Patent Application
20100314861
The present invention relates generally to the field of anti-counterfeiting and authentication methods and devices and, more particularly, to methods and security devices for authentication of documents and valuable products using the moire parallax effect.
Counterfeiting of documents such as banknotes, checks, identity cards, travel documents, etc. is becoming now more than ever a serious problem, due to the availability of high-quality and low-priced color photocopiers and desk-top publishing systems. The same is also true for other valuable products such as watches, CDs, DVDs, software products, industrial products, medical drugs, etc., that are often marketed in easy to counterfeit packages.
The present invention is therefore concerned with providing a novel security element and authentication means offering enhanced security for documents or articles needing to be protected against counterfeits.
Various sophisticated means have been introduced in prior art for counterfeit prevention and for authentication of documents or valuable products. Some of these means are clearly visible to the naked eye and are intended for the general public, while other means are hidden and only detectable by the competent authorities, or by automatic devices. Some of the already used anti-counterfeit and authentication means include the use of special paper, special inks, watermarks, micro-letters, security threads, holograms, etc. Nevertheless, there is still an urgent need to introduce further security elements, which do not considerably increase the cost of the produced documents or goods.
Moire effects have already been used in prior art for the authentication of documents. For example, United Kingdom Pat. No. 1,138,011 (Canadian Bank Note Company) discloses a method which relates to printing on the original document special elements which, when counterfeited by means of halftone reproduction, show a moire pattern of high contrast. Similar methods are also applied to the prevention of digital photocopying or digital scanning of documents (for example, U.S. Pat. No. 5,018,767 (Wicker), or U.K. Pat. Application No. 2,224,240 A (Kenrick & Jefferson)). In all these cases, the presence of moire patterns indicates that the document in question is counterfeit.
Other prior art methods, on the contrary, take advantage of the intentional generation of a moire pattern whose existence, and whose precise shape, are used as a means of authenticating the document. One known method in which a moire effect is used to make visible an image encoded on the document (as described, for example, in the section “Background” of U.S. Pat. No. 5,396,559 (McGrew), U.S. Pat. No. 5,708,717 (Alasia) and U.S. Pat. No. 5,999,280 (Huang)) is based on the physical presence of that image on the document as a latent image, using the technique known as “phase modulation”. In this technique, a uniform line grating or a uniform screen of dots is printed on the document, but within the pre-defined borders of the latent image on the document the same line grating (or respectively, the same dot-screen) is printed in a different phase, or possibly in a different orientation. For a layman, the latent image thus printed on the document is hard to distinguish from its background; but when a revealing layer comprising an identical, but unmodulated, line grating (respectively, dot-screen) is superposed on the document, thereby generating a moire effect, the latent image pre-designed on the document becomes clearly visible, since within its pre-defined borders the moire effect appears in a different phase than in the background. However, this previously known method has the major flaw of being simple to simulate, since the form of the latent image is physically present on the document and only filled by a different texture. The existence of such a latent image on the document will not escape the eye of a skilled person, and moreover, its imitation by filling the form by a texture of lines (or dots) in an inversed (or different) phase can easily be carried out by anyone skilled in the graphics arts. A second limitation of phase modulation methods resides in the fact that they do not provide a dynamic visual effect such as scrolling, magnification, rotation, etc.: the image revealed by the superposition of the base layer and the revealing layer is always fixed, and it has precisely the same shape, location, size and orientation as the latent image that is embedded in the document.
U.S. Pat. No. 7,305,105 (Chosson and Hersch) teaches an authenticating method relying on a superposition image obtained when superposing a base layer embedding a shape elevation profile and a revealing layer formed by transparent lines. The superposition image then yields the shape elevation profiles level lines. But here, too, the image obtained by the superposition cannot be shifted by moving the revealing layer.
Other moire based methods, in which the presence of moire intensity profiles indicates the authenticity of the document, have been disclosed by Amidror and Hersch (the present inventors) in U.S. Pat. No. 6,249,588 and its continuation-in-part U.S. Pat. No. 5,995,638, both of which are herein fully incorporated by reference. These methods completely differ from the above mentioned techniques, since no phase modulation is used, and furthermore, no latent image is present on the document. On the contrary, all the spatial information which is made visible by the moire intensity profiles according to the inventions of Amidror and Hersch is encoded in the specially designed forms of the individual dots which constitute the dot-screens. These inventions are based on specially designed two-dimensional periodic structures, such as dot-screens (including variable intensity dot-screens such as those used in real, full gray level or color halftoned images), pinhole-screens, or microlens arrays, which generate in their superposition two-dimensional periodic moire intensity profiles of any chosen colors and shapes (letters, digits, the country emblem, etc.) whose size, location and orientation gradually vary as the superposed layers are rotated or shifted on top of each other.
In a third invention, U.S. Pat. No. 6,819,775, which is herein fully incorporated by reference, the present inventors disclosed new methods improving their previously disclosed methods mentioned above, and which make them even more difficult to counterfeit. These new improvements make use of the theory developed in the paper “Fourier-based analysis and synthesis of moires in the superposition of geometrically transformed periodic structures” by I. Amidror and R. D. Hersch, Journal of the Optical Society of America A, Vol. 15, 1998, pp. 1110-1113, and in the book “The Theory of the Moire Phenomenon” by I. Amidror, Kluwer, 2000. Based on this theory, said third invention discloses how to use geometric transformations of originally periodic structures which in spite of being aperiodic in themselves, still generate, when they are superposed on top of one another, periodic moire intensity profiles with clearly visible and undistorted elements, just like in the periodic cases disclosed by Amidror and Hersch in their previous U.S. Pat. Nos. 6,249,588 and 5,995,638. Furthermore, it was disclosed there how even cases which do not yield periodic moires can still be advantageously used for anticounterfeiting and authentication of documents and valuable products.
Yet a different category of moire based methods in which the presence of moire intensity profiles indicates the authenticity of the document has been disclosed by Hersch et al. in U.S. Pat. No. 7,194,105, in U.S. patent application Ser. No. 10/879,218 filed Jun. 30 2004 and Ser. No. 11/349,992 filed Feb. 9 2006, and in U.S. Pat. No. 7,295,717, all of which are herein fully incorporated by reference. These methods are based on the fact that an originally periodic rectilinear (but possibly geometrically transformed) base band grating incorporating any chosen original shapes superposed with an appropriately designed originally periodic rectilinear (but possibly geometrically transformed) revealing layer yield in their superposition rectilinear moire bands comprising moire shapes which are a magnified transformation of the original shapes incorporated within the base band grating. Here, too, the resulting moire effects dynamically move across the superposition as the revealing layer is shifted on top of the base layer, in contrast to the above mentioned phase modulation methods. patent application Ser. No. 11/349,992 mentions explicitly the possibility of having a fixed setup of base and revealing layers separated by a gap, which upon tilting, generates dynamically moving repetitive moire bands.
A further invention, U.S. Pat. No. 7,058,202 (Amidror), herein fully incorporated by reference, is based on the fact that if, instead of superposing two periodic or repetitive geometrically transformed dot screens, we superpose two specially designed random or pseudorandom dot-screens which are fully or partially correlated, a moire intensity profile will be generated in the superposition, which is not repeated throughout, as in the periodic or repetitive cases, but consists of one instance of the moire intensity profile whose size, location and orientation gradually vary as the superposed layers are rotated or shifted on top of each other, again, in contrast to the above mentioned phase modulation methods.
It should be stressed that the moire based methods developed by the present inventors completely differ from the above mentioned phase modulation techniques since in our methods no latent image is present, and the moire patterns resulting from the superposition of a base layer and a revealing layer are a transformation of the original pattern shapes embedded within the individual elements (dots or lines) of the base layer. This transformation comprises always an enlargement, and possibly a rotation, a shearing, a mirroring, and/or a bending transformation. In addition, in our methods, translating or rotating the revealing layer on top of the base layer yields a dynamic displacement, rotation or magnification of the moire intensity profiles. Phase modulation techniques are not capable of smoothly displacing, rotating or otherwise transforming the revealed latent image when the revealing layer is moved on top of the base layer.
