[WIP] Active S-3D dual projector system

[Tril]

I own eDimensional shutter glasses. I have a 21 inch monitor that supports 120 Hz so they don't flicker but there's ghosting, probably because the phosphor are not fast enough. I wanted an upgrade that would increase the screen size and reduce ghosting so I made a passive dual projection system.

The passive system is currently a work in progress. So far I'm unsatisfied with the amount of ghosting I get. I have two 2300 lumens projectors and I can't get the picture to completely disappear, except if I decrease the brightness and contrast a lot or use a black screen. Both of these solutions are not acceptable.

It got an idea and from my first quick test, it looks promising. If I can find the hardware for a reasonable price, I know I can probably do it.

For my test, I placed eDimensional shutter glasses in front of the projector , used a 9V battery to darken one of the shutters (don't do it for long or else you'll damage the glasses) and it completely (or very close to completely) darkened the picture. It was much better than what I've been able to get with my passive system.

I want to place an electronic shutter in front of each projector and wear shutter glasses. The stereo ouput will be configured in the NVIDIA drivers as Dual Stereo Output. I'll use an external circuit to drive the lcd glasses and the shutters in front of the projector at the frequency I wish to use (120 Hz or more). Since the two projectors are always projecting a picture, I can make the glasses and the shutters switch at any frequency I wish without being synchronised to the signal. All I need is for the shutter glasses and the shutters in front of the projector to be syncronized to each other.

This last summer, I made myself a circuit to control LC glasses using an ATMEL microcontroller and it was coded in C (for those curious). It used the DDC and the VSYNC signal and it worked. If I can find some shutters suitable for this, I know that I can take care of the hardware and software side of the project.

The eDimensional shutter glasses are unsuitable for this because each shutter is too small (1 inch by 1,25 inch). I need something bigger but that also means more expensive. It also needs to support 120Hz or more. There's also the risk of frying the shutter.


If anyone knows of companies selling electronic shutters, please share the names of those companies.

If anyone knows of shutter glasses that can still be bought that use shutters bigger than the eDimensional glasses, please share the names of those glasses.

So far, I found one company that sold a product that would have worked.
Boulder Nonlinear Systems (http://www.bnonlinear.com/)
They quoted around 2000$ for each shutter and I need two. That's out of my price range.

If you can buy shutter glasses around 30$ to 100$, it's probably possible to find another product with similar characteristics that's not much more expensive and that is bigger.

[Likay]

Hmmm. You might look for the shutterdevice in active welding eyeprotectionglasses. (those which get dark when using them). You probably need to modify them slightly to suit your purpose. You can either get damaged glasses with the shutterdevice intact or try searching for spare parts.

Might be worth a shot.

Cheers

[sharky]

Dear tril,

i am for shure going to follow this topic, because its one of the most interesting here.. actually its the first one witch is a REAL diy thread... iVery like your idea. i don't understand anythig of electronics, but i have spoken to Ragedemon some weeks ago about this kind of things. as oyu know he is our electronics-guru. He said that if you want high frequencies its not enough to swich the shutters on and off, because the shutters need some time to get black. he said that you have to over voltage them in the first part, then to giv ethem the correct voltage and for svitching off you need to reverse it. else they are too slow and won't make a good effect without ghosting.

i don't know if the welding shields work, but you can try fr shure. i even don't know if they use an lcd pannel.. i don't think. i only know that they are relatively expensive, and that they don't get completely dark or completely transparent...

http://cgi.ebay.it/Auto-Helm-Pro-Series ... dZViewItem

bye

sharky

[LukePC1]

You want to make first shutters in front of the projectors and then wear shutterglasses in addition?
What shall the shutters in front of the projectors do? If your Projectors work at 120hz (DLP?) this shouldn't make any difference. It might be using a monitor at 120hz without glowing phospor...

Your solution would make the image darker (waste energy), because of more shutters and polarizers (which are a part of the shutters).

Is it not enoug to wear just the shutterglasses?

How do you configure dual Stereo output - eg. for a superlarge (wide) screen? When I connect 2 Monitores (not in clone mode) only one has 2 Different pictures on it (just one is 3D the other 2D)

Try to convince me of your project...

