The Dangers of Stacking Projectors for Passive 3D

Mr. Walter,

I agree with your points here given that this is a home theater or commercial application where content would be delivered through a satellite or cable box and a 3D BluRay player.

It is worth saying however that we have implemented “stacked” 3D in museum venues over the years where it has been a natural fit. 

Venues where they are using custom produced media, (perhaps even filmed with a 3D camera), that is run from a server or servers up to 1080p over VGA or DVI, and output through dual projectors with polarization filters stacked properly can benefit from the passive technology as the ongoing costs of replacing lost/stolen/broken glasses in a public venue can be extremely high.

Of course utilizing a higher level single projector passive system would work as well, (like a cinema projector with a retractable polarization or dichromatic spinning wheel) although sometimes are cost prohibitive.

Danger, Danger Will Rogers, everyone is finding danger in 3D. It’s not dangerous, and its probably not nearly as important to the future of home entertainment as the market would like to suggest, but really, are we afraid to use it creatively? Do we need articles to warn us of the dangers? IMAX digital 3D was widely acknowleged as the best viewing experience for Avatar, the watershed moment for commercial 3D. Their system is indeed dual projo, linear polarized passive, and it generates 22fL in 2D and they run 3D at 8fL minimum. They are Rebels with a Cause! Somehow they got past all those dangers mentioned above. Their screens are bigger, brighter, and filled with the image of twin 2k DLP projectors. The Runco D-73 is modeled after that reference technology adding digitally modulated light sources for good measure. That means no drift, no assymetries (the actual known cause of viewing discomfort), and via the global geometry processing, perfect and permanent convergence alignment, yes, right to the corners. Colorimetry must be calibrated with memories for ‘night view’ akin to a mastering lab, ‘day view’ for added color saturation, albeit with a bit of a departure from Rec 709 standards, (but hey, it can double the perceived brightness so the ball game looks good, in high ambient light). A great trick is it can do it without damaging fleshtones the way mass market displays do. And of course there are 2 memories for 3D modes as well. 3D is not only color shifted due to the glasses, but 3D is dimmer by design, and color is pushed in cinema to compensate for our dim light perception shift, as it should be in the home, if we are to match the standard. LED DLP gives us the range to do that. So although the list of ‘hazards’ mentioned in this article are relevant perhaps to a DIYer, a CEPro has a turnkey solution with the D-73 which handles screens up to 10’ or 11’ wide in the scope format. Go up a step and the SC-50/60 models can do active 3D for screens from 11’ to 22’ in scope and still get IMAX light levels. Take it a step further and stacked SC’s are available to do IMAX passive or active style 3D implementations, choose on the fly based on preference, or glasses & head count!
As to the headache arguments that invariably support the 3D political position of idealogs of a particular approach, I say poppycock. There is no clarity on when or if viewing fatigue will be an issue with any particular approach. The inter-eye flicker of active is evident when sync and blanking aren’t right, but they can be made right, and passive head tilt issues for linear systems aren’t reported by IMAX patrons,  nor are problems reported for RealD, or Dolby3D any more than the others. Half of European cinema is active and the flagship Arclight theater in Hollywood is active, and they get premium money and fill the seats as well. So for high end personal cinema designers we know they all can work well, so get over the 3D tech choice arguments and start with what matters most; the viewing geometry, screen size, viewing distances and an immersive experience comparable to the best Hollywood can offer. The technology we use for the ‘3D’ part of the design is open to question, and the answers come from the clear set of experience objectives the Personal Cinema Architects I associate with lay down on day one of the design process. Wider, brighter, and better is the starting point, and then dual passive or single active is in the tool kit today for those creative enough to explore the differences and reasons for selecting either one. The market would love us to watch our 3D on 50 inch flat panels with ‘faster phosphors’ and refresh rates…At the end of the day, 3D is eyeball manipulation, and seeing 50” in 3D and the lamp next to it in 2D will always cause discomfort as you have conflicting focus and vergence cues. And now some flat panel perfomance for 2D is going backwards to create better 3D. That’s a great reason to buy for the 2D image quality first and foremost. 3D is not little screen friendly, and it never will be, but make the screen big, like real big, and now you’re talking. And of course 2D will always be the best viewing experience (sorry JC), and guess what, wider, brighter and better is what makes that dance as well. For CEPro’s 3D confusion is our opportunity to educate, demonstrate, and sell what really matters;
A superior and genuine cinema experience at home!
That’s my story and I’m sticking to it.

