Moiré methods for the protection of documents and products: A short survey

Moiré effects have long been used for various applications in many different fields, including metrology, strain analysis, optical alignment, etc. In the present survey we describe some of the main applications of the moiré effect in the field of document and product security. We review the main families of moiré-based anticounterfeiting methods, compare them, and explain how they can be used for such security applications

Authentication of documents and articles by moire patterns

The present invention relies on the moiré patterns generated when superposing a base layer made of base band patterns and a revealing line grating (revealing layer). The produced moiré patterns comprise an enlargement and a transformation of the individual patterns located within the base bands. Base bands and revealing line gratings may be rectilinear or curvilinear. When translating or rotating the revealing line grating on top of the base layer, the produced moiré patterns evolve smoothly, i.e. they may be smoothly shifted, sheared, and possibly be subject to further transformations. Base band patterns may incorporate any combination of shapes, intensities and colors, such as letter, digits, text, symbols, ornaments, logos, country emblems, etc... They therefore offer great possibilities for creating security documents and valuable articles taking advantage of the higher imaging capabilities of original imaging and printing systems, compared with the possibilities of the reproduction systems available to potential counterfeiters. Since the revealing line grating reflects a relatively high percentage of the incident light, the moiré patterns are easily apparent in reflective mode and under normal illumination conditions. They may be used for the authentication of any kinds of documents (banknotes, identity documents, checks, diploma, travel documents, tickets) and valuable articles (optical disks, CDs, DVDs, CD-ROMs, packages for medical drugs, bottles, articles with affixed labels)

Model-based synthesis of band moire images for authenticating security documents and valuable products

The present invention relies on a band moiré image layout model capable of predicting the band moiré image layer layout produced when superposing a base band grating layer of a given layout and revealing line grating layer of a given layout. Both the base band grating layer and the revealing line grating layer may have a rectilinear or a curvilinear layout. The resulting band moiré image layout may also be rectilinear or curvilinear. Thanks to the band moiré image layout model, one can choose the layout of two layers selected from the set of base band grating layer, revealing line grating layer and band moiré image layer and obtain the layout of the third layer by computation, i.e. automatically. A computing system may automatically generate upon request an individualized protected security document having specific base band grating and revealing line grating layouts

Authentication of secure items by shape level lines

The disclosed method and system may be used for creating advanced protection means for various categories of documents (e.g. bank notes, identity documents, certificates, checks, diploma, travel documents, tickets) and valuable products (e.g. optical disks, CDs, DVDs, CD-ROMs, prescription drugs, products with affixed labels, watches) hereinafter called "secure items". Secure items are authenticated by shape level lines. The shape level lines become apparent when superposing a base layer comprising sets of lines and a revealing layer comprising a line grating. One of the two layers is a modified layer which embeds a shape elevation profile generated from an initial, preferably bilevel, motif shape image (e.g. typographic characters, words of text, symbols, logo, ornament). In the case of an authentic document, the outline of the revealed shape level lines are visual offset lines of the boundaries of the initial bilevel motif shape image. In addition, the intensities, respectively colors of the revealed shape level lines are the same as the intensities, respectively colors of the lines forming the base layer sets of lines. By modifying the relative superposition phase of the revealing layer on top of the base layer or vice-versa (e.g. by a translation or a rotation), one may observe shape level lines moving dynamically between the initial bilevel motif shape boundaries and shape foreground centers, respectively background centers, thereby growing and shrinking. In the case that these characteristic features are present, the secure item is accepted as authentic. Otherwise the item is rejected as suspect. Pairs of base and revealing layers may be individualized by applying to both the base and the revealing layer a geometric transformation. Thanks to the availability of a large number of geometric transformations and transformation parameters, one may create documents having their own individualized document protection. The invention also proposes a computing and delivery system operable for delivering base and revealing layers according to security document or valuable product information content. The system may automatically generate upon request an individually protected secure item and its corresponding authentication means

Authentication of documents and articles by moire patterns

The present invention relies on the moiré patterns generated when superposing a base layer made of base band patterns and a revealing line grating (revealing layer). The produced moiré patterns comprise an enlargement and a transformation of the individual patterns located within the base bands. Base bands and revealing line gratings may be rectilinear or curvilinear. When translating or rotating the revealing line grating on top of the base layer, the produced moiré patterns evolve smoothly, i.e. They may be smoothly shifted, sheared, and possibly be subject to further transformations. Base band patterns may incorporate any combination of shapes, intensities and colors, such as letter, digits, text, symbols, ornaments, logos, country emblems, etc... They therefore offer great possibilities for creating security documents and valuable articles taking advantage of the higher imaging capabilities of original imaging and printing systems, compared with the possibilities of the reproduction systems available to potential counterfeiters. Since the revealing line grating reflects a relatively high percentage of the incident light, the moiré patterns are easily apparent in reflective mode and under normal illumination conditions. They may be used for the authentication of any kinds of documents (banknotes, identity documents, checks, diploma, travel documents, tickets) and valuable articles (optical disks, cds, dvds, cd-roms, packages for medical drugs, bottles, articles with affixed labels)

Printing color images visible under uv light on security documents and valuable articles

In the present invention, we propose a method of creating fluorescent color images visible under UV light. It relies on the new colorants that can be achieved by superposing ink dots, possibly at a reduced size, in order to avoid quenching effects. It also relies on juxtaposed halftoning, which ensures that colorants are printed side by side and do therefore not overlap, thereby preventing quenching effects. It also support the selection of a fluorescent set of inks which comprises at least one ink whose emission spectrum yields a color different from the standard red, green and blue colors, for example a yellow color emitting ink. The method comprises the following techniques: (a) creating new colorants by superposing carefully selected amounts of the fluorescent inks, (b) mapping the gamut of the image to be reproduced into the gamut of the resulting fluorescent colorants and (c) creating the target fluorescent color image by juxtaposed halftoning of the fluorescent colorants. Juxtaposed halftoning avoids quenching effects by creating diagonally oriented pre-computed colorant screen dots, which are printed side by side.' Thanks to gamut mapping and juxtaposed halftoning, we create color images, which are invisible under daylight and have, under UV light, a high resemblance with the original images. Applications comprises the protection of security documents such as bank notes, passports, ID cards, entry tickets, travel documents, checks, vouchers or valuable business documents as well as valuable articles such as CDs, DVDs, software packages, medical drugs, watches, personal care articles, and fashion articles. And a last application is art, decoration, publicity, fashion, and night life, where fluorescent images viewed under UV illumination at night or in the dark have a strongly appealing effect

Visually-Based Color Space Tetrahedrizations for Printing with Custom Inks

Printing with custom inks is useful for extending the gamut of printed images, for creating artistically appealing designs or for providing protection against counterfeiting (security documents). The basic colors we consider, consist of the custom inks, their superpositions and the white paper. Color separation for custom inks requires to determine the relative amounts of the basic colors allowing to render each desired input color. To achieve this goal, one may tetrahedrize the set of basic colors on a given 3D color space. However, even for a few basic colors, there are many different tetrahedrizations (for example with 8 points in 3D space, one may build more than 120 different tetrahedrizations)