[sharky]

maybe you got it wrong.. the two shutters in front of the two projectors just darken first one projector and then the other one. your eyes to dthe same.. if there youldn't be the shutters infrotn of the projector your active eye woudl see both images..

bye

sharky

[Tril]

I can use one of the DLP projectors I have at 60 Hz or 85 Hz with shutter glasses. At those two frequencies, it produces visible flicker and at 85 Hz, there is a color difference between the two eyes.

I currently have a passive system working. I have two projectors in clone mode using Dual Stereo Output and it works. I'm using two DVI cables. When using the passive system, there are polarizing filters in front of the projectors and I wear polarized glasses. Both of these cut down the brightness.

Here's another explanation of what I propose for the active system. When using Dual Stereo Output, each projector projects at 60 Hz. What I wanted to do is have a filter block one projector and one eye at the same time, then afterward switch to the other projector and other eye. I can have the switching work at 120 Hz even if the projectors work at 60 Hz.


Let's look at the brightness of the passive vs active systems.

- LC shutters like those found in shutter glasses have a polarizing filter in them. So the light drop in a LC shutter placed in front of a projector (when letting light pass) is about the same as a polarizing filter.
- The same thing applies to the LC shutter glasses vs polarizing glasses.
- In the passive system, the left eye always sees the output of the left projector and the right eye always sees the output of the right projector.
- In the active system, each eye sees black half the time.
- The eD glasses have a green tint to them and the polarizing glasses have a grey tint to them.


Disadvantages of the active system :
- It might be about half the brightness of the passive system.
- It will need some tweaking of the colors to diminish the green tint.
- Wearing the wired active glasses (wired because it's easier to make a control circuit for wired glasses and because they don't need batteries). The eD glasses don't fit well over my prescription glasses while the theme park style passive glasses fit well. The glasses lenses of the passive glasses are bigger then the eD glasses and are more suited to watch a big screen.

Advantages for the active system :
- The screen does not need to preserve polarization.
- If the shutters of the projectors and the shutters of the glasses are dark enough, there will be no ghosting or very small ghosting.


The active system has many disadvantages. I want the lowest possible ghosting at the highest possible brightness and contrast so it might still be worth trying.

I'll do another test to see if the idea is worth trying. I'll connect one projector. I'll make my glasses flash at 120 Hz, I'll put a polarizing filter in front of the projector (to simulate having LC shutter letting light pass from the projector to the screen) and I'll close one eye. That will give me an idea of the brightness achievable.

[Likay]

Well, you know Sharky: The weldingglasses are lcd technique. You might need to make your own driver circuit though (like what Ragedemon said) to make them enough fast. It's almost impossible to completely darken light by just using polarization and that's why weldingglasses actually works (when they're darkened you'll be able to see what you're doing since the lightbeam enlights your weldingpoint ,excuse bad english ) . I'm figuring if Tril would be able to get damaged helmets with at least the lcdpanel working he might have a go. And really cheap too. However the work needed is another q. But after all it's a DIY section.

note: i had thinkings of doing this kind of rig since i already had e-d glasses but after a second thought i decided to go elseway to get 3d on a big screen. Still curious if it might work though.

cheers

[Jahun]

Well.. good idea Tril

And I have a great paper for you on it, let me look it up.. ofcourse I didn't put it in my favorites... grrr

Google rocks, first hit on my search:
http://ieeexplore.ieee.org/iel5/10813/3 ... mber=34092

They do sort of what you want, only they use the shutters to distinguish between 2 persons, in conjunction with polarized. It is nice work and they did more, you may find some. Also from these papers you can see what they managed to do in terms of switching speeds etc.


A few things from me:

- According to
http://www.barco.com/VirtualReality/en/ ... lumens.asp shutters would be even worse than just 50% less bright than polarized.

-This may seem to negate ghosting, but you are just reducing overall brightness so much, it gets closer to ambient light. In fact, there is *no* reason why shutterglasses would produce less ghosting imho. They are exactly like your polarized setup, just contain an active element in between....

- How bad is your ghosting? I was skeptical at first too, but now, like Likay, I think it is less than minimal.. in games I need to look for it. I was very impressed. Be sure to check your filters though. What filters do you use? and which screen?

Check:
http://www.advisol.co.il/Articles/Polar ... s-talk.pdf for info on how to improve you passive system.

