Plate 01 · single-image random-dot stereogram

Look through
the screen

A shape hidden in noise. Tyler and Clarke worked it out in 1979; by 1993 it was on every poster in every shopping centre. It is all arithmetic — the dots repeat at slightly different intervals, and your two eyes read the mismatch as depth.

How to see it

1. Hold the screen close, nearly touching your nose. Let everything go soft — don't try to focus.
2. Look past it, as though at something far behind the screen. The two dots above the plate will drift apart and become three.
3. Draw the screen slowly away, holding those three dots steady. The shape lifts out of the noise and stays there.
4. If it won't come, shorten the pattern repeat and try again. Smaller repeats ask your eyes to diverge less.

Built with the Thimbleby–Witkin–Wiseman algorithm (1994). Each row is walked left to right; for every pixel the code works out how far apart its two copies must sit given the depth there, links those two positions as the same dot, then fills the row backwards with random colour. Occluded points are dropped so near surfaces hide what's behind them.