EP1319219A1 - Method for preventing counterfeiting or alteration of a printed or engraved surface - Google Patents

Method for preventing counterfeiting or alteration of a printed or engraved surface

Info

Publication number
EP1319219A1
EP1319219A1 EP01964793A EP01964793A EP1319219A1 EP 1319219 A1 EP1319219 A1 EP 1319219A1 EP 01964793 A EP01964793 A EP 01964793A EP 01964793 A EP01964793 A EP 01964793A EP 1319219 A1 EP1319219 A1 EP 1319219A1
Authority
EP
European Patent Office
Prior art keywords
watermark
signature
printed
image
visible
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP01964793A
Other languages
German (de)
French (fr)
Other versions
EP1319219B1 (en
Inventor
Frédéric JORDAN
Roland Meylan
Martin Kutter
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ALPVISION SA
Original Assignee
ALPVISION SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ALPVISION SA filed Critical ALPVISION SA
Priority to EP10174049.6A priority Critical patent/EP2261867B1/en
Publication of EP1319219A1 publication Critical patent/EP1319219A1/en
Application granted granted Critical
Publication of EP1319219B1 publication Critical patent/EP1319219B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/004—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using digital security elements, e.g. information coded on a magnetic thread or strip
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/005—Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations
    • G07D7/0054—Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations involving markings the properties of which are altered from original properties
    • G07D7/0056—Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations involving markings the properties of which are altered from original properties involving markings of altered colours

Definitions

  • a method of preventing counterfeiting or altering a printed or engraved surface is a method of preventing counterfeiting or altering a printed or engraved surface.
  • the present invention relates to a method for preventing counterfeiting or alteration of a printed or engraved surface.
  • Special ink printing uses special chemical properties of the ink to provide a specific reaction to a particular action.
  • fluorescent inks become very bright when they are lit by a particular wavelength, some inks are even invisible to natural light, other inks change color according to their orientation or their temperature (and can be reveal by heating the paper with a finger), etc.
  • Special inks have one thing in common: particularly expensive and necessitate making modifications in the usual industrial production chain (additional mask for offset for example).
  • additional mask for offset for example.
  • Codes using invisible inks allow digital information to be hidden. These codes can be characters, bar codes, 2D codes, etc. In addition to its high cost and specific to invisible inks, this system has two major drawbacks. On the one hand, due to the nature of the codes used, it is located on a certain part of the document or of the packaging and it is therefore possible to destroy it without altering the entire surface. On the other hand, the codes used always have geometric characteristics (bars, geometric figures, characters, etc.) clearly identifying them as anti-copy devices. This greatly facilitates the task of the pirate seeking to reveal and reproduce the ink. In addition, as soon as the pirate knows how to make this reproduction, he ipso facto has the means to reproduce the code.
  • systems based on on-board memories or processors combine the disadvantages of being very expensive, unattractive and localized. Their main application is more to secure a communication, or to dynamically store information rather than to distinguish an original from a copy.
  • One of the aims of the present invention is to remedy the drawbacks of known methods making it possible to prevent counterfeiting or alteration of documents printed or engraved by digital means.
  • the present invention relates to a method intended to prevent counterfeiting or alteration of printed or engraved documents characterized by the incorporation of a digital watermark in part or in the whole of the document.
  • the digital watermark technique also known as digital watermarking, is a technique for hiding information in a robust and imperceptible way in multimedia data such as music, video, images, documents, etc.
  • the information that is hidden is called the signature.
  • This signature can for example be a number, a name or even an image.
  • “Hide” has a very specific meaning in this context: for example in the case of an image, we will slightly change the color of certain pixels, and in the case of music we will slightly modify the sound from time to time.
  • Imperceptible means that the changes introduced are such that an individual cannot distinguish the original data from the data signed by his own senses. For example, a signed image must have exactly the same appearance as a normal image, a signed music must appear completely normal, the same for a video or any other data. The whole problem is to make a computer capable of detecting this hidden information when it escapes our senses. There are also applications where a visible watermark is acceptable or even desirable. This allows in particular to further increase the robustness and a visual check for the presence of a watermark. The principle that remains is that the watermark should not be visually disturbing.
  • the "robustness" of a watermark means that one must be able to find the signature after any manipulation of signed data. Take for example the case of a signed image: we must be able to compress, print, scan or rotate it without ever losing the signature.
  • Many publications have been made on the various techniques allowing to hide a watermark in an image, in a video or an audio signal. With regard to images, the latter can be classified according to the technique used for marking: some operate modifications directly in the spatial domain (see for example [1] M. Kutter, F. Jordan, F. Bossen, "Digital watermaking of color images using amplitude modulation", Journal of Electronic Imaging, vol. 7, n ° 2, pp.
  • the digital watermark technique has so far been used in order to find the signature on a possible copy to prove the origin of the information present on the copy, thanks to the presence of the watermark that the 'found on the copy. This in all cases involved the use of a robust watermark.
  • the purpose of incorporating the digital watermark on the surface is different, since its presence is intended to prevent authentication or alteration of the surface concerned, i.e. provide proof that this is the authentic surface if the watermark is present or that it is a copy or that the surface has been altered if the watermark is missing.
  • the robustness of the watermark must be reduced so that a copy of the surface results in a failure to read the watermark digital.
  • a "fragile" watermark A typical example of application consists in preventing the counterfeiting of securities such as banknotes. If the watermark is incorporated to avoid alteration of all or part of the surface, the watermark may be strong or fragile.
  • the watermark is printed using colors and resolutions that are invisible to the naked eye. This therefore makes it possible to protect, for example, a package without its graphics being altered, which is important for marketing reasons.
  • the watermark can cover the entire surface of a printed document. It is therefore not possible to erase it without altering the document, for example by scratching the surface. In practice, this property makes it possible, for example, to avoid gray markets, ie products sold by unauthorized distributors. Indeed, they sometimes erase the code (invisible 2D code for example) identifying their reseller by "milling" the surface of the packaging where the code is printed. • Price
  • the watermark is printed using traditional printing systems. Regarding industrial printing (offset, etc.), it is fully integrated into the production chain and does not incur any additional costs. Regarding personal printing (inkjet, laser, etc.), it is fully compatible with commercial printers. In both cases, the reading is done with a standard digital scanner. This low price opens up new markets: firstly for industrial printing, packaging for luxury or pharmaceutical products, as well as certificates, checks, entry tickets, etc. On the other hand for personal printing, it allows anyone with standard equipment to create and verify secure and personalized documents. For example, a doctor may hide the names of the drugs prescribed in the paper used to print the prescription. It is possible to program a printer so that it hides a watermark in any printed document thus allowing later identification of the date of printing, the name of the user, etc.
  • the watermark contains digital information (typically several tens of bits per square centimeter) which is encoded or retrieved using a key.
  • this storage makes it possible, for example, to secure information printed in visible text (therefore liable to be modified). Indeed it is then possible to encode the same information in the watermark and therefore to be able to detect any modification in the text of the document (date, amount, identity, etc.).
  • One application concerns contracts for which we want to be sure of the date of issue.
  • Another example with banknotes the serial number can be hidden in each note, so it is impossible to create counterfeit notes with different numbers because it would be necessary to generate each time the corresponding watermark.
  • Figure 1 the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The four peaks illustrate the effect of a symmetrical modulation of this signal obtained by locally increasing or decreasing its intensity.
  • the present invention proposes to asymmetrically modulate the color of the pixels.
  • Figure 2 gives an example of asymmetric modulation obtained by darkening the color of certain pixels. This modulation can then be positive or negative depending on whether color is added or removed.
  • the graph in the figure shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The two peaks illustrate the effect of an asymmetrical modulation of this signal obtained by only decreasing its intensity.
  • Figure 3 gives some examples of digital watermark images.
  • Another object of the present invention is therefore to propose a method for hiding and / or finding a digital watermark, characterized by the use of an asymmetrical modulation of the amplitude of a visible or invisible light component.
  • FIG. 1 illustrates an example of symmetrical modulation
  • FIG. 4 illustrates the implementation of the integrated process with a standard offset printing technique
  • FIG. 5 illustrates the implementation of the method with a separate offset printing step
  • FIG. 8 is a block diagram of the process for signing a material in three stages
  • - Figure 9 is a block diagram of the process for reading a uniform image signed in three stages; and - Figure 10 is a block diagram of the process for reading a non-uniform image signed in three stages.
