Remember those red-and-green glasses that made some movies look 3-D? Now there’s an easy way to create similar effects on any printed matter-without glasses. A new color-rendering process from Xerox Research and Technology in Webster, NY, prints two images on a single piece of paper in such a way that each image shows up only under specific lighting-red versus blue light, say. The heart of the system is new software that allows precise control over the process. The user tells the program which wavelengths of light should reveal each image, and it translates that into instructions for a standard printer. The technology could make document authentication that uses hidden watermarks cheap and simple, as well as allow for popcorn boxes that display different images depending on the light from a movie screen. Xerox has filed for patents on the technology.