Film-Tech Forum ARCHIVE: Real D & Dolby 3-D

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Topic: Real D & Dolby 3-D - What is the difference?

Julio Roberto
Jedi Master Film Handler

Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008

posted 01-15-2009 01:09 AM

Both systems, Real-D and Dolby, "suck up" a lot of light. At least 70%. On some setups, as much as 85%.

That means it would roughly leave you with an image that is 1/4 as bright as your projector/setup would otherwise normally do 2D.

As a result, all the light you can get from those systems is of help.

One way to get more light to the audience is by getting a high gain screen. If you use a high gain screen, both 2D and 3D images would appear "twice as bright" (i.e.) to those sitting in the preferred cone of illumination for the screen.

As a result, you can lower the lamp output for 2D. But with 3D, even a high gain screen would still need a boost. Remember you only got (roughly) less than 1/4 of the needed light. If you double that up with a high gain screen, you are still 1/2 short. Only half way through to the same 2D level.

Since Real D basically needs a silver screen, and these are usually of very high gain, there is no "way" around it anyway. But yes, Real D benefits from high watt lamps for 3D as much as from a gain screen, so usually both are needed (and resulting light levels are still under 6fl in many cases).

Say you are currently using a 3000w lamp with a 35mm (or digital) projector. If you change your screen from matte white to a silver 2.4 gain screen, all of the sudden you could start using (roughly) a 1500w lamp to obtain the same light level for the select group of individuals sitting in the screen's "preferred cone". If your theaters is very wide, this could be a problem, as audience sitting on the front corners could start seeing a seriously dimmed image.

That's why a silver screen is said to be very directional. It helps convey a brighter image to those sitting in front of it at the expense of a darker image those sitting "on the sides" at wide angles.

Dolby 3D doesn't require a silver screen, and could use a regular matte (or low gain) one. But since it also requires some sort of brightness boosting to obtain good light levels, besides a brighter projector's lamp, a high gain screen (silver or not) may be the most effective way to obtain it.

Color on silver screens preferred cone of illumination can be fine, but if you are sitting close to the screen the colors may seem to dull-out as you look at the corners of the screen as the angle increases. Some silver formulation also have a different gain figures for different light wavelenghts (different colors). This can be compensated by color correcting the digital projector, though.

Real-D decided that their business model was going to obtain a stream revenue from movie theaters by charging them yearly contract prices and percentages on 3D tickets (surcharges) in return for installing/mantaining the Zscreen and supplying glasses.

Bill of material COST of paper glasses from Real-D are about 1 cent each. Manufacturing COST would depend on whoever is manufacturing them's operation effeciency. Regardless, it is always below 25cents per pair, possibly 10cents after everybody is accounted for. Remember manufacturing COSTS don't really mean much. You have to account for transportation, warehousing, taxes, profits, etc.

Dolby doesn't charge a percentage royalty or yearly "lease". But they do charge (dearly) for their glasses. Their manufacturing cost is far (far-far) more expensive, and they retail for about $28 each to theaters. As a result, they can not be given away or anything like that. A system has to be put in place to recover them from the audience, clean them, and reuse them.

Still, the cost of replacing broken/lost/scratched/whatever glasses is significant, and Dolby's business model is to obtain a regular stream of income by selling these glasses.

RealD could also do the same if they wanted. Charge a couple thousand for the 3D adapter and sell glasses at 40cents each and profit from that. I'm not sure why they didn't go that way. I guess they were afraid soon they'll have competition on the price of the glasses from cheaper manufacturers. By using their "royalties" contract, the glasses are "free" (pre-paid) to the theater and therefore it doesn't make sense the theater owner would look at another (cheaper) glasses' supplier.

Similar systems to RealD could come up in the market, though, as the technology is in no way exclusive to them. A similar system with a rotating disc (instead of a LC plate) was said to be marketed for theater usage. But the market is not too large and I doubt many people would be interested in a couple thousand 3D screens and a couple of 3D movies per year in a market with already 3 or 4 strong players (RealD, Dolby, Masterimage, Xpand).

Xpand system doesn't need any special screens or any modification to the projectors whatsoever. A simple interface box connects to your projector and a transmitter broadcasts a signal in the auditorium. Their active glasses select the appropiate image for each eye. Light loss is similar to other systems. The dissadvantage, as in Dolby's case, is the cost and life of the glasses. When Xpand's glasses batteries die, it's time to purchase a new pair. Collecting them and washing them for reuse is also a good idea if you don't want to go bankrupt.

Masterimage has also an Infitec (Dolby) copy-cat product, but I haven't seen it and I don't know if it carries a price advantage (probably). Perhaps they are just also reselling Infitec's products like Dolby is.

Real D's system is the worse in crosstalk. It means is the most likely to produce double images (ghosting). As a result, they want to pre-process the films to KILL THE CONTRAST on those parts of the image where the parallax (I guess you could call it the 3D) is too large *and* the foreground and background contrast is too large (i.e. a foreground flashlight in a dark, distant background).

So their "ghostbusting" pre-process is but another image-quality-killer for the already not-so-hot digital 3D images of today.

Remember the 3D reality of today compared with 2D:
-increased JPEG2K compression
-half the color resolution 4:2:2 sampling, reduced color depth 10bits
-reduced resolution on projectors older than a few months (TI chipset not able to cope with full 2K 48fps)
-reduced light levels with dim 4fl images
-144hz "flicker"
-High gain screen's "artifacts"
-and now, "ghostbusted prints" with contrast wiped out in "hot" 3D areas ...

And, of course, a tiny bit of image "quality" is loss when the images go through a system like real-d's zcreen (unlike dolby's, where the filter goes BEFORE the imager, not in front of it, although Dolby adds reduced colorspace to their lists of cons) and ALL systems always suffer somewhat when the image goes through (doubious quality) glasses. But that's just minute compared to all the rest.

Don't we just all love 3D [Smile]

It's digital, so we know it's perfect.

[ 01-15-2009, 08:40 AM: Message edited by: Julio Roberto ]