  • FIG. 1 An example of symmetrical modulation is illustrated in Figure 1.
  • the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position.
  • the four peaks illustrate the effect of a symmetrical modulation of this signal obtained by locally increasing or decreasing its intensity.
  • FIG. 2 An example of asymmetric modulation is illustrated in Figure 2.
  • the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position.
  • the two peaks illustrate the effect of an asymmetrical modulation of this signal obtained by only decreasing its intensity.
  • One way of obtaining a positive asymmetric modulation consists in using an overprinting technique by printing the watermark over the own colors of the material and other information already printed and therefore without taking account of local variations in the colors on the surface of this material.
  • This approach requires that the values of the color components of the material can only be darkened during the signature since additional ink is added. Mathematically, this corresponds to a positive asymmetric modulation of the color of the points. In principle, this approach can be applied to any printing process. Some specifics of watermark printing may depend on the printing process. The specific cases of offset and inkjet type printing for achieving positive modulation are detailed below.
  • Figure 4 illustrates the implementation of the above method using positive modulation with an industrial printing technique of offset type in the case of simultaneous printing of the watermark.
  • a four-color printing 45 is carried out (for example for a packaging 40) which means that four different ink colors are used for each of the yellow masks 41, cyan 42, magenta 43 and black 44.
  • the digital watermark can have a single color, it is generally desirable to use one of the colors already selected for standard printing for the watermark.
  • Figure 4 shows how the different masks can then be applied.
  • the watermark printing is fully integrated into the standard industrial printing chain and therefore does not incur any additional cost.
  • the yellow mask can be used simultaneously for two different things: on the one hand it contains the yellow component of the image to be printed and on the other hand it contains the image of the watermark.
  • the IT tools used when flashing the offset film make this integration easy.
  • FIG. 5 Another possible alternative is to use a separate mask for the watermark as shown in Figure 5.
  • the watermark is overprinted in an additional step with a mask and possibly its own ink (here magenta) .
  • the mask 51 then defines the watermark points which are printed over the previously printed material 50.
  • This method although more costly to implement by the printer, has the advantage of being able to easily change the watermark during the production. This allows for example to apply a watermark identifying different countries of sale to a series of identical packages. It should be noted that when non-covering inks are used, it is also possible to print the final image over the digital watermark, as illustrated in Figure 6. In this case, the reverse process is used.
  • the watermark being previously printed 60 on the material, the final image being overprinted during an additional step.
  • the masks yellow 61, cyan 62, magenta 63 and black 64 are used to overprint the pattern.
  • the ink being transparent, the watermark 60 located under the pattern can still be detected in the final result 65.
  • FIG. 7 Another usable printing method is of the inkjet type as illustrated in FIG. 7.
  • the illustration shows an example of an inkjet printing system using four colors, yellow 71, cyan 72, magenta 73 and black 74, their print heads 75 and the printed material 70.
  • the watermark is overprinted on the material. Setting up an inkjet printer for printing a watermark is particularly simple since the vast majority of printer drivers automatically manage the mixing of colors to obtain a particular shade. The four-color decomposition step is therefore most often unnecessary. It should however be noted that, depending on the drivers and printers, it may sometimes be desirable to choose a watermark color corresponding to the basic colors of the printer, this in order to avoid obtaining dithered colors or printing problems. alignment between dots of different colors.
  • watermark printing can be simultaneous with the information or patterns intended to be printed normally. It is also possible to print the watermark separately, over or under the final design. In particular, text can be overprinted on the signed material itself, this text possibly being linked to the watermark. For example, the key figures of a contract can thus be hidden in the watermark of the paper and thus make it possible to guarantee its integrity.
  • Negative modulation can be achieved during simultaneous printing by following the same principle as described above because it is always possible to subtract color from the electronic file: on the pattern to be printed, the points corresponding to the watermark are then cleared up.
  • To achieve a separate printing with negative modulation it is however necessary to use a particular ink: for example, in the case of visible ink, one solution consists in using a covering type ink. The summary of different watermark printing possibilities is presented in the table below:
  • Size of the points this is the diameter of the watermark points obtained after printing.
  • the minimum dot size is set by printing technology. Values between 300 and 1200 dots per inch are common.
  • Color of the points Depending on the color, texture and possible patterns applied to the materials, certain colors may be more or less visible. For example, it is usual to use a yellow color for white backgrounds (separate or simultaneous positive modulation).
  • Density of the watermark This defines the ratio between the number of dots printed per unit area (also measured in dots). Typical values of 0.02 or less can be used. A very fine stitch size increases the density of the watermark.
  • Screening The screening technique (halftone) makes it possible to reproduce any color from the different fundamental colors. It is then preferable that the size of the screening is sufficiently fine compared to the size of the points.
  • Type of ink Non-visible substances can also be used.
  • the influence of some of these parameters is illustrated in Figure 3.
  • the watermark 1 is visible.
  • the lower visibility of watermark 2 is obtained by simultaneously decreasing the density and size of the dots.
  • the watermark 3 also has a clarification.
  • the main difficulty lies in the ability to find the asymmetrical watermark.
  • most tattoo techniques can extract information from the signed image without using the original image.
  • Certain techniques first make a prediction of what the original image was from the signed image and can then deduce what the signature is. This technique is still applicable in the present case.
  • the material has a uniform and known initial color, it is possible to suppress this prediction. This is particularly the case with a sheet of white paper.
  • This increases the reliability of the detection and therefore reduces the visibility of the watermark up to the extreme limit of sensitivity of an optical scanner. Consequently, this makes it very difficult to duplicate the signed material, for example by photocopying: in fact, the losses specific to any reproduction system generally weaken this signature below the detectability threshold.
  • One application is to include such a watermark on paper which one wishes to avoid copying, such as banknotes for example.
  • One embodiment of the invention consists in using as a basis a digital watermark algorithm of the spatial type with symmetric amplitude modulation, such as for example that described in [1].
  • c (k) ' c (k) + v.b.a (k) (1)
  • Equation (1) the set of points defined by vba (k) constitutes the watermark ( Figure 8, step 84) which is added to the original image c (k) to give the signed image c (k ) It is the latter which is then printed according to the present invention.
  • Equation 8 gives a block diagram of the complete method: the set of points constituting the watermark 85 is calculated 84 on the basis of the value of the bit to be hidden 81 and of the key 82 defining the random sequence a (k). The value of the points being positive or negative, as defined by equation (1). Equation (2) is equivalent to thresholding 86 the values of the watermark 85 while keeping only the positive values and then adding 88 these values 87 to the image to be signed 83 to obtain the signed image 89.
  • this technique is qualified as “asymmetric amplitude modulation”.
  • the sign of the modulation ba (k) being positive, the modulation is said to be positive.
  • Equation (2) It is also possible to obtain a negative modulation by printing a uniform color or "pierced” by the watermark. Equation (2) then becomes:
  • the new point value c (k) ' can be measured on the printed sheet using an optical scanner. Two cases then arise depending on whether the color of the material is uniform and known or not.
  • Figure 9 is a block diagram describing the process: the signed image obtained by scanner is subtracted from the original image in order to restore the watermark. The bit constituting the signature is then calculated, optionally, an additional filtering step can be carried out if visible information has been printed over the signed uniform image. The signed image 91 is previously filtered 92 in order to eliminate any noise (scratches, dirt, text printed over the watermark, etc.).
  • the image obtained 93 is then subtracted 94 from the original image 95 in order to extract the watermark 96.
  • the value of bit b is then found according to conventional watermark detection techniques, as described in article [5] M . Kutter, "Watermarking resisting to translation, rotation, and scaling.”, Proceedings of SPIE International Symposium on Voice, Video, and Data Communications, November 1998, which consists essentially of reversing equation (2) and statistically correlating the value bit b found 99 on several pixels k in order to guarantee good robustness to possible errors which may for example arise during the digital acquisition of the image.
  • This method can be generalized to several bits b and then makes it possible to code any digital information such as a number or a character string.
  • the second case is illustrated by the block diagram of FIG. 10 where the original image is predicted from the signed image, the signed image is subtracted from the predicted image in order to restore the watermark, the bit constituting the signature is then calculated.
  • a denoising filter 105 for example of the Wiener type, is used to make a prediction 106 of the original image o (k) from the signed image 101.
