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From: dgary@ecsvax.UUCP (D Gary Grady)
Newsgroups: net.graphics
Subject: Re: Stereo Picture TV
Message-ID: <1587@ecsvax.UUCP>
Date: Mon, 8-Jul-85 16:26:09 EDT
Article-I.D.: ecsvax.1587
Posted: Mon Jul  8 16:26:09 1985
Date-Received: Thu, 11-Jul-85 00:32:20 EDT
References: <8794@ucbvax.ARPA>
Organization: Duke U Comp Ctr
Lines: 59

> When is somebody going to come out with a good stereo picture tv system?
> 
>    It seems like all that is needed is an electrically controllable
> polarizer in front of the screen, say a fast liquid crystal panel.
> Alternate images would be visible to each eye if you wore polarized glasses.
> 					Paul Bradley

I suspect the technique suggested won't work very well for a number of
reasons.  First, phosphors don't decay rapidly enough.  Second, even if
they did, experiment has determined that the images for both eyes need
to "flicker" in synchronization to avoid unpleasant sensations in the
viewer (I'm personally quite surprised the human eye is that sensitive,
but stereo systems using to projectors locked together require even
that their shutters be synchronized).

Lenny Lipton has written an excellent overview of 3-D techniques in film
that would be excellent reading for anyone interested in the subject.

By the way, broadcast stereo TV has been quite successful as a novelty
item.  About 6 or 8 years ago a syndicator made a lot of money with a
godawful 3D movie "Gorilla At Large".  Viewing glasses were sold at
7-Elevens and the thing was heavily promoted.  It used color anaglyph
3-D, which means the two images were separated by the "lenses" of the
viewing glasses which were different colors.  Many people (me included)
find this type of 3-D very uneffective.  Polaroid anaglyph is MUCH
better, but still requires excellent technical support to be really
acceptable.

There are ways of producing 3-D images that don't require glasses.  Most
people have seen 3-D postcards that use a lenticular screen to separate
two images (the way lenticular screens have been used to, say, produce a
plaque that alternates between saying VISA and Master Card).  There is a
projection analog of this that has been used in the USSR.  (See the
SMPTE Journal, about 14 years ago.)  Another system used with computer
graphics involves a mirror that wiggles in and out.  I haven't seen this
but I understand it is only of use for doing computer generated images
at the moment.  Like holograms, these images are full 3-D and not just
two-eyeball stereo.  (It's possible to produce a similar kind of
lenticular stereogram, called a parallax panaramogram, by the way,
using a special camera that slides the back and the lens during
exposure.)  Then there are holograms.  Sometimes stereo pairs are
holgraphically encoded (as in the famous "Kiss" moving hologram), but
of course true holograms are incredible.  Unfortunately, they are not
projectable and I'm unaware of a successful movie system using true
holograms.

A final note:  How about 4-D pictures?  A computer graphics researcher
whose name eludes me used to go around showing stereo pairs that were of
4-dimensional objects (computer generated, of course).  How?  The third
dimension comes from the angling of the eyes in and out (as with normal
3-D) and the fourth from tilting the head from side to side.  Supposedly
one could train the mind to actually perceive 4-D images...  Stand by
for Buckaroo Banzai Part 4, in 4-D, I suppose.

-- 
D Gary Grady
Duke U Comp Center, Durham, NC  27706
(919) 684-3695
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