It’s All in How You Look at It

If you have ever seen a picture that appears to change, or move, when viewed from different angles, that is accomplished through the use of lenticular lenses. Dating back to the nineteenth century, this use of these lenses is hardly a new idea, which has found uses in products ranging from toys to eyeglasses and televisions. Despite the amount of time lenticular lenses have been in use, it turns out that they still have some tricks left to be discovered.

Lenticular prints are created by placing layers of lenticular lenses on a sheet that contains color patterns that make up multiple images. Light enters the lenses at different angles, depending on viewpoint, which causes that light to reflect off of a different part of the color pattern. Accordingly, an observer will only see the specific image encoded in one color pattern from each angle of view.

Lenticular prints have historically been limited to two dimensions, due to limitations in fabrication processes. In order to create such a print in three dimensions, it is necessary to print high resolution color patterns, and lenses, on curved surfaces. A team from MIT has leveraged advances in 3D printing, which makes multi-material prints possible. They used a Stratasys J55 to print optically clear materials for the lenses, and CMYK materials to make up the color pattern.

To make this work, the researchers developed a tool that plugs into the existing 3D modeling environment, Rhino3D. Using this software, designers can first load a 3D model, then define both the viewpoints, and the desired appearance of each viewpoint. The tool then automatically determines the best placement for each lens, and defines the color patterns associated with each lens. A preview tool allows the final design to be viewed from various viewpoints before printing. By using a multi-material 3D printer, the designs can be printed in a single pass.

To test the real world applicability of the technique, several experiments were conducted. In one case, a kettlebell weight was created, in which an indicator was placed on the front to inform a user if they were using proper form in their exercises. When viewed from angles that were too high or low, arrows would be visible that inform the user to adjust their pose. When in the correct position, a green checkmark is visible.

As it currently stands, lenses are printed on top of a 3D design, which adds about three millimeters to the print. In some cases, this may be problematic, so the team is working to integrate the lens substrate into the object itself to minimize protrusion. Having the lenses on the surface of the object also changes its tactile qualities. The researchers do not have a solution for this issue at present, but hope that future advances in 3D printing may allow lenses to be sufficiently small, such that they would be unnoticeable to the touch. In the meantime, the techniques laid out in this work offer some interesting possibilities for low-tech smart devices.