Re: Pulfrich and Real vs. Artifial 3D

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Sun, 8 Jun 1997 21:53:42 -0500
>From: "P3D  Dr. George A. Themelis"  <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
>Subject: Pulfrich and Real vs. Artifial 3D

>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.

That's pretty close to the "working definition" that I included in
the long post (sent out before reading this), except that I didn't
attempt to distinguish between "real" and "artificial".

I think Pulfrich *can be* "real" by your definition, provided that some
very specific requirements are met:
 - the thing that's photographed is a real scene
 - the camera tracks at a uniform and "reasonable" rate, in a straight line
 - the camera is pointed perpendicular to the direction of motion
 - nothing in the scene moves.

Under these conditions, any perceived depth is a function of the true
depth in the scene.

Note that the Pulfrich scenes that have actually been broadcast generally
don't fully meet all of these requirements except for occasional brief
periods of time. But that's because of cost considerations, other production
values, desire not to put the audience to sleep, etc. - not because of any
fundamental limitation.

John R


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