Another moire based method, in which the presence of moire patterns indicates the authenticity of the document, has been disclosed by Drinkwater et al. in U.S. Pat. No. 5,712,731. In this patent a moire based method is disclosed which relies on periodic 2D microlens arrays. But this disclosure has the disadvantage of being limited to the case where the superposed revealing layer is a periodic microlens array and the base layer on the document is a periodic constant 2D array of identical dot-shapes that are replicated horizontally and vertically. Thus, in contrast to the inventions of Amidror and Hersch, this disclosure excludes the use of dot-screens or pinhole-screens as revealing structures, as well as the use on the document of full, real halftoned images with varying tone levels (such as portraits, landscapes, etc.), either in full gray levels or in color, that are made of halftone dots of varying sizes and shapes—which are the core of the methods disclosed by Amidror and Hersch, and which make them so difficult to counterfeit. Similar 2D microlense arrays are also disclosed by Steenblik et al. in U.S. Pat. No. 7,333,268, filed Nov. 22, 2004, U.S. patent application Ser. No. 11/438,081, priority May 18, 2005, and U.S. patent application Ser. No. 11/770,592, filed 28 Jun. 2007. These inventions also consider a compound layer of a periodic microlens array and a periodic dot shape array separated by a gap, where, thanks to the well-known parallax effect, changing the observation orientation has the effect of moving or changing the size of the resulting 2D moire patterns. But neither of these inventions can be applied to the case where the two layers of the compound layer are not periodic but rather correlated random (or pseudo-random) layers, as disclosed for the first time in the present invention.
It should be mentioned that the well-known parallax effect has been also used in many other applications, for example for the generation of 3D displays or imaging systems (like in U.S. Pat. No. 7,265,775 (Hirayama) or U.S. Pat. No. 5,113,213 (Sandor et al.)); for various animation displays (like in U.S. Pat. No. 2,432,896 (Hotchner), U.S. Pat. No. 2,833,176 (Ossoinak) or U.S. Pat. No. 6,286,873 (Seder)); for postcards, keyholders or toys that show two or more distinct images when they are being tilted; etc. But these devices are not based on moire intensity profiles, but rather on a completely different technique, where the device contains interleaved stripes (or dots) from two or more predesigned latent images; when viewed through an appropriate line grating or lenticular revealing layer, these stripes (or dots) are integrated by the viewer's eyes thanks to the parallax effect into slightly different views, thus producing a typical 3D or kinematic effect. Yet another technique, also unrelated to moire intensity profiles, appears in U.S. Pat. No. 6,494,491 where Zeiter et al. disclose a further variant of the phase modulation technique mentioned above that is based on the parallax effect: it consists of having similar periodic line segments printed in registration on two sides of a thin transparent layer of a certain width; thanks to the parallax effect the superposition of both layers can be viewed either in phase or out of phase depending on the observation angle. But in all of these previous applications parallax effects were obtained with periodic revealing layers. And indeed, the surprising fact that parallax effects can generate moire intensity profiles between two correlated random or pseudo-random layers (such as random dot screens or random line gratings) was not known until now, and it is disclosed for the first time in the present Application, thus making it clearly distinct from all prior art applications that are based on the well-known parallax effect between periodic layers.
Finally, it should be noted that our present invention is completely different from the 3D nonwoven random structure mentioned in p. 211 of the book “Optical Document Security” edited by R. van Renesse, Artech House, 1998, second edition (hereinafter, [Renesse98]). In that invention, a machine-readable 3D random pattern is generated by mounting two layers containing a nonwoven structure of randomly placed fibers in both sides of a transparent window in the security document. An optical sensor captures two images of the random structure under different viewing angles. Because the document has a certain depth (approximately 0.3 mm) the two captured random images are distinctly different due to parallax effect; this parallax is an authentication measure of the document. As clearly understood, in that invention the images obtained by the optical sensor consist of a random pattern of fibers, which are only machine-detectable but not intelligible to the eye. In our present invention, on the contrary, the random layers consist of randomly located tiny elements (dots or lines) having specially designed shapes (for example, letters, digits, logos, etc.), and the parallax moire effect that is obtained consists of a magnified version of these shapes that are easily observed and recognized by the viewer, and which dynamically change (scroll, rotate, etc.) according to the viewing angle.
The present invention relates to new methods and security devices for authenticating documents (such as banknotes, trust papers, securities, identification cards, passports, credit cards, security labels, etc.) or other valuable products (such as optical disks, CDs, DVDs, software products, medical products, watches, clocks, hand-held phones, hand-held computers, etc.), by means of s-random moire parallax effects.
The parallax effect between two repetitive layers is well known in the art, and it has been used for many different applications, as explained above in the section “Background of the invention”. In the present invention, however, it is disclosed for the first time that moire parallax effects can be also obtained between two layers which are not repetitive but rather random or pseudo-random, if the random element locations in the two layers are correlated. This new discovery that the parallax moire effect also generates intensity profiles in the case of correlated random layers now opens the way to the introduction of new powerful authentication and anti-counterfeiting methods and devices which are disclosed for the first time in the present invention. The main difference between the repetitive case and the random case is that in the repetitive case the dynamic parallax moire effect that is obtained is repetitive, while in the random case the dynamic parallax moire effect consists of only one instance of the repetitive effect that is obtained in the repetitive case.
It is therefore an aim of the present invention to show how we can advantageously use for the authentication of documents and valuable products parallax moire effects which occur in a compound layer consisting of two correlated 2D or 1D random layers (a base layer and a revealing layer) that are fixed together with a certain small distance (gap).
A major advantage of the 2D or 1D random moire methods used in the present invention is in their intrinsically incorporated encryption system due to the arbitrary choice of the random number sequences for the generation of the specially designed random dot screens (or line gratings) that are used in this invention.
Throughout the present disclosure the terms “random screen”, “random grating”, “random base layer”, “random revealing layer”, “random microlens array”, etc. should be understood as screens, gratings, microlens arrays, etc. whose individual elements are located arbitrarily, not in a strictly periodic way. Their element locations can be determined in various different ways, for example by using random, pseudo-random, or deterministic methods (including aperiodic sequences such as Fibonacci series, or even aperiodic sequences modulo k that repeat after k elements), which are used either directly to determine the element locations or indirectly by applying perturbations to an underlying periodic lattice of element locations. To clearly reflect this intended largest possible meaning, the terms “s-random” and “simili-random” are also used interchangeably as synonyms throughout the present disclosure, englobing all the possible variants of the traditional terms “random”, “pseudo-random”, “non-repetitive”, “non-periodic deterministic”, etc., as explained above.
Furthermore, throughout the present disclosure the terms “moire”, “moire shape”, “moire intensity profile”, and “moire shape intensity profile” are used interchangeably as synonyms.
Also, the term “base layer element shape instances” means either “s-random dot shapes” or “s-random base band elements”, and the term “underlying periodicity” means the periodicity of an original structure before it has been s-randomly perturbed. The term “cylindric microlens array” (hereinafter also called “1D microlens array” or “1D microlens”) refers to cylindric microlenses capable of sampling lines of the underlying base layer and making the sampled base layer lines visible to the observer. They generally have a cylindric shape, but they can have other shapes as well. The cylindric microlenses need not be continuous. They may be composed of separate cylindric segments.
Moreover, we use the terms “bent” and “curvilinear” interchangeably, and the terms “unbent” and “rectilinear” are also used as synonyms.
Also, throughout this disclosure the terms “valuable item” or “valuable product” stand for any valuable document (such as banknotes, checks, trust papers, securities, identification cards, passports, credit cards, security labels, etc.) or valuable article (such as optical disks, CDs, DVDs, software products, medical products, watches, industrial packages, luxury products, hand-held phones, hand-held computers, etc.).
Finally, the terms “print” and “printing” refer throughout the present disclosure to any process for depositing, affixing or transferring an image onto a support, including by means of a lithographic, photolithographic, photographic, electrophotographic or any other process (for example: engraving, etching, ablation, perforating, embossing, coating, foil transfer, hot stamping, thin film deposition, de-metallization, laser marking, gluing, serigraphy, offset, flexography, gravure, intaglio, ink jet, thermal transfer, dye sublimation, etc.). Security devices according to the present invention may be used on various supports, including but not limited to transparent synthetic materials.
The disclosed method for creating counterfeit-proof valuable items such as valuable documents and valuable articles relies on a compound layer incorporated into the valuable item. The compound layer displays a dynamically moving single moire shape instance. This compound layer is formed by the superposition of a base layer and a revealing layer with a gap between them. The base layer is an s-random base layer comprising substantially identical (or gradually varying) base layer elements laid out at s-random locations. The revealing layer is an s-random revealing layer comprising substantially identical revealing layer elements laid out at s-random locations, the s-random locations of the revealing layer elements being derived from the s-random locations of the base layer elements. The base layer element locations and the revealing layer element locations are therefore strongly correlated. In one embodiment, the s-random locations are determined by applying s-random perturbations or displacements to a periodic set of locations. When tilting the compound layer, the superposition of said s-random base and revealing layers yields a single moire shape instance, which dynamically varies in its size or orientation and/or moves along a trajectory determined by the respective layouts of the base layer and the revealing layer. In particular, layouts are available where the moire shape moves along a direction substantially perpendicular to the tilting direction.
