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Author Topic: Real D & Dolby 3-D - What is the difference?
Claude S. Ayakawa
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From: Waipahu, Hawaii, USA
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 - posted 12-12-2008 06:00 PM      Profile for Claude S. Ayakawa   Author's Homepage   Email Claude S. Ayakawa   Send New Private Message       Edit/Delete Post 
Hawaii now has three theatres capable of showing digital 3-D movies. The first one at Regal's Dole Cannery 18 in Honolulu is equipped with a Real D projection system. The two others are Consolidated Theatres operated by Reading International and they just put in Dolby 3-D for Walt Disney film, BOLT. One installation is at the Ward Centre 16 in Honolulu and the other is on Maui at the Kaahumanu Theatres in Kahului. I have seen several 3-D films at the Dole Cannery already but I have never seen any in Dolby 3-D. The Dole Cannery ads for the film states that there is an additional $2.50 charge for the glasses. Consolidated does not indicate that there is an extra charge for their glasses. Is this due to the fact that they might be using reusable glasses? Regarding the two process, what are the difference and is one better than the other? With the exception of JOURNEY TO THE CENTRE OF THE EARTH in Real D which I thought was projected too dark, I like Real D. I am planning to see BOLT next week at the Ward Centre in 3-D and would like to know in advance what to expect.

-Claude

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Monte L Fullmer
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 - posted 12-12-2008 07:03 PM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
..another Beta vs VHS war, basically - both did the same but different ways of doing the playback.

Real D:

1-Silver screen..you're gonna have to sit in the middle to enjoy the movie do to the high contrast presentations.
2-Toss away plastic glasses
3-A leased system with royalties to Real D for usage

Dolby 3D:

1-Uses existing screen
2-Glasses that must be returned at the boxoffice for cleaning.
3-Theatre owner owns the system - no lease involved.

..the basics of the systems.. prob is more where others can chime in with the details.

-Monte

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Claude S. Ayakawa
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 - posted 12-12-2008 08:13 PM      Profile for Claude S. Ayakawa   Author's Homepage   Email Claude S. Ayakawa   Send New Private Message       Edit/Delete Post 
There was a big difference between BETA & VHS formats. When they were first introduced, I used both formats eventually settling with the top of the line Sony Extended Definition BETA and JVC's Super VHS machines in my home theatre system and I have found BETA was a much superior system with sharper picture and contrast on my special Sony Profeel 25 inch monitor.

I am pretty sure there is a noticeable difference between Real D and Dolby 3-D and my gut feeling tell me the Dolby system is much better than Real D after reading the product description at the Dolby site.

-Claude

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Monte L Fullmer
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 - posted 12-12-2008 08:48 PM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
At least with the Dolby, you can see 3D anywhere in the house, whereas with the silver screen, it's like the olden days of 3D - gotta sit in the middle due to the high contrast of the silver screen.

Sorry, didn't mean to do the video war comparision as in quality, just they played back on the same TV screen. We know that Beta walked all over VHS in terms of quality.

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Mike Olpin
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 - posted 12-12-2008 09:21 PM      Profile for Mike Olpin   Email Mike Olpin   Send New Private Message       Edit/Delete Post 
I've never had a problem watching Reel-D, even from extreme angles. The polarization process for Reel-D is circular, so the standard 45 degrees from the center of the screen rule that applies for linear polarization does not apply here. On both systems all seats see 3D and there is little to no ghosting, even if you tilt your head.

[ 12-12-2008, 10:32 PM: Message edited by: Mike Olpin ]

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Julio Roberto
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 - posted 12-12-2008 09:32 PM      Profile for Julio Roberto     Send New Private Message       Edit/Delete Post 
Well, the systems are similar in the intent and quite different in the execution. The aim of both systems is to project two full color images on the screen so that only one of them can be seen by one eye and the other by the other eye.

In both systems, the projector quickly alternates the projected picture between the left and right eye images, at 144 times per second. To the bare human eye, this looks like both images are on the screen "at the same time" (or close enough to fool the brain).

