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: Fri, 28 Aug 1992 17:22:47 GMT

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

>In article <BtnIzJ.GGJ@ie.utoronto.ca> drascic@ie.utoronto.ca (SpIke) writes:

>>Parallel camera models, such as the one you are
>>suggesting, place the graphics in an area IN FRONT OF the monitor.

>Placement of grapics in front or in back of the monitor is not a
>function of camera convergance.  It's a function of stereo window placement.

You are assuming that everyone is doing what you are doing, whatever that
is.

When working with stereosopic photography, it may be quite easy shift the
images horizontally relative to each other.

When working with computer graphics, it may or may not be quite easy,
depending on the flexibility of your graphics system.

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).  If one has the option
of sliding the left and right eye views AT THE DISPLAY, then "stereo window
placement" ALSO contributes.  But it is NOT an either-or situation, as Mr.
Wilson suggests.  Both are important factors.

>With any picture, with any camera method, you can move the grapics up to
>your nose or way off in the distance by adjusting the stereo window
>(i.e. cropping the edges properly). 

You can do it, certainly, but you are introducing distortions in your images
by doing so.  In some situations these distortions may be of no
significance, particularly if you are simply viewing stereo images for
enjoyment.  But if you have to work with stereo displays for several hours
at a time doing telerobotic work, it is important to reduce distortions to a
minimum.

Furthermore, sliding the left and right images horizontally with respect to
each other reduces the useful stereoscopic area.  Sliding the CCDs in video
cameras or the photographic plates in still cameras can achieve the same end
(moving the viewer space relative to the monitor) without this problem.

>When you make a stereo picture you are not trying to reproduce what
>the eye sees.  You are trying to reproduce reality, so the eye can see
>it properly. Reality is parallel, not converged.  With parallel cameras
>your eyes can then converge on any part of the picture.  With converged
>cameras you have told the eyes that they should converge in only one
>place to see a proper picture.  If the eyes try to converge elsewhere
>in the picture then they are doing a "double transform", so to speak,
>and they see a distorted picture.

>Parallel cameras are correct, and stereo window manipulation is
>usually needed.

It is impossible to reproduce what the eye sees.  It is also impossible
to reproduce reality.  What those of us who work with SV are trying to
do is to create conditions under which the observer can perceive as
useful and as comfortable image as possible.

Reality is neither parallel nor converged.  Reality consists of a three
dimensional world, not 2 two dimensional low-resolution images
thereof.  In trying to create conditions under which users can perceive
a good image, it is impossible to use a simple geometric model of
vision in order to decide, as Mr. Wilson has done, what is "correct".
While a casual reading of the literature may suggest that vision is
well understood, nothing could be farther from the truth.  In the same
way that the reality of an electron is not a small ball rotating around
a nucleus, as we were taught in grade school.  Human perceptual systems
are completely non-linear.  Eyes are not even remotely "cameras".

Using geometric analysis as a starting point, it is necessary to
conduct psychophysical experiments in order to establish what is and
isn't successful, useful, and acceptible.  I have done a few.  Many
others have and are continuing to do this as well.  The issues are far
from being as decided as Mr. Wilson is.

	David Drascic
	Dept of Industrial Engineering
	University of Toronto
	drascic@ie.utoronto.ca
Newsgroups: alt.3d