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From: gwyn@brl-tgr.ARPA (Doug Gwyn )
Newsgroups: net.periphs,net.research,net.graphics
Subject: Re: volumetric displays
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Date: Wed, 2-Oct-85 04:28:33 EDT
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> > > Obviously, resolution is a function of the third power of the bandwidth ...
> > 
> > That's not obvious at all.  Once you get near the eye's resolving
> > ability, further improvement buys nothing.  Not only that, but very
> > effective stereoscopy has been done with two 512-pixel square images;
> > pixel-to-pixel coherence makes the depth resolution argument less
> > significant.
> 
> Are rare instance when Doug misses the point.  A stereoscopic display
> consisting of two 512-pixel square images is fine if all you want is a nice
> *static* picture of Granny in front of Old Faithful.  However, a dynamic
> sequence showing Granny walking to the right spot, Old Faithful gurgling
> and spitting before finally starting to spout at full speed etc., etc. will
> require about 30 * 2 * 512 * 512 = 1.57 * 10 ^ 7 pixels per second if each
> pixel is either on or off and if we want to avoid excessive flicker.  If we
> assume that 8 bits are needed for a decent gray scale, 1.26 * 10 ^ 8 bits per
> second are necessary, a fairly hefty bandwidth for a pretty crummy picture.

Well, thanks for calling it "rare".  I believe the original "third power"
argument was that DEPTH needed the same resolution as HEIGHT and WIDTH.
TIME had nothing to do with it..  Maybe I really did miss it..

The bandwidth for a movie is significant, all right, but 512x512 is
about the same as Super-8, so stereoscopic movies are not much of a
problem.  512x512 is also about what a good TV signal might attain
so all these are in the same general ballpark.  Of course one would
have to get better effective bandwidth than today's commercial TV
broadcasts.  The Japanese are working on it, but I don't think they're
planning on stereoscopy (just better pictures).

It is interesting to note (if one hasn't thought about it before)
that considerably less bandwidth is needed for typical moving
pictures than simple calculations show.  Back in the days of the
PicturePhone, the BSTJ was full of articles on delta modulation
and related techniques for exploiting this feature of typical
source material.  I don't know whether there are any good methods
for doing these things at video scan rates..