[visionlist] [cvnet] Trying to demonstrate stereoscopic vision remotely

Ben Backus ben.backus at gmail.com
Sun Mar 22 19:25:21 -04 2020

Thanks James for that.

You know, to be honest I don't think this matters for an introductory
lecture on stereo. Stereo effects are pretty robust. There's no harm
free-fusing pictures taken with toe-in cameras. You'll still get a nice
stereo effect. Better to get students trying things, right?

This is probably not appropriate for most students, but technically, you
*can* use toe-in cameras to perfect effect, if the stereo images are
displayed in a haploscope, with the arms set to the same convergence angle
as the amount of toe-in. In that case the optic arrays would be preserved,
so both the perspective and the vergence demand would be correct. That
could be the situation Mike C had in mind when he asked the question
(either that, or else convergent free fusion of the two images), whereas I
was describing what happens when images are displayed in a standard
stereoscope or movie theater.

On Sun, Mar 22, 2020, 2:36 PM James P. Herman <hermanj at gmail.com> wrote:

> Ben --
> My apologies but I found your answer(s) to Michael Crognale's question
> difficult to follow, and I was also perplexed by the notion that
> translation and not translation+rotation is the way to go for DIY
> stereoscopy!
> I found a website that describes the problematic (but not impossible to
> contend with) distortions of perspective induced by using "toe-in"
> (relative camera rotation in addition to translation) when taking
> stereoscopic images.
> The short answer is that if you rotate the camera in addition to
> translating it (between taking photos), the change in perspective can
> result in identical parts of an image having different sizes in the two
> photos (the dangerous vertical disparity mentioned previously). I must
> admit it's not clear to me why any movement of the camera wouldn't
> potentially cause such distortion, but I suspect it's a matter of scale
> (translation causes little distortion, rotation causes more). In any case,
> here's the link:
> http://www.binocularity.org/page12.php
> Enjoy!
> -- jph
> --
> James P. Herman, PhD
> Laboratory of Sensorimotor Research
> National Eye Institute
> Building 49 Room 2A50
> National Institutes of Health
> Bethesda, MD 20892-4435
> office: (301) 496-9376
> mobile: (212) 663-0407
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