From: gourdol@imag.imag.fr (Gourdol Arnaud)
Subject: Re: VR/Video
Date: 21 Apr 91 20:33:10 GMT
Organization: IMAG Institute, University of Grenoble, France



In article <1991Apr20.165305.6080@milton.u.washington.edu> decwrl!well.sf.ca.us!
well!lilj@uunet.UU.NET (Joshua Neil Rubin) writes:
>As I see it, the problem in quickly synthesizing a new computer-
>generated virtual perspective of a scene from a single stereopair 
>isn't that you need skillabytes of data.  The problem is that you need 
>sophisticated object recognition programs to recognize what 
>stereographers call the "homologous points" in the two images which 
>make up the stereopair.  These are, as the name implies, the two 
>points, one per image in a stereopair, which represent the same 
>location in actual space.  (You derive depth information from a 
>stereopair by comparing the distance between two points on one image 
>of the stereopair with the distance between the two homologous points 
>in the other image.)
>
>Humans can pick out homologous points easily enough.  In fact we do it 
>automatically whenever we use depth perception.  Computers currently 
>have a harder time than we humans do parsing scenes into objects and 
>recognizing analogies between imperfectly-matched patterns  Once the 
>homologous points have been identified, however, it is a simple matter 
>to do the arithmetic required to reconstruct the relative depths of 
>the various points in the scene.
>
>I'll grant you that we're talking about immense amounts of computing 
>speed and power and memory to do all of that object recognition so 
>fast.

Well, it can be done.
A friend of mine is working on an interesting project. The idea
is to use two cameras to film the hands of a user. The two images
are then analyzed, a 3d model of the hands are built, and the
information about the position and posture of the hands are
transmitted as a set of angles and coordinates.
That's a nice replacement for datagloves! No physical devices
needed, no cable, you can pick the phone while you're working,
and so on.
Well, anyway, this is supposed to work in real time with a Sun-4
and a specialized chip.

Of course, this is a special case. The contrast must be good,
there are few objects moving, and they are well known.
A more ambitious project deals with an autonomous robot.

If you want more information, you can contact Patrice de Marconnay
(he works on the hand recognition project) :
marconna@lifia.imag.fr

For more information on 3D reconstruction, contact James Crowley:
crowley@lifia.imag.fr

Arno.

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