Is there a name for showing two unique images (which I wager are first cut into fine strips and laid in an alternating fashion) overlaid by a clear, plastic sheet of tiny ridges or bubbles to grant two unique images, often suggesting motion or a before-and-after change? When viewed from one direction, you see image A. And when viewed from the opposite side, you will see image B. In general, the picture appears to have a sheen and seems to be comprised of many tiny, clear vertical ridges pressed tightly together.
You may have seen this on toys and novelty items. Nowadays, you can even have two poses of yourself put into one such photo. A good example is on the covers of all Brady Bunch DVDs. Check it out at a store sometime. This technique is an old idea, but it has regained popularity. Some mistake it for a hologram, but a hologram is an entirely different animal.
The weird plastic piece you put over the top to do this consists of a long set of cylindrical lenses, so this is called a lenticular display. Not only can it show before-and-after, but it can be used (since it sends a different image to each eye) to make 3D postcards and the like. You can find out more about it in books and websites devoted to 3D.
A company I used to work for sells software that allows you to take two pictures (right-and-left, or before-and-after, if you wish) and turn them into alternating strips of picture that you simply slide into a lenticular holder.
One reason for the current popularity (besides the way the computer revolution has made this a lot easier to do) is because consumer studies have shown that people tend to be attracted by the effect (OOhhhh! Shiny!) and to pick up CDs, DVDs, etc. with such 3D covers. Once they’ve picked it up, you’re that much closer to a sale.
By the way, you can “multiplex” more than two images. You often see lenticular sheets that have several frames rom a movie, so that as you tilt it you can see a brief sequence.
The idea showed up ages ago in a patent for 3D TV that no one ever bought into. There is a theater in Moscow that was built with a lenticular screen for glasses-free 3D movies. As far as I know, it’s the only such glassless 3D theater in the world. No one’s ever tried to build another. They made a umber o 3D movies for it, that can only be shown there.
25 years ago the “Nimslo” camera took 3D pictures this way – they’d process them and send them to you with the lenticular screen laminated in place. It didn’t succeed. About 15 years ago they tried again, with a disposable 3D camera. That died, too. Sometimes a really good idea – lenticular 3D cameras, TV, and movies – just doesn’t seem to catch on.
One thing to add, in most cases, the array is not prisms, but cylindrical lenses. These collimate the strip along a particular angle.
The reason, I think, it didn’t really catch on is that the lenticular array material is fairly expensive. I had to purchase some for a project (I was using it as a diffuser, allowing a diode laser to cover a large solid angle) and it was a real pain to obtain. It was kind of funny actually, the supplier would not accept credit cards, nor extend credit, and I was working for a fortune 5 (yes 5) company who’s purchasing department went nuts over having to send a check prior to delivery.
This is the company I bought the material from. I think they actually prefer to deal with small orders, so if anyone wants to experiment they may be helpful.
From their site, This PDF goes into detail about how the arrays work, and production techniques if you are interested.
The Moire effect is a totally different one – it’s the creation of patterns by the “beating together” of two other patterns, which may or may not be different. You can see the effect by placing two combs together, or looking at the patterns between two fences. No lenticular mask is required. You don’t get 3D effects from Moire patterns.
I was going to ask isn’t Moire similar to two screens passing over each other? I believe I read that the apparent velcoity of the resulting pattenr is faster than the individual component(s) in motion. I will see if I can find the link to this. Maybe I misunderstood? (My understanding came from an online experiment posted on a Georgia U website…let me look back in my notes to find as this effect struck me as an item of curiosity.)
Bonus Q: Are Moire patterns related to Lizijoux (sp?) patterns? These are patterns observed when plucking a stray wire poking our from a mesh, for example. The wire will “weave and bob” in circles, ellipses, or figure eight patterns (and the like) depending on circumstances.
As I say above, Moire patterns are indeed the result of two patterns passing over each other. But Lenticular Screen images aren’t. They’re different things. I’ve got a couple of books from Dover that have transparent Moire screens you can pass over patterns of various types, or of old engravings with high-frequency spacing of lines. In both books the results are pretty neat to see and play with, but the screens are flat and have opaque patterns over them. Lenticular screens aren’t flat – they have regular ridges that are prismatic or lenticular (rounded), and you can feel the texture with your finger. The plastic screen is made of many cylindrical lenses (or, sometimes, prisms) that direct different images in different directions, creating the “moving” image or the 3D effect. Totally different things.
Lissajous figures are what you get when you sum up sinusoidal inputs whose frequencies stand in a low ratio to eacj other, at right angles. You can do this pretty easily on an oscilloscope, using two signal generators into the x- and y- inputs. You can generate them on a mathematical spreadsheet0-type program like MatLab or MathCAD or even Excel. Th classic way to do it is to bounce a light beam off two tuning forks held at right angles to eachj other. (They were doing this before the days of lasers, although it’s easier to use a laser).
Am I the only one who has problems seeing lenticular images? I always seem to get stuck halfway between both images, and can never seem to get one image completely stable and in focus… are my eyes just spaced weirdly, or is this a common experience?