John Bishop
Personal Cinema Architect

I find it ironic that CE Pro runs an article that poo poos on dual projector LED for 3D when it gave Runco the
2010 CE Pro Best Award for it’s
3Dimension™ D-73d Series

Indeed.

Scoopcity - It’s a technical perspective, written by the vp of a projector manufacturer with extensive engineering experience.  So why would CE Pro not run it?

That being said, you’re exactly right to question how well the judges understood the functionality and performance of the product they chose for a Best Award.

Hi Scoopcity, we open to both sides of the argument, good 3D is not an absolute formula, think of it like a Les Paul vs. a Stratocaster.

Both are fine guitars, and arguably the best in the world of music. Choosing one comes down to a matter of personal preference.

I may be wrong, but Mr. Walter’s opinion of twin projector LED 3D may be a bit one sided.

sure, but in the above posts, there are other opinions coming from a particular perspective too.

Like I said Scoopcity, it’s the video world’s version of Les Paul vs. Strat. You’re not going to go wrong with either approach because DP’s 3D looks awesome and Runco and SIM2’s 3D looks awesome too.

Great point, Bob - that’s why we didn’t write a shill piece promoting one specific projector or another (or manufacturer, for that matter).  Simply wanted to highlight the apparent challenges of an existing solution as an educational resource.

Open conversation that tackles different engineering approaches is supposed to invite discussion and debate.

Thanks Michael for reading and contributing. I think most industry members respect the technology DP is bringing to market.

The thing for all of us in the industry is to try to remain open minded to not only 3D, but also to the technologies that are driving the interest in 3D.

Everyone..I love the feedback.

First, my view was the “DANGERS of stacking 2 projectors to accomplish passive 3D.”  Not in anyway bashing 3D.  In fact, I have spent the last 2 years traveling the country promoting 3D at trade events, seminars and dealer shows.  John has attended at least one of my presentations so I’m sure he knows my views on 3D.  IN fact, I’m probably one of the biggest supporters of 3D on the planet.

The biggest obstacle 3D faces is expectations.  Dealers and end users expect 3D to be equal or exceed the performance and simplicity of their current 2D systems, and that just isn’t the case.

I did not write the article to bash any of the competitive products.  As a representative of a major projector manufacturer who has been offering 2 projector 3D solutions for almost 10 years, I base my warnings on customer feedback.  The reason Digital Projection spent millions of dollars developing the single projector, 3D solution was to respond to a marketplace that consistently told us that maintaining performance with 2 projector systems was too expensive and time consuming.

As for the IMAX reference, we are very familiar with IMAX as they owned us for 2 years.  In fact it was DPI that introduced IMAX to DLP.  This is reference is excellent to support my view.  IMAX uses highly trained technicians to operate their dual projection systems, and those systems are tweaked daily to maintain peak performance.  The reason IMAX uses 2 projectors is to illuminate the massive screens they deploy, not for benefits of two projector passive 3D. 

I have no reason to put down LED solutions as DPI also offers LED illuminated projectors with similar performance characteristics of the model mentioned.  DPI could offer a similar solution based on stacked LED projectors immediately.  We chose not to.

For the record, DPI demonstrated stacked DLP projectors for passive 3D solutions 4 years ago at CEDIA on the show floor.

Runco and Sim2 made beautiful 3D images this year at CEDIA.  I commend them for embracing the opportunity to expand the industries knowledge and appreciation of what great 3D images can look like. 

Thanks again to everyone for your comments.