  • the difference 102 between these two images then constitutes the watermark 107 which can be decoded 103 using the key 108 to find the bit 104 in the same way as before ( Figure 9).
  • the prediction error being significantly greater than in the first case, the number of bits b coded in this way is systematically lower.
  • the implementation of the detection requires an optical scanner capable of scanning the document on which the watermark is printed. Since positioning on the scanner is never perfect, it is necessary to be able to find the information coded by the watermark after possible translations and rotations.
  • a suitable technique consists in using the method described by [5] which is based on an autocorrelated watermark (to compensate for rotations) and an intercorrelation technique (to compensate for translations).
  • the process can also be applied to sectors other than printing.
  • a laser to engrave metal surfaces, stones, ceramics, etc., and thus encode a digital watermark.
  • the applications concerned are then, for example, parts from the automobile or aeronautical industry or luxury objects in the jewelry or objects sectors. of values.

Abstract

A 'fragile' signature in the form of a numerical watermark is incorporated in a part or whole of the document. The watermark has asymmetric modulation of amplitude of a visible or invisible component. To detect the presence or absence of the signature the surface has to be of uniform color. Pre-treatment of the image is carried out in order to eliminate visible printed or engraved data which does not contain the watermark. During searching for the signature the image defining the original surface is predicted from the image of the signed surface. The signature can also be printed so that it is visible on the surface. During searching for the signature the numerical watermark is digitized by a scanner, or portable device. The non visible property of the ink is used to form the asymmetric modulation. Different signatures can be hidden in different regions of the surface.

Description

Procédé destiné à prévenir la contrefaçon ou l'altération d'une surface imprimée ou gravée.A method of preventing counterfeiting or altering a printed or engraved surface.
Domaine techniqueTechnical area
La présente invention concerne un procédé destiné à prévenir la contrefaçon ou l'altération d'une surface imprimée ou gravée.The present invention relates to a method for preventing counterfeiting or alteration of a printed or engraved surface.
Etat de la techniqueState of the art
Les systèmes usuels destinés à prévenir la contrefaçon ou l'altération de documents imprimés ou gravés peuvent être classés en différents groupes:The usual systems intended to prevent counterfeiting or alteration of printed or engraved documents can be classified into different groups:
• les hologrammes, les impressions de motifs spéciaux • les impressions avec encres spéciales• holograms, prints of special patterns • prints with special inks
• les codes utilisant des encres invisibles• codes using invisible inks
• les systèmes à puce• chip systems
Les hologrammes, motifs spéciaux et autres décorations sont difficiles à reproduire car leur réalisation nécessite un équipement spécial. Ils sont spécialement conçus pour interférer avec les systèmes de photocopie classique de telle sorte que la copie soit visiblement différente de l'original. Ces systèmes peuvent être contrôlés visuellement sans l'aide de dispositifs particuliers mais présentent l'inconvénient d'être coûteux, assez connus pour être reproduits sans problèmes par des experts en contrefaçon, et finalement leur visibilité nuit à l'esthétique de l'objet protégé (emballage de parfum par exemple). Leur visibilité est également la raison de leur efficacité limitée dans la mesure où un pirate peut facilement identifier l'élément de sécurité, soit pour le copier, soit pour l'effacer physiquement.Holograms, special patterns and other decorations are difficult to reproduce because their production requires special equipment. They are specially designed to interfere with conventional photocopying systems so that the copy is visibly different from the original. These systems can be visually controlled without the aid of special devices, but have the disadvantage of being expensive, well-known enough to be reproduced without problems by counterfeiting experts, and ultimately their visibility damages the aesthetics of the protected object. (perfume packaging for example). Their visibility is also the reason for their limited effectiveness since an attacker can easily identify the security element, either to copy it or to erase it physically.
Les impressions avec encres spéciales utilisent des propriétés chimiques particulières de l'encre pour fournir une réaction déterminée à une action particulière. Ainsi, les encres fluorescentes deviennent très lumineuses quand elles sont éclairées par une longueur d'onde particulière, certaines encres sont même invisibles à la lumière naturelle, d'autres encres changent de couleur en fonction de leur orientation ou de leur température (et peuvent se révéler en chauffant le papier avec un doigt), etc. Les encres spéciales ont comme point commun d'être particulièrement coûteuses et de nécessiter d'opérer des modifications dans la chaîne de production industrielle habituelle (masque supplémentaire pour l'offset par exemple). De plus, bien que plus robuste à la contrefaçon que le groupe précédent, il est également possible de reproduire leurs effets dans la mesure où le pirate peut contrôler par lui-même la fidélité de sa copie par rapport à l'original dès qu'il dispose du dispositif faisant réagir l'encre.Special ink printing uses special chemical properties of the ink to provide a specific reaction to a particular action. Thus, fluorescent inks become very bright when they are lit by a particular wavelength, some inks are even invisible to natural light, other inks change color according to their orientation or their temperature (and can be reveal by heating the paper with a finger), etc. Special inks have one thing in common: particularly expensive and necessitate making modifications in the usual industrial production chain (additional mask for offset for example). In addition, although more robust to counterfeiting than the previous group, it is also possible to reproduce their effects insofar as the pirate can control by himself the fidelity of his copy compared to the original as soon as he has the device reacting the ink.
Les codes utilisant des encres invisibles, à la différences des deux groupes précédents, permettent de cacher une information numérique. Ces codes peuvent être des caractères, des codes barres, des codes 2D, etc. En plus de son coût élevé et propre aux encres invisibles, ce système a deux inconvénients majeurs. D'une part, du fait de la nature des codes utilisés, il est localisé sur une certaine partie du document ou de l'emballage et il est donc possible de le détruire sans altérer la totalité de la surface. D'autre part, les codes utilisés ont toujours des particularités géométriques (barres, figures géométriques, caractères, etc) les identifiant clairement comme des dispositifs anti-copie. Cela facilite grandement la tache du pirate cherchant à révéler et à reproduire l'encre. De plus dès que le pirate sait réaliser cette reproduction, il détient ipso facto le moyen de reproduire le code.Codes using invisible inks, unlike the two previous groups, allow digital information to be hidden. These codes can be characters, bar codes, 2D codes, etc. In addition to its high cost and specific to invisible inks, this system has two major drawbacks. On the one hand, due to the nature of the codes used, it is located on a certain part of the document or of the packaging and it is therefore possible to destroy it without altering the entire surface. On the other hand, the codes used always have geometric characteristics (bars, geometric figures, characters, etc.) clearly identifying them as anti-copy devices. This greatly facilitates the task of the pirate seeking to reveal and reproduce the ink. In addition, as soon as the pirate knows how to make this reproduction, he ipso facto has the means to reproduce the code.
Finalement les systèmes basés sur des mémoires ou processeurs embarqués cumulent les inconvénients d'être très coûteux, inesthétiques et localisés. Leur application principale consiste plus à sécuriser une communication, ou à stocker dynamiquement une information plutôt qu'à distinguer un original d'une copie.Finally, systems based on on-board memories or processors combine the disadvantages of being very expensive, unattractive and localized. Their main application is more to secure a communication, or to dynamically store information rather than to distinguish an original from a copy.
L'un des buts de la présente invention est de remédier aux inconvénients des procédés connus permettant de prévenir la contrefaçon ou l'altération de documents imprimés ou gravés par voie numérique.One of the aims of the present invention is to remedy the drawbacks of known methods making it possible to prevent counterfeiting or alteration of documents printed or engraved by digital means.
A cet effet, la présente invention concerne un procédé destiné à prévenir la contrefaçon ou l'altération de documents imprimés ou gravés caractérisé par l'incorporation d'un filigrane numérique dans une partie ou dans l'ensemble du document. La technique du filigrane numérique, également connue sous le nom de tatouage numérique, est une technique permettant de cacher des informations de manière robuste et imperceptible dans des données multimédia telles que la musique, la vidéo, les images, les documents, etc. L'information qui est cachée s'appelle la signature. Cette signature peut être par exemple un numéro, un nom ou même une image. Après la protection des données multimédia avec un filigrane numérique on parle d'image signée, de vidéo signée, etc.To this end, the present invention relates to a method intended to prevent counterfeiting or alteration of printed or engraved documents characterized by the incorporation of a digital watermark in part or in the whole of the document. The digital watermark technique, also known as digital watermarking, is a technique for hiding information in a robust and imperceptible way in multimedia data such as music, video, images, documents, etc. The information that is hidden is called the signature. This signature can for example be a number, a name or even an image. After protecting multimedia data with a digital watermark, we speak of signed image, signed video, etc.
