color gamut," he emphasizes. "If you took the standard master created for Xenon projection and just pushed it up [in the grading process] to the wider display gamut, it would be super saturated, and flesh tones, in particular, would not look pleasant at all [when viewed on a laser projector]."

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How best to see wider color gamut during the grading process is yet another issue, at least until commercial laser systems are available in post-production environments. The need to do such re-grading work would also likely require new measuring technologies, Kennel suggests, although he points to so-called "gamut mapping," or 3D volumetric analysis, as showing great promise for these kinds of applications (see the June 2011 SMPTE Newswatch for more explanation on this process).

 

"If you were grading on a wide gamut laser system, you could use a gamut mapping LUT during that process," he says. "It would have to be a 3D LUT to take the wide super saturated colors and essentially squeeze them down into the more narrow color space of a Xenon projector [for theatrical display]. That technology could be used to create a single master, and then you run it through the gamut-mapping LUT to create a second master. However, you would still need to compare the two of them, to make sure you didn't step on any colors during that process."

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"If you were grading on a wide gamut laser system, you could use a gamut mapping LUT during that process," he says. "It would have to be a 3D LUT to take the wide super saturated colors and essentially squeeze them down into the more narrow color space of a Xenon projector [for theatrical display]. That technology could be used to create a single master, and then you run it through the gamut-mapping LUT to create a second master. You would still need to compare the two of them, to make sure you didn't step on any colors during that process."

 

In any case, Kennel suggests the day will come when brighter cinema projection systems, multi-primary color home displays, and sophisticated color grading processes for content will combine to allow viewers to indeed experience wider color gamut in cinemas and at home than they have ever seen before. But will it be worth it? Will it be noticeable to the average consumer's eye?

 

Most definitely, insists Glenn Kennel. "It will be very noticeable--there is a very well-defined definition of the visible spectrum, after all," he says. "There are things in the real world, like deep, dark, cyan aqua blues, that are still outside today's P3 color gamut, the digital cinema gamut, and way outside the gamut of Rec.709 televisions. Ironically, print film can display those kinds of blues, but other colors, like really bright reds and greens, film cannot reproduce as well. Film does well with dark cyans and magentas and yellows, but not with bright reds, greens, and blues. It is kind of a misnomer to suggest film has a bigger color gamut; it has a different color gamut. It depends on how you look at it, but, in the digital world, with these next-generation displays, you will eventually see a much bigger color gamut than you can see right now."

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