Café Wall Illusion
Published on February 15, 2026
• Built with HTML5 Canvas, Geometry, Perception
The Illusion
The Café Wall Illusion is a geometrical-optical illusion in which parallel straight dividing lines between staggered rows with alternating black and white “bricks” appear to be sloped. It was first described by Doctor Richard Gregory after he observed this curious effect in the tiles of the wall of a café at the bottom of St Michael’s Hill, Bristol, in 1973.
How it Works
The illusion depends on the interaction between the high-contrast tiles and slightly lighter (intermediate) mortar lines.
- Irradiation: Bright areas (white tiles) tend to spread into darker areas (black tiles) in our perception.
- Border Locking: Our visual system attempts to lock onto the borders of high-contrast objects.
- Tilt Induction: The local tilts created by the stagger and the mortar lines are integrated by the brain, causing us to perceive the long horizontal lines as tilted.
This demo allows you to adjust the “mortar” thickness and the “stagger” offset, which are the two critical components for the effect.