Jusqu'ici, la technique du filigrane numérique n'a été utilisée que dans le but de retrouver la signature sur une éventuelle copie, pour prouver l'origine de l'information.So far, the digital watermark technique has only been used to find the signature on a possible copy, to prove the origin of the information.
« Cacher » comporte un sens bien spécifique dans ce contexte : par exemple dans le cas d'une image, on changera légèrement la couleur de certains pixels, et dans le cas d'une musique on modifiera un peu le son de temps à autre."Hide" has a very specific meaning in this context: for example in the case of an image, we will slightly change the color of certain pixels, and in the case of music we will slightly modify the sound from time to time.
« Imperceptible » veut dire que les modifications introduites sont telles qu'un individu ne peut pas distinguer les données originales des données signées par ses propres sens. Par exemple, une image signée doit avoir exactement la même apparence qu'une image normale, une musique signée doit sembler tout à fait normale, de même pour une vidéo ou n'importe quelle autre donnée. Tout le problème consiste à faire en sorte qu'un ordinateur soit capable de détecter cette information cachée alors qu'elle échappe à nos sens. Il existe aussi des applications où un filigrane visible est acceptable voire même souhaitable. Cela permet notamment d'augmenter encore la robustesse et un contrôle visuel de la présence d'un filigrane. Le principe qui demeure est que le filigrane ne doit pas être dérangeant visuellement."Imperceptible" means that the changes introduced are such that an individual cannot distinguish the original data from the data signed by his own senses. For example, a signed image must have exactly the same appearance as a normal image, a signed music must appear completely normal, the same for a video or any other data. The whole problem is to make a computer capable of detecting this hidden information when it escapes our senses. There are also applications where a visible watermark is acceptable or even desirable. This allows in particular to further increase the robustness and a visual check for the presence of a watermark. The principle that remains is that the watermark should not be visually disturbing.
La «robustesse » d'un filigrane signifie que l'on doit pouvoir retrouver la signature après n'importe quelle manipulation de données signées. Prenons par exemple le cas d'une image signée : on doit pouvoir la comprimer, l'imprimer, la scanner ou la tourner sans jamais perdre la signature. De nombreuses publications ont été faites sur les différentes techniques permettant de cacher un filigrane dans une image, dans une vidéo ou un signal audio. En ce qui concerne les images, ces dernières peuvent se classer en fonction de la technique utilisée pour le marquage : certaines opèrent des modifications directement dans le domaine spatial (voir par exemple [1] M. Kutter, F. Jordan, F. Bossen, "Digital watermaking of color images using amplitude modulation", Journal of Electronic Imaging, vol. 7, n° 2, pp. 326-332, April 1998.), d'autres opèrent ces modifications dans un domaine transformé (par exemple le domaine fréquentiel) voire des domaines intermédiaires comme les ondelettes (voir [2] Shelby Pereira, Sviatoslav Voloshynovskiy and Thierry Pun, Optimized wavelet domain watermark embedding strategy using linear programming, In Harold H. Szu and Martin Vetterli eds., Wavelet Applications VII (part of SPIE AeroSense 2000), Orlando, Florida USA, April 26-28 2000.).The "robustness" of a watermark means that one must be able to find the signature after any manipulation of signed data. Take for example the case of a signed image: we must be able to compress, print, scan or rotate it without ever losing the signature. Many publications have been made on the various techniques allowing to hide a watermark in an image, in a video or an audio signal. With regard to images, the latter can be classified according to the technique used for marking: some operate modifications directly in the spatial domain (see for example [1] M. Kutter, F. Jordan, F. Bossen, "Digital watermaking of color images using amplitude modulation", Journal of Electronic Imaging, vol. 7, n ° 2, pp. 326-332, April 1998.), others operate these modifications in a transformed domain (for example the domain frequency) or even intermediate domains such as wavelets (see [2] Shelby Pereira, Sviatoslav Voloshynovskiy and Thierry Pun, Optimized wavelet domain watermark embedding strategy using linear programming, In Harold H. Szu and Martin Vetterli eds., Wavelet Applications VII (part of SPIE AeroSense 2000), Orlando, Florida USA, April 26-28 2000.).
Ces techniques peuvent également être utilisées pour le marquage de vidéo, moyennant certaines adaptations. D'autres techniques, spécifiquement dédiées au marquage de vidéo sont aussi possibles en définissant de nouveaux domaines transformés comme les sous-bandes 3D ou les vecteurs de mouvements (par exemple, voir [3] brevet US 5,960,081 , Video watermarking using motion vectors et [4] demande de brevet EP 0762417 A2, Video watermarking in the compressed domain).These techniques can also be used for video tagging, with certain adaptations. Other techniques, specifically dedicated to video marking are also possible by defining new transformed fields such as 3D sub-bands or motion vectors (for example, see [3] US patent 5,960,081, Video watermarking using motion vectors and [ 4] patent application EP 0762417 A2, Video watermarking in the compressed domain).
Comme on l'a déjà mentionné, la technique du filigrane numérique a été jusqu'ici utilisée dans le but de retrouver la signature sur une éventuelle copie pour prouver l'origine des informations présentes sur la copie, grâce à la présence du filigrane que l'on retrouve sur la copie. Ceci impliquait dans tous les cas l'utilisation d'un filigrane robuste.As already mentioned, the digital watermark technique has so far been used in order to find the signature on a possible copy to prove the origin of the information present on the copy, thanks to the presence of the watermark that the 'found on the copy. This in all cases involved the use of a robust watermark.
Dans le procédé de la présente invention, le but de l'incorporation du filigrane numérique sur la surface est différent, puisque sa présence est destinée à prévenir l'authentification ou l'altération de la surface concernée, c'est-à-dire de permettre d'apporter la preuve qu'il s'agit de la surface authentique si le filigrane est présent ou qu'il s'agit d'une copie ou que la surface a été altérée si le filigrane est absent. Dans le cas où le filigrane est incorporé à des fins d'authentification de la surface par rapport à des copies, la robustesse du filigrane doit être réduite de façon qu'une copie de la surface se traduise alors par un échec de la lecture du filigrane numérique. On parle alors de filigrane "fragile". Un exemple typique d'application consiste à empêcher la contrefaçon de papiers-valeurs comme les billets de banque. Dans le cas où le filigrane est incorporé afin d'éviter l'altération de tout ou partie de la surface, le filigrane peut être robuste ou fragile.In the method of the present invention, the purpose of incorporating the digital watermark on the surface is different, since its presence is intended to prevent authentication or alteration of the surface concerned, i.e. provide proof that this is the authentic surface if the watermark is present or that it is a copy or that the surface has been altered if the watermark is missing. In the case where the watermark is incorporated for the purpose of authenticating the surface against copies, the robustness of the watermark must be reduced so that a copy of the surface results in a failure to read the watermark digital. We then speak of a "fragile" watermark. A typical example of application consists in preventing the counterfeiting of securities such as banknotes. If the watermark is incorporated to avoid alteration of all or part of the surface, the watermark may be strong or fragile.
La présente invention réunit simultanément un ensemble de caractéristiques présentes seulement de manière isolée dans les systèmes connus destinés à prévenir la contrefaçon ou l'altération de documents imprimés ou gravés mentionnés plus haut :The present invention simultaneously combines a set of characteristics present only in isolation in the known systems intended to prevent counterfeiting or alteration of the printed or engraved documents mentioned above:
• Invisibilité Le filigrane est imprimé en utilisant des couleurs et des résolution imperceptibles à l'œil nu. Cela permet donc de protéger par exemple un emballage sans que son graphisme en soit altéré, ce qui est important pour des raisons marketing.• Invisibility The watermark is printed using colors and resolutions that are invisible to the naked eye. This therefore makes it possible to protect, for example, a package without its graphics being altered, which is important for marketing reasons.
