Introducing – Tools for Cinema Quality Assurance


Cinema Test Tools for the non-Technical Manager – Post Installation Quality Assurance Has Begun

Cinema Test Tools is a free resource for the cinema industry, tuned most particularly for the non-technical manager. The tools include several DCPs, all with interesting means of testing the sound and picture quality for the interested by lightly trained staff. The lessons on sound and light are written to provide a foundation to communicate with the technician who must respond quickly and well to the information that they discover.

The key is a free Managers Walk Through Checklist that correlates with the many DCPs. It helps bring an understanding of the many nuances of the auditorium's situation in a straightforward way. 

Exhibitor News

The Spectre of Vision

This weekend brings back Spectre and it is said to be terrific. It should be all the more terrific since it is playing at a local Dolby Vision cinema, an AMC Prime auditorium – The Burbank 16.

It is not a huge room, nor a huge screen. But it is a huge amount of light being thrown across the distance of 16 rows of executive plush leather seats by a couple of souped up Christie built laser projectors, then splashing onto a low gain white screen. Manufactured by Christie, but the secret sauce is all Dolby.

The measured brightness is set for 106 candela per square meter (cd/m2), a term which is often called 'nits' in the biz. (If you want the deprecated term of foot-lamberts, divide by pi. ) [edit: We have later been told that the translation from foot lambert to candela per meter square should be on the high side – that is, the dual laser system is putting out 108 cd/m2. The low-gain white screen is critical since the opposite (high-gain and/or high-gain and spray-painted aluminum flakes, often called 'silver screens') is notorious for having extremely out of spec hot spots and poor smoothness and dim contrast and horrid vignetting of both darkness and color shift. . . not talked about much since one doesn't like to pi. . . well, one doesn't like to do a lot of things that make associates look bad. . . OK. . . associates looking bad might be OK or not OK, but you don't want clients looking bad, and high-gain screens was one solution for many clients with Dolby 3D systems.  

Nonetheless, they basically are pumping up the bright by 2 – and getting the studios to create and distribute a custom master print – but it is the dark that Dolby wants you to concentrate on. Want to or not, you will notice it. If there were black masking drapes to compare the screen to, the screen may be darker than the drapes, which is truly a terrific phenomena after a decade and a half of getting better and better digital cinema but, until now, no great blacks. They will not give a measured amount of darkness in nits or candela, nor will they tell you how the magic is done. But they will give a curiously round number of a million to one as the contrast ratio being presented. Isn't it great when the laws of physics give round numbers? Let's see. Move the decimal to the left a few times and a few times more and viola~! Less than 0. 0001 nits is the amount of dark that the Dolby Vision system is able to present. High Dynamic Range.

Let's be clear about what that means, since there is a great demo associated with the system. A circle in a field of black is presented and we are told that this is the standard 48 candela/meter2 against a black field that the typical digital cinema projector is delivering at your cinema. What they are presenting is a 2000:1 ratio circle of white to field black, which they say is a test pattern for the standard. They are being very kind when saying that this is the contrast of the typical cinema. In fact, the specification in the SMPTE and ISO standards (or is that a Recommended Practice?), the one that requires a nominal 2000:1 value is the Sequential Contrast test. This standard actually allows 1500:1 for a review room and no less than 1200:1 for a Theatrical room. But they are making the point without confusion because of what they are going to do next, which is increase the light output and decrease the dark output. Let's slide into that with a little tangent.

First, a white circle on a black field is a test pattern, but it isn't a sequential test pattern. The Sequential Test doesn't need a pattern since you just shoot the room with the projector blazing all white (RGB 4096,4096,4096 while putting 106 nits on the screen), then when the projector is blazing as close to black as it can translate the R, G, B values of 0,0,0 you grab a measurement and divide it into the measurement of the previous slide and call it a ratio of something to 1. Alluding to this as an industry standard test pattern is still a valid way to show their point, and just because it is condensing science and art to communicate a point that might otherwise take minutes to show doesn't make it wrong. On the other hand, it also isn't a test if you only give one score of the game. Wasn't there a George Carlin routine where he only gave half the baseball scores for games? Dolby is giving the dividend (106) and the quotient (a million~!) and saying, "Find your own divisor. " There were 14 runs in the game and the winning team had 2 more than the other team. Or as they said in a recent public demo when being asked for that number, "That is rather difficult. " Yes. Science is difficult. Communicating science is even more difficult.  

So, let's do this. Just because that is what was recommended at the Press Demo – Divide 106 by a million. Pencils for photons as pixels.

