Re: Corrected: Explanation of 3-DVG effect

[P3D Jim Crowell <crowell@xxxxxxxxxxxxxxx>]

At 8:36 AM -0800 4/12/97, P3D wrote:
>
> Jim is correct, I found I could not, in the space allotted to me in the
> Stereo World article, include a description of how the 3-DVG worked.
> However, I did reference the SPIE paper that  attempted to take a stab
> at it.  That reference is repeated  at the end of this document.
>
> In leaving out this information I felt that it was more important for the
> reader to "experience" the 3-DVG effect first.  The reason for this is
> that basically everything about the 3-DVG  falls into the category of
> sounding incredible.   The majority of persons who see it say that
> "had they not seen it they would not have believed it." Professor Bela
> Julesz saw it in 1989 and named it "the Dunkley effect."

Hi Ken,

Good to hear from you.  As you might have guessed, I found the article very
frustrating, and I think you did yourself and the readership a disservice
by not describing the principles at all.  Speaking for myself, I would have
found it a good deal less incredible if I had been told how it worked
instead of being told repeatedly how incredible people found it...it
sounded a little too much like what P.T. Barnum would've said.... :-)

> Jim, what I would like to say to you and other group members  is
> that the visual results of the 3-DVG process cannot readily be
> anticipated or logically derived.

The former I'll buy.

>Ames argued that simple reflecting and refracting
> optical elements could be used to generate definite and true depth
> discrimination (i.e., 3-D) from 2-D images by altering the interoptic
> angle.

I'm not familiar with this--can you summarize the principle?

> Also,  the pinhole effect (includes: monocular depth sensation,
> increased depth of focus, lowered veiling glare, etc.), the oldest
> of the 2-D to 3-D effects, allows the visual addition of the Ames
> effect to the effect called illocal framing.  This happens because
> the frames are situated within the depth of focus range determined
> by the pinhole diameter.

Don't you mean out of the depth of focus range (i.e. out of focus when you
look at the picture)?

> The fourth effect is pinhole generated chromostereopsis which is
> intimately related to the Ames effect and is, in fact, identical to it
> depending on the nature of the observed target under observation.
> Though both processes appear to be governed by the wavelength
> (chromatic) dispersion of off axial rays traversing the eye, the
> Ames phenomenon  appears to be additionally governed by objective
> visual information (i.e., perspective, shading, aerial perspective,
> and know relationships) distributed over the region under observation.
> This objective picture information will in most instances override
> depth information provided by the chromostereoscopic examination
> of small uniform colored targets.

It sounds to me like the "Ames phenomenon" is actually a conglomeration of
effects...

>From what I've understood so far, the device works by (1) removing or
minimizing cues that specify the flatness of the picture, allowing the
monocular depth cues--such as perspective and shape-from-shading--to have
full play, and (2) introducing binocular disparities between colors via
chromostereopsis.  I'm afraid I don't understand your description of the
Ames phenomenon...

>Notice also that
> stereopsis generated by the Ames effect can be observed (though
> much reduced)  when viewing b&w and monochrome photos.

Interesting...

>  I will repeat the offer made earlier of a free demo training unit for group
> member to try out and comment on.   Send me an e-mail with a mailing
> address.

I'd be curious to see one...my address is below.

-Jim C.

----------------------
Jim Crowell
Division of Biology
216-76
Caltech
Pasadena, CA
(818) 395-8337
jim@xxxxxxxxxxxxxxx



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