• Non localité• Non locality
Le filigrane peut recouvrir la totalité de la surface d'un document imprimé. Il n'est donc pas possible de l'effacer sans altérer le document, par exemple en grattant la surface. En pratique, cette propriété permet par exemple d'éviter les marchés gris, c'est à dire les produits revendus par des distributeurs non autorisés. En effet, ces derniers effacent parfois le code (code 2D invisible par exemple) identifiant leur revendeur en « fraisant » la surface de l'emballage où le code est imprimé. • PrixThe watermark can cover the entire surface of a printed document. It is therefore not possible to erase it without altering the document, for example by scratching the surface. In practice, this property makes it possible, for example, to avoid gray markets, ie products sold by unauthorized distributors. Indeed, they sometimes erase the code (invisible 2D code for example) identifying their reseller by "milling" the surface of the packaging where the code is printed. • Price
Le filigrane est imprimé en utilisant des systèmes d'impression traditionnels. En ce qui concerne l'impression industrielle (offset, etc), il s'intègre totalement dans la chaîne de production et n'induit aucun coût supplémentaire. En ce qui concerne l'impression personnelle (jet d'encre, laser, etc), il est totalement compatible avec les imprimantes du commerce. Dans les deux cas, la lecture se fait avec un scanner digital standard. Ce faible prix ouvre des marchés nouveaux : d'une part en ce qui concerne l'impression industrielle, les emballages de produits de luxe ou pharmaceutiques, ainsi que les certificats, les chèques, les billets d'entrées, etc. D'autre part pour l'impression personnelle, il permet à n'importe qui possédant un équipement standard de créer et vérifier des documents sécurisés et personnalisés. Par exemple un médecin peut cacher le nom des médicaments prescrits dans le papier utilisé pour imprimer son ordonnance. Il est possible de programmer une imprimante pour qu'elle cache un filigrane dans tout document imprimé permettant ainsi d'identifier plus tard la date de l'impression, le nom de l'utilisateur, etc.The watermark is printed using traditional printing systems. Regarding industrial printing (offset, etc.), it is fully integrated into the production chain and does not incur any additional costs. Regarding personal printing (inkjet, laser, etc.), it is fully compatible with commercial printers. In both cases, the reading is done with a standard digital scanner. This low price opens up new markets: firstly for industrial printing, packaging for luxury or pharmaceutical products, as well as certificates, checks, entry tickets, etc. On the other hand for personal printing, it allows anyone with standard equipment to create and verify secure and personalized documents. For example, a doctor may hide the names of the drugs prescribed in the paper used to print the prescription. It is possible to program a printer so that it hides a watermark in any printed document thus allowing later identification of the date of printing, the name of the user, etc.
• Stockage d'information• Information storage
En plus d'authentifier l'original, le filigrane contient une information numérique (typiquement de plusieurs dizaines de bits par centimètres carrés) qui est encodée ou retrouvée à l'aide d'une clé. En pratique ce stockage permet par exemple de sécuriser une information imprimée en texte visible (donc susceptible d'être modifiée). En effet il est alors possible d'encoder la même information dans le filigrane et donc de pouvoir détecter toute modification dans le texte du document (date, montant, identité, etc.). Une application concerne les contrats dont on veut s'assurer de la date d'émission. Un autre exemple avec les billets de banque : le numéro de série peut être caché dans chaque billet, ainsi il est impossible de créer des faux billets avec des numéros différents car il faudrait pouvoir générer à chaque fois le filigrane correspondant.In addition to authenticating the original, the watermark contains digital information (typically several tens of bits per square centimeter) which is encoded or retrieved using a key. In practice, this storage makes it possible, for example, to secure information printed in visible text (therefore liable to be modified). Indeed it is then possible to encode the same information in the watermark and therefore to be able to detect any modification in the text of the document (date, amount, identity, etc.). One application concerns contracts for which we want to be sure of the date of issue. Another example with banknotes: the serial number can be hidden in each note, so it is impossible to create counterfeit notes with different numbers because it would be necessary to generate each time the corresponding watermark.
• Système de lecture et d'écriture à clé Afin de pouvoir créer et lire le filigrane, il faut utiliser la même clé. En contrôlant l'accès aux clés, on peut donc contrôler quand et par qui chaque filigrane est créé ou lu, ce qui est essentiel : en effet cela complique beaucoup le piratage consistant à créer un nouveau filigrane (le plus simple restant de copier un filigrane existant). D'autre part le pirate sera dans l'incapacité de vérifier qu'un filigrane a été copié avec succès (car pour le lire, il est nécessaire de connaître la clé utilisée pour le cacher). La sécurité offerte par ce système de clé est donc supérieure à celle d'une information imprimée par exemple avec une encre invisible et révélée par ultraviolet, où le pirate peut aisément vérifier et donc améliorer l'encre qu'il contrefait.• Key reading and writing system In order to create and read the watermark, the same key must be used. By controlling access to the keys, we can therefore control when and by whom each watermark is created or read, which is essential: indeed, this greatly complicates piracy consisting in creating a new watermark (the simplest remaining being to copy a watermark existing). On the other hand, the hacker will be unable to verify that a watermark has been successfully copied (because to read it, it is necessary to know the key used to hide it). The security offered by this key system is therefore greater than that of information printed for example with invisible ink and revealed by ultraviolet, where the pirate can easily check and therefore improve the ink that he is counterfeiting.
• Difficile à identifier visuellement Même en utilisant des dispositifs (filtres, microscopes) particuliers, il est difficile d'identifier la présence d'un filigrane car son aspect visuel se rapproche de celui du grain du papier. Il n'a pas de caractéristique géométrique simple et n'a de sens que pour le programme de détection et muni de la bonne clé. Pour tous les papiers de valeur qui font l'objet d'une analyse fine de la part des pirates, cette qualité est primordiale. • Difficile à copier• Difficult to identify visually Even using special devices (filters, microscopes), it is difficult to identify the presence of a watermark because its visual appearance is similar to that of the grain of the paper. It has no simple geometrical characteristic and has meaning only for the detection program and provided with the right key. For all the papers of value that are the subject of a fine analysis on the part of pirates, this quality is essential. • Difficult to copy
L'utilisation combinée de certaines couleurs Qaune sur fond blanc par exemple) et de hautes résolutions d'impression (1200 dpi par exemple) permet d'obtenir un filigrane difficile ou impossible à reproduire sur un équipement de copie classique.The combined use of certain Qaune colors on a white background for example) and high printing resolutions (1200 dpi for example) makes it possible to obtain a watermark that is difficult or impossible to reproduce on conventional copying equipment.
Les méthodes qui sont entièrement réalisées dans le domaine digital cachent généralement le filigrane en augmentant et en diminuant l'intensité des couleurs de certains points, ce qui signifie que certains pixels sont éclaircis alors que d'autres sont assombris, comme illustré sur la Figure 1 : le graphe montre la variation de luminance des pixels d'une image en fonction de leur position X et pour une position Y identique. Les quatre pics illustrent l'effet d'une modulation symétrique de ce signal obtenue en augmentant ou en diminuant localement son intensité.Methods that are fully performed in the digital realm generally hide the watermark by increasing and decreasing the color intensity of certain points, which means that some pixels are brightened while others are darkened, as shown in Figure 1 : the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The four peaks illustrate the effect of a symmetrical modulation of this signal obtained by locally increasing or decreasing its intensity.
Il est cependant certains cas où une modulation symétrique est impossible à réaliser, soit pour des raisons mathématiques (image à signer entièrement blanche ou noire) ou pratiques (liée à la technique d'impression).There are however certain cases where symmetrical modulation is impossible to achieve, either for mathematical reasons (image to be signed entirely white or black) or practical (linked to the printing technique).
La présente invention propose de moduler asymétriquement la couleur des pixels. La Figure 2 donne un exemple de modulation asymétrique obtenue en assombrissant la couleur de certains pixels. Cette modulation peut alors être positive ou négative selon que de la couleur est ajoutée ou retirée. Le graphe de la figure montre la variation de luminance des pixels d'une image en fonction de leur position X et pour une position Y identique. Les deux pics illustrent l'effet d'une modulation asymétrique de ce signal obtenue en diminuant uniquement son intensité. La Figure 3 donne quelques exemples d'images de filigrane numériques.The present invention proposes to asymmetrically modulate the color of the pixels. Figure 2 gives an example of asymmetric modulation obtained by darkening the color of certain pixels. This modulation can then be positive or negative depending on whether color is added or removed. The graph in the figure shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The two peaks illustrate the effect of an asymmetrical modulation of this signal obtained by only decreasing its intensity. Figure 3 gives some examples of digital watermark images.