The premise of this piece is
not anti 3d, that’s crystal. But it’s also clear that it is intended to warn against a particular approach to implementing 3D, an approach used by IMAX, the reference in commercial cinema to date. And they do suggest it is better at doing 3D, not just brighter. The point is that among the conventional approaches, single projo passive polarized, or split spectrum Dolby, or the active, or dual passive, all have their positives and all have their challenges to execute. I’ve seen some very bad active, and very good, but I’m not ready to issue warnings about active sync issues, blanking, or color shift. I expect good examples at the high end, and bad at the low end. I am agnostic in the process, I sell both, and have valid reasons for choosing whichever method we go with in a given design. The dangers above are a straw man, no harder or easier to deal with than the design obstacles of any of the methods. The International 3D Society suggests all the current cinema methods are equally good at doing 3D, so that’s a start. From there we go back to cinema design basics; viewing geometry, luminance levels, and fidelity to a cinema standard. I think there is ground for us all to agree on in there somewhere.
Wider, and brighter is better.
JB
PCA

There are two solutions for splitting a 3D signal into L&R signals but they require two boxes.  The Optoma 3D-XL and the Lumagen Radiance mini (perhaps the full size as well) will split 3D signals into L&R streams.

A poster on avsforum was able to do it using two JVC RS40 projectors and two of the Optoma boxes.

The Optoma 3D-XL processor can split one HDMI 1.4 signal into two HDMI 1.3 1080p@60 Hz signals, one for each eye. In fact, you need two of theese to get the job.

As CEPro is one of the important publications within our trade, and as such is a public record of note, I feel it is useful and necessary to clarify the counterpoints to what was posited in this article.
‘Scoopcity’ wondered why CEPro would have published an attack on the fundamental technology behind a product they also recognized as ‘Best of the Year’, the dual engine, passive 3D product by Runco, the model D-73. I believe it’s possible that the article had its roots in DPI’s own experience where using dual projectors in commercial applications of the past proved challenging in the ways George describes, and has nothing to do with his competitors. The IMAX Digital 3D system uses the same method, and is the recognized leader in pro-cinema to date, but wasn’t mentioned in the article, so one can assume the target of the article was the lower echelon commercial world which has used dual projection passive for a decade to their satisfaction even with the problems above. But the higher standards of today’s cinema and the examples of IMAX and Runco specifically, have demonstrated that all of the obstacles mentioned in the article have clearly been solved in our modern state of the art implementations, and that should be made clear, and not confused by the article above. Now we can look at the pictures and decide for ourselves. Yes CEPro awarded the D-73 a Best of 2010 award, and CEDIA gave it their coveted Video Product of the Year award, and Electronic House has given it their product of the year award for 2011. But I don’t think any of the folks involved in the giving of these awards did so ‘without understanding the functionality and performance of the product they chose’ as ‘Mbridwell’ suggested above. That is an outrageous statement and contradicts all logic. The technology of IMAX has been brought to our home cinemas for the first time, and having seen it in action, industry experts are recognizing it with their top awards. That doesn’t suggest their decisions should be in question as ‘Mbridwell’ says, it only suggests people liked what they saw.
Given that the technical ‘hazards’ reported above have all been solved by IMAX and Runco, I would like to clarify the additional comments by George in his response to readers. He suggests that the dual engine approach is ‘too expensive and time consuming’ and that’s why they did not pursue it. He goes on to say the IMAX system ‘uses highly trained technicians to operate their system’, which is ‘tweaked daily to maintain peak performance’. He implies that the dual engine nature of IMAX Digital 3D is the reason for this; it is not. All 3D systems in commercial cinema are operated by trained technicians and every 3D movie studio requires not only daily tweaks, but they demand tweaks before every showing. This has nothing to do with our home cinema environment, it is because in pro-cinema 3D content overflows the active pixel image area in order to avoid a significant artifact that causes discomfort to viewers, the ‘edge conflict’.  At screen edges, you can lose one eye’s view of the object, and the 3D effect collapses. So studios provide a ‘technical spec for projectionists’ which includes a masking frame that must be setup before each showing. That’s true for every system, single projection or dual.
I agree 3D expectations are high, and the content assortment is low. But we have a number of emerging solutions for the high end enthusiast, and that includes Active or Passive systems with single projector or dual engine. As a Personal Cinema Architect, I am glad to have more tools to work with, and will judge them all on their merits as more in field experience is attained.  For now, I’ll put the ‘Dangers of stacking projectors for passive 3D’ which outlines the ‘numerous hazards’ but claims not to be written for the purpose of ‘bashing competitors’ aside, and go on to designing and building the best architected systems we can, using the best tools to achieve the highest goal; a truly cinematic viewing experience at home; 2D first, and 3D just for fun; Hazard free of course.
JB - PCA