The method also allows specifying a desired geometrically transformed moire shape layout, generally a curvilinear or bent moire, generated by a geometric transformation from an unbent moire shape layout. The revealing layer may remain untransformed or be transformed according to a desired geometric transformation. Thanks to the mathematical relationship known from moire theory between moire transformation, revealing layer transformation and base layer transformation, the geometric transformation of the base layer is derived from the selected geometric transformations of the moire and of the revealing layer. The resulting moire shapes may move along radial, spiral or any other curvilinear trajectories.
The authenticity of a valuable item (document or article) is first verified by checking in the compound layer the presence of a dynamically moving moire shape. As an optional second level authenticating measure, an additional revealing layer whose layout parameters and s-random displacement values are known to be authentic may be superposed onto the compound layer and the presence of the moire shape instance is checked. If no moire shape instance is visible, then the valuable item is a counterfeit. This second authenticating measure may also be carried out by authenticating software running on a computing device connected to an image acquisition device.
The compound layer may provide additional security by segmenting its base and revealing layers into spatially distinct juxtaposed sub-domains, each sub-domain having its own layout parameters and s-random displacement values. With appropriately conceived base and revealing layer sub-domains, the resulting moire shape produced by the superpositions of respective base and revealing layer sub-domains move together in a coordinated manner when tilting the compound layer.
The base and revealing layers can be also segmented into multiple partially overlapping sub-domains, each sub-domain having its own layout parameters and s-random displacements, and where different sub-domains generate different partially overlapping moire shapes moving along their own trajectories.
As disclosed in U.S. Pat. No. 5,275,870 (Halope et al.) it may be advantageous in the manufacture of long lasting documents or documents which must withstand highly adverse handling to replace paper by synthetic material. Transparent sheets of synthetic materials have been successfully introduced for printing banknotes (for example, Australian banknotes). And indeed, our present invention applies equally well to both a transparent support and an opaque support.
The fact that moire effects generated between superposed base and revealing layers are very sensitive to any microscopic variations in the individual layers makes any document protected according to the present invention practically impossible to counterfeit, and serves as a means to distinguish easily between a real document and a counterfeited one.
It should be noted that the dot-screens or the base band gratings that are generated on the document in accordance with the present invention need not be of a constant intensity level. On the contrary, they may include dots (or base band elements) of gradually varying sizes, widths and shapes, and they can be incorporated (or dissimulated) within any variable intensity halftoned image on the document (such as a portrait, landscape, or any decorative motif, which may be different from the motif generated by the moire effect in the superposition). To reflect this fact, the terms “base layer” and “revealing layer” used hereinafter will also include cases where the base layers (respectively: the revealing layers) are not constant and represent halftoned images. As is well known in the art, the size of the elements (dots or base band elements) in halftoned images determine the intensity levels in the image: larger elements give darker intensity levels, while smaller elements give brighter intensity levels.
In a further important embodiment of the present invention, the moire shape is buried and hidden within background random noise, so that it is not visible when the compound layer is not tilted, and it only appears and becomes visible upon tilting movement of the compound layer (or when the observer is moving). This happens because upon such movements the random background noise randomly varies, and only the parallax moire shape itself is not varied randomly and remains clearly visible against the varying random background noise. This prevents the appearance of the moire shape in counterfeits made by simple image acquisition (e.g. in a photocopy).
Also described in the present disclosure is the multichromatic case, in which the base layers used are multichromatic, thereby generating a multichromatic moire effect.
The invention will be further described, by way of example only, with reference to the accompanying figures, in which:
The present invention relates to new methods and devices for document or product security which are based on the parallax effects that occur in the cases of 1D random moire or 2D random moire, as disclosed in detail below. But in order to better understand our present disclosure and its advantages, a short review of our previous related disclosures is first provided in the following paragraphs.
In U.S. Pat. Nos. 6,249,588, 5,995,638 and 6,819,775 Amidror and Hersch (the present inventors) disclosed methods for the authentication of documents and valuable articles by using the intensity profile of moire patterns. These methods jointly called hereinafter “2D repetitive moire”) are based on the fact that a specially designed 2D repetitive basic dot-screen comprising tiny dots of any chosen color or shape (such as letters, digits, the country emblem, etc.; see, for example,
In U.S. Pat. No. 7,194,105 and in U.S. patent application Ser. No. 10/879,218 filed Jun. 30 2004 and Ser. No. 11/349,992 filed Feb. 9 2006, Hersch et al. disclosed a different family of moire based methods jointly called hereinafter “1D repetitive moire”). These methods are based on the fact that a periodic rectilinear (but possibly geometrically transformed) base band grating incorporating any chosen original shapes (that are highly flattened like in
In both of these moire based method families (2D repetitive moire and 1D repetitive moire) the two superposed layers are repetitive (either 2D repetitive dot screens as in
However, as stated in the paper “Glass patterns as moire effects: new surprising results” by I. Amidror, Optics Letters, Vol. 28, 2003, pp. 7-9 and in the book “The Theory of the Moire Phenomenon, Vol. II: Aperiodic layers” by I. Amidror, Springer, published May 2007 (hereinafter, [Amidror07]), when the superposed layers are not repetitive but rather correlated random (or pseudo-random) layers, the resulting moire effect in the superposition is no longer repetitive, and it consists of just one instance of the repetitive moire that is obtained by repetitive layers. This is true both in the 2D case (as one can clearly see by comparing the 2D repetitive case shown in
The high potential that exists in such random cases for the authentication of documents and valuable products has been recognized by Amidror in U.S. Pat. No. 7,058,202. This patent discloses a category of moire based methods (henceforth jointly called “2D random moire”), which is the random (or pseudo-random) counterpart of the 2D repetitive moire. In this category of methods the individual, specially designed dots of the base layer and of the revealing layer are randomly positioned, though highly correlated between the two layers (see, for example, the base layer shown in
There also exists a fourth category of moire based methods (henceforth jointly called “1D random moire”), whose application for the authentication of documents and valuable products is disclosed here for the first time, and which is the random (or pseudo-random) counterpart of the 1D repetitive moire (see the theoretical background in [Amidror07, pp. 452-456]). In this category of methods the individual, specially designed base bands of the base band grating and the individual lines of the revealing line grating are randomly positioned, though highly correlated between the two layers (see, for example, the s-random base band grating shown in
It should be noted that in all of these methods (2D or 1D, repetitive or random) the base layer may consist of elements of gradually varying sizes and widths, and thus convey varying gray (or color) levels, so that it can be incorporated (or dissimulated) within any desired halftone image that is printed, deposited or otherwise reproduced on the protected document or product, as explained for the 2D case in U.S. Pat. No. 6,819,775 (Amidror and Hersch) and U.S. Pat. No. 7,058,202 (Amidror) and for the 1D case in U.S. patent application Ser. No. 11/349,992 (Hersch et al.).
Furthermore, all of these methods can be also used in conjunction with various geometric layer transformations, as described for the 2D case in U.S. Pat. No. 6,819,775 (Amidror and Hersch) and U.S. Pat. No. 7,058,202 (Amidror) and for the 1D case in U.S. patent application Ser. No. 11/349,992 (Hersch et al.), thus making the resulting visual moire effect even more spectacular, and much more difficult to counterfeit.
One of the most characteristic properties of all of our above mentioned moire based methods (2D or 1D, repetitive or random), which clearly distinguishes them from other moire based methods such as phase modulation methods (see the section “Background of the invention”), is the dynamic nature of the resulting moire intensity profiles. Unlike in the other methods, when the revealing layer is moved, shifted or rotated on top of the base layer, the resulting moire effect (2D or 1D, repetitive or random) gradually scrolls across the superposition, increases or decreases, rotates, or undergoes other spectacular dynamic transformations (depending on the case and on the geometric transformations undergone by the base layer and the revealing layer). This inherent dynamic behaviour of the moire intensity profiles makes them very spectacular and very easy to recognize by the observer, and hence particularly useful for the authentication of documents and valuable products in many different configurations.
