From: danny@halls1.cc.monash.edu.au (Daniel Jitnah)
Subject: Re: How do I generate the two views for a 3d image (LCD glasses)
Organization: Halls of Residence, Monash University 
Date: Tue, 1 Sep 1992 09:53:46 GMT

In article <Btnt11.9BK@ie.utoronto.ca> drascic@ie.utoronto.ca (SpIke) writes:
>From: drascic@ie.utoronto.ca (SpIke)
>Subject: Re: How do I generate the two views for a 3d image (LCD glasses)
>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