[Lab] Depth Perception

Jason Cobill jason.cobill at gmail.com
Mon Aug 22 16:01:22 EDT 2011

   Alignment's not too tricky - generally, 3D movies aim the cameras
parallel to eachother and let your brain do the tricky work of converging
the images. They don't need to be exactly parallel for this to work, and
this is the reason some people get wicked migraines watching Avatar.

   You can get the same effect as the XKCD experiment (and Avatar) with a
highly simplified process:
   - Find a point on the horizon and take a picture of it.
   - Walk a few feet.
   - Take a picture aimed at the same point on the horizon
   - Bring the two images together side-by-side on the computer (preferably
without border lines between them)
   - Cross your eyes really hard like you're looking at a "magic eye" image,
and they'll converge and you can see your clouds in 3d.

   Or save yourself the effort of going outside and look at these:
   http://phereo.com/   (Be sure to click "Mode" and select "Crossed" if you
don't want to use special glasses)

   The technique is really old - I have a number of friends with collections
of stereoscopic images from the mid 1800's! It was a fun party toy for
   You can find out a bit more here:

   Also worth noting that stereo pairs are extensively used in aerial
surveys - a plane takes two photos in succession and the pair can be
converged to get a 3d view. I've often spotted clouds, boats, and even other
planes in high-altitude aerial surveys. I should mention that the effect is
a little less exciting than the XKCD comic paints it to be. Having a pair of
stereo glasses definitely relieves the stress of staring crosswise and lets
you feel a bit more immersed in the image.

   -Jason Cobill
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