In our previous inventions (see, for example, U.S. Pat. No. 6,819,775 (Amidror and Hersch), U.S. Pat. No. 7,058,202 (Amidror) and U.S. patent application Ser. No. 11/349,992 (Hersch et al.)), there were disclosed several embodiments of particular interest for the authentication of documents and valuable products using our moire based methods. These embodiments can be used with each of the above mentioned moire method categories (2D repetitive moire, 1D repetitive moire, 2D random moire, and 1D random moire). In one embodiment, the moire intensity profiles can be visualized by superposing the base layer and the revealing layer which are both located on two different areas of the same document (banknote, etc.). In a second embodiment, only the base layer appears on the document itself, and the revealing layer is superposed on it by the human operator or the apparatus which visually, optically or electronically validates the authenticity of the document. In a third embodiment, the revealing layer is a 2D microlens array (or a 1D microlens array) rather than a 2D pinhole screen (or, respectively, a 1D line grating). An advantage of this third embodiment is that microlenses offer a higher light efficiency than other revealing layers such as pinhole screens or line gratings. A further advantage of this third embodiment is that it applies equally well to both transparent support, where the moire is observed by transmittance, and to opaque support, where the moire is observed by reflection. The term “opaque support” as employed in the present disclosure also includes the case of transparent materials which have been made opaque by an inking process or by a photographic or any other process. In a fourth embodiment the base layer is reproduced on an optically variable device and revealed by a revealing layer which can be embodied by a 2D or 1D screen, grating, microlens array or diffractive device emulating microlenses.
In all of these previously disclosed embodiments, when the base layer and the revealing layer are superposed in contact, the dynamic effect of the moire is obtained by moving or rotating the revealing layer on top of the base layer. However, as disclosed by Hersch et al. in U.S. patent application Ser. No. 11/349,992 and in U.S. Pat. No. 7,295,717 (both for the case of 1D repetitive moire methods), there also exists a further embodiment, which is based on the parallax effect. In this embodiment the base layer and the revealing layer are fixed (or “sandwiched”) together, one on top of the other, but separated from each other for example by a thin transparent layer of a certain width (generally less than 1 mm, typically between 0.02 and 0.5 mm), as shown in
A more detailed theoretic explanation of the parallax moire effect can be found in the literature, for example in the paper “Moire patterns and the illusion of depth” by J. Huck, Proc. of the fifth Interdisciplinary Conf. of the International Soc. of the Arts, Mathematics and Architecture (ISAMA 2004), Chicago, June 2004 (hereinafter, [Huck04]), or in the paper “Theory of parallax barriers” by S. H. Kaplan, Journal of the SMPTE, Vol. 59, No. 7, 1952, pp. 11-21. This well known explanation of the parallax moire effect relies on the fact that the two involved layers are repetitive. However, surprisingly, it has been now discovered by the present inventors that parallax moire effects also occur when the two involved layers consist of s-randomly located elements, if the s-random element locations in the two layers are correlated. This surprising result seems at first to contradict the fundamental theoretic considerations which govern the generation of the parallax moire effect. But in fact, this surprising result does not contradict the established theory, but simply extends it to new cases which were until now beyond its scope, and thus, excluded from practical use.
The explanation of this surprising result is that the parallax moire effect occurs, in fact, thanks to the correlation in the element locations between the two layers of the compound layer. It should be noted that in the previously known case in which the two layers are repetitive this condition is automatically satisfied; this particular case is, indeed, covered by the classical explanation of the parallax moire effect as it appears in the existing literature, and which relies on the repetitive nature of the two layers involved. But our discovery that the parallax moire effect also works in the case of correlated random layers now opens the way to the introduction of new powerful authentication and anticounterfeiting methods and devices which are disclosed for the first time in the present invention.
It is therefore an aim of the present invention to show how we can advantageously use for the authentication of documents and valuable products parallax moire effects which occur in a compound layer consisting of two correlated 2D or 1D random layers (a base layer and a revealing layer) that are fixed together with a certain small distance (gap).
Because the parallax moire effects that occur in the repetitive case and in the random case are, as we have just seen, one and the same, their dynamic behaviour is exactly the same. And indeed, in both cases the parallax moire effects behave in the same way as the moire effect that is generated between the same two layers when they are superposed in contact, but with an additional optical illusion of depth—meaning that the parallax moire effect may seem to the observer to be floating behind or in front of the two superposed layers, depending on the case (as explained in [Huck04] for the repetitive case). The difference between the repetitive case and the random case is that in the repetitive case the dynamic parallax moire effect that is obtained is repetitive, while in the random case the dynamic parallax moire effect consists of only one instance of the repetitive effect that is obtained in the repetitive case. In the 2D cases (between dot screens) the parallax moire effect may yield movements in two different directions, while in the 1D cases (between basebands and line gratings) it only has a single degree of freedom, i.e. each moire element moves only along a single trajectory. However, by creating a compound layer with several partly superposed 1D base and revealing layers, one can create moire elements moving along different trajectories (see Example 7).
A few possible examples of the dynamic evolution of a parallax moire effect according to the present disclosure are schematically illustrated in
Finally, it should be stressed that the present invention completely differs from the above mentioned technique of phase modulation based on random dot screens (U.S. Pat. No. 5,396,559 (McGrew)), since in the present invention no phase modulation is used, and furthermore, no latent image is present on the document. On the contrary, all the spatial information which is made visible by the moire intensity profile according to the present invention is encoded in the specially designed forms of the individual elements (dots or lines) which constitute the random layers. Moreover, unlike in that technique, in the present invention the moire patterns resulting from the superposition of a base layer and a revealing layer are highly dynamic, and tilting the superposed layers yields a clearly visible displacement of the moire patterns.
One possible way to obtain a random (or pseudo-random) dot screen, base band grating or revealing line grating is by using a random number generator, as widely known in the art. The random numbers obtained by the random number generator can be optionally scaled by an appropriate fixed scaling factor, and then they can be used either directly as the coordinates of the individual element in question (dot, base band line or revealing grating line), or indirectly as random increments with respect to the original location of the same element in an original repetitive layer (that is produced as already explained in our previous disclosures on 2D and 1D repetitive moires, for example in U.S. Pat. Nos. 5,995,638 and 6,819,775 (Amidror and Hersch) for the 2D repetitive case and U.S. patent application Ser. No. 11/349,992 (Hersch et al.) for the 1D repetitive case).
A major advantage of the 2D or 1D s-random moire methods used in the present invention is in their intrinsically incorporated encryption system due to the arbitrary choice of the s-random number sequences for the generation of the specially designed s-random dot screens, base band grating, or revealing line grating that are used in this invention. In order that the superposition of an s-random base layer and an s-random revealing layer yields a moire intensity profile, it is required that the random locations of base and revealing layer elements be derived from one another (and possibly slightly scaled or transformed) in order to guarantee a high correlation between the two s-random layers. Thus, if the s-random number sequence being used to derive the coordinates of each base layer and revealing layer element is the same in both layers, the superposition of the two layers will give a clearly visible moire intensity profile. But if the base layer and revealing layer element locations in the superposed random layers are not generated with the same random number sequence (for example: if they are generated by different random number generators or with different seeds), the superposition of both random layers will not give rise to any recognizable moire intensity profile shapes.
As a consequence, it is clear that given an s-random base layer, the re-generation or inverse engineering of a corresponding s-random revealing layer that will be able to reveal the moire intensity profile is only possible if the s-random number sequence being used for the generation of the s-random base layer is known. Similarly, given an s-random revealing layer, the re-generation or inverse engineering of a corresponding s-random base layer that will provide a moire intensity profile is only possible if the s-random number sequence being used for the generation of the s-random revealing layer is known. This provides the present invention with a built-in encryption system due to the choice of the s-random number sequences. For example, the s-random base layer and the s-random revealing layer may be generated using an s-random number sequence that is kept secret, thus preventing unauthorized production of an s-random revealing layer that can reveal the moire intensity profile. As a further example, if the s-random number sequence depends on the serial number of the document, or on any other parameter of the document (or series of documents), it becomes impossible for a potential counterfeiter to generate an appropriate revealing layer that will be able to reveal the moire intensity profile. This encryption may be further coupled with different covert variants of the base layer, for example, variants where the base layer is a masked basic screen, thereby offering a covert means of authentication and making the re-engineering of the basic screen of the document extremely difficult, as explained by Amidror and Hersch in U.S. Pat. No. 5,995,638.
These advantages will be further elucidated in the following sub-section, which describes, in nonexclusive and non-limiting manner, a possible application for personalization or individualization of pairs of s-random base and revealing layers.
Digital print technologies allow to create different printed image variants on each document, thereby allowing to personalize or individualize the base layer (for example, by printing it using an s-random number sequence that depends on the serial number of the document, etc.).
