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A lenticular lens is an array of magnifying lenses, designed so that when viewed from slightly different angles, different images are magnified. The most common example are the lenses used in lenticular printing, where the technology is used to give an illusion of depth, or to make images that appear to change or move as the image is viewed from different angles.

Examples of lenticular printing include prizes given in Cracker Jack snack boxes that showed flip and animation effects such as winking eyes, 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]

Contents 1 Corrective lenses 2 Lenticular screens 3 Lenticular printing 3.1 Uses for lenticular prints 4 History of lenticular image technology 5 Manufacturing a lenticular product 5.1 The design images 5.2 Lenticular mastering 5.3 Printing 5.3.1 The offset press UV 5.3.2 UV dryers 5.3.3 UV Ink 5.3.3.1 The pigments 5.3.3.2 The prepolymers 5.3.3.3 The monomers 5.3.3.4 The photoinitiator 5.3.3.5 The additives and inhibitors 5.3.3.6 Diluents 5.3.4 Water wetting 5.3.4.1 The TH (French: Title "Hydrotimétrique"), water hardness 5.3.4.2 The pH (potential hydrogen) 5.3.4.3 The interfacial tension and the surface tension 5.3.4.4 The conductivity 5.4 Defects 5.4.1 Defects on conception: 5.4.2 Prepress defects 5.4.3 Printing defects 5.4.4 Defects of cutting lenticular 6 See also 7 Notes and references 8 Bibliography 9 External links

Lenticular lenses are sometimes used as corrective lenses for improving human vision. A bifocal lens could be considered a simple example.

Lenticular eyeglass lenses have been 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 40 mm in diameter but may be smaller, as little as 20 mm, 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.

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).

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 different 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 processors 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.

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.

Images that change when viewed from different angles predate the development of lenticular lenses. In 1692 Gois-Clair, a French painter, created paintings containing two distinct images, with a grid of vertical laths in front. Different images were visible when the work was viewed from the left and right sides. Examples of his work can be seen at the Rosenborg Castle in Copenhagen and the Brussels Museum of Arts.^[1]

In 1936, patents were filed^{[attribution needed]} for lenticular flip images and stereo images using linear lenses, though certain similar technologies existed in the mid-1890's. The term "lenticular" was used in the patent to describe the linear lenses. This patent led in the end to the 1948 formation of Vari-Vue New York by Victor Anderson.^[vague] Vari-Vue created the first mass-produced animated images.^{[citation needed]}

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.

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Manufacturing a lenticular product requires not only a sound knowledge of optics, of binocular vision, of computing and of the graphic chain, but also stringency in work and substantial precision throughout the manufacturing process.

Animation is a sequence of images making up the full range of an expressed movement or the gradual transformation of objects (known as morphing) or enlarging and reducing in size by zooming.

To really understand the functioning of images in three dimensions, we need first to know how the brain uses images perceived by our two eyes to recalculate depth.

If an object is photographed from different angles, the images obtained cannot be superimposed. In the same way, images received by our two eyes are different. The brain interprets these differences to estimate depth.

These may be images that represent a panoramic observation suitably organized around a point, thus giving the impression of movement. The result will be that depth is perceived.

The word "lenticule" is a synonym of "lens", but may also have the meaning of a leaf of long thin lenses. The lenticular network contains a series of cylindrical lenses modeled in a plastic substrate. The principle is to present a variety of images to the eyes, depending on the angle of vision.The lens focuses on an image on the rear side of a lenticular network. The lenticular image is designed in such a way that the line of each viewing eye is concentrated on different strips. Source images are cut into strips and arranged side by side to make up a different final image.

The equipment must be adapted to print on sensitive thermoplastic materials.
The press must allow adjustments in steps of 10 µ (circumferential, lateral and diagonal register).

The Ultraviolets, in the electromagnetic spectrum, are between 100 and 380 nm, whereas the area of visible ranges between 380 and 700 nm. It is therefore necessary to use a lamp specific if we want the ink to dry properly.

