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How’d he do that?
When I went to get a passport picture for
my trip to South Africa, I noticed that the two passport photos weren’t
exactly identical - they were taken from slightly different angles.
The passport camera had two lenses, spaced a little ways apart,
projecting very slightly different images side-by-side onto the
Since the way the brain perceives depth is by comparing the two
slightly-different pictures it gets from the two eyes, similarly
spaced a little ways apart, it occured to me that I could use
two passport pictures as a stereoscopic (3-D) image.
(Thanks to the folks at
tummy.com who wrote and sold the
XVscan extension to
xv, which I used to scan in the picture back before there was widespread
scanner support for Linux.)
How do you see the effect?
To see the 3-D effect, you either look at the cross-eyed version
and cross your eyes until the two images fuse, or look at the
wall-eyed version and defocus your eyes (as if you were looking
at something far in the distance) until the two images fuse.
Some people have an easier time with one technique than the other.
(Myself, I can only see these kinds of things cross-eyed.)
last modified 2009.12.01