Color display blocks prying eyes

Researchers from the University of Tokushima in Japan have built a computer display that can be viewed only from directly in front of the screen. People looking at the display from even slight angles see only a random pattern of color pixels.

The method makes it possible to better protect sensitive information displayed in public spaces, including automatic teller machines, computers used to process medical and financial records, and access devices like the touch screen of a safe, according to the researchers.

Each pixel on the display is divided into three black, one red, one green and one blue subpixel arranged in a pattern. A decoding mask that contains three transparent and three opaque subpixels decodes the view directly in front of the image. The subpixel pattern in the decoding mask determines which subpixels on the display show through to provide red, green, blue, cyan, magenta, yellow, black or white.

Every pixel in the secret image is encrypted by a randomly chosen combination of display subpixel patterns. Because there are eight possible decoding mask subpixel patterns per pixel, a secret image of 256 by 256 pixels has 8^{256 times 256} possible decoding mask subpixel patterns, according to the researchers. That number is approximately a 1 followed by 59,185 zeros.

The visual decoding method does not require encryption information to be held in computer memory or contained in the display signal.

The display could be used in practical applications in five years, according to the researchers. The work appeared in the April 5, 2004 issue of Optics Express.