Highest refresh for dual LCD's?

[kekewons]

I'm investigating the possibility of building a DIY stereo projector using a pair of strobed LCD's* in concert with shutterglasses (or polarizers).

[*Another method is to use shutterglasses with a single DLP projector (which I am currently doing)--it's pretty good for an "off the shelf" setup but there are a few problems too I'd still like to overcome, and I wonder if a dual LCD projector isn't going to be the most straightforward solution to those in the end]

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IDEALLY, and just because it's probably the simplest to implement, both LCD's would be driven off a single video card. Hopefully at a pretty high overall combined refresh rate. If it's going to work at all, each LCD will almost certainly have to be driven off a single connector, which means 1600x1200 is the highest resolution that could be used, given the current state of the art where connectors are concerned.

Also given the current overall state of things, this would also almost certainly be best tried using Nvidia's stereo drivers, which confines me to Nvidia cards (I bought a 7800GS AGP card last year for use with just this sort of implementation, but it won't be fast enough to render at this level today).

The obvious candidate then (it seems to me) would be a 8800GTX....

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The first question then is pretty basic: Can anyone tell me how quickly this very fast card can render/refesh a pair of...

A) 1280x1024 LCD's? @60Hz and 75Hz?

B) 1600x1200 LCDs? @60Hz and 75Hz?

(Assume for purposes of the question that each LCD is rendering a different 3D scene--it's still unclear how this can be set up with the Nvidia drivers, but that's another issue anyway. Right now I need to know if even the fastest card can crank out sufficient frames....

Assume too that neither HDMI nor Vista need be factored into this for the moment.)

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Hopefully someone will tell me the vertical refresh rate of each of the two LCD's is still going to be the limiting factor (because I really don't want to have to start thinking it terms of using SLI too with the stereo drivers--too many ways it can break down), but I'd thought I'd better ask.

Thanks for any replies.


k

 

[Matthias99]

If it's going to work at all, each LCD will almost certainly have to be driven off a single connector, which means 1600x1200 is the highest resolution that could be used, given the current state of the art where connectors are concerned.

You can run 1920x1200 off single-link DVI, and 2560x1600 off dual-link DVI.

(Assume for purposes of the question that each LCD is rendering a different 3D scene--it's still unclear how this can be set up with the Nvidia drivers, but that's another issue anyway. Right now I need to know if even the fastest card can crank out sufficient frames....

I don't think you can get 3D acceleration on the second display if you run them as separate desktops (unless the stereo drivers have some way to do this?) If you run as one big spanned desktop (at 3200x1600) you can open multiple 3D-accelerated apps and put them on either monitor, but I'm not sure if you can stagger the displays' refreshes like that.

Assuming you can get accelerated 3D windows on both monitors, a modern GPU like a 7900GT or 8800GTS/GTX could easily refresh two 3D windows at 75Hz at 1600x1200. The question is how much 'stuff' it can really be rendering before you start dropping frames.

 

[rbV5]

You can run 1920x1200 off single-link DVI, and 2560x1600 off dual-link DVI.

Interestingly, single link DVI can drive all the way to WQUXGA (3840x2400) using both reduced blanking and reduced refresh rate.

In theory, single- and dual-link support have a clear dividing line. Single-link DVI supports resolutions up to 1600 x 1200 (165 MHz), and dual link can support much higher resolutions (330 MHz and greater) (Figure 23). But in reality, single link can support up to 3840 x 2400 (Figure 24).

Link

They show this example;

Basically, a 9 megapixel display can be divided into four quadrants of 1920 x 1200, or two of 1920 x 2400. This allows the display to be driven by one, two or four single-link DVI ports.

I'm not sure any of this is helpful to the OP, but DVI itself is very flexable for resolution/refresh support.

 

[Matthias99]

Originally posted by: rbV5

You can run 1920x1200 off single-link DVI, and 2560x1600 off dual-link DVI.

Interestingly, single link DVI can drive all the way to WQUXGA (3840x2400) using both reduced blanking and reduced refresh rate.

I guess, if you want like a 10Hz display or something.

I assumed he wanted to stay at 60/75Hz...

They show this example;

Basically, a 9 megapixel display can be divided into four quadrants of 1920 x 1200, or two of 1920 x 2400. This allows the display to be driven by one, two or four single-link DVI ports.

You can't do that with a standard monitor. You'd have to be running into a monitor or display converter that understood how to stitch the separate signals together.

I'm not sure any of this is helpful to the OP, but DVI itself is very flexable for resolution/refresh support.

Yes, DVI is way cool. :thumbsup:

 

[rbV5]

I guess, if you want like a 10Hz display or something.

Yup, but I'm thinking the converse as well.

On a related note to the OP. Yesterday I saw "Magnificent Desolation: Walking on the Moon 3D" at the new IMAX at the Evergreen Aviation Museum (home of the "Spruce Goose") The film and presentation were very good despite the lack of "real" footage, I'd definately recommend it.