  • 106 is one to one.
  • 10. 6 is ten to one.
  • 1. 06 is a hundred to one.
  • 0. 106 is a thousand to one.
  • 0. 0106 is ten thousand to one.
  • 0. 00106 is a hundred thousand to one.
  • 0. 000106 is a million to one. 1,000,000:1 – Seven orders of magnitude.

The first statement that many engineers make is "Perhaps that low end number can't really be measured, maybe?" 

Yes. Individual photons can be detected if need be. Not with typical industry tools of course since they aren't designed to measure in the range required. Tools in the same families as the high end tools will get close, and there are specialty companies that go even deeper. Length of time and number of measurements and repeatability all become a mirage that needs to be approached with caution, and if a marketing person were in the room they would say, "Look at that!!! Let's say Infinity to One. " Or, they can say that the score is 106 to a million.

Before we go back to the absolute awesome next step in the demo. . . and that is said with no hyperbole. . . , one more point to clear up the last detail of 'test pattern'. The spot on the black field is closer to what is called the Intra-frame spec. This is a technique for measuring the projector's ability to produce simultaneous light and dark. Usually this is done with a checkerboard grid of black and white and the spec is not anywhere close to 2000:1. The nominal number is 150:1, and both review and theatrical are allowed to hit 100:1 minimum.  

This is only interesting because measuring (and mis-measuring) grey level and black and white levels were a huge point of contention in the consumer market and yet again the market is being saturated with number noise (and marketing bits) due to a concept called HDR. In the past, a number would be made up and then the science would be made to fit it. Not by Dolby, of course. . . they be science people. But as an example of bad actors in the past, for one common spec the marketeers would define black as 90% grey and white as 10% white and measure from those. There were projector manufacturers who would use a clever technique of dynamic irising to increase their contrast ratio. There is currently one large screen system which uses a variation on this by using a faster and anamorphic lens and a dark, high gain screen. The re-reflection of a bunch of gold filigreed wall decorations in an auditorium with that system and everything takes on a green cast.  

But seriously, from a fanboy viewpoint, it may not matter if it is a million or 10 thousand to one if the entire system isn't adjusted for the movie environment. We can't have a lot of light in the darkened theater, or we'd be blinded every time there is an actual multi-thousand nit explosion of light. The eyes protective bleaching will kick in and it will be another 30 minutes before we get the benefit of all that dark again. . . or color at all. This is the HVS's (human visual system's) magic of accommodation, and Dolby's design and AMC's implementation try to take every advantage possible to make it work for us in our seats.

The Dolby Vision entrance announces with an inviting corridor of slowly moving scenes from the coming movie which get your eyes going into dark right away. The auditorium itself is black on black with highlights of deep red. You know that red. . . it is the long wavelength that you remember from scenes of a darkroom. Some magic allows the eyes to use the red without making all the other internal parts get stimulated. In a nice touch, each of the speakers. . . and there are a lot of them on the walls and in the ceiling for this Atmos system. . . each of them is lit with enough red light to see the details of the cones in the arrays or hanging boxes.  

Very cool. If only they lit up the speakers behind the screen. Wonder if they tried it. Did the red show through the micro-perfs of the screen and look cool or did that show the screen shaking devices? We'll probably not find out. There might be interest in dynamic irising, but there is just as much interest in how one keeps a screen tight when the room changes with humidity and temperature. Will it be an invitation for some smartass to come up with a term like the Aurora Borealis effect when the frequencies get out of balance and the waves make a pattern across parts of the sheet? Or did Dolby nail this problem already? Will have others who are in the big-screen-with-laser-equipment business, those who still need to use screen shakers to keep the speckle down? 

OK; back to the test pattern. After a few seconds of letting the eyes get used to the 2000:1 contrast of white to grey/black, suddenly there is a visual pop. The white does something, but the eyes really see the grey drop several levels to black black black. The intensity of the black is matte on matte. . . or is it that the matte on matte takes on its own kind of intensity vacuum? It is somewhat, that the existence of non-existence that gets triggered. As in, you look at a dark pair of pants in a scene and if you have some contrast you can see that it isn't just dark but there can be shadows in the dark. With more contrast there will be texture in the faintly lit parts of the fabric that may be darker or lighter than the shadows, and so on. This is the opposite. You notice that there is no subtle shade darker than what you are 'seeing', but that you sense that you would have the ability to see a range if it weren't so dang perfectly black.

