In graphics, a stereo pair is a set of two images of the same scene, viewed from two slightly different positions, side by side.

Each image represents the view from one eye - the horizontal displacement replicates that of your eyes.

If you arrange it so that each eye sees one image, your brain will use the differences between the images to reconstruct the scene in 3D. If you get the images the wrong way round, the 3D information will be reversed.

One cheap and cheerful way of doing this is by a controlled crossing of your eyes. This is a knack you can acquire with practice - the same trick is used to view random-dot stereograms.

Looking at a stereo pair, cross your eyes. You now see a total of four images - two for each of the pair. Now relax the eyes so that the middle two images become superimposed. You can try this with the primitive stereo pair I've created below - line up the two * marks above the 'images' and they should leap out into solid 3D ascii-vision.

Don't strain your eyes!

* * || || || || || || || @|| __ || @ || __ || @@|| ' ` || @@ || ' ` || @@@|| | | ||@@@ || | | || || `__' || || `__' || || || || || ||
In ray tracing, stereo pairs can be generated very simply, by rendering once, then 'moving' the 'camera' sideways (usually this means varying its x and z coordinates a little) and rendering again.

In stereophotography, stereographs or stereo photographs are taken with special stereo cameras and are usually viewed using a stereoscope.