Pulfrich and Real vs. Artifial 3D

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Gabriel writes:

>Well, respectfully I would have to disagree. I wondered about the 
>reference about Pulfrich being an "illusion" and not being true 
>stereoscopic 3D a while back. 

To clarify things:  Pulfrich is stereoscopic.  Whether a person 
chooses to call it "illusion" that's their choice.  I have heard 
people (some of them into stereoscopic photography) call "true" 
stereoscopic imaging an "illusion" (as opposed to "direct" 
stereoscopic vision?)

During my first public stereo presentation in May 6th in the first 
meeting of the Cleveland Stereo Club, I made the following 
distinction:

- "Real" stereo
- "Artificial" stereo
- "Virtual" stereo

By "real" stereo I am referring to a real scene photographed
stereoscopically where the depth seen in the images represents
(is caused by) true depth (variation in the 3d dimension) in
the scene.  Examples include most forms of stereoscopic
photography, including hyper/hypo stereos, pictures of the moon,
etc.

By "artificial" stereo I am referring to situations where there is
stereoscopic imaging but the depth seen is artificial, i.e., does
not relate to variations in the 3d dimension in the real object.
Examples of that are:  3-D pictures of comments or eclipse of the
sun recorded from the same station, situations where only one
object is being shifted in the scene during recording from same
location.  One application in my research was visualizing plastic
strains.  I treated two pictures taken during the deformation of
a sample as a stereoscopic pair and was able to visualize the
plastic deformation as a change in depth.  In this category I
put Pulfrich too.

By "virtual" stereo I am referring to situations where a real 
object does not exist.  Examples:  Stereoscopic drawings (first
application of stereoscopic imaging back in 1836 in Wheatstone's
classic paper), computer 3d, etc.

All these categories include "valid" true stereoscopic images and
have applications in science and entertainment.  I personally
would prefer to see the "real" than "artificial" stereo in TV
when it is used in connection with real objects.  Someone called
Pulfrich the "basement bargain" of 3D motion pictures and I tend
to agree with the characterization.

-- George Themelis


------------------------------