But the real-3D system uses polarized light to make the selection as to which image goes to each eye. The image coming out of the projector's lens intended for one eye (say the right eye) goes through a linear polarizer placed in front of the lens and then a very thin liquid cristal plate that is made to become a quater-wave retarder. When the plate is in a "relaxed" state, the light leaving the plate is polarized in a circular rotation direction that is opposite to that produced when the liquid cristal material in the plate is aligned (which adds another half-rotation), which happens when a high enough voltage is applied to each side of the plate.

Texas instrument DLP based projectors have a signal in their imaging electronic board that is perfectly tuned to the rate the images are formed in the micromirrors. You can use this signal to perfectly sync a colored wheel in home projectors to alternate a red-blue-green images on the screen at up to 144 times per second and produce that way an image that to the naked bare eye looks in color from just one micromirror device.

In TI digital cinema projectors (and some home projectors), this is not needed as 3 micromirror devices produce each color image (red-green-blue) at the same time. But this same synch signal is used by the real-3d active light polarizer to change the direction of the rotation of the light polarization 144 times per second, matching left-and-right images.

To preserve the polarization of the light after it bounces (off the screen), a metalic screen is needed. The light then reaches the eyes of the audience after going through their 3D glasses. The glasses are composed with each lens having a circular polarizing filter of opposite rotations. The result is that one filter blocks the incorrect image for one eye while allowing the correct one to go through. 144th of a second later, the other image arrives to the other eye in the opposite-rotation polarization state.

In the Dolby system (developed by Infitec), the projector is fitted with a circular filter wheel which rotates in front of the formed image in sync with the pictures in the micromirror devices, which also alternate quickly between the right and left images. But this rotating filter actually allows only a specific and narrow band of the green, red and blue light to shine through, blocking the rest of the color spectrum. When the image for the other eye is formed, the filter rotates and allows a different but equally narrow band of red-green-and-blue.

The lenses fitted on the audience glasses have similar filters that only allow a narrow set (band) of green/red/blue to go through, different bands on each eye.

As a result, each eye sees a slight different shade of all three colors, which when combined, produces a "full" color image. The image on screen is color corrected to compensate (as much as possible) for this slightly-different-per-eye color palette, but the brain combines disparities in color far better than most people think. It's actually difference in luminance on each eye that the brain has a real tough time dealing with.

Because the Dolby system uses colors instead of polarized light, there are no issues with orientation or with the screen having to be metallic, etc.

In a way Dolby system is similar to anaglyph (blue/red 3D glasses) in that color is used to separate the left and right eye images, but unlike anaglyph, all 3 primary colors are allowed to go through each lenses. You can read more about it here: http://www.infitec.net/infitec_english.pdf

None of these systems are perfect, of course. They each have their issues and they both don't present the images for the left and right eyes at exactly the same time, but 144th of a second apart is not really noticiable.

They both exhibit a degree of crosstalk (showing the wrong image to the wrong eye, which is seen as "ghosting" or double image), but this can be small enough to be almost neglible if done right. The Dolby system has some limitations on the color palette that can be rendered plus a slight rivalry between the colors of each eye (but absolutely nowhere near the problem of red/blue anaglyph glasses). The brain can easily adapt to that. The necessary use of a metallic (silver) screen on the Real 3D system brings some problems endemic to such screens: their inherited directionability and color spectrum, which makes brightness and color appear to change quickly depending on what angle you are looking at the screen. A curved screen (or a lenticular one) can help disperse the light a bit more evenly across, but at the expense of its own set of problems. The angle of the viewer with the screen also plays a role on how aligned the polarization of the light arrives with respect to the glasses' filters. But this is far less of an issue with circular polarization as used in Real-3D than it is with linear polarization, mostly used in the past for film-based 3D systems.

The main problem with the Real-3D system is greed: the manufacturers want a cut (royalties) for what is a very simple and cheap liquid crystal plate. You would not, I repeat, would not EVER EVER EVER imagine what is the total cost of manufacture of a plate system like the Real-3D z-screen. EVER. (Hint: it's a really really low two figure number).