Furthermore, novel technologies such as ink jet of plastic material allow to deposit on the fly 2D microlense arrays or 1D microlense arrays, thereby allowing to deposit a fixed personalized revealing layer on top of the base layer, thus generating on the document a personalized compound layer.
By choosing different s-random locations for the individual elements of the layers, while keeping the correlation between the two layers, one may completely personalize or individualize pairs of base and revealing layers.
In one possible variant, the base layer and the revealing layer can be deposited on the document successively or simultaneously by the entity (official government office, credit card company, etc.) which issues the personalized document (passport, identity card, driving license, credit card, etc.).
In a second possible variant, the base layer is pre-printed (or pre-deposited) by a centralized office or printing facility on the paper (or substrate) that will be used later to produce the individual documents, and the revealing layer is affixed or deposited on top of it only later, for example in one of several local offices that issue the final documents to the public. As explained in detail above, the two layers must be produced using the same sequence of s-random numbers, thus making it impossible to counterfeit the revealing layer even on an authentic official pre-printed paper that has been obtained illicitly.
Similarly, in a third possible variant the revealing layer is pre-deposited (engraved, etched, embossed, etc.) on one face of the substrate by the manufacturer of the substrate (plastic card, etc.), and the base layer is later printed or deposited on the opposite face of the substrate, for example in one of several offices that issue the final product to the public. Here, too, the two layers must be produced using the same sequence of s-random numbers, thus making it impossible to counterfeit the base layer even on an authentic official pre-fabricated substrate that has been obtained illicitly.
Note that the specific layout of the element locations within the base or revealing layer may be made apparent by superposing a third, authenticating layer on the base or revealing layer in question. For example, as shown in
In order to add further protection and to make counterfeiting even more difficult, it is also possible to apply to one or both of the layers being used some specially designed geometric transformations. As already explained for the 2D case in U.S. Pat. No. 6,819,775 (Amidror and Hersch) and U.S. Pat. No. 7,058,202 (Amidror) and for the 1D case in U.S. patent application Ser. No. 11/349,992 and in U.S. Pat. No. 7,295,717 (Hersch et al.), it is possible by using certain mathematical rules to synthesize geometrically transformed base and/or revealing layers which in spite of being distorted in themselves, still generate, when they are superposed on top of one another, moire intensity profiles with undistorted elements, just like in the untransformed cases. Furthermore, it is shown in these disclosures that even cases which yield distorted moires can still be advantageously used for anticounterfeiting and authentication of documents and valuable products. In all of these cases, each of the two superposed layers is characterized by an additional set of parameters defining the geometric transformation which has been applied to it.
Because in the 2D and 1D random cases the resulting moire effect is the same as in the 2D or 1D repetitive case, respectively, and only contains a single instance of the corresponding repetitive moire, the mathematical models for the generation of the layer transformations remain in the random cases (either 2D or 1D) precisely the same as in the respective 2D or 1D repetitive cases. These mathematical models have already been explained and illustrated at length in U.S. Pat. No. 6,819,775 (Amidror and Hersch), U.S. Pat. No. 7,058,202 (Amidror) and U.S. patent application Ser. No. 11/349,992 (Hersch et al.). These mathematical models allow to predict the transformation undergone by the resulting moire from the transformations undergone by the two layers, or, even more interestingly, they allow to compute from the transformation of one of the two layers and from the desired moire transformation the transformation of the other layer that will produce it.
As already shown in the above mentioned disclosures, there exist many different variants based on layer transformations, for example:
The use of geometric transformations in our present invention can be elucidated by means of the examples below, which are provided in an illustrative and non-limiting manner.
In this example, the base layer consists of randomly located “1”-shaped dots, as shown in
Now, thanks to the “basic rule of the parallax moire effect” (see above), the dynamic evolution of a parallax moire effect when tilting the compound layer (or moving the eyes) horizontally (or respectively, vertically) is the same as the dynamic evolution of the same moire effect when the two layers are superposed in contact, and one of the layers is shifted on top of the other horizontally (or respectively, vertically). Therefore, the dynamic behaviour of the parallax moire in the present example is the same as illustrated and mathematically explained in the paper “Unified approach for the explanation of stochastic and periodic moires” by I. Amidror, Journal of Electronic Imaging, Vol. 12, No. 4, 2003, pp. 669-681, or in [Amidror07 pp. 54-59]: when the compound layer is tilted horizontally the parallax moire effect moves vertically (as in
If, instead of applying a rotation to one of the two layers as in the previous example we apply a scaling transformation, the resulting dynamic parallax moire effect is not an “orthoparallax” effect but rather an “intuitive” parallax effect, namely, when the compound layer is tilted horizontally the parallax moire effect moves horizontally (as in
This example shows a strongly non-linear case, in which a horizontal tilt of the compound layer gives a circular rotation of the moire (as shown in
In order to obtain this moire effect we start with two original random dot screens having identical dot locations, one of which consists of dots having the shape of tiny “1”s, as shown in
where ε is a small positive constant. Note that by using here the logarithm of the radius rather than the radius itself we obtain gradually increasing elements along the radial direction, which is more visually pleasing than keeping fixed sized elements along the radial direction. Now, according to the mathematical theory disclosed in our previous disclosures (see for example U.S. Pat. No. 6,819,775 (Amidror and Hersch) and U.S. Pat. No. 7,058,202 (Amidror)), all that we need to do is to apply to our two layers two transformations gB(x,y) and gR(x,y) such that gB(x,y)−gR(x,y)=gM(x,y). For example, we may choose to leave the revealing layer untransformed, meaning that gR(x,y)=(x,y), and apply to the base layer the geometric transformation gB(x,y)=gM(x,y)+gR(x,y), namely:
In a similar way one can also design 1D random parallax moire effects using the mathematical theory originally disclosed in U.S. patent application Ser. No. 11/349,992 (Hersch et al.) for the 1D repetitive case. For example, 1D random parallax moire effects with linearly transformed base and/or revealing layer may give moire shapes that move horizontally when the compound layer is tilted horizontally, moire shapes that move vertically when the compound layer is tilted vertically, moire shapes that move horizontally when the compound layer is tilted vertically, or moire shapes that move vertically when the compound layer is tilted horizontally. Furthermore, using the same mathematical theory, 1D random parallax moire effects with non-linearly transformed base and/or revealing layer may give even more spectacular results under horizontal or vertical tilts of the compound layer, for example a radial displacement of the moire shape, a circular displacement of the moire shape, a spiral like displacement of the moire shape, etc. As already mentioned above, in all such 1D random examples the mathematical calculations used are the same as in the corresponding 1D repetitive examples (that are largely illustrated in U.S. patent application Ser. No. 11/349,992 (Hersch et al.)), but the resulting moire effect in the random case consists of a single instance of the corresponding repetitive moire effect. Examples of 1D parallax moire shapes are given in the next sections.
Finally, thanks to the availability of a large number of geometric transformations and transformation variants (i.e. different values for the transformation constants), one may create, for additional protection, documents having their own individualized moire layout. This can be done, for example, by using a different geometric transformation for each class of documents, or as a function of the serial number of the document, etc.
The synthesis of a parallax moire shape layout is generally carried out in two successive coarse steps: first a rectilinear parallax moire is specified, together with its moire shape movement, and then an additional generally non-linear geometric transformation may be specified, which bends the linear moire shape movement into a non linear moire shape movement. Hereinafter, we show in detail possible embodiments of the method to generate parallax moire shape layouts. Other embodiments and variations are possible. Since the 1D parallax moire uses the same underlying layout rules as the 1D repetitive moire described by Hersch and Chosson in U.S. patent application Ser. No. 11/349,992, the cited formulas are similar or identical to thoses in that patent application.
In a possible embodiment the following steps allow generating 1D rectilinear parallax moire shape, see
One chooses for the curvilinear moire a preferably non-linear geometric transformation and its geometric transformation parameters according to a desired moire shape movement. Preferred geometric transformations are the transformations described by Hersch and Chosson in U.S. patent application Ser. No. 11/349,992, but instead of having repetitive, dynamically moving moire shape bands, we only have here a single moire shape band moving dynamically when tilting the compound transformed base and revealing layers horizontally, vertically or diagonally
In the following formula, the geometric transformations are expressed as transformations from transformed space (xt, yt) back to rectilinear space (xm, ym). The general equation (5), which enables calculating a transformed base layer from a desired geometrically transformed moire layer described by its transformation xm=mx(xt, yt) and yr=my(xt, yt) and a possibly transformed revealing layer described by its transformation yr=gy(xt, yt), is the same as in in U.S. patent application Ser. No. 11/349,992 (Hersch and Chosson):
If the revealing layer remains untransformed, the identity transformation gy(xt, yt)=yt is inserted in Eq. (5). The resulting geometric transformation TGB from transformed base layer to rectilinear base layer is expressed according to Eq. (5) by hx(xt, yt) and by hy(xt, yt).