- The coloration of the shutterglasses kan come from the problem that shutters use polarisation and your LCD projectors are polarized too. (that is, if you do have LCD projectors). Shutterglasses are liquid crystals in between 2 linear polarizers (heck I am quite sure you can modify an old 15" tft to make your huge shutterglass ) and these will react to your polarised beam you start with. Green is polarised at 90 degrees from blue and red. Do you still see green coloration if you rotate it in the beam?



Passive works great for me, that is with +- 1000 lumens projectors in a totally dark room. So I guess similar to 2500 projectors in a sort of lit room..

But I am interested to know what you can come up with..

[Jahun]

Wait a second, do you even have a screen yet?


As I said, I was skeptical at first too (when I just tested my progjectors without actual play), but your eyes may play a trick on you if you try to estimate the amount of light rejected. Your eyes are extremely sensitive to low light, their response is logarithmic I believe. So it may seem that not that much is rejected, whereas your eye has just responded.

If you use a silverscreen and beam with both projectors at the same time, this residual light is easily obscured by the light that IS supposed for the respective eye. Be happy though that your eyes are sensitive to low light.. eyes are extremely sensitive tools, it will take ages to make something as sensitive with silicon


If I take my polarizers and cross them and look to outside on a sunny day, I can see the houses etc. It doesn't matter. Your Edmunton Optics polarizers are rated 0.01% transmission crossed. (it would have been nice if they gave more info but ok). So your polarizers are say.. 500:1 in keeping polarization. Let me tell you, your silver screen will be 50:1, so it will get even worse!


Still, I have no ghosting issues. If gaming is what you look for, passive works perfect. And there is no solution imho in shutterglasses (to reduce ghosting) or adding multiple polarizers on top of eachother. And even though I can appreciate a good diy, I prefer my light and easy (and soon sexy IZ3D! type) glasses any time.

ps: polarizers don't need to be expensive to be good. Mine are +- 40$ for 2x A4 size and they are perfect. Likay's rock too though, but that's another story.


On that note, how are your new ones doing Likay?

[Tril]

I'm much more interested in using a passive system than an active system because I hate wearing the shutter glasses. That's a good enough reason to drop the active solution but I thought it might be interesting to test the results before judging.

I thought about it a bit more and it might not work as I thought with a DLP projector because of the color wheels. I might see some weird color changes if I'm not synced to the frame rate.

I have screen samples from many companies, a few samples I made and a whole screen I painted black myself. I was curious to see what kind of result I would get by using a black screen. The paint was cheap. It works and it produces black that is very black but apart from that, it's not really a good idea.

I tested the samples by using only one projector and looking at the samples with each eye while wearing polarized glasses. Tested this way, all samples give about the same amount of ghosting and I still see much of the picture on the polarization orientation that should give a black picture. I based my ghosting results from that but you may be right that I'll get much better results by using both projectors at the same time. I'll try that and report back my findings later.

It makes sense. By watching a bright picture, you eyes adjust themselves to not get blinded and you see what's dark, darker than it looked when you only looked at a dark picture. When you only look at a dark picture, your eyes adjust themselves to let the highest amount of light in.

I also bought filters from polarization.com and to me, it looks like the exact same stuff as what I bought from Edmund Optics (NT45-668). Same color, same thickness and same protective bluish plastic on both sides. I'm using the polarization.com filter.

[Jahun]

Hmm can you name a few screen brands you tested?
You say you used a self made black screen too, that makes me think...

You do know that this only works on silverscreens right? And the best on specific silver screens? If you try it on a random screen, indeed ghosting will be huge.

If you don't have a silver screen, just take the back side (the diffuse side) of aluminum foil and use that to check ghosting. But I must admit, usually silver screens are a little bit worse than aluminum foil. (and with good reason)

[Tril]

I know it only works on silverscreens. To make my own samples, I tested many paints to see if they worked. I tried around 15 to 20 different paints to find out which preserved polarization and to try to find a good one. There are many paints out there that preserve polarization at least a little.

Here's the criteria I think are important. A paint and screen need to :
1- Not sparkle too much.
2- Does not add a texture to the projection.
3- Appear the darkest possible when the polarization of the glasses and of the projector are crossed.
4- Appear the brightest possible when the polarization of the glasses and of the projector are the same.
5- Have the highest ratio between the last two points (bright/dark).


I have samples of :
Silver 3-D from Stewart
Silver Vision from Da-Lite
Silver Matte from Da-Lite
SilverFabric Silver 3D from silverfabric.com
ST-Power-Screen-3D from Screen-Tech

I'll test the samples again.

