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: Thu, 27 Aug 1992 20:31:47 GMT

gold@imp.sim.es.com (Bruce Gold) writes:

>In article <BtLrJ3.MKC@ie.utoronto.ca>, David (SpIke) Drascic writes:
>> Another approach uses a parallel camera configuration.  The problem with
>> this is that everything appears in front of the monitor, making it pretty
>> awful to use.  On the other hand, some distortions and vertical disparities
>> are reduced.

>> In order to move the display space back with respect to the monitor, you can
>> manually slide the left and right views, thereby creating a
>> psuedo-convergence point.  You can slide the views at the display
>> (electronicially, or through software), or at the camera, by shifting the
>> CCD sensor relative to the lens.

>I believe the claim that everything appears in front of the monitor is
>an artifact of the test set-up and that David's second paragraph points
>in the right direction to a more general software model.  It is
>actually simple enough that I don't think shifting the CCD is actually
>necessary.

The parallel camera setup quite deliberately places the entire viewer space
in front of the monitor.  The horizontal image shifting I allude to are
relatively recent developments.

As for simple, I guess it depends on what you are talking about.  With
photographs, it is trivially simple to slide one image relative to another.
With computer graphics, it may or may or may not be simple, depending on the
flexibility of your graphics library.  With stereoscopic video, it is far
from simple.  It can be done electronically, but then you loose some of the
usable image, and the hardware costs are large.  It is often simpler to do
it by moving the camera's CCDs.  A colleague of mine, Andrew Woods, at the
School of Electrical and Computer Engineering, Curtin Univ of Tech, Perth,
Australia, has been using such a set up for several years now for underwater
telerobotics with considerable success.

>I offer as counter examples all commercial 3D movies made
>in the 1950s and the 3D Disneyland/Disneyworld movie with the blowing
>dandilion seeds and the witch.

Why didn't 3D movies become standard?  Because the stereo wasn't well done,
for the most part, resulting in eye-strain and nausea.

Also, you don't seem to be making a distinction between computer desktop
monitors, and large theatre projection screens.  When the monitor is very
far away, it may be appropriate to have the viewer space entirely in front
of the display surface.  But when the monitor close to the viewer, this is
NOT appropriate.

>A better example is the range of
>peripheral vision of a human.  While peripheral vision is symmetrical
>with both eyes, each eye alone has an asymmetrical field of view.
>Stereoscopy is only available in the region of overlap; about 90
>degrees.  Since it's not important for your eyes' fields of view to be
>remotely the same its not important for your cameras' or virtual
>cameras' to be exactly the same either.

Not true, I'm afraid.  If you want to produce a good image that your users
will feel comfortable with, it is EXTREMELY important to make the left and
right eye views as similar as possible.  The ONLY desirable different is the
horizontal disparity.  All other differences, such as vertical disparities,
colour, brightness, contrast, magnification, etc, lead to eye-strain, and in
many circumstances render the images un-useable.

>Thomas Busey sounded slightly apologetic for using a "low-tech"
>implimentation.  No need to apologize for that.  For fun, I use an
>old-fashioned stereoscope, a standard camera, and the side-step
>method.

I, now I see a problem: when you say "camera", you mean photography.  When I
say "camera", I mean video and computer graphics models.  Perhaps this is
why we seem to be talking about different things.

>How do I keep the two images parallel?  I use the farthest
>landmark I can see, not my picture's subject, as an aiming queue.  This
>indicates that I'm REALLY using a model a little like the one I'm givng
>David a hard time about.  But mine is less accurate.  Actually I'd love
>to see your work sometime, David.

I've got lots on video tape, but that doesn't transmit well over the net
yet. :-)  Besides, you need liquid crystal shutter glasses to view it.

>My stereoscope results are uniformly successful (if not artistically
>excellent) because the visual cortex can handle divergences in X and Y
>gracefully.  I think it's related to two facts: Almost nobody's eyes
>line up perfectly.  Almost everybody has pretty good stereoscopic
>vision anyway.

The human visual system is remarkably robust, and can "handle" stereo images
of dreadful quality, in that one still is able to detect differences in
depth.  However, the better the stereo is done, the happier the eyes are,
especially if long viewing times (3 to 4 hours, for instance) is required.
Furthermore, there is more useful depth information in a well-matched stereo
pair: vertical disparities interfere with this.

For an example of the robust nature of the stereopsis system, try viewing a
complex stereo scene (i.e. photos are okay, video is better, wireframe
graphics not quite) with the left and right eyes reversed.  Most people can
still see a "stereoscopic" image.  It just isn't any fun, and doesn't look
"right".  But then switch things back, and they'll all be amazed.

>For an entertaining experiment, see how much misalignment is
>comfortable and how much is possible in: X, Y, convergence angle, and
>(this is the killer) image rotation.

You can get away with a lot in the short term, but if you have to work with
the images for any length of time, you need to keep things as symmetrical as
possible.

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