The main problem with the Dolby 3D system is greed-and-cost: the filters used for their glasses are somewhat expensive to manufacture and Dolby/Infitec want to make a high profit selling them for good $$$. If Dolby would price their glasses at $6 (and one day they may), they'll own the market.

There are other 3D systems available for e-cinema, such as those using active glasses, which are glasses with batteries and liquid crystal shutters that turn black/transparent quickly in sync with a signal "broadcasted" in the theater in sync with the left/right images on the projector. The glasses completely block all the light in one eye while the image for the other is on the screen. No especial screen is needed for this system nor is anything needed in front of the projection lens. Only an electronic interface is hooked to the projector to "broadcast" (infrared or radio) a signal to the auditorium to which the glasses synch to know when to turn one eye "black" and the other transparent, and viceversa. Problem with this system: cost of glasses (although can be as low as $20), batteries (although a $1 battery can last over a week of constant use), plus your usual ghostings (if the glasses are not quick enough to go from full-black to full-transparent when the image on the screen changes, momentanealy allowing the wrong image to be seen by the wrong eye). If you can not manufacture shutters that switch fast enough, you can trade ghosting for flicker (not good either). Also, the glasses can obviously not be overly small (i.e. cardboard glasses) or cheap or lightweight as they need to house the button battery, the synch receiver (infrared or radio antenna), drive electronics and the liquid crystal shutter panels.

There is another system similar to Real-3D but with a rotating polarizing filter wheel instead of a static electronically activated liquid crystal plate, all the rest being the same (in practical terms) as the Real 3D.

And of course, you can also use dual projectors with either a simple polarizing filter (linear or circular, your choice) in front of each one or an Infitec color filter for the Dolby glasses. The advantages of dual systems being: double the light output, no royalties, cheap add-on (simple passive filters), simultaneous images for both eyes, more efficient separation (i.e. better polarizers than a LC plate), etc. Main disavantages: cost of two projectors instead of one and not perfect "registration" (keystoning, lens aberrations, etc) and not 100.00% perfect even illumination (two light sources, two incident angles, two different lenses, etc).

And we won't even talk about anaglyph (red/blue) systems. Although they don't need a special screen or lens or electronics or almost anything, each eye can only receive an image that is all mostly in one color, not to mention each eye gets a different color. The headache trying to fuse such different images coming from each eye can be epic for a lot of people, not to mention the resulting image having really wacked out color palette and uneven brightness. To make matters worse, the separation of the filters is usually not too good and a lot of ghosting is usually present. The only good thing about it is that nothing but $0.10 glasses are needed. No screen, no lens, no nothing. It can sort of work for a black and white film if done right, but that's not the case today.

If you ask me which way to go, I'd say dual projection. A system can be designed to allow one of the two projectors to move around to other screens when not needed for 3D, or to be used as back up, etc.

Expensive at first, but perhaps worth it in the long run. If a projector goes down, the other can continue carrying 2D shows.

But not really feasible until manufacturers stop asking for $100k for a projector that should cost $30k at most.

So what is left? Dolby is good enough. Now, if they would only lower the price of those [evil] glasses.

[ 12-14-2008, 12:39 AM: Message edited by: Julio Roberto ]

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Cameron Glendinning
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 - posted 12-12-2008 09:47 PM      Profile for Cameron Glendinning   Email Cameron Glendinning   Send New Private Message       Edit/Delete Post 
I've only seen the real d 3D set up myself and watched "Journey To the Centre of the Earth". Personally I thought it looked very impressive, granted that I saw it in a typical multiplex cinema with a common hight wall to wall screen.

I sat in the front left of the auditorium and had no issue with the quality of the effect nor brightness on screen, then again that actual cinema design does not allow you to sit way off center! The last 3D process I had seen (well worked with) was Imax 15/70mm 3D which also used a silver screen. I was surprised that there was not a very big difference in overall effect, obviously the Imax screen was bigger!

