Re: Stereogram on the "Stereo Window"

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Thu, 19 Jun 1997
>From: P3D Paul Talbot  comments:
>
>Adjusting the spacing of the chips alters the appearance of objects
>relative to the stereo window, as any experienced slide mounter
>knows.  But which is moving, the objects in the scene, or the
>window itself?  

*****  In 3D slides the window is formed by the edges of the mounting
device, unless additional masking places it elsewhere. In that sense, moving
the chips always moves the scene, not the window. The stereo window is
defined as the plane containing points of coincidence between left and
right. The slide mounts form coincident points and become equivalent to the
window. The image can be moved to include the window or be in front of or
behind it.

Relativistically speaking one could refer to either one being moved as
compared strictly to each other.

>.......  The *apparent distance
>of the window* from my eyes does *not* appear to me to change when
>I adjust the chip spacing.  

****  It can't unless you mask a different edge parameter than provided by
the mounting material.

>.....However, if I look at a slide in a RB
>and then look at the same slide in a viewer with longer FL lenses,
>such as the $3 viewer, with the longer FL lenses it *does* appear
>that the window moves relative to my eyes.  In fact it does move,
>because the slide must be moved farther away from my eyes to use
>the longer FL lenses.

****  The window is always that plane which is fully coincident. Changing
the FL relocates the window relativistically, but the window is still the
plane of coincidence. The scale of access has changed (vantage point), but
not the principle quality of the window, which is still coincidence. That
is, the part of the stereo image that exhibits no stereo disparity, all
elements and points in this plane are equally spaced and aligned realtive to
left and right image. 

When the image is mounted so that everything in the scene is behind the
window, there is no coincidence within the image itself. Move the chips
relative to the fixed mount and you move it relative to the window. When
it's moved sufficiently that the scene includes areas that pass through the
window, those specific areas, at the window only, are of equal palcement.
Like looking straight down at the water line on a countour of land shapes.

Stereodisparity that shifts left and right image elements one direction
behind the window shifts in exactly opposite directions when in front of the
window. The window forms a focal point for elements of disparity between
left and right.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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