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Light and color

Mach bands

Each strip of gray looks shaded, lighter at one edge and darker at the other. It is perfectly flat.

By Illusions Blog · Updated · How we make them

TypeLight and color
InteractiveYes: sliders and a check
First described1865

Every strip seems to get lighter near its darker neighbor and darker near its lighter neighbor.

Try this

  • Tick Show a brightness graph: the real brightness is a set of flat steps.
  • Change Number of steps.

Why it happens

Ernst Mach described these bands in 1865. Your visual system exaggerates edges: cells that respond to a patch are inhibited by their neighbors, so the edge of a light strip next to a dark one is pushed lighter, and vice versa. Floyd Ratliff's 1965 book on Mach bands made the link to lateral inhibition in the retina. Edge enhancement helps us see outlines quickly, at the cost of seeing bands that are not there.

Did you know?

Radiologists know Mach bands well: they can create false lines at the edges of structures on X-rays.

References

  • Graham C. (1965). Retinal Interaction Processes: Mach Bands: Quantitative Studies on Neural Networks in the Retina . Floyd Ratliff. Holden-Day, San Francisco, 1965. xiv + 365 pp. Illus. $13.95.. Science, 150, 596-597. doi:10.1126/science.150.3696.596
  • Background on Wikipedia

The illusion on this page is drawn by code written for this site. Last checked 1 November 2026.

Frequently asked questions

What causes Mach bands?

Edge enhancement in the visual system, linked to lateral inhibition.

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