As for Dolby well nobody markets themselves better! When I visit their web site I even tend to forget that they are less than best to DTS with digital cinema sound! I look forward to seeing whether the difference is more media spin or science?

Claude, did you sit off center in the cinema or did the cinema feature a huge screen? My gut reaction is that IMAX digital 3D or MARK. G [TM] 3D with 2 projectors may be noticeably better but I suspect that it will more be the case of auditorium design and installation quality that defines the better experience more than brand.

edited for spelling

[ 12-13-2008, 05:08 AM: Message edited by: Cameron Glendinning ]

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Mark Gulbrandsen
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 - posted 12-12-2008 10:53 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Comparing theses systems isn't at all like comparing apples and oranges... The Dolby system is clearly(pun intended!)far superior to Real-D. Not only is the color space perfect but you can sit anywhere in the theater and experience the same quality 3-D image you can even walk right up to the screen itself. You can't achieve perfect color space or get the same 3-D effect with Real-D because of the required silver screen and its inherent directionality. The Dolby glasses are also IMHO far more comfortable to wear.

quote: Mike Olpin
The polarization process for Reel-D is circular, so the standard 45 degrees from the center of the screen rule that applies for linear polarization does not apply here.
Actually the company that custom made our polarizing filters for the Zion Canyon Theater manufactures the Real-D polarizing equipment. He said it's neither true circular nor linear... but more like eliptical polarizatioion. He unfortunately wasn't in a position to give me extreme details though. What ever they are using their glasses are not compatible with any other "off the shelf" polarization process.

BTW: In an assembled circular polarization filter there are both linear and circular filters that are stacked and sandwiched in between sheets of 2mm AR optical glass!! Linear filters of course just have the one linear filter material sandwiched.

Mark

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Chris Slycord
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 - posted 12-12-2008 11:13 PM      Profile for Chris Slycord   Email Chris Slycord   Send New Private Message       Edit/Delete Post 
quote: Mark Gulbrandsen
He said it's neither true circular nor linear... but more like eliptical polarizatioion.
[pedantic mode]Circular is elliptical... just the two focal points happen to be on top of each other. [Razz]

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Julio Roberto
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 - posted 12-12-2008 11:22 PM      Profile for Julio Roberto     Send New Private Message       Edit/Delete Post 
Yeah, I guess it has always been called circular polarization, but it all depends at what you are looking at.

http://en.wikipedia.org/wiki/Circular_polarization

They are all forms of elliptical polarization [Smile]

http://en.wikipedia.org/wiki/Elliptical_polarization

quote: Mark Gulbrandsen
BTW: In an assembled circular polarization filter there are both linear and circular filters that are stacked and sandwiched in between sheets of 2mm AR optical glass!! Linear filters of course just have the one linear filter material sandwiched.
Well, not exactly: circular polarizers often have a linear polarizer and a WAVE RETARDER (quarter wave) sandwiched in the substrates. Adding the retarder to the polarizer is what makes the wave "rotate" and change the polarization from linear to circular.

In pratical terms: a circular polarizer is nothing more than a linear polarizer and a piece of cellophane of the correct thickness in front. You can sandwich them in glass or polycarbonate if you want for protection etc ... specially the polarizer film as it's usually too thin and fragile to be by itself and not in-between glass or (non-depolarizing) plastic. What most people think is a polarizer film is actually a sandwich of two optical plastics sheets with the actual polarizer film in the middle. Most cheap film polarizers are made of polyvinyl alcohol polymer film and is manufactured so thin and flimsy it would be useless without some "support".

And "some form of elliptical polarization" only means that one would align the quater wave retarder (i.e. cellophane film) at an angle different of 45º with respect to the fast/slow axis when mounting it over the linear polarizer. In practical terms: move the plastic a little clockwise or counterclockwise. There. You have an elliptical polarizer.

Hmmm ... I wonder if there is a market selling Real-3D compatible glasses ... probably not as long as they keep a royalties system they can afford to give them away or sell glasses below cost.

Making Dolby glasses is both impractical and not legally possible.