The UV spectrum is divided into three parts:

• UV-C radiation (100-280 Nm): They make it possible to primarily reticulate ink or varnish on the surface and ensure a fast and complete final reaction.
• UV-B radiation (280-315 Nm): They are essential to reticulate in-depth film of ink.
• UV-A radiation (315-380 Nm): They are the rays closest to the visible light, they ensure the hardening of the layers of in-depth ink.

Today, there are different types of UV driers, but generally, dryers lamps containing mercury vapor is the most employees. Indeed, these lamps emit UV radiation in a broad spectrum and provide an optimum drying.

The power lamps commonly used is 160-200 Watts / cm.

The choice of pigments in the formulation of UV inks has been difficult in the early years because of the partial absorption of UV radiation in some of them (eg. Titanium dioxide, black and dark pigments). The result is a slow drying of the film and possibly curing a difference between the surface and the interior of the film. In addition, some pigments (particularly blacks and dark) can react with photoamorceurs, which inhibits the process of drying. Since then, photoinitiators privileged pigmented for products, such as inks, are selected to have a higher efficiency of absorption systems non-pigmentés in the region 330 to 400 nm.

The prepolymers are the equivalent of resins used in inks non-UV. These are molecules that contain insaturations and who are not completely polymerized. With radical mechanisms, prepolymers are used type acrylate / methacrylate or unsaturated polyester resins, while with cationic mechanisms, they are epoxy resins or phénoxides and vinyl ethers.

Free radicals from photoinitiators initiate the reaction of polymerization of monomers and prepolymers. The second phase is the spread of the polymerisation reaction which can gradually increase the size of macromolecules and therefore viscosity), which gradually solidifies the ink film.

The monomers are sometimes called reactive diluents. They play an equivalent solvent inks quickset: pigment wetting and adjust the rheological properties. In addition, they participate in the polymerization reaction.

The photoinitiator are products which, under the effect of UV radiation, provide reactive species (free radicals or cations) likely to initiate the chain reaction involving prepolymers. Today, 90% of the formulations are based on mechanisms radical and 10% on cationic mechanisms. In EB inks, photoinitiators are not necessary. The electrons provide enough energy to initiate polymerization reactions between different prepolymers and monomers or oligomers. Thus, the formula of an EB ink is generally the same as that of a UV ink without photoinitiators.

The additives are added in small quantities to adjust their rheology, increase the stability of the ink or give a particular feature (slippery, and so on.). The inhibitors are needed to avoid a premature gelling system.

Diluents play several roles: adjustment of rheological properties, solubilization of solid prepolymers, pigment wetting, improve the properties of the final dry film.
In EB and UV inks, reactive diluents are, which means they are involved in the polymerization reaction with prepolymers.

The number of these compounds actually used in the formulation of ink is relatively small because many of them are discarded because of their toxicity, their volatility or their smell. It should be noted that a working group consisting of HSE (Health and Safety Executive-England), BG (Berufsgenossenschaften-Germany) and the CNAMTS (Caisse Nationale d'Assurance Maladie des Travailleurs Salariés) study all aspects related to a correct use of UV printing. They work particularly on the classification of components not yet included in the European directives.

• Incidence of water hardness on the mooring

Generally speaking, it will avoid working with water with a degree "hydrotimétrique" higher than 25.

A degree "hydrotimétrique" higher than 25 can induce changes in pH.

• Effects of pH in offset printing

Taking into account all the previous settings, we must maintain the pH of the water wetting between 4.9 and 5.4. Outside these limits, some problems may occur.

• Importance of surface tension and interfacial tension in offset printing

It is these elements that relies offset printing.

On the one hand, the basic principle lies in the opposition between the ink (fat) and water. Over the interfacial tension between the two bodies, the less they are mixed, so there will be less chance of forming an emulsion (mixture of ink and water).

