P3D Re: My 3D Litmus test

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Greg W writes:

>I've always found
>Paul to be a person who is not quick to leap to snap judgements.  Paul
>has always appeared to me as a very objective and acute observer who has
>been a great moderating influence on this list.  

I continue to view Paul this way and his preference of "discontinuous 
depth" does not frustrate me.  Having been around in this list for some 
time now I have come to accept the fact that different people have 
different reactions in the way they perceive stereo.

Personally, like Greg, I like depth graduations and find them more 
pleasing than discontinuous depth.  I also enjoy pairs which are very 
good photographically (exposure, sharpness) but have little depth because
the main subject is far away (as in an aerial view taken with a regular
stereo camera).  Sometime back some people went as far as to say that 
this kind of photography is equivalent to "cheating" and a definite waste 
of the stereo medium (might as well be recorded and presented in 2d).

In this particular discussion I understand Paul's point of view.
If you want to test people's ability to see stereo, a stereo pair that 
has graduated depth and lots of monocular depth cues is not the best one 
to use.  Telling them to close one eye and "see" the difference for many 
people does nothing because they already have formed a mental image of 
how the scene looks in space.  Most times it makes no difference to me 
to close one eye after I have viewed the scene in 3d.  That's why the 
most effective tests for stereopsis are the ones where there is no image 
in 2d, like in a random image stereogram.  Only by fusing the two images 
a three-dimensional picture is formed.  The depth in such pairs is 
discontinuous.

What makes a good test for stereopsis and what makes a pleasing stereo
picture are of course two different things.  From previous discussions
it is clear to me that there are wide differences in the degree that
different people perceive the stereo effect.  There are people, like
myself, who are very sensitive to small differences that built up
the stereo image, while others (like Paul perhaps) need a stronger input 
to see the stereo effect.  People like Paul might prefer the discontinuous 
depth that emphasizes stereopsis while people in the first group might 
prefer more gentle effects where monocular cues contribute and enhance 
the (not necessarily) pronounced stereoscopic effect.

I am inclined to believe that with continuous exposure to stereo images 
people tend to shift from strong to more gentle binocular cues and tend 
to appreciate other (photographic) qualities of stereo pictures more than
the sheer depth information.

George Themelis


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