Now, if I could only get $0.10 for each person (i.e. pair of glasses) that is going to watch Cameron's Avatar in 3D in the world ...

[ 12-13-2008, 12:47 AM: Message edited by: Julio Roberto ]

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Monte L Fullmer
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 - posted 12-13-2008 12:24 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
..silly analogy here below.. if it counts..

(Elliptical polarization is like the optical camera of a reverse scan being out of phase: a point swinging back and forth while the circle turns and Linear polarization is when the camera is in phase - a point swinging 45* off vertical center in a straight line - stuff you see on an O'scope when doing "A" chain alignments)

-monte

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Mark Gulbrandsen
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quote: Julio Roberto
Well, not exactly: circular polarizers often have a linear polarizer and a WAVE RETARDER (quarter wave) sandwiched in the substrates. Adding the retarder to the polarizer is what makes the wave "rotate" and change the polarization from linear to circular.

Exactly! And you flip just the retarder over to allow it to rotate the light in the opposite direction for the other eye...

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Claude S. Ayakawa
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 - posted 12-13-2008 03:00 PM      Profile for Claude S. Ayakawa   Author's Homepage   Email Claude S. Ayakawa   Send New Private Message       Edit/Delete Post 
Thanks everyone for all of the informative response to my question regarding the difference between Real D and Dolby 3-D.

Cameron, The Dole Cannery Real D auditorium in Honolulu is one of the larger house at the complex and has a very good size screen. I had learned a long time ago when watching polarized 3-D films, sitting in the centre is the best and I always do that. I had no problem with all of the previous Real D 3-D films I saw there but for some reason the projected image during the screening of JOURNEY TO THE CENTRE OF THE EARTH I saw was too dark for my taste. The 3-D effects however was excellent and I just ignored the darkness of the image on the screen and enjoyed the show

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Mark J. Marshall
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 - posted 12-14-2008 10:08 AM      Profile for Mark J. Marshall     Send New Private Message       Edit/Delete Post 
quote: Julio Roberto
To the bare human eye, this looks like both images are on the screen "at the same time" (or close enough to fool the brain).
Not true. Although most people can't tell the difference because they are unfamiliar with what two images being on the screen in perfect sync look like compared to two images that are not in sync.
quote: Julio Roberto
They each have their issues and they both don't present the images for the left and right eyes at exactly the same time, but 144th of a second apart is not really noticiable.
That's a little more accurate, but it is noticeable. For me, it's annoyingly noticeable.

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Steve Guttag
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 - posted 12-14-2008 12:03 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
quote: Mike Olpin
I've never had a problem watching Reel-D, even from extreme angles. The polarization process for Reel-D is circular, so the standard 45 degrees from the center of the screen rule that applies for linear polarization does not apply here.
No so fast, wonder-kid.

With any Silver-Screen you have the physics of light to contend with. Almost any silver screen is going to be down to half its light by the time you are 20 or so degree off the directly reflected light ray. As such, an acceptable cone of light is going to be, AT BEST, about 45-degrees...forgetting about the 3D effect entirely...just talking about the light.

You can increase that by curving the screen, but it will never have the uniformity of a matte-white screen. Even a gain white screen, like pearlescents with gains in the 1.5-1.8 range start out with a more acceptable area of light and need to be curved much less to get a reasonably uniform light over the entire screen surface.

As for the 3D effect side...yes, the circular polarization is a vast improvement, in my opinion, over the more traditional linear polarization. I strongly prefer Dolby's form of wavelength filtering as the image look more natural to begin with (close one eye and look at the image...while certainly darker, it doesn't have the 3D metallic look to it).

Where you sit ALWAYS has an affect on the 3D image...can't get around the physics...your perspective of the image is different than the camera's as you move about. If you have a 3D system set up...do a test afterhours....freeze and image on the screen and then go downstairs and walk around the theatre...everyone's perspective is different. Note, this true in 2D too BUT it is exaggerated in 3D because you are being given visual cues based on the camera's perspective too.

Steve

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