Now You See It, Now You Don'tNow You See It, Now You Don't

Look at the photos on this page. They illustrate what researchers at Xerox Corp. call a breakthrough in color printing technology. The technique, called Switch-A-View printing, lets users print one image on top of another image, and then view only one at a time by exposing the document to specific colors of light.

The printing approach resulted from Xerox scientists' research into how to make printed images look best in different kinds of light, such as under sunlight or the glow of florescent lamps. Eventually, the researchers came up with new ways to use their work, says Robert Loce, a principal scientist at Xerox. The resulting work produced images printed in specific shades of red, blue, and yellow; shine red light on the image, and anything printed in red absorbs the light and disappears, leaving only the other colors to be picked up by the eye.

Initially, the Xerox team thought about using the images in advertising--on the side of cereal boxes or as premiums in nightclubs. "It's got a very strong, dynamic impact if you set it up properly," Loce says. "It gets people excited."

Imagine sitting in a movie theater with a large tub of popcorn in your lap. The lights go down, but before the previews roll, the screen turns bright red and the whole room is cast in cherry light. Suddenly, you notice that an image of Harry Potter has appeared on the side of your popcorn bucket. Then the image is gone, disappearing in a flash of blue as the screen changes colors. Now the bucket shows a picture of Dumbledore, Harry's headmaster.

That's just one possible use. Researchers also realized computer screens could be used to produce the proper colors. The technique could drive a kid with a candy wrapper to the manufacturer's Web site to produce the light needed to find out if he's won a prize or solved a puzzle.

But the technique is useful for more than fun and games, Loce says. Paper documents can be printed with hidden images as a sort of watermark, establishing their authenticity. The technology also could be used to prevent fake coupons, which cost businesses more than $700 million a year, he says. "It's useful for low-level anti-counterfeiting," Loce says. "I probably wouldn't use it on the euro or the dollar bill, but I'd use it on coupons and tickets."

The images are fairly easy and cheap to produce, Loce says, and can be made on standard office printers that are properly calibrated. The technology is ready for licensing now, and will probably start popping up on products soon.