Over the surface tension of the fount solution is lower making the anchorage of the plate is good. Water runs well on the plate, it forms a thin film and continuous.

• Importance of conductivity in offset printing

The conductivity measurement is a measure, fine and reliable, content to be added as an addendum wetting in water. It helps determine the ideal amount of the additive to be used.

• Double images on the relief and in depth

The main reason is an exaggeration of the 3-D effect from angles of view or an insufficient number of frames.

Observation of the visual must not show doubling, small jumps or a fuzzy image, especially on objects in relief or in depth. For some visuals, where the foreground and background are fuzzy or shaded, this exaggeration can prove to be an advantage, but in most cases, the detail and precision required do not allow this.

• Image remanence (ghosting)

This is due to poor treatment of the source images and also transitions where demand for an effect goes beyond the limits and technical possibilities of the system. This problem is manifested by image remanence. This gives the impression that the images do not really disappear. Logically the transitions should be clear and precise. One must be aware, however that even if the lens focuses our vision, the entire print (the master) appears more or less by transparency and in accordance with the lighting of the visual.

• Synchronisation of the print (master) with the pitch*

The chief reason is poor calibration of the material. This is a lack of anticipation. The passage of one visual to the other must be simultaneous over the entire format. But when this problem appears there is a time lag in the effects. At one end of the visual we have one effect and at the other end another effect on the same incline (impression of a veil or curtain crossing the visual). This phenomenon is felt less for the 3-D effects, but is manifested by a jump of the transverse image.

• Discordant harmonics*

This phenomenon is unfortunately very common, and is explained either by incorrect calibration of the support or by incorrect parametrisation of the prepress operations. It is manifested in particular by streaks that appear parallel to the lenticules during the phases of transition from one visual to the other.

• Colour synchronisation*

One of the main difficulties in lenticular printing is colour synchronisation. The causes are varied, they may come from a malleable material, incorrect printing conditions and adjustments, or again a dimensional differential of the engraving of the offset plates in each colour.

This poor marking is shown by doubling of the visual; a lack of clarity; a streak of colour or wavy colours (especially for four-colour shades) during a change of phase by inclination of the visual.

The requared color synchronisation is about 0.02 mm. But printing mashine can have a distortion deffects about 0.1 mm. On the image Black and cyan rectangle must be printed on the same place. But because of machine distorsion we get this picture.

• Synchronisation of parallelism of the printing to the lenticules*

The origin of this problem is a fault in the printing and forcibly generates a phase defect. The passage from one visual to another must be simultaneous over the entire format. But when this problem occurs, there is a lag in the effects on the diagonals. At the end of one diagonal of the visual, we have one effect, and at the other end we have another.

• Phasing*

In most cases, the problem comes from the standard of the cutting of the material. Nevertheless, poor printing and rectification conditions may also be behind it.

In theory, for a given angle of observation, one and the same visual must appear, for the entire batch. As a general rule, the angle of vision is around 45°, and this angle must be in agreement with the sequence provided by the master. If the images have a tendency to double perpendicularly (for 3-D) or if the images provided for observation to the left appear to the right (top/bottom), there is a phasing problem.

At the same production batch:
This [first image] shows a cut of the leaf at about 150 µ of the first lens which show irregularities cutting of the leaves lenticular and this [second image] shows a cut of the leaf at about 30 µ of the first lens.
The impression is always to the same distance from the edge. This defect leads to a serious problem of phase. It is necessary to make regular prélevements to adjust printing at the edge of the lens.

• Integral imaging, the precursor of lenticular imaging
• Holography
• Autostereoscopy

1. ^ Didik, Frank X. (2001). A brief history of stereo images, printing and photography from 1692–2001. Retrieved on 2007-12-22.

• Bordas Encyclopedie: Organic Chemistry
• L'offset of Jean-Claude Sirost

• Lecture slides covering Lenticular Lenses (.ptt)