Re: PePax and dollhouse effect

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

Hi All,

I'm new to PePax and can't discuss it's pros and cons but the discussion of
image reconstruction has elements that are hard to understand.

> John Bercovitz writes:
>1) Changing the relative separation of the two camera perspectives 
>has a linear scaling effect on all three dimensions of the 
>reconstructed image.  If the separation is 130 mm, twice the 
>separation of the eyes, the reconstructed image is scaled down by 
>a factor of two.  This rescaling is of all three dimensions and 
>this _includes_ the distance of the image from the person viewing.

If I take my SLR and take a shot of a subject from a given distance, all
other shots of that subject from the same distance will have the same x,y
scale. I could move around the subject in a compete circle taking shots
every few degrees of that circle and all have the same scale. I can match up
side by side pairs from varying degrees of separation and until the parallax
is too great, they still merge in a stereo view with the same x,y. (camera
not remaining parallel)

To eliminate other distortions, suppose I keep the camera parallel to itself
for each shot and only record images that appear in the frame. This would
only be an arc of the circle but if I remain the same distance from the
subject, the x,y of the subject again remains the same. 

Other distortions enter into the situation but a linear shrinking in all
axis just doesn't make sense. The z axis, or depth, changes relative to the
degree of separation of the images and is directly related to parallax. The
x and y appear to remain the same. Obviously I've missed something in the
explanation of this phenomena. Where does the dollhouse effect happen? I
can't see any example of it due to a wide stereo base.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/


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