What does all this contrast mean? We don't watch black and white movies. And color is. . . well, color. They're different parts of the physiological input system. Cones and rods and the twain where they meet. And that cones-based color system gathers data from only 40% of your field of vision, give or take 10% or so. To 'see' this, put your hands at 90° from each other, then cut that in half for 45°. Place that in front of your eyes. In the center angle is what the color wavelength sensitive cones are 'seeing'. Outside of that is what the black and white sensing rods are receiving. Any colors you 'see' there is either made up or residual memory from the last time your eyes scanned that part of your field of vision. . . . or something like that.  

A peripheral representation of the peripheral vision

When studying light and color, there is a lot of math and quite a bit of science. But when dealing with light and color perception, suddenly all the papers come from the psychology department. Another thing that is quickly noticed is that no matter what you knew 10 years ago, all the new papers will contradict or refine that data. How all this contrast affects the color images is difficult to discuss because it approaches magic. So, case in point, it was thought that we don't see color outside of a cone that is 30° of our vision. Now it might be 40 or with certain colors, up to 60°. Everything else is perceived in blacks and greys and white, but the point is that what one knew is no longer true and not only from an empirical (more or less) vantage. The new data comes from a tangent. It isn't colors from cones, but colors from a mental opposing color mechanism unique to one branch of the evolutionary chain. Opponent colors? That is so 1890's and Goethe. Wherever it comes from, there is a richness to the color and Dolby has been great with seminar papers and web seminars trying to up our game.

Well, you might ask – those who have upped their game, perhaps the richness comes from laser's capability to indulge us in a wider set of primary colors, a bit deeper blues and slightly deeper reds and a bit more green (and thereby brightness. ) But we were told at the AMC/Dolby Press Briefing that this extra color space capability – known as Rec. 2020's color gamut – is entirely a Creatives' decision and that thus far only one scene of one movie has used the extended gamut (that being the monster scene in Inside/Out. ) We were also told that using 2020 had no negatives, including no extra energy draw. Turns out that this is because the laser diodes happen to be at frequencies that are conducive to 2020 and need no more encouragement to deliver that gamut. . . and that every manufacturer is drawing from the same set of parts. But, that isn't the reason for the extra pop.

In fact, we are so used to seeing colors in terms of horseshoes that we forget that there is a range of lightness and darkness for all the colors that we are aware of. Just as with understanding sound, we sense quite a lot more than we often understand, then we realize that there is not only much more nuance but much more complication like 'squares of the distance' and reflections at certain frequencies, and physical things that happen at some harmonics more than it happens at others.  

Unraveling magic is all we're left with. Nothing wrong with that. How contrast affects color perception is a great field of study. All we know for certain is that the HVS wants to have a white point to hang its hat on and will let the gooiest brown be white if that is the best it can get. And it will then use that spot as the reference for everything else. We also know that while we can see a range of 14 orders of magnitude of light (ten million to one), at any one time we can only grab about 5 orders of magnitude (10 thousand to one) – again, not so different from our sound capabilities.

Using sound as an example, we might be able to make amplifiers and speakers that could create sound pressure levels that are beyond 2 or 3 multiples of the loudest we have now, but we cannot use it. The ears would clamp down, using its versions of chemical and electrical desensitising, just like the vision system shuts down to protect itself. We're limited at the top. This being the case, instead of cranking up the amount of light we want bouncing off the screen, refining down into the blacks makes sense. You get the mind thinking that the sun light level is correct and the orders of magnitude of depth are the luxury it craves.

Now that we have learned entendu, (if only the French had a word for it), and how that affects the efficiency of using light and power at the DLP in the projector, we get to learn the human analog, the land of Mr. and Mrs. Troland's son Leonard. What can go efficiently and effectively into the eye? This isn't nano stuff, but the iris of the eye makes it is square millimeter stuff and single nits and steradians that actually can be allowed to get into the eye. . . What Mr. Troland has to say about whether there is special magic in a million to one or whether 10 thousand to one would serve just as well will be the musings of a future article.

Fortunately and notwithstanding, we have our tickets to see Spectre in a Dolby Vision room, and we'll have our Suspension of Disbelief set onto 11, 'cause that's one more. . . or as the case may be, -11, 'cause that's one less. Impressions later.  


Oh, and to be certain, there is no pretense at extra super secret knowledge in any of the above. After the Press event your author sent a dozen questions or so to the press and engineering people at Dolby and got no response. More on those questions later as well – suffice to say that this system is the high end of the format wars, and it will be a closed system boutique and nuanced experience for a long time. They don't need to show us no stinking badges, or tell us about multiple DLPs talking to other DLPs so that no light slips into the cracks.  

Other articles on tangential topics:
Dolby Vision and The Force of Darkness
Lessons of Spectre and the Force (WIP)