The Keystone dEffect

[P3D <Linnstaedt@xxxxxxx>]

In a message dated 96-05-07 Dr. G. Themelis wrote:

>I think you are confusing keystoning with hyperstereo or something else...
>Keystoning will introduce some distortions and it should be avoided.  It has
>the advantage of allowing you to set the stereo window at will without
>masking and loss of image area.

What!! ?? !! The term has to do with projection and perspective distortion.

As I understand, the keystone effect or "keystoning" refers to distortion
created by projection onto a screen not parallel to the image plane.  Another
way to state this is,  the light beam is not perpendicular to the screen.
 The classic example is when one projects from too low, aiming the projector
upward toward the screen.  A square image becomes narrow at the bottom and
wide at the top; a shape reminiscent of a "keystone", "1: the wedge-shaped
piece at the crown of an arch that locks the other pieces in place"
(Webster's).  Take a look at the logo on Pennsylvania license plates for one
version.
PLEASE don't misuse this term.  ;-)  Never.  No, not ever, again.  ;-)

A Keystone:                         A Keystone Effect:
________                             ____________
\             /                            \                   /
 \           /                              \                 /
  \_____/                                 \________/

Pax Stereophotographica, Rev. Robert B. Linnstaedt


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