VMD-L Mailing List

From: John Stone (johns_at_ks.uiuc.edu)
Date: Mon Mar 29 2004 - 19:44:51 CST

Marc,
  You can do stereoscopic projection just as you describe;
instead of using a CRT for display, you simply wire up a projector.
The complications come in with the need for the 120Hz refresh rate,
and the fact that the projector itself must not polarize the light
as this would interfere with the correct operation of LCD shutter
glasses (which use LCD blanking, thus polarization) to block each
eye sequentially. This essentially leaves you with one of two options
for stereoscopic projection, technology-wise:
 1) CRT projectors
   Pros: supports a very wide range of resolutions, typically up to 2048x2048
         and they work with tons of different video signal formats.
   Cons: require significant opto-mechanical adjustment, setup, and occasional
         upkeep, and they are quite dim compared to what you'd find in a
         DLP or LCD projection system. They are also fairly pricey.

 2) DLP projectors
   Pros: extremely bright
   Cons: low-end projectors use a "color wheel" and they interleave their
         projected color images by drawing each frame 3 times
         (for red/green/blue) These low-end projectors don't do a very
         good job with fast moving graphics, and stereo in particular would
         be unusable with a single projector of this type, as even if they
         accept the 120Hz video signal, they will silently drop frames and
         so you'll get a very poor quality stereo effect, if any...
         The high-end DLP projector do a wonderful job, but they cost more
         than even the CRT projectors do. The only "cheap" solution is
         to use _two_ of the low-cost DLP projector, by driving the two
         projectors with separate left/right video channels from the
         graphics workstation. From there, you place polarizing filters over
         each of the projectors (one horizontal, one vertical, as an example)
         and you're good to go. The difficult part with this solution is that
         it is incompatible with 80% of the normal stereoscopic display
         hardware and software. So, while its cheap, it has drawbacks.

Many CRT projectors can easily handle the high scan rate of the stereo
signal, though they typically require a "fast green phosphor" so that you
don't get green "streaks" in your stereo images between frames. We have
a Electrohome Marquee 8500LC Ultra CRT projector with the P43
fast phosphor in our current projection facility.

I'm looking into the "two cheap DLP projectors" solution for our next
generation projector facility here. We could implement this with the
current VMD now, its just not as nice as doing real OpenGL stereo due
to the way normal applications interact with the stereo display.
(they don't realize what's going on...)

Anyway, let me know if you're interested in knowing more about one of these
options, I know a lot more than I have time to write at this moment, but
I thought this quick email would help clarify some of this for you...

  John Stone
  vmd_at_ks.uiuc.edu

On Mon, Mar 29, 2004 at 11:56:37PM +0200, Marc Baaden wrote:
>
> Hi,
>
> we currently use an nvidia graphics card + CRT screen + goggles
> for stereo visualization. I wonder whether it would be possible
> to use a vide projector instead of the CRT screen ?
>
> Eg if the projector was capable of 120 Hz refresh rate, this
> should be possible, or am I missing something ? Anybody has some
> experience with this, or knows any models that fulfill this
> criterium ? (.. we are looking for a low-budget solution .. I know
> there are quite expensive projectors with excellent stereo .. but
> I'd just like to know how far one could get with a say $3000 projector)
>
> Thanks in advance,
> Marc Baaden
>
> --
> Dr. Marc Baaden - Institut de Biologie Physico-Chimique, Paris
> mailto:baaden_at_smplinux.de - http://www.marc-baaden.de
> FAX: +49 697912 39550 - Tel: +33 15841 5176 ou +33 609 843217
> 

-- 
NIH Resource for Macromolecular Modeling and Bioinformatics
Beckman Institute for Advanced Science and Technology
University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801
Email: johns_at_ks.uiuc.edu                 Phone: 217-244-3349              
  WWW: http://www.ks.uiuc.edu/~johns/      Fax: 217-244-6078