I did some quick tests. All the commercial samples preserve the polarization about equally. Here are some comments about what caught my eye.

Sparkle
The worst sparkling screen is the Silver Vision.
The one that sparkle the less is the ST-Power-Screen-3D.

Not adding texture
The most impressive on that is the ST-Power-Screen-3D from Screen-Tech. It's the screen that gives a picture that's closest to what is projected. I can clearly see the individual pixels if I get close to the screen.

The ST-Power-Screen-3D is also the brightest of the screens. Right now, if I had to choose between any of the samples, I would choose the ST-Power-Screen-3D because it's the brightest and it gives the clearest picture. I could also use it as a 2D screen since I don't have one.

I won't buy any screen for now. I'm not ready yet (just after buying two projectors) to spend the amount necessary for a good screen.

I bought two recertified Optoma EP739 for 600 CAD each at TigerDirect.ca. They are 1024x768 projectors. I would have prefered higher resolution projectors but I did not want to spend more than that.

[sharky]

hi! you could try to read the "silver screen" topic in the DIY section.. we got some results there.. maybe you could help us out. mybe trying a little sample...

bye

sharky

[Jahun]

Sorry about that then Tril, was just wondering since you didn't write about the screens you tested yet.. and I am amazed ghosting is so bad..

I know it only works on silverscreens. To make my own samples, I tested many paints to see if they worked. I tried around 15 to 20 different paints to find out which preserved polarization and to try to find a good one. There are many paints out there that preserve polarization at least a little.

Here's the criteria I think are important. A paint and screen need to :
1- Not sparkle too much.
2- Does not add a texture to the projection.
3- Appear the darkest possible when the polarization of the glasses and of the projector are crossed.
4- Appear the brightest possible when the polarization of the glasses and of the projector are the same.
5- Have the highest ratio between the last two points (bright/dark).

I think one really big factor is the specularity. You are testing small samples I assume (great that you got so many! keep sharing your thoughts about them with us please).

All the things you say about the ST-Power-Screen-3D make sense to me, and are depending on the fact that is it probably the closest to a mirror. Therefore you have highest brightness, little texture, best polarisation properties. This sounds all great, but do please make sure that it is not too reflective. It is hard to test with a small sample, but all these things you like about it come at a cost, and that is probably a very small viewing cone. Try looking and comparing it to the other screens when you look at it from the sides.

For instance backside of alu foil works pretty good, but it is specular as hell. A big screen of it would be very bad. Huge bright spot in the middle and dark edges etc..

If not, then it may be the perfect screen! Just saying you should check a thing like that too.. it would suck to look at a very non uniform screen.

[Tril]

The testing method I was using before was wrong. I was testing with one projector, one filter and one eye open wearing polarized glasses to see how dark the picture was getting.

I tested ghosting again, this time with two projectors while projecting in S-3D and it's not that bad. In fact, the results are very good. It's not perfect but it ghost about the same amount (maybe a bit more or less) as what I get with shutter glasses and my crt monitor (hp p1230). It's definitely acceptable. Now, I just need a good screen. I might paint one myself for the time being (before I buy one) as I have some left over paint.

If was serously considering buying a S-3D projection screen. I emailed all the companies I mentionned and asked for samples. They all sent them for free except Screen-Tech.

The viewing cone of the ST-Power-Screen-3D is indeed small and I was looking at it from an angle where it's the brightest. If it was bigger, the center might get brighter than the corners. It's hard to be sure if it's acceptable or not without seeing a full screen. I'll do some more thorough testing of all solutions before deciding on what to get.

I'm dropping the project of the active dual projectors system. If anyone else give it a try, share you results with us.

[Likay]

I think you made the right choice though. In a matter of fact i had the same plans as you in the beginning but after some gooli'n around i decided for passive projection. It's expensive, yes. But when you're there...

However i was a bit curious on how it might worked out with active for you. hehe. Guess i still have to wonder.

cheers

[Jahun]

Woops, I retract my point that shutterglasses would ghost the same amount, that is not true. I forgot you wouldn't need the silverscreen, which does quite alot of depolarisation..

I made the same mistake as you did Tril, I checked with only 1 projector at first. It looked really bad that way.. but with the other projector on, it will be minimal, don't worry. Let us know how the DIY paint works out for you...