Computational Creation of a New Illusionary Solid Sign

We present a computational method to create a new illusionary solid sign inspired by two kinds of illusions, "hollow mask illusion" and "crater illusion". The three dimensional vertices of the illusionary solid sign are obtained by the straight line Voronoi diagram for a given base shape. We also provide a specific example of our new illusionary solid sign, so-called hollow arrow sign. Just like the name implies, our new sign has a hollow structure. However, we perceive the sign as a bulgy shape, when it is illuminated from below.