Re: A few more drachmas regarding pseudos..

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Mon, 3 Feb 1997
>From: P3D  Dr. George A. Themelis writes:
>OK, ... let the record show that I have experimented with "pseudo
>stereos".........One must be careful of when
>and how to use them, especially with ordinary stereophotographed scenes.

*****  Perhaps some of them end up as *interesting in themselves*, but my
reference to them was in how they exist in all stereo images, interesting or
not.

>..........
>One thing I learn from Ted's set is that the pseudo is viewed better 
>if turned upside down.  

*****  That sounds worth trying.

>
>Any time you reverse a regular stereo, you have a conflict between
>the reversed stereoscopic depth and the of the depth-related monocular 
>cues.  In many cases this conflict results in confusion.  

******  Again, spend a moment getting familiar with the reversed image. ALL
the depth cues are reversed so the mind is capable of eventually accepting
this reversal as a constant, at which point the confusion melts away. It's a
different experience but all relationships are still present, even though
out of the normal perspective.

>That's not
>going to work.  But, there are cases where a new & interesting scene is 
>born.  One needs to experiment a lot to get a feeling of what is going
>to work and what is not going to work.

****  Perhaps if your goal is an inverted presentation piece, otherwise it's
simply there to be viewed anyway.

>
>As expected, if the scene does not have strong monocular depth cues,
>especially overlapping, like SEM stereo pairs or simple computer 
>models, reversing the images can cause no conflict and this can be a 
>problem if the correct visual interpretation is the goal.

****  I understand what you are saying, but it's a narrow interpretation
based solely on the *usual* method of viewing a stereo image. A presentable
representation is not necessarily intended. It's simply always there.

>
>The human face is a classic example of an object that is impossible
>to experience with reverse depth.  Reversing a stereo of a human face
>results in a flat image, not one where the nose goes back.

****  You better look again, George. If the nose is flat in the reversed
mode, then it's flat in the usual viewing mode too. The illusion that causes
you to think it's flat is from not examining all the relationships present.
The depth is there and I've found some of the reversed faces I've looked at
rather interesting. Remember that according to physics, the stereo-disparity
is still present, so if you don't see it you haven't examined it
sufficiently to have understood all the reversed cues. Perhaps this is
something one has to study for awhile... a casual glance isn't sufficient to
process all those reversed shadows and other cues. The subconscious
interpretation process is such that what isn't understood and which doesn't
easily fit into the expected placement, is either ignored or misinterpreted
as something else. (probably the typical result) Of course it's confusing at
first but if that's where you stop, that's as far as you get with it.

I think spending the time to figure out a few of the reversed images is
worth the effort because it greatly expands one's *feel* for the 3D
environment. I try it frequently while working with images. This process for
me isn't dependent on the reversed image being profound photographically.
What's profound about it is the ability to eventually *grok* the totality of
the reversed images. Generally if I like the usual view of an image pair, I
enjoy it's reversed aspect too. I often see details that way I missed
viewing the regular way.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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