New Injket Printing Can Hide a Photo Within a Photo

Lenticular prints use an array of lenses to cause an image to change before your eyes as you view them from different angles. Scientists have now figured out how to do a “changing photo” trick without lenses using an inkjet printer and metallic sheets.

The technique was discovered by scientists at the Swiss university École Polytechnique Fédérale de Lausanne. They found that by printing inkjet photos onto a metallic sheet in a certain way, they can print entirely different two images together, and have one visible at any time depending on the angle of view. To view the second image, simply rotate the print 90 degrees.

Here’s a video of the technology in action:

The demo mostly shows color changes, but you can do entirely different images as well (e.g. one showing a colorful butterfly and the other showing the Mona Lisa).

“When the halftone is printed along lines onto metallic sheets, the researchers noticed that the resulting colour depends on the viewing angle,” EPFL writes. “This is because incoming light traversing the ink lines cast shadows onto the metallic surface.”

Ink lines show as “strong colors” and “weak colors” depending on whether they’re parallel to incoming light or not. If you rotate the print 90 degrees, strong colors become weak and weak ones become strong.

This technique only works on metallic sheets — you wouldn’t notice anything different about the prints on ordinary papers, as they diffuse light and get rid of directional shadows. Researchers say this printing technique could one day be used for everything from currency to anti-counterfeiting measures. Maybe one day it’ll find its way into the world of photography as well.

(via EPFL via Engadget)