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Marshall Brain

Hi, I’m Marshall Brain with today’s question: what are motion cards and how do they work? Motion cards are appearing everywhere these days. You can see them on book covers, on DVD cases, even sometimes on boxes of cereal. They’ve been around for a long time, but lately, they’ve increased dramatically in the number of images on a card. Early versions only had two or three images, but the new ones can hold enough images to simulate a couple seconds of video. Motion cards use a special technology called lenticular printing.

This process takes a batch of images and prints alternating strips of each image on the back of a transparent plastic sheet. The plastic sheet has a series of curved ridges embossed on it. Each curved ridge is a lenticule. Each lenticule is approximately .3 millimeters wide. You can see them if you look really closely at the motion card and you can also feel the ridges made by the lenticules. If you can get a magnifying glass and get up next to the edge of the card, you can actually see that each one makes a little curved lens.

When light passes through the plastic sheet, it’s reflected from smooth white paper under the plastic sheet and the returning light passes through the images strips printed on the plastic sheet. The lenticule is made in such a way that it refracts the returning light at a specific angle and it magnifies the image. The strips are aligned so that all the strips for a particular image are reflected at the same angle. Because of the refraction and the magnification, what you see is a single complete image that appears to cover the entire card.

As you change the angle of the card in relation to your line of sight, you see the different image strips as a series of complete images. The whole thing with motion cards started decades ago, but the printing and alignment technologies of the time really only allowed two images in the card. Today, with much higher resolution printing possible and better lens manufacturing and alignment, they can fit in ten or more images. It’s possible to get the alignment so close now that it’s possible to put a different image into each eye because of their different viewing angles, and this lets them create a 3D kind of effect with motion cards.