Subject: Re: PS stereograms

From: [email-masked] (Govindaraju Rao)
Date: 25 Jul 92 23:28:00 GMT

Johan writes:
   >> When I print them (RDS) on our standard laserwriter 
   >> (Apple type 300 dpi ?) it doesn't seem to produce 
   >> the wanted effect.
  
I printed them on a HP LaserJet III (300 dpi) and they seem to
be fine. However, I have encountered the following problems.
  
   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. I viewed it in
      both orientations i.e. arrow marks away from me and towards
      me; still the same result. 
  
   2) In the Ram's Horn sterogram I see two "objects" shaped like
      a comma (,), one larger than the other. Both these are at the
      same elevation, between and close to the upper tips of 
      the horns. When I try to "lock" onto them they disappear.
      Are they really there or is my eyesight going downhill ??
      If they exist, are they intentional, or artifacts of the
      generating algorithm? 
 
  3) I am having great difficulty with the Toroid stereogram.
     I am unable to keep the image formed even fleetingly. 
     What exactly am I supposed to see in this one? I see
     "ridges" on the left and right side and a large circular
     depression in the center, with another conical (?) projection
     in the dead center of the depression. Sometimes the conical
     projection appears as a floating disk. Is anyone else having
     trouble with this one ? I think my technique is correct since
     I see all the others easily. 
 
Please e-mail replies to <[email-masked]>. Will post summary
if warranted. (Preferably please do not reply to e-mail address
in the header of this posting.)
  
Thank you.
 
G.S.K. Rao <[email-masked]>

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From: [email-masked] (Eric J. Olson)
Date: 26 Jul 92 02:28:37 GMT

>      me; still the same result. 

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.  You're having the same problem with the toroid; look for a
half-donut embedded in the page, inside view.

Your view isn't incorrect because different people view stereograms
different ways; for example, I can't view them crosseyed, and my
father can't view them at infinity.  Just go with what you can do.

Eric Olson <[email-masked]>

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From: [email-masked] (Ian Collier)
Date: 28 Jul 92 17:38:09 GMT

>>      a blister, or hemispherical soap bubble.

>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
[email-masked] | [email-masked]

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From: [email-masked] (Fredrick Wilson)
Date: 28 Jul 92 23:06:35 GMT

>was unable to see anything except an amorphous circular blob for some time,

Are you guys perhaps looking at the TRANSPARENT bubble and TRANSPARENT
torus?  They have been posted here too, and are more advanced viewing
subjects.  You would likely see the inside of the bottom surface first
since they are closest to the back plane.

      Rick   Wilson             Rick Wilson       Cross-eyed STEREO
      --------------           --------------
     |       O      |         |      O       |
     |    O         |         |     O        |    [email-masked]
     |              |         |              |    Tektronix
     \    _     O   |         |\    _  O     |    Beaverton, Orygun
     |\  /      _   |         | \  /   _     |
     | \/   \  /    |         |  \/\  /      | 
      --------------           --------------

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From: [email-masked] (Simon)
Date: 28 Jul 92 23:01:22 GMT

>[email-masked] | [email-masked]

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