Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!clyde!watmath!watcgl!drforsey
From: drforsey@watcgl.waterloo.edu (Dave Forsey)
Newsgroups: comp.graphics
Subject: Re: Interactive Stereo Viewing
Message-ID: <3005@watcgl.waterloo.edu>
Date: 21 Jan 88 19:45:03 GMT
References: <4615@tut.cis.ohio-state.edu> <146@rocky8.rockefeller.edu> <1396@pixar.UUCP> <5039@well.UUCP>
Reply-To: drforsey@watcgl.waterloo.edu (Dave Forsey)
Organization: U. of Waterloo, Ontario
Lines: 40

>In article <1396@pixar.UUCP> flip@pixar.UUCP (Flip Philips) writes:
>
>	You have two eyes.  These can be thought of as two cameras into a
>world space, seperated horizontally by a fixed distance (2.5" typically).
>
>	As said before, both camera focus on the exact same point.  If they
>don't, the stereo effect will be diminished greatly.  The viewpoint (where
>the line of sight of the two cameras converge) will appear precisely on the
>surface of your screen.  All points between the viewpoint and the camera
>will appear to leap off the screen, and all those behind the viewpoint will
>sink back into the monitor.  As a personal preference, I gear all my 3D to
>appear behind the screen, as I have a hard time focusing on stuff leaping out.

By aiming the two cameras have you not forced the viewer to focus on
one specific part of the screen?  If the viewers actual focus wanders
to another part of the CRT, won't the visual information presented to
each eye be incorrect? When viewing a 3D still or movie, the centre of
attention may wander all over the screen, not just the part that the
cameraman has decided to focus on.

The cameras used for the 3D Imax film, "Transitions" shown at the
Vancouver expo, shot in parallel - partially to ensure that people
could look at any part of this 5-story tall screen and still get
a good visual effect. I believe (Dave Martindale can correct me on this),
that the computer generated portions were rendered with two "cameras"
aimed in parallel.

Another factor is that the movie screen is essentially at infinity as
far as the human eye is concerned. A CRT may not be. Perhaps this is why
Flip constructs his 3D-images with a focus point.

The visual effects of the Imax film were certainly impressive -
a balloon floated on top of the head of the person sitting in front of me,
and when the robot arm suddenly cracked an egg, myself, along with 3/4
of the audience, whipped their legs apart in an involuntary reflex to avoid
getting egg on their laps!

Dave Forsey
Computer Graphics Laboratory
University of Waterloo.