Ainsi, un autre objet de la présente invention est de proposer un procédé pour cacher et/ou retrouver un filigrane numérique, caractérisé par l'utilisation d'une modulation asymétrique de l'amplitude d'une composante lumineuse visible ou invisible. Description détaillée de l'inventionAnother object of the present invention is therefore to propose a method for hiding and / or finding a digital watermark, characterized by the use of an asymmetrical modulation of the amplitude of a visible or invisible light component. Detailed description of the invention
La description qui suit, donnée à titre d'exemple, se réfère au dessin annexé sur lequel: - la Figure 1 illustre un exemple de modulation symétrique;The description which follows, given by way of example, refers to the appended drawing in which: FIG. 1 illustrates an example of symmetrical modulation;
- la Figure 2 illustre un exemple de modulation asymétrique;- Figure 2 illustrates an example of asymmetric modulation;
- la Figure 3 illustre des exemples de filigranes asymétriques;- Figure 3 illustrates examples of asymmetric watermarks;
- la Figure 4 illustre la mise en oeuvre du procédé intégré avec une technique d'impression offset standard; - la Figure 5 illustre la mise en œuvre du procédé avec une étape d'impression offset séparée;- Figure 4 illustrates the implementation of the integrated process with a standard offset printing technique; - Figure 5 illustrates the implementation of the method with a separate offset printing step;
- la Figure 6 illustre la mise en œuvre du procédé avec une étape d'impression offset séparée;- Figure 6 illustrates the implementation of the method with a separate offset printing step;
- la Figure 7 illustre la mie en œuvre du procédé avec une imprimante à jet d'encre;- Figure 7 illustrates the implementation of the method with an inkjet printer;
- la Figure 8 est un schéma bloc du procédé de signature d'un matériau en trois étapes;- Figure 8 is a block diagram of the process for signing a material in three stages;
- la Figure 9 est un schéma bloc du procédé de lecture d'une image uniforme signée en trois étapes; et - la Figure 10 est un schéma bloc du procédé de lecture d'une image non-uniforme signée en trois étapes.- Figure 9 is a block diagram of the process for reading a uniform image signed in three stages; and - Figure 10 is a block diagram of the process for reading a non-uniform image signed in three stages.
Un exemple de modulation symétrique est illustré à la Figure 1. Le graphe montre la variation de luminance des pixels d'une image en fonction de leur position X et pour une position Y identique. Les quatre pics illustrent l'effet d'une modulation symétrique de ce signal obtenue en augmentant ou en diminuant localement son intensité.An example of symmetrical modulation is illustrated in Figure 1. The graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The four peaks illustrate the effect of a symmetrical modulation of this signal obtained by locally increasing or decreasing its intensity.
Un exemple de modulation asymétrique est illustré à la Figure 2. Le graphe montre la variation de luminance des pixels d'une image en fonction de leur position X et pour une position Y identique. Les deux pics illustrent l'effet d'une modulation asymétrique de ce signal obtenue en diminuant uniquement son intensité. Impression du filigraneAn example of asymmetric modulation is illustrated in Figure 2. The graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The two peaks illustrate the effect of an asymmetrical modulation of this signal obtained by only decreasing its intensity. Watermark printing
Différentes stratégies sont envisageables pour imprimer un filigrane à modulation asymétrique, selon qu'il est positif ou négatif. De plus, il est possible de choisir soit une impression séparée, soit une impression simultanée à l'impression d'un autre motif visuel (fond, texte ou graphique).Different strategies can be envisaged for printing an asymmetrically modulated watermark, depending on whether it is positive or negative. In addition, it is possible to choose either a separate print or a print simultaneously with the printing of another visual motif (background, text or graphic).
Une manière d'obtenir une modulation asymétrique positive consiste à utiliser une technique de surimpression en imprimant le filigrane par-dessus les couleurs propres du matériau et autres informations déjà imprimées et donc sans tenir compte des variations locales des couleurs à la surface de ce matériau. Cette approche impose que les valeurs des composantes de couleur du matériau ne peuvent qu'être assombries lors de la signature puisque de l'encre supplémentaire est ajoutée. Mathématiquement, cela correspond à une modulation asymétrique positive de la couleur des points. Dans son principe, cette approche peut être appliquée à n'importe quel procédé d'impression. Certaines spécificités de l'impression du filigrane peuvent dépendre du procédé d'impression. Les cas particuliers de l'impression de type offset et jet d'encre pour la réalisation d'une modulation positive sont détaillés ci-dessous.One way of obtaining a positive asymmetric modulation consists in using an overprinting technique by printing the watermark over the own colors of the material and other information already printed and therefore without taking account of local variations in the colors on the surface of this material. This approach requires that the values of the color components of the material can only be darkened during the signature since additional ink is added. Mathematically, this corresponds to a positive asymmetric modulation of the color of the points. In principle, this approach can be applied to any printing process. Some specifics of watermark printing may depend on the printing process. The specific cases of offset and inkjet type printing for achieving positive modulation are detailed below.
La Figure 4 illustre la mise en œuvre du procédé ci-dessus utilisant une modulation positive avec une technique d'impression industrielle de type offset dans le cas d'une impression simultanée du filigrane. Dans cet exemple, une impression quadrichromie 45 est réalisée (par exemple pour un emballage 40) ce qui signifie que quatre couleurs d'encre différentes sont utilisées pour chacun des masques jaune 41 , cyan 42, magenta 43 et noir 44. Le filigrane numérique pouvant comporter une couleur unique, il est en général souhaitable d'utiliser pour le filigrane une des couleurs déjà sélectionnées pour l'impression standard. La Figure 4 montre comment les différents masques peuvent alors être appliqués. Dans ce cas, l'impression du filigrane s'intègre totalement dans la chaîne d'impression industrielle standard et n'induit donc aucun coût supplémentaire. Par exemple, le masque jaune peut être utilisé simultanément pour deux choses différentes : d'une part il contient la composante jaune de l'image à imprimer et d'autre part il contient l'image du filigrane. Les outils informatiques utilisés lors du flashage du film offset permettent de réaliser facilement cette intégration.Figure 4 illustrates the implementation of the above method using positive modulation with an industrial printing technique of offset type in the case of simultaneous printing of the watermark. In this example, a four-color printing 45 is carried out (for example for a packaging 40) which means that four different ink colors are used for each of the yellow masks 41, cyan 42, magenta 43 and black 44. The digital watermark can have a single color, it is generally desirable to use one of the colors already selected for standard printing for the watermark. Figure 4 shows how the different masks can then be applied. In this case, the watermark printing is fully integrated into the standard industrial printing chain and therefore does not incur any additional cost. For example, the yellow mask can be used simultaneously for two different things: on the one hand it contains the yellow component of the image to be printed and on the other hand it contains the image of the watermark. The IT tools used when flashing the offset film make this integration easy.
Une autre alternative possible consiste à utiliser un masque séparé pour le filigrane comme illustré sur la Figure 5. Dans ce cas, le filigrane est surimprimé lors d'une étape supplémentaire avec un masque et éventuellement une encre qui lui est propre (ici le magenta). Le masque 51 définit alors les points du filigrane qui sont imprimés par-dessus le matériau préalablement imprimé 50. Cette méthode, bien que plus coûteuse à mettre en œuvre par l'imprimeur, présente l'avantage de pouvoir aisément changer le filigrane lors de la production. Cela permet par exemple d'appliquer un filigrane identifiant différents pays de vente à une série d'emballages identiques. Il est à noter que lorsque des encres de type non couvrantes sont utilisées, il est également possible d'imprimer l'image finale pardessus le filigrane digital, comme illustré sur la Figure 6. Dans ce cas, c'est le procédé inverse qui est utilisé, le filigrane étant préalablement imprimé 60 sur le matériau, l'image finale étant surimprimée lors d'une étape supplémentaire. Les masques jaune 61 , cyan 62, magenta 63 et noir 64 sont utilisés pour surimprimer le motif. L'encre étant transparente, le filigrane 60 situé sous le motif peut encore être détecté dans le résultat final 65.Another possible alternative is to use a separate mask for the watermark as shown in Figure 5. In this case, the watermark is overprinted in an additional step with a mask and possibly its own ink (here magenta) . The mask 51 then defines the watermark points which are printed over the previously printed material 50. This method, although more costly to implement by the printer, has the advantage of being able to easily change the watermark during the production. This allows for example to apply a watermark identifying different countries of sale to a series of identical packages. It should be noted that when non-covering inks are used, it is also possible to print the final image over the digital watermark, as illustrated in Figure 6. In this case, the reverse process is used. used, the watermark being previously printed 60 on the material, the final image being overprinted during an additional step. The masks yellow 61, cyan 62, magenta 63 and black 64 are used to overprint the pattern. The ink being transparent, the watermark 60 located under the pattern can still be detected in the final result 65.
