Re: Why 3D

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

>The only depth cue we get in stereo photos that's not in flat photos 
>is parallax ("convergence" in the eye), 

That's not true.  As it has been stated many times here, convergence of the
eyes conveys a very weak depth information.  It is fusing the small
differences in the pair through a brain function known as "stereopsis"
that gives the sense of depth.  I think (it's been a long time since I
studied this) flashing a stereo pair in the eyes (to produce after-images)
is a proof of this.  In the after-images the eyes cannot change convergence
since these are "etched" in the retina, but the brain can still see stereo.

>but when viewing a stereo photo, our eyes are focussed at a single
>depth. I can easily see depth, in the real world, with one eye, by holding my
>finger out at arm's length, and alternately looking at my finger and at
>things in the background.  

I don't know about you, but I cannot see depth like that.  I can tell that
one object is perhaps in front of the other but I do not see any depth.
This focusing is also a weak depth indicator.  Plus, if the objects are
beyond 10 feet, accommodation changes very little but stereopsis is still
going strong.

-- George Themelis


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