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

Barton Anderson barton.anderson at sydney.edu.au
Mon Mar 23 00:07:58 -04 2020

OK, so a figure to clarify my argument (and hopefully clarify the misunderstand I had with Ben’s comments).  The figure below compares the vertical disparities generated by spherical eyes (the circles)  and a planar focal plane of a camera (the straight lines behind the circles.)  The figure depicts a ‘plan’ view of two vertical lines at two different depths. The eyes/camera are oriented to  converge on  the line (represented as a dot) of the left image.  Because this line is closer to the left eye, it will be slightly larger in  the left eye than the right eye, and therefore have some vertical disparity (say, VDL).  The magnitude of this  disparity will be the same for the camera, because the distance to the imaging plane is identical in both cases. However, the same is not true for the right vertical line (represented as a dot in this picture). It is closer to the right eye and will therefore form a slightly larger in the right eye (let’s call this VDR).  Note, however, that the path lengths needed to reach the image plane of the camera are not equal in the  two eyes; this creates and additional vertical disparity difference of the non-fixated image.  This is why will not appear right if you just free-fuse them or view them in a simple stereoscope; the vertical disparities would be too large. However, if you set up a haploscope that forces observers to converge at the  same angles and place the camera images in front of the eyes, you can then reconstruct the optic array (this was Ben’s point). Any other method of viewing won’t really work because of the exaggerated vertical disparities, although you will still probably experience some stereo in some parts of the images near the fixation  point.

Hope this helps.

[cid:image001.png at 01D60124.A1FBEA20]

From: Michael A Crognale <mcrognale at unr.edu>
Date: Monday, 23 March 2020 at 10:18 am
To: "James P. Herman" <hermanj at gmail.com>, Ben Backus <ben.backus at gmail.com>
Cc: 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

It seems to me that if we are replicating the retinal images then the only differences between rotating and not rotating is that it would be moving the reference plane  for the disparity.  If you do not rotate you are simulating the images in the eye for when we view a distant object when you rotate (inwards) you simulate the retinal images that happen when we are focusing (converging) on a close object.  In each case relative disparity exists and should be fine. I myself have no problem fusing images that are “rotated” to a closer horopter.

Michael Crognale, PhD, CFII
Professor, Cognitive and Brain Sciences Program
Chair, Dept. of Psychology /296
University of Nevada, Reno
Reno, NV 89557
775 784-6828

From: James P. Herman <hermanj at gmail.com>
Sent: Sunday, March 22, 2020 2:36 PM
To: Ben Backus <ben.backus 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; David Peterzell <dpeterzell at berkeley.edu>
Subject: Re: [cvnet] [visionlist] Trying to demonstrate stereoscopic vision remotely

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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