Un autre procédé d'impression utilisable est de type jet d'encre comme illustré par la Figure 7. L'illustration montre un exemple de système d'impression à jet d'encre utilisant quatre couleurs, jaune 71 , cyan 72, magenta 73 et noir 74, leurs têtes d'impression 75 et le matériau imprimé 70. Le filigrane est surimprimé sur le matériau. La mise en œuvre d'une imprimante à jet d'encre pour l'impression d'un filigrane est particulièrement simple dans la mesure où la grande majorité des pilotes d'imprimantes gèrent automatiquement le mélange des couleurs permettant d'obtenir une teinte particulière. L'étape de décomposition quadrichromique est donc le plus souvent inutile. Il faut cependant noter que, dépendant des pilotes et des imprimantes, il peut parfois être souhaitable de choisir une couleur de filigrane correspondant à des couleurs fondamentales de l'imprimante, ceci afin d'éviter d'obtenir des couleurs tramées ou des problèmes d'alignement entre des points de différentes couleurs. Comme avec l'impression offset, l'impression du filigrane peut être simultanée avec les informations ou motifs destinés à être imprimés normalement. Il est également possible d'imprimer le filigrane séparément, pardessus ou par-dessous le motif final. En particulier, du texte peut être surimprimé sur le matériau signé lui-même, ce texte pouvant éventuellement être lié au filigrane. Par exemple, les chiffres clés d'un contrat peuvent ainsi être cachés dans le filigrane du papier et permettre ainsi d'en garantir l'intégrité.Another usable printing method is of the inkjet type as illustrated in FIG. 7. The illustration shows an example of an inkjet printing system using four colors, yellow 71, cyan 72, magenta 73 and black 74, their print heads 75 and the printed material 70. The watermark is overprinted on the material. Setting up an inkjet printer for printing a watermark is particularly simple since the vast majority of printer drivers automatically manage the mixing of colors to obtain a particular shade. The four-color decomposition step is therefore most often unnecessary. It should however be noted that, depending on the drivers and printers, it may sometimes be desirable to choose a watermark color corresponding to the basic colors of the printer, this in order to avoid obtaining dithered colors or printing problems. alignment between dots of different colors. As with offset printing, watermark printing can be simultaneous with the information or patterns intended to be printed normally. It is also possible to print the watermark separately, over or under the final design. In particular, text can be overprinted on the signed material itself, this text possibly being linked to the watermark. For example, the key figures of a contract can thus be hidden in the watermark of the paper and thus make it possible to guarantee its integrity.
La réalisation d'une modulation négative peut être réalisée lors d'une impression simultanée en suivant le même principe que décrit précédemment car il est toujours possible de soustraire de la couleur au niveau du fichier électronique: sur le motif à imprimer, les points correspondant au filigrane sont alors éclaircis. Pour réaliser une impression séparée avec une modulation négative, il est par contre nécessaire d'utiliser une encre particulière : par exemple, dans le cas d'une encre visible, une solution consiste à utiliser une encre de type couvrante. La synthèse de différentes possibilités d'impression du filigrane est présentée dans le tableau ci-dessous :Negative modulation can be achieved during simultaneous printing by following the same principle as described above because it is always possible to subtract color from the electronic file: on the pattern to be printed, the points corresponding to the watermark are then cleared up. To achieve a separate printing with negative modulation, it is however necessary to use a particular ink: for example, in the case of visible ink, one solution consists in using a covering type ink. The summary of different watermark printing possibilities is presented in the table below:
Paramètres contrôlant la visibilité du filigraneParameters controlling the visibility of the watermark
Quels que soit le type de modulation ou d'impression choisis, la visibilité finale du filigrane ainsi que sa fragilité à la duplication est contrôlée par un ensemble commun de paramètres :Whatever the type of modulation or printing chosen, the final visibility of the watermark as well as its fragility when duplicated is controlled by a common set of parameters:
• Taille des points : il s'agit du diamètre des points du filigrane obtenus après impression. La taille minimale des points est fixée par la technologie d'impression. Des valeurs entre 300 et 1200 points par pouces sont courantes.• Size of the points: this is the diameter of the watermark points obtained after printing. The minimum dot size is set by printing technology. Values between 300 and 1200 dots per inch are common.
Plus la taille des points est petites, moins le filigrane est visible.The smaller the size of the points, the less visible the watermark.
• Couleur des points : En fonction de la couleur, de la texture et des motifs éventuels appliqués au matériaux, certaines couleurs peuvent être plus ou moins visibles. Par exemple, il est usuel d'utiliser une couleur jaune pour des fonds blancs (modulation positive séparée ou simultanée).• Color of the points: Depending on the color, texture and possible patterns applied to the materials, certain colors may be more or less visible. For example, it is usual to use a yellow color for white backgrounds (separate or simultaneous positive modulation).
• Densité du filigrane : Cette dernière définit le ratio entre le nombre de points imprimés par unité de surface (mesurée également en points). Des valeurs typiques de 0.02 ou moins peuvent être utilisées. Une taille de point très fine permet d'augmenter la densité du filigrane.• Density of the watermark: This defines the ratio between the number of dots printed per unit area (also measured in dots). Typical values of 0.02 or less can be used. A very fine stitch size increases the density of the watermark.
• Quantité d'encre : Lorsque le procédé d'impression le permet, il est intéressant de jouer sur la quantité d'encre utilisée pour imprimer chaque point.• Amount of ink: When the printing process allows, it is interesting to play on the amount of ink used to print each point.
• Tramage : La technique de tramage (demi-teintes) permet de reproduire n'importe quelle couleur à partir des différentes couleurs fondamentales. Il est alors préférable que la taille du tramage soit suffisamment fine par rapport à la taille des points.• Screening: The screening technique (halftone) makes it possible to reproduce any color from the different fundamental colors. It is then preferable that the size of the screening is sufficiently fine compared to the size of the points.
• Type d'encre : Des substances non visibles peuvent également être utilisées.• Type of ink: Non-visible substances can also be used.
L'influence de certains de ces paramètres est illustrée sur la Figure 3. Le filigrane 1 est visible. La visibilité plus faible du filigrane 2 est obtenue en diminuant simultanément la densité et la taille des points. Le filigrane 3 comporte en plus un éclaircissement.The influence of some of these parameters is illustrated in Figure 3. The watermark 1 is visible. The lower visibility of watermark 2 is obtained by simultaneously decreasing the density and size of the dots. The watermark 3 also has a clarification.
Lecture du filigraneReading the watermark
La difficulté principale réside dans la capacité à retrouver le filigrane asymétrique. D'une manière générale, la majorité des techniques de tatouage peuvent extraire l'information de l'image signée sans utiliser l'image originale. Certaines techniques réalisent d'abord une prédiction de ce qu'était l'image originale à partir de l'image signée et peuvent ensuite en déduire quelle est la signature. Cette technique est encore applicable dans le cas présent. Dans le cas où le matériau possède une couleur initiale uniforme et connue, il est possible de supprimer cette prédiction. C'est en particulier le cas d'une feuille de papier blanc. Cela permet d'augmenter la fiabilité de la détection et donc de diminuer la visibilité du filigrane jusqu'à l'extrême limite de sensibilité d'un scanner optique. En conséquence, cela rend très difficile la duplication du matériau signé, par exemple par photocopie : en effet, les pertes propres à tout système de reproduction affaiblissent en général cette signature au-dessous du seuil de détectabilité. Une application consiste à inclure un tel filigrane sur des papiers dont on souhaite éviter la copie, comme des billets de banque par exemple.The main difficulty lies in the ability to find the asymmetrical watermark. Generally speaking, most tattoo techniques can extract information from the signed image without using the original image. Certain techniques first make a prediction of what the original image was from the signed image and can then deduce what the signature is. This technique is still applicable in the present case. In the case where the material has a uniform and known initial color, it is possible to suppress this prediction. This is particularly the case with a sheet of white paper. This increases the reliability of the detection and therefore reduces the visibility of the watermark up to the extreme limit of sensitivity of an optical scanner. Consequently, this makes it very difficult to duplicate the signed material, for example by photocopying: in fact, the losses specific to any reproduction system generally weaken this signature below the detectability threshold. One application is to include such a watermark on paper which one wishes to avoid copying, such as banknotes for example.
