P3D My 3D Litmus test

[Paul Talbot <ptww@xxxxxxxxx>]

Bob_Maxey@xxxxxxxxxxxx wrote re: Dunkley effect:
 
> I think the above is called the "Imagination Effect". To be, as you
> put it "Truly Stereoscopic" you need a left and right eye view.

Bruce Springsteen, Boris Starosta, and Abram Klooswyk have also
contributed comments on the Dunkley and ChromaDepth effect(s).  I
have not witnessed either effect, but I'm surprised that none of
the discussions of the effect(s) mention "airspace."  Whenever
I am unsure about whether I'm seeing something as 2D or 3D, I
compare the one-eyed and two-eyed view.  If the two-eyed view
reveals airspace that is not discernible in the one-eyed view,
it passes my 3D litmus test.

When I first started shooting stereo and showing slides to friends
and acquaintences in a $3 viewer, some people would sometimes
hesitate, seemingly unsure of whether there was anything "special"
about what they were looking at.  When that happened I would
instruct them to close one eye briefly, then to look again with
both eyes, and to observe how the air space between objects
opens up when they look with both eyes.  "Oh, YEAH!" would be
the typical reaction.  With an appropriate subject matter, if
you cannot see the airspace between the objects, you aren't
looking at a 3D image.  IMO, how well your brain has managed
to reconstruct the z-axis relationships, or thinking you can
discern "roundness" in the objects themselves, doesn't go far
enough.  Look for the airspace.  The objects should clearly have
visible airspace between them when viewing with two eyes, and
the airspace should appear to close up (causing depth-displaced
objects to seem touch each other) when one eye is closed. If not,
I vote with Bob for calling it an "imagination effect."

Some subject matters are not well suited to applying this litmus
test.  Images with "continuous depth", like a large field of
smoothly cut grass, train tracks, or long corridors make it
very difficult or impossible to perceive the airspace under
normal viewing circumstances.  That has a lot to do with why
I find stereo images with continuous depth of this sort quite
boring.  Why not just shoot them in 2D?  The non-stereoscopic
depth cues are so strong that stereoscopy adds little information.

I'm curious as to whether those who have seen the ChromaDepth
effect and the Dunkley effect can perceive the air space between
objects in the images.

Paul Talbot


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