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<p class="MsoNormal">Hmmm, well I don’t think this is right Ben. Let’s take the case of two vertical lines side by side. The left one is nearer than the far one and is the one that is fixated, so it has not vertical or horizontal disparities. The right line
will be slightly closer to the right eye, and therefore generate slight vertical disparities at its top and bottom (larger in the right eye). This is unaffected by the convergence angle; the vertical disparities are a function of differences in distance
(because the eyes are spherical). Now consider what happens with two cameras with a flat projection plane. The right line will project to the temporal side of the right image, which has been rotated forward; and to the ‘nasal’ side of the left eye, which
has been rotated away. So for flat planes, the vertical disparities will be in the same direction, but the vertical disparities in the flat planes (cameras) will be much larger. You can actually experience this in pictures where the cameras are rotated;
the regions away from the point of convergence are hard to fuse.<o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Ben Backus <ben.backus@gmail.com><br>
<b>Date: </b>Monday, 23 March 2020 at 10:25 am<br>
<b>To: </b>"James P. Herman" <hermanj@gmail.com><br>
<b>Cc: </b>Michael A Crognale <mcrognale@unr.edu>, Barton Anderson <barton.anderson@sydney.edu.au>, David Peterzell <davidpeterzell@me.com>, cvnet <cvnet@mail.ewind.com>, Christopher Tyler <cwtyler2020@gmail.com>, "visionlist@visionscience.com" <visionlist@visionscience.com>,
David Peterzell <dpeterzell@berkeley.edu><br>
<b>Subject: </b>Re: [cvnet] [visionlist] Trying to demonstrate stereoscopic vision remotely<o:p></o:p></span></p>
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<p class="MsoNormal">Thanks James for that. <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">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?</span><o:p></o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal">On Sun, Mar 22, 2020, 2:36 PM James P. Herman <<a href="mailto:hermanj@gmail.com" target="_blank">hermanj@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Ben --<o:p></o:p></p>
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<p class="MsoNormal">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!<o:p></o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal">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:<o:p></o:p></p>
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<p class="MsoNormal"><a href="https://protect-au.mimecast.com/s/bvhkC0YKPviJnWY5Hw6aa3?domain=binocularity.org" target="_blank">http://www.binocularity.org/page12.php</a><o:p></o:p></p>
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<p class="MsoNormal">Enjoy!<o:p></o:p></p>
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<p class="MsoNormal">-- jph<o:p></o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">James P. Herman, PhD<br>
Laboratory of Sensorimotor Research<br>
National Eye Institute<br>
Building 49 Room 2A50<br>
National Institutes of Health<br>
Bethesda, MD 20892-4435<br>
office: (301) 496-9376<br>
mobile: (212) 663-0407<o:p></o:p></p>
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