From: msimon@physics.ucla.edu (Simon)
Subject: Re: PS stereograms
Organization: UCLA Department of Physics
Date: Tue, 28 Jul 92 23:01:22 GMT

In article <2397.imc@uk.ac.ox.prg> imc@prg.ox.ac.uk (Ian Collier) writes:
>In article <1992Jul26.012844.23784@raven.alaska.edu>, ejo@kaja.gi.alaska.edu (Eric J. Olson) wrote:
>>In article <1992Jul25.232800.26343@ccu.umanitoba.ca> rao@ccu.umanitoba.ca (Govindaraju Rao) writes:
>
>>>   1) In the bubble stereoram I see an "inverted" bubble. It
>>>      appears bowl-shaped (concave away from observer). Is this
>>>      correct or should it appear convex towards the observer, like
>>>      a blister, or hemispherical soap bubble.
>
>>It's "correct" in that you see something, but you're viewing the
>>opposite of what was intended.  If you allow your eyes to relax and
>>focus on infinity, the bubble will be convex.  When you view the
>>images crosseyed, the depth information is inverted, and it becomes a
>>bowl.
>
>I viewed the bubble and the torus in wide-eyes mode, and I saw the same.  I
>was unable to see anything except an amorphous circular blob for some time,
>mind you.
>
>What I saw was a hemispherical bowl sitting on top of the background
>surface, similar to the first poster above.  Similarly, when viewing the
>torus I saw half a torus sitting on the background with the hollow face
>towards me - though I was only able to see anything while by looking at the
>upper half of the picture.
>
>So, if these apparitions are incorrect, then something strange is happening
>- not just that we are viewing them "inside out" in cross-eye mode.
>
>Ian Collier
>Ian.Collier@prg.ox.ac.uk | imc@ecs.ox.ac.uk


As I said when I first posted these, translucent surfaces are "harder
to see" than  solid surfaces.  This was an experiment to see whether
translucent surfaces would work all.  Most people can see them with
little trouble, especially if they know what they are looking for.
Because these RDSs have objects in front of other surfaces, they are
not good candidates for pseudoscopic viewing (cross-eyed in this case).
    Because the top and bottom surfaces of the bubble and toroid are
at different heights, it requires some work on the part of the viewer
to see both surfaces.  You must "look around" at different heights.
It sounds like you are only seeing the inner surfaces.  If you "look"
at the region further from the paper towards you, or follow the surface
that you see upward, slightly changing the convergence of your eyes as
you go, you will see the top surface of the toroid or bubble.  There is
some intermediate point where you can see both surfaces at the same time.
    What you "should" see is the following:
    Bubble--A very large bubble in front of a flat background.  With one
           convergence you should be able to see the outer surface
           (convex) of the bubble.  Looking further back, or following
           the surface downward you should see through the outer surface
           to the inner concave surface.
    Translucent Toroid--A toroid floating above a wavy surface.  Both
           the inner and outer surfaces should be apparent at different
           depths.  The lower wavy surface can be seen through the
           donut hole.

Good Luck and have fun!

Martin Simon
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