However,

a quick little short prior to the movie was "fantastic" with some little fish and some kind of alligator monster swimming toward the viewer. The 3d effect was outstanding, much better than I had anticipated based on all my prior experience. Now I'm wanting to see a 3D IMAX film that really showcases the technology in a bad way. I can see why someone would want to do this considering that :thumbsup:

 

[kekewons]

Not immediately useful for my problem, no...but still helpful nonetheless.

For example, it's clear I was wrong when I surmised the current state of the art where "connectivity" is concerned might be a limiting factor. Sounds like the DVI-connector family in and of itself is up to the task.

Better to say instead something like "the state of connectivity as currently implemented on commercial video cards...". I'm thinking here of the fact that many of these large LCD's tie up both of a cards DVI outputs in order to function at all (or at least they did the last time I looked).

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I AM also hoping, btw, to be able to see each eye at something like 60-75Hz, yes. My recent experience using the 1024x768 DLP projector has me thinking I could live with overall refresh as low as 75Hz, but 85Hz is certainly better*, and past experience using the glasses on a 21" high-refresh CRT is that 100Hz-120Hz was quite a bit better still.

[*there are some color problems I think even at 85Hz]

If it works at all, I would ideally like to get something a bit better than what's available with a commercial DLP solution, so I suppose at a minimum I'll say I'd like to see 50Hz for each eye. 100Hz overall. Unless I can get this level, there's not much point in trying the whole DIY route anyway--I'll just stick with the off-the-shelf solutions.

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I just stumbled across a partial answer to my original questions at evga.com (8800 OC .pdf):

Turns out one of their 8800 GTX OC cards will send output/refresh a single "monitor" of 1280x1024(32 bit color) at 150Hz. 1600x1200(16 bit color) at 120 Hz, and 1600x1200(32 bit color) at 100Hz.

Given the tradeoff between those color (bit) refresh limitations and overall resolution, my first thought is I'd prefer to have the higher pixel resolution over the higher color resolution. Particularly when I'm "triangulating" on distant objects with stereo vision, so I'll tend, I think, toward the large LCD solution. These days 21" monitors aren't very much more expensive than 17-19's, and it doesn't look like anything on the cutting edge will be needed (not if 50-60Hz is all that will be demanded of each).

Next question is: Can I configure (or just fool) the Nvidia drivers+card into thinking they are connected to a single monitor which can handle that high refresh rate (when in fact the card is connected to two monitors, each of which can handle only half that high rate)?

Might be as simple as unchecking the box which says "hide refresh rates this monitor can't handle"...but somehow I suspect things will find a way to become more difficult....

And of course the rest of it: How to connect them so I'm sure each LCD DOES get only half the overall rate (and thus only every other frame)....

Slowly getting there, in any case.

Thanks for the help peeps.


k

 

[Matthias99]

A few things to note:

Those super-high refresh rates (AFAIK) are for VGA outputs. I don't know if their DVI outputs will go that high in terms of refresh rate.

Next question is: Can I configure (or just fool) the Nvidia drivers+card into thinking they are connected to a single monitor which can handle that high refresh rate (when in fact the card is connected to two monitors, each of which can handle only half that high rate)?

Might be as simple as unchecking the box which says "hide refresh rates this monitor can't handle"...but somehow I suspect things will find a way to become more difficult....

You should be able to set it to output whatever you want and it is capable of. If the driver panels won't do it, Powerstrip should.

And of course the rest of it: How to connect them so I'm sure each LCD DOES get only half the overall rate (and thus only every other frame)....

...that's the real problem, I think. You can run them each as independent monitors at 60Hz or 75Hz or whatever, but then you won't get 3D acceleration on the second display. If you use a spanned mode you can get acceleration on both monitors, but Windows will just see it as a single gigantic display. I'm not aware of any way to automatically make it refresh "half" of the screen and not the other (unless NVIDIA's stereo drivers can do this), let alone to synchronize them. I know the Quadro cards have some support for stereo imaging, but I'm not sure exactly how it is implemented.

If you use two video cards (not in SLI, just two cards), will the refreshes be synchronized? That would let you have acceleration on both displays, and you'd have even less of an issue with performance. But your software has to be written to support it. And you don't actually want the refreshes to be synchronized, you want it to go back and forth...

 

[kekewons]

Points to be aware of, thx, M (and rbV5 too).

I've stumbled across a possible alternative solution in another forum which might allow for more conventional connections and refresh rates. It's a "planar type" projection idea, in which both LCD's are instead run side by side in realtime--the two different eye-triangulation inputs are split using polarized reflection (and passive, IMAX type glasses) from the screen surface. More demanding, in terms of screen requirements, but perhaps also the simpler solution than my own idea in the end too.

Bottom line at the moment is: I don't know which way I'll go (seems there might even be a third method, using circular polarized projection).

You are quite right, in that my proposed "splitting up" of the output signal could be a real problem, should I go that route. Moreover, as someone who is only marginally capable himself when it comes to electronics, this could be a real hurdle--perhaps an insurmountable one--so on that basis alone I'm going to look hard at the possible alternatives.

Thanks for your help (both of you) and for the notes and issues you've brought up.


k