At 11:51 PM 11/1/99 +0100, you wrote:
>at the beginning of this year I got an email from Andreas Potschka, who wrote
>about a trick when viewing images with cross eyed view. Here's what he wrote
>(translated by me):
>"... There was something disturbing the illusion: the two 'shadows' left and
>right of the 3d image. The reason for them is that the mind doesn't know what
>to do with the other partial image, which is only there for the other eye.
>This disturbing effect can be avoided by moving the two hands (opened towards
>the eyes) in front of the face at that distance the thumb has been before.
>There has to be a gap between the hands of approximately two centimeters size.
>The screen then seems to be only half as wide as before, and the two disturbing
>shadows have vanished, because each eye only can see the corresponding partial
>image, while the wrong part is hidden behind the hands."
>I found this trick to be very interesting and it works!
Yes, that's a very good illustration. I've known about it for quite awhile
without thinking of it as an aid to viewing on the PC. It only works for
cross eyed viewing, not for parallel viewing. Actually I had thought of
doing essentially that with printed images in a gallery setting. I would
designate a viewing location, and provide a black surface at the edges of
the viewing area.
It's analogous to the so-called finger method of learning to cross-view. One
watches their finger as it's moved between the eyes and the images. When you
get that third middle image to form you have found the place of right
geometry for the eye direction. Then one has to learn to relax the eyes and
allow them to accomodate the different *focal distance* of this virtual image.
In the beginning one tends to lose it very easily, especially if you already
know how to view by parallel means (crossed viewing requires training the
eye muscles to react in an opposite direction than what they already know).
When you have your finger in the right viewing location, it's easy to start
the process over - the same location to hold your hands to block the ghost
images. When you get the knack, you remove your finger, and follow the
It gets easier with practice. The usual mistake is to try too hard. Oh, with
cross-eyed viewing, it gets easier if you move farther away from the images.
Make it easy in the beginning by viewing from a greater distance than you
might normally choose.
BTW, about another stereo viewing method, called anaglyphic. (red/blue
glasses). I read a message on the Photo3D group the other day where this guy
claimed that after spending a day wearing them and viewing anaglyphs full
time, he found that for about an hour and a half after he took them off, he
could literally *freeview* anaglyphic images! It's only a temporary effect.