Dubbed Conversation, this installation piece by Swiss artists Drzach & Suchy, uses a patent-pending surface called a Shadow Casting Panel (SCP). Each pixel in the portrait corresponds to a shadow-casting pixel on the panel. Think of it like "digital illumination".
Each pixel in the portrait is designed to either cast a shadow or not depending on the direction of light hitting it; shadows are zeros, white spaces are ones. By changing the angle of the incoming light, the pixels can switch from showing a shadow to not or vice versa. Thus, the image of Einstein is transformed into Marilyn simply by moving the light source from the left corner of the portrait to the right.
To do this, images are first rasterised, then "encoded" with one of the four shadow-casting pixel types. The type of block depends on whether the individual pixel is white in both images, black in both images, changes from white to black, or from black to white.
The technique was originally devised by Drzach in 2004 and has since been developed into the novel image display you see here. The same idea can be applied to colour images — using transparent tinted film rather than shadows — and to multiple image displays (three or more pictures) — by adding additional shadow-casting shapes and light sources to the array. [Drzach&Suchy via Fast Co Design]