P3D Re: Stereo Nomenclature (part 3[b] of 3)

[Larry Berlin <lberlin@xxxxxxxxx>]

> Date: Wed, 15 Dec 1999
> From: Bruce Springsteen <bsspringsteen@xxxxxxxxx>
> .........
> Why I dislike the "Viewing Base = Recording Base" condition, and the First
> Deformation of classic ortho-stereoscopy:
> 
> 1. RECORDING vs VIEWING.  I prefer a definition of orthostereo that
> pertains only to viewing.  .........
> Nodding to this absurdity, we usually offer the solace that the normal
> "range" of human eyespacings will not yield *perceptible* scale
> differences if an "average" recording value is selected (6.5 cm? 6.2
> cm?...).  But that's a fuzzy ex post facto practicality, not the stuff of
> fundamental principle, and only points up the vagueness of this basic
> stereo rule.  I suggest that, once the terms of my Definition I have been
> met, any stereogram has been duly "encoded", and the burden of "decoding"
> it accurately in terms of ortho is solely the responsibility of the
> viewer.  There is no orthostereo recording.

****  For practical everyday images yes. For the principle itself, no.

All stereo viewing is relative to many things including the taking 
circumstances. It therefore seems appropriate to have such a thing 
as Ortho, so narrowly defined in both taking and viewing. It does 
NOT follow, that the dictates of orthoness should overwhelm the taking 
and viewing of stereo images. It's merely a guidepost along the way.

> 
> 2.  INTENT vs ACCIDENT.  While all of the other non-ortho "deformations"
> are inadvertent and undesirable effects (at best we say that they are
> often unnoticeable until a certain threshold is reached), the effects of
> scaling/base changes are almost always intentional and specifically for
> exploitation of the effect.  It seems conceptually inconsistent and unfair
> to place a usually deliberate recording choice at the head of a list of
> usually accidental distortions.  Hypo- and hyper-stereo deserve better
> company.  I can't accept that David Lee's scenic hypers, or Pat
> Whitehouse's nature hypos, belong in a category with deformations like
> stretch, squash, frustum, and skew that are nearly always a side-effect of
> vicissitudes in viewing.

*****  I agree!!! The standard that should be applied should only deal 
with the viewing side of the equation, which would easily include hypos 
and hypers alongside the best of ortho images. The goal isn't and 
shouldn't be raw orthoness, but overall appropriate viewableness. A 
balance of factors in the results, no matter what the taking 
circumstances.


> 
> 3.  RESIZING vs DISTORTING.  .........
>  Similarly, the creation of hypers and hypos does not "distort" anything,
> it merely scales space in a way that a Gulliver could easily navigate as
> he did the "real" earth, once he assumed the proper scale.

*****   Yes! This equates to the virtual reality of the situation. 


> 
> 4.  OBJECTIVE vs SUBJECTIVE.  ...........
> image?  If I make three drawn anaglyphs of a great stellated dodecahedron,
> each with a different base in proportion to the object, which drawing is
> "ortho?"  Our classic ortho-standard is half geometry and half ego - a
> strange brew!   

****  A strangely accurate description of the term!!! 


> .....  The recording base
> condition is too arbitrary and idiosyncratic to be a basic requirement for
> "right-viewing", IMO.  

****  Very true! But in reference to my earlier comments, it's the 
mis-application of importance in the term that is the problem, not 
necessarily the term itself.

As described officially, it is grounded in an average human physical 
situation. There is value in that as a reference point, but not as the 
rigid design circumstance it's been made into.


> ...........
> This is the same condition as viewing a single 2D photograph from the
> "correct" perspective with one eye.  We are just doing it with two images.
>  Note that base expressed as an absolute distance (so many centimeters) is
> gone, and we now refer to parallax/convergence preservation in terms of an
> alignment.  The actual distance between left and right images is not a
> fundamental issue - ...........

*****  I am in agreement and was going to not comment, but you've
arrived 
at the critical juncture here. It is the viewing angles that should be 
referenced carefully, NOT the base dimensions. They are universal across 
the range of taking and viewing circumstances.

It is still true however, that our notion of correct viewing angles is 
itself derived from the spacing of our eyes. However, working with the 
angles instead of the more superfluous base dimension makes the working 
environment consistent over a huge range, not limited to the narrow 
ortho definition.

So perhaps this issue is an artifact of the early efforts to design and 
build a good stereo camera. Now that we are well beyond that point, the 
significance of factors can be seen in a more wholistic sense. We no 
longer need to make the same set of assumptions. Nor to repeat previous 
assumptions rote, just because they were stated by an historically 
important person/entity.

> 
> Also absent is any reference to focal length of camera or viewer.  Those
> terms relate to a specific method of stereoscopy, hand-viewed
> transparencies, and so are inappropriate in a general definition of
> orthostereo.   

****  As I suggested, it may have been a largely equipment and 
technology based bias. It is relatively dangerous to accept the 
pronouncements of -any- relatively singular manufacturing 
entity/process (no matter how well intentioned),
as fully applicable to an entire science. The chosen terms and methods 
usually reflect a strong bias for the particular product or process 
being promoted. The science side of things becomes shortchanged because 
often continued thinking on any topic is limited by the words we use 
to describe circumstances within the topic. 

A more modern example of this effect is in computer software and OS...
(Most won't understand this reference for another 10 years...)

> Av = Ar will be free to imply different practical
> requirements in different forms of stereo - anaglyphic, projected, print -
> favoring no one method by speaking in its peculiar terms.   Too often we
> express the rules of stereoscopy in terms of secondary, not primary
> requirements, related to some specific practical necessity - leaving the
> impression that we have defined a primary requirement.   

*****  This is termed a marketing ploy, and as such it is deliberately 
deceptive, though accepted generally as somehow unavoidable. Yet we DO 
have a choice to exercise. Thanks to stereoscopic history, we can see 
the dynamics of this phenomenon quite clearly.

Being aware of this factor in history, we can choose to become aware of 
it's continuation in the present (in all sectors), and deliberately 
thwart that tendency to the betterment of the present and future.

Thanks Bruce for pursuing a detailed evaluation of the ortho issue.
-- 
Larry Berlin

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