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 same film.

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.)

Jay Sekora <js@aq.org>
last modified 2009.12.01