Re: Converging fields of view

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

Hi All,

Semantics, words, language, where would we be without such problems?


In digest 1381, Gregory J. Wageman writes:
>The only problem with settling for the
>term "offset" is that, as we have seen here, it does not convey to everyone
>the important fact that the fields of view do, in fact, converge. 

It is true that the fields overlap but it is NOT true that they converge.
The fields spread out fan like and OVERLAP as they proceed in a generally
parallel arrangement. The center of each field is OFFSET from the other and
these centers are supposed to be parallel for the least amount of
distortion. It is the viewer's eyes that converge on one pair of details or
another within the overlapping areas of these fields of view. If there were
no offset and overlapping areas you would not have stereo information. 

For a wonderfully detailed and revealing discussion of this topic visit
Andrew Woods' web pages where he discusses his underwater stereo video
system. One system uses cameras that DO converge. He evidently worked up the
exact distortions so that the stereo scenes could be corrected for viewing.
He has some interesting charts to illustrate the specific distortions that
result from "converged" fields of view. The URL is:

        http://info.curtin.edu.au/~iwoodsa

As to the "window", it may be relatively fixed for a given stereo camera but
it is by no means a fixed entity generally speaking. Since I create stereo
images in my computer or modify photo 3D pairs, the effective window is
wherever I want to put it. Only in a fixed stereo camera is the window a
fixed entity. However you can change it within some range by selective
masking of the results. Such masking is far easier in a computer than with
actual pieces of film. The dawning age of digital cameras will no doubt have
profound effects on what 3D'ers have to do to prepare and enjoy their work.
Since I can place a "window" wherever I want it, the window has no direct
bearing on whether or not the fields of view represented by the images were
converged or not. Again, it is the viewer's eyes that do the converging.

Enjoy,




Larry Berlin

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


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