The curvilinear transformed base and revealing layers are preferably generated from the corresponding rectilinear layers by the following steps:
Stacking the base and revealing layer together, with a small gap between them, enables creating the desired compound layer exhibiting the curvilinear dynamic moire shape movement upon tilting it in respect to the observation sensor (image acquisition device or human eye).
The 2D parallax moire shapes are generated in a similar manner as 1D parallax moire shapes, but with the additional parameters provided by its two degrees of freedom. 2D parallax moire shapes can be generated, for example, by performing the following steps:
Possible main steps for synthesizing parallax moire shapes, both 1D and 2D, are illustrated by
The resulting compound layer is to be integrated with the document or valuable article to be protected from counterfeits. For example, the compound layer may be fixed onto the valuable item or integrated within the valuable item, for example integrated within a plastic identity card.
The compound layer shows, due to the superposition of the s-random base and revealing layers, a single moire shape instance which, when tilting the compound layer in respect to the observation orientation, varies in its size or its orientation, as illustrated in
The steps described above need not be carried out in the order shown above. It is also possible to “learn by experience” by producing moire shapes with different s-random base layer and revealing layer layouts and retaining the base layer and revealing layer layout parameters yielding the most convenient moire shape, i.e. an adequate shape size, an adequate moire shape movement, and possibly an adequate moire shape size modification during the movement of the moire shape. Such a “learn by experience” approach does not require steps 1 and 2 above.
Creating the perturbations in the base and revealing layers can be carried out by alternative means, for example by generating a sequence of s-random numbers which can be directly used for positioning the base layer element shapes and the revealing layer lines, respectively dot elements.
The following embodiments illustrate s-random 1D parallax moire shapes. Many other examples can be obtained by modifying parameters and selecting other geometric transformations. An example of 1D rectilinear parallax moire shape is given in
By selecting an oblique moire replication vector Pm=(pmx, pmy), the moire displacement will be oblique. For example with pmx=½pmy, the moire shape moves along the arctan(2)=63.4 degrees orientation (see
A horizontal or slightly oblique moire displacement can be produced upon vertical tilt of the compound base and revealing layer.
This case is analogous to the previous one. One may conceive a horizontal moire movement with oblique revealing layer lines as in Example 6 and turn the compound layer by 90 degrees. This yields a compound layer (
The present case is the combination of Example 5 and 6. This can be simply achieved by creating a compound layer comprising the layouts of the two corresponding base layers and of the two corresponding revealing layers. For example, one may create two substantially perpendicular sets of revealing layer lines.
It is also possible to produce rectilinear moire shapes with curvilinear base and revealing layers, as described in “Example A. Rectilinear moire image and a cosinusoidal revealing layer” in U.S. patent application Ser. No. 11/349,992 (Hersch and Chosson). By applying s-random displacements to the base bands and to corresponding revealing layer lines, we generate the same moire shapes as in U.S. patent application Ser. No. 11/349,992, but with only one band of the moire shape. Cosinusoidal revealing layer lines are especially attractive, since their main orientation departs only slightly from corresponding horizontal or vertical revealing layer lines and the achievable parallax effect is therefore similar to the one achievable by horizontal, or slightly oblique revealing layer lines (slope |s|<1). By turning them by 90°, they may achieve parallax effects similar to ones achievable with vertical or strongly oblique revealing layer lines (of absolute slope |s|>1).
The following examples show curvilinear moire shapes which move along radial, curvilinear orientation, or circular orientations, in a similar manner as their counterparts in U.S. patent application Ser. No. 11/349,992 to Hersch and Chosson. Here however, because of the s-randomness of the revealing layer lines, only one instance (band) of the curvilinear moire is visible and not several instances as in that patent application.
The present example is similar to Example C in U.S. patent application Ser. No. 11/349,992. The desired moire is a circular moire. Here we choose a rectilinear revealing layer. The desired circular moire layout is given by the transformation mapping from transformed moire space (xt, yt) back into the original moire space (xm, ym), i.e.
where constant cm expresses a scaling factor, constants cx and cy give the center of the circular moire image layout in the transformed moire space, wx expresses the width of the original rectilinear reference band moire image and the function atan(y,x) returns the angle α of a radial line of slope y/x, with the returned angle α in the range (−π<=α<=π). We take as revealing layer a rectilinear layout identical to the original rectilinear revealing layer, i.e. gy(xt,yt)=yt. By inserting the curvilinear moire layout equations and the curvilinear revealing layer layout equation gy(xt,yt)=yt into the band moire layout model equations (5), one obtains the derived curvilinear base layer layout equations
These curvilinear base layer layout equations express the geometric transformation from transformed base layer space to the original base layer space. The corresponding curvilinear base layer in the transformed space is shown in
Instead of a rectilinear revealing layer, one could choose a cosinusoidally transformed revealing layer (
U.S. patent application Ser. No. 11/349,992 (Hersch and Chosson) teaches how to extend the curvilinear base layer layout equations in order to produce an ellipsoidal layout. This is carried out by inserting into formula (7) instead of a radial distance from a point (xt,yt) to the center of a circle √{square root over ((xt−cx)2+(yt−cy)2))}{square root over ((xt−cx)2+(yt−cy)2))} the corresponding distance from a point (xt,yt) to the center of an ellipse √{square root over (((xt−cx)/a)2+((yt−cy)/b)2))}{square root over (((xt−cx)/a)2+((yt−cy)/b)2))}, where a and b are freely chosen constants. This enables extending the previously considered concentric circular moire layout to a concentric elliptic moire layout. We therefore call “concentric layouts” both the circular and the elliptic layouts.
The example shown in
As shown in the examples given above, both in the 1D and in the 2D cases the moire shapes are surrounded by a noisy, random background. Depending on the layout and the s-random parameters of the base and revealing layers, more or less visible noise can be introduced. This can be advantageously used in yet another important embodiment of the present invention, in which the moire shape is buried and hidden within background random noise, so that it is not visible when the compound layer is not tilted, and it only appears and becomes visible upon tilting movement of the compound layer (or when the observer is moving). This happens because upon such movements the random background noise randomly varies, and only the parallax moire shape itself is not varied randomly but rather evolves continuously, and thus it remains clearly visible against the randomly varying background noise. This further improves the protection provided by the compound layer, since it prevents the appearance of the moire shape in counterfeits made by simple image acquisition (e.g. in a photocopy).
In addition, it is also possible to mask the base layer, for example by superposing on it masking patterns as described by Amidror and Hersch in U.S. Pat. No. 5,995,638. In this case the s-random base layer is masked by tiny patterns, hiding the moire shape instance when the compound layer does not move, and showing the moire shape instance dynamically evolving and moving along its trajectory when the compound layer is tilted. This can completely prevent the appearance of the moire shape when the compound layer does not move and make it appear only upon tilting of the compound layer (or movements of the observer).
In the case where the base layer is embodied by a diffractive device creating interference colors (rainbow colors), the background random noise shows scrambled rainbow color elements. When tilting the compound layer, a clearly appearing moire shape instance is formed by rainbow colors which dynamically evolve and/or move along a trajectory.
In the case where the base layer is embodied by an optically variable device (OVD) creating different light intensities, the background random noise shows scrambled intensity variations. When tilting the compound layer, a clearly visible moire shape instance is formed by light intensities which dynamically evolve and/or move along a trajectory.
The base layer may also be embodied by juxtaposed color elements (see section “the multichromatic case”). In such a case, the background random noise shows scrambled color elements, such as small color strokes or stains, giving the impression of an artistic creation. When tilting the compound layer, a clearly appearing moire shape instance is formed by color shapes which dynamically evolve and possibly move along a trajectory.
As shown in Example 7, it is possible to aggregate within a base layer, respectively revealing layer, several sets of base bands, respectively sets of revealing lines, by complete superposition, partial superposition or juxtaposition. In the corresponding compound layer, each set of base bands and set of revealing lines produces its own moire element, defined by its shape, its layout and the way it moves when tilting the compound layer. The different moire shape movements of the layer composition (aggregation) may be coordinated as in Example 7 (
A strong means of individualizing and increasing the protection of a document against counterfeits consists in dividing the domain (
A similar aggregation of the base and revealing layers can be also done in the 2D case.
