"gimi" <gim### [at] psicoch> wrote in message news:3E1### [at] psicoch...

Hallo gimi,

> hi Andrew, hi Jaap (this is your first name, i guess?)

Yes, Jaap is my first name and Frank is my family name.
(Anne Frank is not family, there have been many Frank's
which were not related.)

> which is basically the same method to obtain the same effect,
> the only difference is the "point of view" (POV.. duh ;), which
> is either in front or behind the image. this difference in turn
> results in the "image" (that you perceive) being flipped
> back-to-front, for the reasons Jaap explained well already.
>
> but there is another main difference you did not make clear:
> there are (real) stereograms consisting of two separate images
> to be viewed by either eye, and "Single Image [Random] Dot
> Stereograms" (SI[R]DS), which, as the name implies, result
> from a single picture - which contains information for both
> of your eyes.

I think the SIRDS are the same principle as the red-green
double pictures that you have to view with a red and a green
glass for your eyes. Only the different colors are replaced
with a spaced random dot pattern and then superimposed.
Am I correct?

> the pictures that Andrew posted, including the ascii example,
> are SIDS, whereas Jaap posted a (double image) stereogram
> combined in a single picture file..
[..]
> so you approximate a parallel projection for either of the two
> objects in order to avoid the "curvature" that andrew mentioned.
> - did you try using orthographic projection instead?

It's one picture with two identical objects placed beside each
other without overlap and then viewed with one camera with a
small viewing angle. The camera is a normal perspective one.
You can do it yourself easily.
There's one drawback with this method. You can't make a
3D picture from inside an object, because the objects will
overlap then.

> i think that it would work very well. you just have to rotate
> the two objects a little to get different angles for each eye;
> then you can get both "crossing eye" and "magic eye" pictures,
> as you call them, depending on which way you rotate them.

If you use an orthographic camera, indeed you have to rotate
the objects to get the right configurations. I've never done
that, but it's another possibility. As long as you get the correct
differences it's oke. Maybe the 'perspective method' gives
you the normal distortions and the 'orthographic method'
will not give the right distortions for depth, but you can try
both with the same object and compare then.
If the orthographic camera doesn't work, you can rotate
the objects to make "magic eye" pictures.

Regards,

Jaap Frank

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