What are lenticular images, and why do they look so awesome?
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.
It was a match.
“I’ve found that people get drawn into them in a way they don’t get drawn into my

flat pictures,” Canzoneri said. The way viewers engage with the content “comes — at

least in part — from the fact that the viewing experience is broken up and blended in an

unusual way.”
It can also lead to happy accidents. In the print seen in the video at the top of this

post, women’s marches from 1913 and 2017 intersect. Because of the way the images

overlap, when viewing the black-and-white image, you can see a slight pink glow above the

1913 marchers’ heads.
How it works
Canzoneri’s prints use the old-fashioned accordion style, not the plastic lens. It’s

a more hands-on endeavor, and one that took some experimenting to refine.
It starts, of course, with two images. Using Photoshop, Canzoneri stitches together

strips from each image, for a final product that looks like this when printed:Then, using

a carpenter’s square, she carefully folds it into the accordion shape. After a few tries,

Canzoneri found the right type of paper to use and the correct fold depth (about an inch).
Double Takes
Which brings us to “Double Takes” — Canzoneri’s exhibit of lenticular photographs

on view now at The Art League. You can catch these images through February 4, 2018.
Bring your walking shoes — the better to interact with the artwork. And, Canzoneri

says, she hopes the photos encourage viewers to “go outside and look around with fresh

eyes.”
Have you ever walked past an exhibit graphic that seemed to move? Or maybe the image

suddenly shifted? Your eyes weren’t playing tricks on you … the graphic was playing a

trick on your eyes.
These types of graphics are known as lenticular prints.
What Are Lenticular Prints?
Today’s lenticulars aren’t the moving image stickers you used to get at the doctor’

s office as a kid (or adult—no judgment here). You know the ones: if you swiveled it a

bit it looked like She-Ra was raising her sword, or a transformer was … transforming.

Well now that same concept makes things that do this:One of the advantages of lenticulars

is that visitors can get a nice pop of 3D or animation without needing any additional

equipment. As cool as everyone looks wearing those 3D glasses, it’s a bit of waste to

supply those for one panel. Lenticular prints simulate motion and/or dimension using

specially fabricated two-dimensional prints.
HOW DO THE 2D PRINTS MAKE IT LOOK 3D?
It’s called stereoscopy. It’s a visual effect created by providing slightly offset

views to both of your eyes at the same time. When your brain mushes (technical term) the

two visuals together, you see the combined image with additional depth and volume. In

other words, your brain takes Image 1 and Image 2 and turns into a much more awesome

optical illusion. To do that, the designer has to interlace the images.
One of the advantages of lenticulars is that visitors can get a nice pop of 3D or

animation without needing any additional equipment. As cool as everyone looks wearing

those 3D glasses, it’s a bit of waste to supply those for one panel. Lenticular prints

simulate motion and/or dimension using specially fabricated two-dimensional prints.
HOW DO THE 2D PRINTS MAKE IT LOOK 3D?
It’s called stereoscopy. It’s a visual effect created by providing slightly offset

views to both of your eyes at the same time. When your brain mushes (technical term) the

two visuals together, you see the combined image with additional depth and volume. In

other words, your brain takes Image 1 and Image 2 and turns into a much more awesome

optical illusion. To do that, the designer has to interlace the images.
Other than they’re really fun? Lenticular prints add impact to displays of static

photographs and other images. They can also create a depth of content. By layering images

on top of each other, a lenticular can show a before and after, or a variety of images on

a theme in a way that shows shifts. Recently, Smithsonian Libraries worked with SIE to

create lenticular prints for their exhibition Magnificent Obsessions: Why We Collect.

Visitors could see the image of a prized possession, and then it would shift, showing the

collector. Visitors can see a visual connection between the two images, and figure out

that the stories behind those two images are intertwined.