P3D Re: The need for depth in stereographs

["Greg Wageman" <gjw@xxxxxxxxxx>]

-From: Project3D@xxxxxxx <Project3D@xxxxxxx>
Bob Aldridge:

>I'm sorry, but just because you can't resolve the amount of depth in
the
>distant scene into full rounded 3-D because the angles are too small
doesn't
>stop the image from being a stereograph. It would be perfectly possible
to
>enlarge the images with computer enhancement to overcome the
limitations of
>the film grain, lens resolution etc, to the extent that the depth clues
would
>become detectable. The fact that the two images were not taken from
EXACTLY
>the same viwpoint means the we automatically get a stereograph. Whether
you
>like it or not.


I'm sorry too, but this is factually false.  Take a picture of the clear
night sky with a normal stereobase, and the only differences between the
two images will be due to the differences in the film grain structure
and the slightly different aberrations in the two optical systems.

If it weren't the case, astronomers wouldn't have to wait 6 months in
order to detect parallax between the nearer and farther stars, using the
baseline of the earth's orbit around the sun; they could do it nightly
using your methodology.  There IS a distance at which a normal baseline
will not provide enough disparity to trigger stereopsis, and whether one
"like it or not" has nothing to do with the fact.

>And because the image doesn't display much in the way of depth doesn't
make it
>"trickery" to show it.


"Not much" is still greater than zero.  Like with many things there is a
continuum between the shots with maximum depth and the shots with no
perceptable depth.  I wouldn't want a steady diet of either extreme.  My
opinion is that shots tending toward the latter extreme are a poor use
of the stereo medium.  What's so controversial about that statement?

The example cited is unfortunately a bit extreme, but seemed necessary
to emphasize the point.  An *educated* stereographer passing off an
image with no detectable depth (not "little depth", but "no detectable
depth") as a stereograph is, again in my opinion, on par with the
charlatans who give 3D a bad name.

>I personally think that the audience would find it very strange if I
stopped a
>stereo show every time a distant subject came up, made them take off
their
>polarising spectacles, installed a white screen, switched to a mone
projector
>for the "flat" slide, then returned to the stereo setup for the next
bit of
>the show - until another "flat" image arrived.


Indeed they would.  But then if you came to see a show of ostensibly 3D
images, and every one were of a sunset from the top of  a mountain or a
distant mountain range taken from the edge of a cliff, no matter how
glorious the image, wouldn't you be a bit disappointed?  You had been
told, after all, that you were going to see 3D.

>And "1", :"2" and "3" all suggest that Greg is always thinking in terms
of
>images in isolation, which is why I was pleased to see "4" even if it
does
>seem to imply that Greg doesn't approve of this approach!


It is true that I don't plan my images when I'm taking them in the
context of  a show or presentation.  I would tend to do that kind of
selection after the fact.  If you can do that in camera, then you are
godlike in your stereo prowess and I am not worthy of cleaning your
lenses.

Most competitions limit the number of images one can present, and mix
them with other peoples' images.  Could you count on the preceding image
being just the right one to offset the lack of depth in yours, or
shouldn't you plan on your image standing on its own?

     -Greg W. (gjw@xxxxxxxxxx)



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