P3D Re: Cardboarding

[Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Fri, 23 Jan 1998
>From: boris@xxxxxxxxxxxx (Boris Starosta) writes:
>...............
>
>
>>Date: Thu, 22 Jan 1998 16:30:00 -0800
>>From: michaelk@xxxxxxxxxxxxxxxxxx (Michael Kersenbrock)
>>
>>Although I suspect this may be a semantics discussion rather than an
>>optical effect one, to me cardboarding is more commonly something else.
>
>Exactly the problem.  Because I think cardboarding is a very subtle effect
>in most slides, many people (you all) have different thoughts about it,
>different perceptions of it.  Nevertheless, I propose that it is a
>definable optical effect.  My proposal specifically hopes to overcome
>semantics.

*****  It is a definable optical effect but it's still a subjective
experience along with the effect and it most certainly is NOT limited to
slides. The fact is that many who are new to stereo imagery will observe
genuine *cardboarding* in scenes that you and I would determine don't in
fact have any cardboarding. I've had a few people exclaim about cardboarding
in Hyper stereo!!! (they didn't even know there was such a term)

>
>>I think you well describe a source of cardboarding, but it doesn't seem
>>that source is an exclusive source to cardboarding.
>
>In stereo photography not involving cardboard subjects, I propose that it is.

****  I have to agree with Michael Kersenbrock's conclusion. Your effect may
at times contribute to the cardboard effect but it certainly isn't the total
causation. The problem is that cardboarding is a very relative term. It's
relative to too many factors to be able to narrowly define it as a form of
*squash*. There are lots and lots of stereo pictures that do not have
cardboarding yet look fine under *squash* conditions. And there are many
images that DO have cardboarding even when viewed under stretch conditions.
Since overall resolution is contributary to this effect, an image with
definite measurable cardboarding will look like cardboard cutouts at any
viewing circumstance. It's also relative to the viewer's experience with
stereo viewing overall and experience with various viewing methods and devices.

In short there is no way to define it except as a subjective experience
determined by relativistic circumstances.

>
>>To me, "cardboarding" makes me think of the effect I see most often
>>in lenticulars where I see a cascade of flat 2D images at various
>>depths. ...................
>
>Actually, my theory would apply/explain your impressions of lents quite
>well.  ............

****  Your theory does explain lenticular cardboarding, but not a host of
other circumstances.

>.............
>>I think you are very right that a telephoto lens portrait
>>could cause the same effect with things at the right distances
>>and w/o hyper "quasi-compensation".
>
>Now you're throwing in another variable, namely stereobase.  Attempting to
>compensate for cardboarding by extending the stereobase will fail, as was
>discussed on P3D late last year (I think - certainly within the last six
>months).

*****  This statement is without foundation. Of course stereobase is a
significant part of the situation since it definitely affects the appearance
of cardboarding by affecting *local parallax* for objects themselves. There
are lots of Realist pictures of landscapes around that exhibit a high degree
of cardboarding. The same scenes taken with a wider stereo base have less of
that particular effect. Again it's not a direct and total correlation, but a
very very significant contribution. When you want to talk about cardboarding
on small images viewed on computer monitors, extending the stereo base is
one of the most useful methods of avoiding cardboarding. The true kind where
there is NO parallax in objects themselves and minimal parallax between
different objects. You can't get more cardboard than that even with
cardboard models! Extending the stereo base for these images helps to insure
that parallax for each object does actually exist even after the resolution
has been reduced to a relatively small image. Unless your theory can account
for the entire range of the experience, including stereobase variables, it
can't be considered to be THE definition. I readily accept that your
observation contributes to the effect under some limited conditions.

By the example I've used with digital images of small scale, I could propose
that cardboarding is better defined by the simple rule as stated by Gregory
Wageman. His rule of thumb works under any of the possible conditions:

>My working definition of "cardboarding" for some time now has been:
>Lack of stereopsis *within* an object, while stereopsis is present *between*
>objects.

Note that he used the word *stereopsis* which refers to the visual
experience rather than to the parallax in the image itself. This allows the
beginners statement about cardboarding to be valid even though you and I
wouldn't observe the effect in the same image. It also describes accurately
cardboarding where there is a real parallax situation resulting in the
effect. It is also universal enough to cover the subjective experience for
any kind of image or viewer option, including squash or field of view issues.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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