Optical illusions: why equal grey tiles look different

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1 / 7 Four illusions in one galleryEach station rebuilds a known illusion in 3D: a checkerboard with a shadow, a distorted room, two size figures and a waterfall test. The bar under the picture jumps between them, and the box in the corner holds the measuring tools.

Drag to turn. Scroll or pinch to zoom.

01
Four illusions in one gallery
Each station rebuilds a known illusion in 3D: a checkerboard with a shadow, a distorted room, two size figures and a waterfall test. The bar under the picture jumps between them, and the box in the corner holds the measuring tools.
02
A dark tile in light, a light tile in shadow
Tile A is a dark tile in full light. Tile B is a light tile in the cylinder's shadow. Almost everyone sees B as much lighter. Drag to look at the board from another angle; the impression stays.
03
Read the screen
The eyedropper reads the pixels in the middle of A and B straight from the picture. The numbers match. Try Move a piece to lift a square of A and lay it inside B, or Cover to hide everything else.
04
Looking into the Ames room
This is the view through the peephole. The room looks square, the windows look level, and the figure on the right looks about 1.75 times the height of the one on the left.
05
The room from the side
From outside, the real shape shows. The left corner is far away and the floor slopes. The two figures are the same size; the left one is simply further from the hole.
06
Measure the bars and discs
The yellow bars are the same length and the orange discs the same size. The readout gives their length on screen in pixels, and you can drag the yellow ruler over them yourself. Switch Surroundings off to see them alone.
07
A short waterfall test
Press Start and keep your eyes on the dot in the stripes for 20 seconds. When they stop, look at the rock. Many people see it drift upward for a moment. The stripes never flash.

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