Hand-waving decodes invisible images in new signs

[Nipuna]

Sandrine Ceurstemont, editor, New Scientist TV

VIDEO

Soon you could have access to secret information just by waving your hand. New digital signage allows you to decode invisible images by quickly moving your fingers in front of the screen.

The system, developed by Hirotsugu Yamamoto and colleagues from University of Tokushima in Japan, uses a newly developed LED panel that can display 480 images per second. In this video, a pair of images of the New Scientist logo (one black, one matching the background colour) is embedded into the background. When displayed alternately at a high speed, they are invisible to the naked eye. "A hidden image is presented 10 times faster than the frame rate used at the cinema," says Yamamoto.

Waving your fingers in front of the sign blocks some of the flashing images, revealing the hidden text. Since hand motion isn't synchronised with the alternating display, it can take a few seconds for the image to be perceived.

This video gives an impression of how the system works but in reality the decoded logo would be much more obvious. Thanks to a brain trick, the areas obscured by moving fingers would be filled in with the rest of the image. "Viewers in front of the LED panel perceive that the black regions are filled with an afterimage," says Yamamoto. The effect is much more apparent with maximum brightness.

Yamamoto hopes to develop the system to create personalised digital signage. Instead of hand-waving, high-speed video cameras could be used to decode messages for specific viewers.

The LED system will be presented in a few weeks at the IAS annual meeting in Las Vegas, Nevada.

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