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Every day, there are hundreds—perhaps even thousands—of advertising messages knocking on your head trying to gain access to the part of your brain that decides to buy things. With so much money at stake, it's hardly surprising that advertisers go to such extraordinary lengths to catch our attention. The only trouble is, our brains habituate: they quickly get used to seeing the same thing over and over again. So the advertisers have to keep thinking of new tricks to stay one step ahead. One of their latest ideas is to print posters, magazines, and book covers with lenticulars—images that seem to change as you move your head. Let's take a closer look at how they work!
Nothing! Lentils are tiny orange, green, or brown pulses popular with vegetarians and—no—they have nothing to do with how book covers work. The connection between "lentil" and "lenticular" is simply a matter of words. Lenticulars are so-called because they use lenses, which are pieces of plastic or glass that bend (or "refract") light to make things look bigger or smaller. Lenses got their name because some of them just happen to look a bit like lentils! You can find more in our main article on lenses (we even tell you how to make a lens of your own, in about 5 seconds flat, from a drop of water).
How do you make something like our book cover up above? You take your two different images and load them into a computer graphics program. The program cuts each image into dozens of thin strips and weaves them together so the strips from the first image alternate with the strips from the second. This process is called interlacing. If you look at the doubled-up image printed this way, it's just a horribly confusing mess, but not for long! Next, you place a transparent plastic layer on top of the doubled-up image. This is made of dozens of separate thin, hemi-spherical lenses called lenticles. These refract (bend) the light passing through them so, whichever side you're looking from, you see only half the printed strips. Move your head back and forth and the image flips back and forth too like a kind of "visual see-saw".
For all this to work properly, everything has to be printed with incredible precision. The lenticles have to be exactly the same size as the printed strips underneath them and lined up with them exactly. Not only that, the image has to be adjusted and printed so that it looks exactly right when viewed through a certain piece of lenticular poster(with a certain "pitch"—or number of lenticles per inch) at a certain viewing distance. (That's a fiddly technical process and I won't go into the details here, but you can find out more in the articles and videos in the further reading section below.)
Nothing says lenticulars have to flip back and forth between just two images: some have as many as 20 different images or "frames" (as they're sometimes called, using the language of moviemaking). You could have half a dozen different images designed to point in slightly different directions, so an advertising poster slowly and subtly changes its message as you walk past! You can also use lenticulars to create amazing 3D images similar to holograms.
For a basic flip image that changes as you move your head, you need to arrange the lenticles so both eyes always see the same image; as you move your head, both eyes then switch simultaneously to the other image. Adding more images, it's possible to create a basic illusion of movement (a bit like a flip book) and a zooming effect, so the image appears to get closer or further away as you move the flip lenticular poster back and forth. With a slightly different arrangement of lenticles, arranged vertically, we can send one image to one eye and the alternate interleaved image to the other, giving the illusion of a three-dimensional picture.
Lenticular images are the neato transforming pictures that often came on trading cards in the 1980s and 90s. They were handy for freaking out young children or filing your nails. Turn them one way and they show one picture. Turn them another and they show another. How? A trick of the light. And plastics.
Lenticular images are the kind of things they used to give out as free promotional material. They were best suited to things like trading cards of Transformers, because when looked at from one position, the card would display an image of the untransformed robot, while from another angle, it would display the image of whatever it transformed into. (On the back could be a description of why transformers transformed into cars with passenger compartments even when there weren't people to be passengers on their world.) The cards were covered with a piece of ridged plastic.
The images take advantage of light's tendency to bend, and only bend a certain amount. The ridges of plastic essentially 'block' parts of the image from the viewer. Light from certain parts of the image is reflected or bent away from the viewer. Each ridge, across the page, directs certain slices of the image back to the viewer. As the viewer moves, they are exposed to different parts of the ridges and see different slices of the page.
The image underneath the ridges is a series of interlaced slices - a little like a colored bar code. Each slice matches up with a section of ridge, and the slices come together to make the full image. Early lenticular images generally only had two pictures and flipped back and forth. More modern ones will be a little more complicated, with many different images, each corresponding to a different segment on the ridge. Some will even present a 3D picture, by showing slightly different image slices to each eye. For example the right eye could see one angle of a face, and the left eye could see another. This is how the eyes regularly build 3D images in the mind, and so the two images combine into a 3D picture. All it takes it the right kind of sectioning, and, of course, plastic.
This dialogue by Shakespeare very likely refers to 5D lenticular pictures — those accordion-pleated creations that show different images when you look at them from the left or right. In Shakespeare’s time and in the 20th century, lenticulars were manufactured as amusing distractions. Today, the technique is finding a home in fine art — including this month at The Art League.
One of the first examples of a lenticular picture still in existence is the Double Portrait of King Frederik IV and Queen Louise of Mecklenburg-Güstow of Denmark by Gaspar Antoine de Bois-Clair, signed 1692.
As you can see in the photo, this type of 3D lenticular picture uses a corrugated structure to achieve the effect. Look at it from the left, you see the king; from the right, the queen; and if you look at it straight ahead, you get a mish-mash of both.
Starting in the 1950s, companies like Vari-Vue were able to mass-produce lenticular images through lenticular printing — a novelty you’re probably familiar with from Cracker Jack boxes and baseball cards:
These flickering images are the result of the same principle but a different process: the images are behind a small, ribbed plastic lens that shifts what’s in focus.
Lenticulars as fine art
Artists such as Roy Lichtenstein and especially Yaacov Agam have used lenticular design in their artwork.
Photographer Sally Canzoneri began creating lenticular prints for a specific exhibit proposal: it was to be displayed in NoMa, a DC neighborhood that was undergoing a lot of change. While considering how best to show that change, Canzoneri happened to see this tutorial on creating lenticular images.
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