Such an aggregation of sub-domains may be created by the software that creates the base and revealing layers, by creating many different variants for the base and revealing layers. These variants are created by varying layout properties while keeping the same target moire properties (moire height, moire displacement, geometric transformation from curvilinear moire to rectilinear moire). Layout properties that can vary are, for example: the geometric transformation and its transformation parameters applied to the set of revealing elements (1D: revealing lines; 2D: revealing dots) as well as the s-random displacement values (s-random displacement vector comprising one (1D) or a pair of displacement values per entry (2D)). The different variants generate the same moire, and the same moire displacement. Then, sub-domains can be cut out in each of the variants and assembled together to form the aggregated base and revealing layers of the compound layer. In addition, the resulting aggregated revealing layer, formed by the assembly of the different sub-domains, can be stored in digital form on a computer server in order to serve as an authenticating revealing layer (see next section).
The authenticity of a compound layer (possibly made of a base layer and a revealing layer with partially superposed or with juxtaposed sub-domains, as explained in the previous section) can be verified by superposing on the compound layer (e.g.
Since the authenticating revealing layer is available only to authorized persons, and since it may be very hard to deduce from a compound layer (e.g. with a revealing layer produced with 1D microlenses having an underlying period lower than 100 microns), this compound layer authentication procedure is robust. The authenticating revealing layer may be also made available to authorized persons by a Web server (digital files to be printed on film, on transparencies or by an device capable of printing or depositing lenses), upon secure login and identification of the authorized person.
A compound layer, possibly made of aggregated sets of base layers and of revealing layers, may also be authenticated by image acquisition and by processing the acquired moire image with an authentication software. The authentication software may verify the presence of the moire shapes, for example with template matching techniques well known in the art, and/or verify that the revealing layers on the compound layer are those of the authentic document.
In an additional embodiment, the digital authenticating revealing layer is made available to the authenticating software in digital form, e.g. by secure transfer from a Web server. The moire shape image (e.g.
The authentication of the compound layer by the authenticating software can be carried out, for example, as shown in
Another possibility of authenticating a compound layer consists in acquiring the information expressed by the moire shapes (
As previously mentioned, the present invention is not limited only to the monochromatic case; on the contrary, it may largely benefit from the use of different colors in any of the dot-screens or base band gratings being used.
One way of using colored dot-screens (or base band gratings) in the present invention is similar to the standard multichromatic printing technique, where several (usually three or four) dot-screens (or base band gratings) of different colors (usually: cyan, magenta, yellow and black) are superposed in order to generate a full-color image by halftoning. As it is already known in the art, if the layers being used for the different colors are independent (i.e. non-correlated) s-random dot screens (or s-random base band gratings), no moire artifacts are generated between them, even if the number of color layers exceeds the standard number of three or four. If one of these colored random layers is now used as a random base layer according to the present invention, the moire intensity profile that will be generated with a corresponding random revealing layer will closely approximate the color of the color base layer.
Another possible way of using colored dot-screens (or base band gratings) in the present invention is by using a base layer whose individual elements are composed of sub-elements of different colors, as disclosed by Amidror and Hersch in their previous U.S. Pat. No. 5,995,638, also shown in
Hence, counterfeiters trying to counterfeit the color document by printing it using a standard printing process will also have, in addition to the problems of creating the base layer, problems of color registration. Without correct color registration, the base layer will incorporate distorted screen dots (or basebands). Therefore, the intensity profile of the moire in a counterfeited document will clearly distinguish itself, in terms of form and intensity as well as in terms of color, from the moire profile obtained in an authentic document. Since counterfeiters will always have color printers with less accuracy than the official bodies responsible for printing the original valuable documents (banknotes, checks, etc.), the disclosed authentication method remains valid even with the quality improvement of color reproduction technologies.
One possible way for printing color images using standard or non-standard color inks (standard or non-standard color separation) has been described in U.S. Pat. No. 7,054,038 (Ostromoukhov, Hersch) and in the paper “Multi-color and artistic dithering” by V. Ostromoukhov and R. D. Hersch, SIGGRAPH Annual Conference, 1999, pp. 425-432. This method, hereafter called “multicolor dithering”, uses dither matrices similar to standard dithering, and provides for each pixel of the base layer (the halftoned image) a means for selecting its color, i.e. the ink, ink combination or the background color to be assigned for that pixel. A random or geometric transformation can be then applied to this dither matrix in the same way as in the monochromatic case. It should be noted, as explained in detail in the above mentioned references, that the multicolor dithering method ensures by construction that the contributing colors are printed side by side. This method is therefore ideal for high-end printing equipment that benefits from high registration accuracy, and that is capable of printing with non-standard inks, thus making the printed document very difficult to counterfeit, and easy to authenticate by means of the disclosed method, as explained above.
Another advantage of the multichromatic case is obtained when non-standard inks are used to create the base layer. Non-standard inks are often inks whose colors are located out the gamut of standard cyan magenta and yellow inks. Due to the high frequency of the colored patterns located in the base layer and printed with non-standard inks, standard cyan, magenta, yellow and black reproduction systems will need to halftone the original color, thereby destroying the original color patterns. Due to the destruction of the microstructure of the base layer, the revealing layer will not be able to yield the original moire effects. This provides an additional protection against counterfeiting.
Finally, using special inks that are visible under ultra-violet light (hereinafter called UV inks) for printing the base layer allows to reveal moire images under UV light, but may either hide them completely or partially under normal viewing conditions. If UV inks which are partly visible under day light are combined with standard inks, for example by applying the multicolor dithering method cited above, photocopiers will not be able to extract the region where the UV ink is applied and therefore potential counterfeiters will not be able to generate the base layer. In the resulting counterfeited document, no moire image will appear under UV light.
The base layer and the revealing layer may be embodied using a large variety of technologies. For example, the layers (the base layer, the revealing layer, or both) can be generated by offset printing, ink-jet printing, dye sublimation printing, foil stamping, etc. The layers may be also obtained by a complete or partial removal of matter, for example by laser or chemical etching or engraving.
The revealing layer can be embodied by an opaque film or plastic support incorporating a set of transparent lines (in the 1D case) or a set of pinholes (in the 2D case).
In another embodiment, the revealing layer may be made of a microlens structure, namely, an s-random microlens array (in the 2D case) or an s-random 1D microlens array (in the 1D case). Microlens arrays are composed of a multitude of tiny lenslets that are traditionally arranged in a periodic structure (see, for example, “Microlens arrays” by Hutley et al., Physics World, July 1991, pp. 27-32), but they can be also arranged on any s-random grid. They have the particularity of enlarging on each grid element only a very small region of the underlying source image, and therefore they behave in a similar manner as screens comprising small transparent dots or pinholes. Similarly, cylindric microlens arrays (1D microlens arrays) behave in a similar way as line gratings comprising thin transparent line slits. However, microlens structures have the advantage of letting most of the incident light pass through the structure. They can therefore be used for producing moire intensity profiles either by reflection or by transmission. It should be noted that the role of microlens arrays in generating moire effects where a periodic microlens array is superposed on a periodic array of identical objects having the same pitch is known since long ago (see, for example, “New imaging functions of moire by fly's eye lenses” by O. Mikami, Japan Journal of Applied Physics, Vol. 14, 1975, pp. 417-418, and “New image-rotation using moire lenses” by O. Mikami, Japan Journal of Applied Physics, Vol. 14, 1975, pp. 1065-1066). But none of these known references disclosed an implementation of this phenomenon for document authentication and anti-counterfeiting. Furthermore, none of them has forseen, as the present inventors did, the possibility of using real halftoned images with full gray levels or colors as base layers, or the possibility of using s-random microlens structures and s-random base layers—neither for document authentication and anti-counterfeiting nor for any other purpose.
It should be noted that it is also possible to emulate a microlens array with a diffractive device made of Fresnel Zone Plates (see B. Saleh, M. C. Teich, Fundamentals of Photonics, John Wiley, 1991, p. 116). In a similar way, one may also use instead of cylindric microlenses a diffractive device emulating the behavior of cylindric microlenses.
