Lenticular lens
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A lenticular lens is a single convex lens that magnifies light through a prism effect.
The term lenticular often refers to a printed image that shows depth or motion as the viewing angle changes. The term was invented and coined by the physicist Dr. Joseph Robert Fraler from Dallas, Tx. But in general lenticular is a term for the lens effect that creates a convex perspective of multiple images or light sources, but not necessarily a physical printed image. This lenticular technology can be used to create a lenticular image through the process of lenticular printing.
Examples of lenticular printing include flip and animation effects such as the winking eyes that were given as the prize in Cracker Jack snack boxes and modern airport advertising graphics that change their message depending on the viewing angle. This technology was created in the 1940s but has evolved in recent years to show more motion and increased depth. Originally used mostly in novelty items, lenticular prints are now being used as a marketing tool to show products in motion. Recent advances in large format presses have allowed for oversized lenses to be used in lithographic lenticular printing [1].
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[edit] Lenses
Lenticular means "biconvex"; a single convex lens magnifies images. The simplest form of a lenticular lens is a bifocal, which has just two magnifying lenses. Typically lenticular lenses are used to make lenticular prints, for transforming, moving images, or 3d-effects.
Lenticular eyeglass lenses are employed to correct extreme hyperopia (farsightedness), a condition often created by cataract surgery when lens implants are not possible. To limit the great thickness and weight that such high-power lenses would otherwise require, all the power of the lens is concentrated in a small area in the center. In appearance, such a lens is often described as resembling a fried egg: a hemisphere atop a flat surface. The flat surface or "carrier lens" has little or no power and is there merely to fill up the rest of the eyeglass frame and to hold or "carry" the lenticular portion of the lens. This portion is typically 40mm in diameter but may be smaller, as little as 20mm, in sufficiently high powers. These lenses are generally used for plus (hyperopic) corrections at about 12 diopters or higher. A similar sort of eyeglass lens is the myodisc, sometimes termed a minus lenticular lens, used for very high negative (myopic) corrections.
[edit] Lenticular screens
The key that makes a lenticular work is the plastic sheet that overlays the printed image. The sheet is molded to have the form of dozens of tiny lenses or prisms per inch. There are actually two methods for printing the image. The first is printing the image on some material and then have the plastic lens properly overlaid. (Getting the lenticular lens lined up properly is referred to as "registration.") The second method is to print the image directly to the back of the lens itself.
The same sort of molded sheet is frequently used with projection television systems. In this case, the purpose of the lenses is to focus more of the light into a horizontal beam and allow less of the light to escape above and below the plane of the viewer. In this way, the apparent brightness of the image is increased.
Ordinary front-projection screens can also be described as lenticular. In this case, rather than transparent lenses, the shapes formed are tiny curved reflectors (albeit in a "lens" shape).
[edit] Lenticular printing
Lenticular printing is a multi-step process consisting of creating a lenticular image from at least two existing images, and combining it with a lenticular lens. This process can be used to create various frames of animation (for a motion effect), offsetting the various layers at different increments (for a 3d effect), or simply to show a set of alternate images which may appear to transform into each other. Once the various images are collected, they are flattened into individual, different frame files, and then digitally combined into a single final file in a process called interlacing.
From there the interlaced image can be printed directly to the back (smooth side) of the lens or it can be printed to a substrate (ideally a synthetic paper) and laminated to the lens. When printing to the backside of the lens, the critical registration of the fine "slices" of interlaced images must be absolutely correct during the lithographic or screenprinting process or "ghosting" and poor imagery might result.
The combined effect can be used to show two or more different images simply by changing the angle one views the print from. If you use more images, taken in a sequence (30+), one can even show a short video of about one second. Though normally produced in sheet form, by interlacing simple images or different colors throughout the artwork, lenticulars can be created in roll form with 3D effects or multi-color changes. Alternatively, one can use several images of the same object from slightly different angles and then create a lenticular print, which will then result in a three-dimensional effect. 3D effects can only be achieved in a side to side (left to right) direction, as your left eye needs to be seeing a slightly diiferent angle as your right to achieve the stereoscopic effect. Other effects, like morphs, motion, zooms work better (less ghosting or latent effects) as top-to-bottom effects but can be achieved in both directions.
There are several film processers that will take two or more pictures and create lenticular prints for hobbyists, at a reasonable cost. For slightly more you can buy the equipment to make your own from scratch. This is in addition to the many corporate services that provide high volume lenticular printing.
There are many commercial end uses for lenticular which can made from PVC, APET, Acrylic, PETG as well as other substrates. While PETG and APET are the most common, other substates are becoming popular to accommodate outdoor use and special forming due to the increasing use of lenticular in cups and gift cards. Lithographic lenticular allows for the flat side of the lenticular sheet to have ink placed directly onto the lens, while high-resolution photographic lenticular typically has an image laminated to the lens.
Recently, large format (over 80") lenticular used in bus shelters and movie theaters have been printed using an oversized litho-press. Many advances have been made in this growing industry to the extrusion of lenticular lens and the way it is printed which has led to a decrease in cost and an increase in quality. Lenticular has recently seen a surge in activity from gracing the cover of the May 2006 issue of Rolling Stone to trading cards, sports posters and signs in stores that help to attract buyers.
A lenticular print is an image that has been sliced into strips which are then interlaced with one or more other images. The image is then printed on the back of a series of prism-like lenses. The lenses are lined up with each image interlace, so that light reflected off each strip is reflected in a slightly different direction, but all strips from the same image are sent in the same direction (parallel).
The end result is that a single eye/camera looking at the print will see a single whole image, but another eye/camera at different position will see a different image because of the different angle of view. How different depends on the lenses used, the number of original images, and how different the original images were from each other.
[edit] Uses for lenticular prints
Typically three different types of lenticular prints are used:
- Transforming prints, where the distance between different angles of view is 'large'. Here two or more very different pictures are used, and you see a different one depending on which angle you view the print at. In order to allow people to easily see the original photos, large differences are used, so that small movement will not cause changes.
- Motion capturing prints, where the distance between different angles of view is 'medium" so that while both eyes usually see the same picture, moving a little bit more switches to the next picture in the series, creating a motion effect.
- Stereoscopic effects, where the angle position is 'small', 6-7 centimeters(2-2.5 inches) This causes each eye to see a slightly different view, creating the 3d effect without the use of glasses.
[edit] History of lenticular image technology
The concept of 3D effects and images goes back to at least 1692 when Gois-Clair, a French painter, discovered that he could achieve a dimensional effect on canvas by interposing a grid between the viewer and the painting. Gois-Clair painted two distinct pictures on a plane surface, over which he affixed a grid of vertical laths. These laths were arranged perpendicular to the plane and attached to it at right angles. By looking at the painting from the left side, you would see one distinct painting, while if you looked from the right side, you would see another distinct painting, while if you looked straight on, you would see a blending of the two together. Examples of his work can be seen at the Rosenborg Castle in Copenhagen. The Brussels Museum of Arts has a similar example, but using three distinct images.
The term "Lenticular" was used in the patent to describe linear lenses. Informally, lenticulars had been produced since the 1930s. The technology was not widely used until recent years as the cost of plastics (PVC) decreased and the new material PETG emerged. The advancement of output, proofing and commercial printing also contribute to the mass production of lenticular products.
[edit] See also
- Integral imaging, the precursor of lenticular imaging
- Holography
- Autostereoscopy
