P3D Re: SI anaglyph

[Tony Alderson <aifxtony@xxxxxxx>]

Gabriel Jacob wrote: 
> This is confusing. Your saying "staircasing" is not the same thing, as
> cardboarding? Can you elaborate?

By "staircasing" I am drawing an analogy between the 2D aliasing of
pixel based images, and "stereo" aliasing. When the pixels get larger
than the stereo acuity, then the image will appear to be made of a
series of discrete planes, rather than a continuous curve. The "pixels"
in the SI image are pretty small.

Let's try one of them pesky ascii diagrams. This is a cross-section of
your stereo perception from "above." A cone with stereo aliasing will
appear to be a series of concentric discs:
          _
        _| |_
      _|     |_
     |         |

A carboarding cone will appear to be a plane, regardless of the
resolution of the image or the size of the pixels:
     ___________


Gabriel continues:
> (...) If you stand back a few feet, it's sure not ortho! 
> 

Didn't say it was ortho. It's not ortho from close-up either. I still
think the perspective match is better, but simply matching angles of
view does not make an image orthoscopic, in my understanding of the
term. You can match viewing angles of a 500mm lens, but no matter what
you use for a stereo base, you won't get an "ortho" image. (Except in
the sense that we don't see stereo beyond a few hundred feet, so even a
flattie image, far away, is arguably "ortho".)

Gabriel continues:
> Furthermore, there is no roundness to her arm (if that is what your
> referring to). Granted there more depth, but within her arm there
> is no depth. It looks like a flat piece of cardboard coming at
> you. Same for most of the faces (other than the nose area) and other
> parts of the body.

I disagree. I see roundness in her arm, but maybe I'm just being fooled
by the shading. If "stretch" is happening on her arm, it's happening in
her arm too. I have noticed different people have different
interpretations of the same image.

Gabriel continues: 
> I have to agree with Ray and say, the cardboarding I believe, is due
> to loss of detail. The stretch/squash IMO is another completely
> different factor. Why do you think B&W anaglyphs work much better?
> It's not only because of the color rivalry, but also I believe
> because of the loss of detail in the red channel! Quite a few of
> the images have NO red channel detail, and this is the problem.

I think this is a secondary factor. IMHO, there is enough edges and
shading in the red channels. But why have I seen cardboarding in stereo
slides, where this issue of red channel detail does not apply?

Gabriel continues: 
> For example, look at the Universal Studios ad. This ad has very
> close up shot of a model's face and no stretch is required to see
> the depth in her face. It's the best image in the magazine! Why?
> It's not in color! :-)

I disagree. You are comparing images with unknown variables. I believe a
comparison with controlled variables will show otherwise. I'll try to
find the time and energy to demonstrate this, but I would encourage you
to try your own independent experiments.
 
Gabriel finished:
> (...) I do greatly respect and enjoy,
> Tony Alderson's In Depth 3-D work and knowledge!

Thanks, nice of you to say so. But I notice you don't worship the ground
I walk on!   :-(  or is it  ;-)  ?

Tony