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

Barton Anderson barton.anderson at sydney.edu.au
Sun Mar 22 21:28:10 -04 2020

Sorry, I didn’t read Ben’s original post carefully enough; he’s right that you can rotate cameras under the restricted display conditions he articulates.  My main message was to explain why it doesn’t work in more typical methods of stereo viewing.

From: Ben Backus <ben.backus at gmail.com>
Date: Monday, 23 March 2020 at 10:25 am
To: "James P. Herman" <hermanj at gmail.com>
Cc: Michael A Crognale <mcrognale at unr.edu>, Barton Anderson <barton.anderson at sydney.edu.au>, David Peterzell <davidpeterzell at me.com>, cvnet <cvnet at mail.ewind.com>, Christopher Tyler <cwtyler2020 at gmail.com>, "visionlist at visionscience.com" <visionlist at visionscience.com>, David Peterzell <dpeterzell at berkeley.edu>
Subject: Re: [cvnet] [visionlist] Trying to demonstrate stereoscopic vision remotely

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<mailto: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:



-- 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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