Re: eyes & keystoning

[T3D Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 1:05 PM -0700 5/29/97, T3D John W Roberts wrote:
>
>But if your eyes are converged at some distance closer than infinity,
>they will pick up a keystoning effect on the edges of the ribbon. The
>amount of keystoning will depend on the distance to the object and the
>degree of convergence of the eyes.

Right.  I find it's easiest to think about looking at a square.  If it's
far away, it projects a square image to each eye (well, it would if the
retina were a planar surface, but we'll ignore that).  Close up, it
projects to a pair of trapezoids; in the right eye's image, the right edge
is tall & the left edge is short & vice-versa in the left eye.

This difference in shape is more commonly described in terms of vertical
disparities.  If you consider, say, the top edges of the two eyes' images,
and calculate the difference in vertical position between the right & left
eye images (say Yright-Yleft), it's zero in the middle, increasingly
positive to the right & increasingly negative to the left.  To put it
mathematically, the horizontal spatial derivative of vertical disparity is
non-zero (except for an infinitely distant object) & increases the close
the object is.

The extent to which people use this information is actually one of the
hottest stereo research topics right now...

-Jim C.

----------------------
Jim Crowell
Caltech Division of Biology
216-76
Pasadena, CA
Tel: (818) 395-8337
Fax: (818) 795-2397
jim@xxxxxxxxxxxxxxx



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

End of TECH-3D Digest 171
*************************
*************************
 Trouble? Send e-mail to 
 wier@xxxxxxxxxxxxxxx 
 To unsubscribe select one of the following,
 place it in the BODY of a message and send it to:
 listserv@xxxxxxxxxxxxxxx 
   unsubscribe photo-3d
   unsubscribe sell-3d
   unsubscribe mc68hc11
   unsubscribe overland-trails
   unsubscribe icom
 *************************