In the case that the base layer is incorporated into an optically variable surface pattern, such as a diffractive device, Kinegram, etc., the image forming the base layer needs to be further processed to yield for each of its pattern image pixels or at least for its active pixels (e.g. black or white pixels) a relief structure made for example of periodic function profiles (such as gratings of tiny lines) having an orientation, a period, a relief and a surface ratio according to the desired incident and diffracted light angles, according to the desired diffracted light intensity and possibly according to the desired variation in color of the diffracted light in respect to the diffracted color of neighbouring areas (see for example U.S. Pat. No. 5,032,003 (Antes) and U.S. Pat. No. 4,984,824 (Antes and Saxer)). This relief structure is reproduced on a master structure used for creating an embossing die. The embossing die is then used to emboss the relief structure incorporating the base layer on the optical device substrate (further information can be found, for example, in U.S. Pat. No. 4,761,253 (Antes) or in the chapter “Document Protection by Optically Variable Graphics (Kinegram)” in [Renesse98 pp. 247-266].
It should be noted that in general the base and the revealing layers need not be complete: they may be masked by additional layers or by random shapes. Nevertheless, when tilting the compound layer, the moire patterns will still become apparent.
Furthermore, the base layer can be diffusely reflecting, in order to be viewed in reflection mode, or partially transparent, in order to be viewed in transmission mode.
As already illustrated in the sub-section “Personalization/individualization of pairs of s-random base and revealing layers” above, the compound layer can be produced in many different ways. In one possible variant, the base layer and the revealing layer can be deposited on the document successively by the entity (official government office, credit card company, etc.) which issues the personalized document (passport, identity card, driving license, credit card, etc.). In a second possible variant, the base layer is pre-printed by a centralized office or printing facility on the paper (or substrate) that will be used later to produce the individual documents, and the revealing layer is affixed or deposited on top of it only later, for example in one of several local offices that issue the final documents to the public. In a further variant, the revealing layer is pre-deposited (engraved, etched, embossed, etc.) on one face of the substrate by the manufacturer of the substrate (plastic card, etc.), and the base layer is later printed on the opposite face of the substrate, for example in one of several offices that issue the final product to the public. These variants are provided here by way of example only, in a non-restrictive manner, and it should be understood that many other embodiments, configurations and variants may be also conceived which are covered by the present invention.
Any attempt to counterfeit a document produced in accordance with the present invention by photocopying, by means of a desk-top publishing system, by a photographic process, or by any other counterfeiting method, be it digital or analog, will inevitably influence (even if slightly) the size or the shape of the tiny screen dots or base bands of the base layer comprised in the document (for example, due to dot-gain or ink-propagation, as is well known in the art). But since moire effects are very sensitive to any microscopic variations, this makes any document protected according to the present invention very difficult to counterfeit, and serves as a means to distinguish between a real document and a counterfeited one.
Various embodiments of the present invention can be used as security devices for the protection and authentication of multimedia products, including music, video, software products, etc. that are provided on optical disk media. Various embodiments of the present invention can be also used as security devices for the protection and authentication of other industrial packages, such as boxes for pharmaceutics, cosmetics, alcoholic beverages, etc.
The new authentication and anti-counterfeiting methods and devices disclosed in the present invention have numerous advantages.
First, random (and optionally geometrically transformed) dot-screens or base band gratings are much more difficult to design than their repetitive counterparts, and therefore they are very hard to reverse engineer and to counterfeit.
Second, a major advantage of the 2D or 1D random moire methods in the present invention is in their built-in encryption system due to the arbitrary choice of the s-random number sequences for the generation of the specially designed s-random dot screens, respectively base band gratings, that are used in this invention. This provides an additional protection at the same price.
Thirdly, the validity of the compound layer's encryption can be separately checked by a separate authenticating revealing layer, having the same layout as the revealing layer.
The present invention also presents a significant advantage with respect to the previous U.S. Pat. No. 7,058,202 (Amidror). In this patent the base layer and the revealing layer are random dot screens (or microlens arrays) that can be freely moved on top of each other, so that the resulting single instance of the moire effect freely moves accordingly. In the present invention, however, the two layers are fixed together, and thus the layer superposition (fixed setup) can be manufactured such that the single instance of the moire effect is generated in the center of the zone of interest (e.g. window on the document); and since the two random layers are fixed together, the moire effect cannot move too much away or scroll outside this region, and thus disappear to the eye. Moreover, the high registration that is required between the two layers of the fixed setup to guarantee the centering of the moire effect provides a further major difficulty for potential counterfeiters, and thus offers a further degree of security against counterfeiting.
Furthermore, the fact that moire effects generated by superposing tiny base layer elements and revealing layer sampling elements are very sensitive to any microscopic variations in the layers makes any document protected according to the present invention very difficult to counterfeit, and serves as a means to easily distinguish between a real document and a counterfeited one.
Since the mathematical theory used for the design of 2D or 1D moires allows, for a given moire layout, to freely choose the layout of the revealing layer, one may optimize the layouts of the base and the revealing layers so as to reveal details which are only printable at the high resolution and with the possibly non-standard inks of the original printing device. Lower resolution devices or devices which do not print with the same inks as the original printing device will not be able to print these details and therefore no valid moire effect will be generated.
A base layer that is designed in accordance with the present invention may be populated with opaque color patterns printed side by side at a high registration accuracy, for example with the method described in U.S. Pat. No. 7,054,038 (Ostromoukhov, Hersch). Since the moire effects are very sensitive to any microscopic variations of the pattern residing in the base layer, any document protected according to the present invention is very difficult to counterfeit. The revealed moire patterns serve as a means to easily distinguish between a real document and a falsified one.
A further important advantage of the present invention is that it can be used for authenticating documents printed on any kind of support, including paper, plastic materials, diffractive devices (e.g. holograms or kinegrams) etc., which may be opaque, semi-transparent or transparent. Furthermore, the present invented method can be incorporated into halftoned B/W or color images (simple constant images, tone or color gradations, or complex photographs), and it can be even incorporated into the background of security documents (for example by placing the base layer or the entire fixed setup in the background and by allowing to write or print on top of it). In a further embodiment, the halftoned image may also be visible in the back side of the document, while in the front side, when looking through the revealing layer, only the moire parallax effect is visible.
Furthermore, the random base layers printed on the document in accordance with the present invention need not be of a constant intensity level. On the contrary, they may include base layer elements of gradually varying sizes and shapes, and they can be incorporated (or dissimulated) within any variable intensity halftoned image on the document (such as a portrait, landscape, or any decorative motif, which may be different from the motif generated by the moire effect in the superposition). This has the advantage of making counterfeiting still more difficult, thus further increasing the security provided by the present invention.
One of the most characteristic properties of all of our moire based methods (2D or 1D, repetitive or random), including the new methods of the present disclosure, and which clearly distinguishes them from other moire based methods such as phase modulation methods (see the section “Background of the invention”), is the dynamic nature of the resulting moire intensity profiles. In the present invention, any tilting or change of viewing angle causes the resulting moire effect (2D or 1D) to gradually scroll across the superposition, increase or decrease, rotate, or undergo other spectacular dynamic transformations (depending on the case and on the geometric transformations undergone by the base layer and the revealing layer). This inherent dynamic behaviour of the moire intensity profiles makes them very spectacular and very easy to recognize by the observer, and hence particularly useful for the authentication of documents and valuable products in many different configurations.
Moreover, thanks to the availability of an unlimited number of geometric transformations and transformation variants (e.g. different values for the transformation constants), one may create classes of documents where each class of documents has its own individualized or personalized document protection. Thanks to the unlimited number of geometric transformations being available, a large number of base layer and revealing layer designs can be created according to different criteria. For example, the triplet formed by base layer layout, revealing layer layout and moire layout may be different for each individual document, for each class of documents or for documents issued within different time intervals. The immense number of variations in base layer layout, revealing layer layout and moire layout makes it very difficult for potential counterfeiters to counterfeit documents whose layouts may vary according to information located within the document or according to time.
In addition, different pairs of base and revealing layers may be juxtaposed, partially superposed or completely superposed to yield moires shapes which either move independently of one another, or move in a coordinated manner, for example by coming together and forming a composed shape at a certain tilt angle of the compound layer.
Furthermore, if the compound layer is designed to include sufficiently strong background random noise (for example by an appropriate choice of the s-random sequence being used), then the resulting moire effect completely disappears within the random background noise, and it can only be seen upon tilting movement of the compound layer (or movements of the observer). This prevents the appearance of the moire shape in simple image acquisitions such as photocopies and digitized images.
Finally, the acquired moire shapes may represent information, such as a succession of letters or digits, which, when entered or transferred to an authenticating Web server, allow, according to the reply of the Web server, to validate or not the information appearing as moire shapes and therefore to authenticate the valuable item displaying these moire shapes.
