Bulging lines illusion

Bulging lines illusion was invented by the Japanese artist and vision scientist Akiyoshi Kitaoka. It is so called because for some distributions of colors (e.g., GLWB) the lines appear to be bulging away from the center of the drawing. However, for other color distributions (e.g., GLBW) they appear to bend towards the center.

(The color designation is G for gray, L for light gray, B for black, and W for white.)

Note that in the applet there are two layers of the drawing. The top layer is mildly transparent. It also draggable. You can move it around and, by overlaying the straight lines, convince yourself that their bulging is indeed nothing but a visual illusion.

References