From: rick@tekig1.PEN.TEK.COM (Fredrick Wilson)
Newsgroups: alt.3d
Subject: Re: How do I generate the two views for a 3D image (LCD glasses)
Date: 9 Sep 92 01:50:19 GMT
Organization: Tektronix, Inc., Beaverton,  OR.

In article <1992Sep7.130324.1@cc.curtin.edu.au> rwoodsaj@cc.curtin.edu.au writes:
Lot's of stuff.

Thanks for the additional insight.


>We have both a pair of Stereographics Crystaleyes Active LCD glasses and
>Tektronix SGS410 Polarising screen.  The Crystaleyes definitely have less
>crosstalk, not by much but there is definitely a difference.  This probably
>comes from the fact that the active glasses only use a small piece of LC cell
>in front of each eye rather than a large LC cell over the entire face of the
>monitor.  We prefer the polarising screen though because the passive glasses
>(like sunglasses) and less obtrusive than the large Crystaleyes.


The SGS410 is a kit that fits on your own CRT.  Tektronix has no
control over the persistance of the phosphor in your CRT, and a long
persistance would definitely add to crosstalk.  The timing of the sync
signal coming out of your display would effect it too.  There is 
a possibility that your phosphor and sync are less than optimum
compared to a full Tek system, such as the SGS425.

You might also be correct that the size of the LC shutter is a factor.
I don't know what the propagation speed of polorization is through
that stuff.


>Rick writes:
>>I think I just had a lightbulb turn on concerning the different
>>geometries of a split pair vs. an overlaped polorized pair.  But for
>>what I'm thinking about to be optimum the camera convergence needs to match
>>and track the eye convergence as the eyes scan in and out of the image
>>space.  Is that true?  
>
>NO WAY!  If the convergance of the cameras changes with the changes in
>convergence of the eyes then the brain would become incredibly confused.  I'm
>talking MEGA-SPEW here.  I personally believe eyes should percieve a
>relatively stable image (in the depth dimension anyway).  Apart from
>relatively slow changes in camera parameters they should stay the same while
>an operator is concentrating on the image (eg. in teleoperation), otherwise
>the image would appear to more back and forth in front of you all the time.


I certainly see how it could be set up badly and cause mega-spew, but
I still feel that if convergence AND seperation were dynamically controlled
and displayed on a polorizing system where both halves are at the same
location on screen (as opposed to slit pairs of prints) there just
*might* be a way to avoid convergence error.
It would be done so the depth is constant of course.  I could be
very wrong, but that light bulb was nagging me.


>Rick, your photo of a water faucet (tap in this part of the world) may be a
>case of excessive camera separation increasing the effect of keystone
>distortion in the image from the converged camera configuration.  

(It's a hose bib to the construction people.)  Anyway,
That's entirely it.  It was an exaggeration which pointed out why the
shots with less separation and convergence were sometimes annoying.



      Rick   Wilson             Rick Wilson       Cross-eyed STEREO
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     \    _     O   |         |\    _  O     |    Beaverton, Orygun
     |\  /      _   |         | \  /   _     |
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