Re: Nimslo Prints vs Slides

[crowell@xxxxxxxxxxxxxxxxx (Jim Crowell)]

At 4:39 AM 2/29/96, John Bercovitz wrote:
>
>Here's another, possibly better, way of thinking about it or
>saying it.  The world has a geometry.  If distorted geometry is
>presented to the subject then to the first order the subject will
>see a distorted world.  However, the world, regardless of how it
>is presented, is seen through many powerful algorithms which can
>correct these distortions at least partially*.
>

Hmmm...I think it makes more sense to think of  multiple
independent sources of information which, in the typical stereo
viewing situation, are presenting the subjects with _different_
geometrical interpretations.  The percept is a compromise that
seems to vary somewhat from person to person.  For example, from
the little I've served as a subject in our stereo experiments it
looks like I rely on information for viewing distance from
convergence of the eyes (& perhaps accomodation) more heavily
than other people in the lab.  This may explain why I have
trouble accepting your basic observation as being universally
applicable.  :-)

>
>*I saw a most striking counter-example recently when Andrew Woods
>showed me stereo video taken with toed-in (converged) cameras.
>The hyberbolic distortion of space due to toe in (see one of
>Andrew's papers in bobcat for geometric proof and description of
>the shape of the distortion) is undeniable.  I think the reason
>for this is that as the camera pans a scene, the distortion moves
>with it and so an object becomes reshaped as it is moved from one
>part of the cameras' field to another.

Yes, and the same thing can happen in mono!  And for basically
the same reason.  When you're watching a movie & the camera
moves, there's an "ortho seat" where the motions on the screen
re-create the motions in the world exactly (assuming the camera
lens acts ike a planar projection, anyway).  Being in front or
behind this distance doesn't matter too much if the camera
translates; everything just scales with viewing distance.  On
the other hand, if the camera rotates ("pans"?  I always forget
if a pan is a rotation or a sideways translation of of the
camera) & you're not at the right distance, there's no longer a
valid rigid interpretation of the scene.  This was particularly
evident at one of those virtual rides at Busch Gardens in Tampa.
There were lots of pans & the "ortho seat" was around the
second row of a ten-row auditorium.  I was in the back row &
almost tossed my cookies; the distortions were very disturbing.

-Jim C.


------------------------------------------------
Jim Crowell
U.C. Berkeley School of Optometry
360 Minor Hall, Berkeley, CA 94720
(510) 642-7679
jim@xxxxxxxxxxxxxxxxx



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