Re: Stereogram on the "Stereo Window"

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Greg Wageman is using the disparity to explain the stereo window.
This explanation is easy to understand in projection (or the computer 
screen) where the two images overlap.  In a viewer things are different.

>You are not "moving the window"; to do that you would have to shift the
>masks closer or farther apart.  You are in fact manipulating the plane
>of zero disparity in the image, which can make the image appear closer
>to, or farther behind, the fixed window.  

I agree that the window is located at screen level and it is not moved.
However it has moved with respect to the scene and changed in size.  

Example:  I have a scene with the closest object (a rock) at 15 feet
and some mountains at infinity.  I take two identical stereo pairs.
I mount the first pair with the chips so that the stereo window is 
located at about 7 feet from the camera.  Since the closest object
is at 15 feet, there is quite a bit of distance from the window to
the closest object.  I mount the second pair with the window at
15 feet from the camera, so that the rock is just at window level.

I say that the difference between the two slides is the location of
the window that has changed w/respect to the fixed scene.  In the
first cace I have a smaller window at 7 feet.  In the second case
I have a larger window at 15 feet.  When I project the images in the
screen I have both windows at screen level, only these windows have 
different sizes.

Greg et al. say that the window is fixed in real space (and I am
asking where?  7 ft., 15 ft., somewhere else?) and the scene has
moved with respect to the window.  It is hard to accept that the
rock has moved closer to the camera without increasing in size
and depth and tha the mountains have moved in half infinity.

I accept the fact that by putting the window at 15 feet I reduce
the separation of infinity points and have my eyes converge when
looking at infinity.  However this does not make the mountains be
any closer to me than infinity.  Convergence is overriden by
other stronger cues.

Other than that, I fully agree with Greg's explanation of the 
window violation as a:

>conflict between the depth cue provided by binocular
>disparity, which "says" the object is in front of the window, and 
>the depth cue of the object being cut off by the window (occlusion)

-- George Themelis


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