From: drascic@ie.utoronto.ca (SpIke)
Subject: Re: How do I generate the two views for a 3d image (LCD glasses)
Organization: University of Toronto, Department of Industrial Engineering
Date: Sat, 29 Aug 1992 17:59:41 GMT

rick@tekig1.PEN.TEK.COM (Fredrick Wilson) writes:

>In article <BtpExz.4t3@ie.utoronto.ca> drascic@ie.utoronto.ca (SpIke) writes:

>>When working with stereosopic photography, it may be quite easy shift the
>>images horizontally relative to each other.
>>When working with stereoscopic video (SV), it is FAR from easy.  Must of the
>>work I do involves the use of SV and stereoscopic graphics (SG).  And I'm
>>afraid that camera convergence DOES contribute to the location of the viewer
>>space (i.e. where the viewer sees the final images).  

>Well, yes, because by converging the cameras you are adjusting the window.
>(You are also creating convergence error.) If you change convergence in
>such a way as to leave the window alone, the depth won't change.
>If you change the window and leave the convergence alone, the depth
>will change.  Depth is set only by the window, but changes in camera
>convergence without changing camera seperation also have the effect 
>of changing the window.

What you mean by "stereo window" is not clear.  There certainly is no
standard terminology for such things.  I would appreciate a definition.
I'd also appreciate whether you are speaking about photographic, computer
graphics, video, or all three.  You've made no distinctions that I could
see.

In the mean time, I certainly agree that a parallel camera configuration
with horizontally shifted left and right views, whether by shifting the
CCDs or the left and right images at the display, CAN result in fewer
distortions for stereoscopic video.  However, the cost of modifying the
cameras or developing suitable electronics is quite high, and experiments
conducted here at the University of Toronto and elsewhere have shown that
properly designed converged camera setups can produce an image that is
highly pleasing to the viewer, even for long periods of time.

Stereoscopic computer graphics (SG) on the other hand are a different
question.  Using an image-shifted parallel camera model when generating the
left and right views is generally the best way to go, but the parameters of
camera separation and image shifting must be carefully decided.  Several
papers in the literature discuss these issues in depth.

>Convergence error can be compensated for to some extent by rotating
>the images (and cropping again) but you can only fix part of
>the picture at a time.  You can't fix the whole picture at once without
>fancy image processing.

This will work for computer graphics, but not for video.

>>Furthermore, sliding the left and right images horizontally with respect to
>>each other reduces the useful stereoscopic area.

>You have a choice.  Good stereo with a little of the edge cropped off,
>or painful convergence error.  I used to do the latter, now I do the
>former because it's more pleasing to view.

"Painful"?  Hmm.  All blanket statements are incorrect, including this one.
The effects of the "convergence error" can be controlled by choosing your
camera separation and field of view (i.e. focal length).  Further, the
complex, rich images with anti-aliased edges of video are much easier to see
in stereo than the relatively simple computer graphics images.  Distortions
that may produce an unacceptible image with graphics may be quite
acceptible, even unnoticeable, with video.

>BTW, I don't mean to be confrontational.  I'm just trying to help you
>understand what I think you are missing.

Your last paragraph IS confrontational, I'm afraid.  Personally, I find I
learn a lot more from people who are trying to state their own case clearly.
The assumption that you have insight in my thinking (or anyone else's) is
rarely warranted.  While I am happy to discuss the issues, and I'm pleased
to gain from the work and insights of others, I can do without
paternalistic attitudes.

	SpIke.

David Drascic
Dept of Industrial Engineering
University of Toronto
drascic@ie.utoronto.ca