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Discussion Starter · #1 ·
What's the status of using multiple digital projectors, driven by an appropriate video processor or HTPC, to display a single source split across an array of projectors ("projector tiling" ?)


The Matrox Parhelia looks promising for the digital tiling output.


Split an HD or DVD across four $3000 XGA projectors, like the VT540, and you've got QXGA for about $12K. Kind of like projecotr stacking for extra brightness, except you tile the images side to side and top/bottom for increased resolution.
 

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how do you match light output? or color correction, or seamless edges, or or or,
 

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Runco's up and coming VX5000 allows for stacking...


Chris
 

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all projectors allow for stacking. We're talking side by side here
 

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I believe Mitsubishi may have some experience in this area, folks. Please remember their monoblocks seens in so many retail store and other places where the overall picture is made of of multiple displays, including some very tight-seamed displays.
 

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Forum member Mr. Wiggles has the info you might want - I think I remember one of his posts saying he set up a planetarium "stiching" projector pics together. It might have been in the HTPC forum, I'm not sure.
 

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Ramick,


what timing.


With digital projectors is difficult to blend images together because of the non-perfect black levels. To create a good transition you almost have to have some overlap. And with this overlap, you have a region where the blacklevel is far from perfect making it obvious on dark images where the overlap is. On the other hand, trying to "butt" the images up to one another with no overlap requires perfect optical geometry in the output image.


In Houston, at the Planetarium we stitch 6 images from 6 barco 1209's together to create a hemisphere image. Digital projectors simply wouldn't hack it in our demanding set-up.


However, for tiling of images, the new 1800:1 projected images of TI's newest DLP's might make it possible. This would make the overlap regions far less noticeable.


The other cool thing would be to try three images in a panorama so the overlap doesn't happen in the center of the screen where everyone is looking the most. How 'bout putting three xga projectors on their sides to create roughly a 2K X 1K image? This would put the transition regions in other areas other than the center.


This is a big area of interest currently and the companies that do it seamlessly make good money. I think this will be one of the big items at Infocomm this year.


-Mr. Wigggles
 

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I've been reading about a company that makes lenses to do the blending purely in the light . The edges of the lenses slowly become opaque. This allows you to do edge blending seamlessly even with a digital projector, because the light is fully blocked at the edges.


I dont know specifics yet (including cost or if they are even available), but they could be cost-effective for high-end installations.


Andy K.
 

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The old 3 panel Cinerama process blended together 3 35mm images (6 perfs, so each was about 1.00 aspect ratio).


The best blending was done with a little mechanical device that moved and kind of fuzzed up the area where the images met. This was actually invented by the Cinemiracle folks (a competing process bought by Cinerama).


So we are back to the 1950's. Interesting.
 

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Discussion Starter · #11 ·
A 15 digital projector array is in use at Lawrence Livermore National Lab:

http://www.llnl.gov/str/Quinn.html


This one has received attention in the popular press and has been discussed on these forums last year.


I think with careful calibration and tweaking, current model digital projectors may enable acceptablt home tiling.


But what video processor or HTPC components would we need to split the overlay (HTPC) across multiple projector inputs?
 

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RGB, you are essentially asking for the 'killer app' in the world of home theater. Anyone with enough brains, money, and marketing ability will [probably] be able to make a good deal of money.


As a side note, this would also allow those asking for 2.35 format DLP and LCOS projectors to find a 'reasonable' solution to their (and my) madness.
 

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The main problem, in a nutshell, with digital edge-blending is blacks moreso than whites. We already ***** about the absolute black level on digital projectors. Now imagine a vertical bar that is 2x the lumens smack in the middle of the black scene. Too distracting for anyone who is contemplating such a setup.


In fact, it would be less distracting to forego the edge-blending entirely and just butt the two images up against each other, and live with the small seam.


Andy K.
 

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Andy,


The problem with the "small seam" is that it dead center and is rarely small.


The optics are rarely uniform enough to make perfect rectangles.


We really need more pixels out the imagers coming from TI. Maybe they could come up with a process where they could test XGA chips for defects one by one and then shoove four together to make a QXGA chip. I know I'm dreaming.


-Mr. Wigggles
 

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Dreaming? Salivating is more like for me :)
 

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This is certainly possible. The trick is to use software to make up for shortcomings in the hardware. There are various schemes in the research community for correcting color balance, luminance, and geometric distortion when using commodity projectors. Home theater people tend to be very picky, though, and nothing is perfect so I doubt this type of thing is appropriate for this audience.


The first step is to build something to hold the projector that can easily adjust it in all 6 degrees of freedom. This way you can get the images squared up as well as the optics will allow and then lock the projector into place. Next, you put various kinds of calibration patterns on the screen, take pictures of the screen, and process them in the computer to find out how the color varies across and within tiles and what sorts of geometric distortions are present. Your movie playing software then takes this info and pre-distorts the images sent to the projectors with the inverse of whatever distortions each projector has. Bingo! A seamless tiled display. In practice this is mind-bendingly difficult.


There is also no way that it would only cost $12,000. The 4 XGA projectors would cost this much by themselves. An end-user cost of $40,000 is probably more realistic when you take into consideration the cost of the computers, network, screen, etc. This is 20% the cost of the JVC QX1, but still more than most people would be willing to spend. If anyone is *truly* interested in something like this, check out my website ( Visbox ) and get in touch with me.


Here's a picture of the 40 tile display that I recently built. I'm working on color calibration software for it now.


Albert

http://damavand.ncsa.uiuc.edu/DisplayWall/dscf0533.jpg
 

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Actually, it's an aerial photo. The operations people on my campus take pictures every few years to keep track of what's going on. That image is around 10,000 pixels on a side.


Albert
 

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MrWigggles,


Agreed that the seam would be visible in either case. I'm simply suggesting that a thin, black seam would be less distracting than a wide, twice as bright band in black scenes. Besides, Diptych's are in fashion right now :)


akhaksho,


How do you overcome this inherent limitation I am referring to with Digital projectors like the ones in your photograph? What is the absolute black level that you tend to see from any 1 projector?


I wonder if anyone would be willing to put some kind of gradiated transparent->opaque filter inside of a Panamorph, in order to make a home-brewed version of this?


Andy K.
 
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