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From: decwrl!well.sf.ca.us!well!lilj@uunet.UU.NET (Joshua Neil Rubin)
Newsgroups: sci.virtual-worlds
Subject: VR/Video
Message-ID: <1991May13.192039.29588@milton.u.washington.edu>
Date: 13 May 91 01:37:32 GMT
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kost@iias.spb.su (Konstantin E. Popov) writes:

>graphic perfomance, but also AI tools. When you are getting such single
>stereopar, we must decide, at minimum -
>
>(a)     How much can we change point of view?
>(b)     What distortions of made perspectives are suitable?
>        and on the whole, how we can measure this "suitableness"?
>        (i suspect also that it depend upon ****many factors.)
>(c)     How can we will get another piece of data for composing
>        perspectives if you want make it aside our pre-defined ranges?

I believe that the answers are as follows:

(a)      We can theoretically change the point of view to any perspective 
with no distortion as long as no surface was obstructed from either of the 
cameras which photographed the original stereopair (that is, there were no 
hidden surfaces).  If there were hidden surfaces, we cannot change the 
point of view at all without introducing distortions.  Surfaces that are 
hidden from the original perspective create gaps in our information about 
the scene.  For instance, if we were to take a single stereopair of 
somebody's head from directly in front, we only have information about a 
mask-shaped surface, that is, the portion of the face exposed to both 
cameras.  We would lack information not only about the back of the head, 
but indeed about an entire wedge of space projecting backward behind the 
head.  If we wished to synthesize a virtual perspective from the right-hand 
side of the head, we would have enough information to construct a view of 
the mask-shaped surface of the face.  However, projecting backward from 
this mask (or to the left if we are viewing the head from the right-hand 
side), would be a wedge in space about which we lack information.  In our 
synthesized view, we could represent this space as semi-translucent or as a 
wire-frame, denoting that we do not know whether it or any particular part 
of it contains or does not contain an object.

(b)      Suitability would probably depend on the nature of the application 
and the nature of the data.  You can't *gain* information about an actual 
scene by synthesizing a new perspective of the scene from the information 
in a single stereopair.  However, the synthesized perspective might help 
you to better *understand* the information that you have.

(c)      Once you have already parsed the scene into objects in order to be 
able to synthesize a new perspective, it would probably be *relatively* 
easy to interpolate certain surfaces.  For instance, if our object-
recognition program thought it detected a sphere, it would be a simple 
matter to add the hidden surface of that sphere.  Or, of course, you could 
get information from another photograph from another perspective.