Afin d'augmenter la fiabilité de la détection, il est également possible de coder la signature en utilisant la différence entre des paires de pixels et de calculer ensuite la moyenne de ces différences. D'un point de vue statistique, cela augmentera la corrélation de la détection avec pour résultat une signature plus fiable.In order to increase the reliability of the detection, it is also possible to code the signature using the difference between pairs of pixels and then calculate the average of these differences. From a statistical point of view, this will increase the correlation of the detection, resulting in a more reliable signature.
Réalisation de l'inventionRealization of the invention
Une mode de réalisation de l'invention consiste à utiliser comme base un algorithme de filigrane numérique de type spatial à modulation symétrique d'amplitude, comme par exemple celui décrit dans [1]. On parle de modulation symétrique d'amplitude d'un signal lorsque la valeur du signal est augmentée en certains points et diminuées en d'autre points. Dans cette technique, une composante de couleur d'un ensemble de pixels c(k) est modifiée d'une valeur v correspondant à l'amplitude de la modulation et en fonction du signe du bit ={-1 ,1} à cacher ainsi que d'un générateur aléatoire a(k) défini par une clé et donnant deux valeurs {-1 ,1}. c(k)' = c(k) + v.b.a(k) (1)One embodiment of the invention consists in using as a basis a digital watermark algorithm of the spatial type with symmetric amplitude modulation, such as for example that described in [1]. We speak of symmetrical amplitude modulation of a signal when the signal value is increased at certain points and decreased at other points. In this technique, a color component of a set of pixels c (k) is modified by a value v corresponding to the amplitude of the modulation and according to the sign of the bit = {- 1, 1} to hide thus that of a random generator a (k) defined by a key and giving two values {-1, 1}. c (k) '= c (k) + v.b.a (k) (1)
Dans l'équation (1), l'ensemble des points défini par v.b.a(k) constitue le filigrane (Figure 8, étape 84) qui est ajouté à l'image originale c(k) pour donner l'image signée c(k) C'est cette dernière qui est alors imprimée selon la présente invention.In equation (1), the set of points defined by vba (k) constitutes the watermark (Figure 8, step 84) which is added to the original image c (k) to give the signed image c (k ) It is the latter which is then printed according to the present invention.
Dans le cas d'une modulation asymétrique positive (filigrane en surimpression par exemple), ce n'est plus l'image c(k)' mais le filigrane lui-même v.b.a(k) qui est imprimé par-dessus une image c(k). En effet, la composante c du support (bleu, luminance, etc..) a déjà une valeur initiale o(k) et ne peut qu'être augmentée lors de la surimpression. La formule suivante est alors appliquée : Si b.a(k) > 0 alors c(k)' = o(k) + v.b.a(k) sinon c(k)' = o(k) (2) La Figure 8 donne un schéma bloc du procédé complet : l'ensemble des points constituant le filigrane 85 est calculé 84 à partir de la valeur du bit à cacher 81 et de la clé 82 définissant la séquence aléatoire a(k). La valeur des points étant positives ou négatives, comme défini par l'équation (1). L'équation (2) est équivalente à seuiller 86 les valeurs du filigrane 85 en ne conservant que les valeurs positives puis à ajouter 88 ces valeurs 87 à l'image à signer 83 pour obtenir l'image signée 89. Par comparaison avec la formule (1) correspondant à une modulation symétrique de l'amplitude selon le signe de b.a(k), cette technique est qualifiée de «modulation asymétrique d'amplitude ». De plus, le signe de la modulation b.a(k) étant positif, la modulation est dite positive.In the case of a positive asymmetric modulation (watermark overlay for example), it is no longer the image c (k) 'but the watermark itself vba (k) which is printed over an image c ( k). Indeed, the component c of the support (blue, luminance, etc.) already has an initial value o (k) and can only be increased during the overprinting. The following formula is then applied: If ba (k)> 0 then c (k) '= o (k) + vba (k) otherwise c (k)' = o (k) (2) FIG. 8 gives a block diagram of the complete method: the set of points constituting the watermark 85 is calculated 84 on the basis of the value of the bit to be hidden 81 and of the key 82 defining the random sequence a (k). The value of the points being positive or negative, as defined by equation (1). Equation (2) is equivalent to thresholding 86 the values of the watermark 85 while keeping only the positive values and then adding 88 these values 87 to the image to be signed 83 to obtain the signed image 89. By comparison with the formula (1) corresponding to a symmetrical modulation of the amplitude according to the sign of ba (k), this technique is qualified as “asymmetric amplitude modulation”. In addition, the sign of the modulation ba (k) being positive, the modulation is said to be positive.
Dans le cas où le filigrane est réalisé par une impression simultanée, le procédé peut encore être amélioré en opérant de manière à ce que le filigrane domine sur les valeurs du masque original. Mathématiquement, ce concept se formalise de la manière suivante : c(k)' = 0 si b.a(k) < 0 c(k)' = M sinon où M est la valeur maximum autorisée par le masque, c'est-à-dire la valeur correspondant à la couleur du document avant signature. L'équation montre clairement la modulation positive par rapport à zéro et illustre également le fait qu'aux positions où le filigrane est caché, l'image sous-jacente n'est pas prise en compte (domination du filigrane sur les valeurs originales). Ce procédé présente l'avantage que le nombre effectif de points contribuant au filigrane augmente, pouvant atteindre un facteur 2 dans le meilleur cas.In the case where the watermark is produced by simultaneous printing, the process can be further improved by operating so that the watermark dominates over the values of the original mask. Mathematically, this concept is formalized as follows: c (k) '= 0 if ba (k) <0 c (k)' = M otherwise where M is the maximum value authorized by the mask, i.e. say the value corresponding to the color of the document before signing. The equation clearly shows the positive modulation with respect to zero and also illustrates the fact that at the positions where the watermark is hidden, the underlying image is not taken into account (dominance of the watermark over the original values). This method has the advantage that the effective number of points contributing to the watermark increases, up to a factor of 2 in the best case.
Il est également possible d'obtenir une modulation négative en imprimant une couleur uniforme u « percée » par le filigrane. L'équation (2) devient alors :It is also possible to obtain a negative modulation by printing a uniform color or "pierced" by the watermark. Equation (2) then becomes:
S/' b.a(k) < 0 alors c(k)' = o(k) + u - v.b.a(k) sinon c(k)' = o(k) (3)S / ' ba (k) <0 then c (k)' = o (k) + u - vba (k) otherwise c (k) '= o (k) (3)
Dans tous les cas (modulation asymétrique positive ou négative), si le générateur aléatoire a(k) génère le même nombre de valeurs positives et négatives, il en résulte que, statistiquement, la moitié des pixels c(k) est modifiée. Si la valeur de v est choisie suffisamment faible et que la finesse d'impression est suffisamment haute, l'impression de ces points peut être faite de manière invisible.In all cases (asymmetric positive or negative modulation), if the random generator a (k) generates the same number of positive and negative values, it follows that, statistically, half of the pixels c (k) is modified. If the value of v is chosen sufficiently low and the print fineness is sufficiently high, the printing of these dots can be done invisibly.
La nouvelle valeur des points c(k)' peut être mesurée sur la feuille imprimée en utilisant un scanner optique. Deux cas se présentent alors selon que la couleur du matériau est uniforme et connue ou non.The new point value c (k) 'can be measured on the printed sheet using an optical scanner. Two cases then arise depending on whether the color of the material is uniform and known or not.
Dans le premier cas, l'information b est alors aisément retrouvée dans la mesure où o(k)=Constante, v et a(k) sont tous connus par avance. La multiplicité des points modifiés crée une redondance permettant d'assurer la robustesse de la technique au bruit par corrélation statistique. La Figure 9 est un schéma bloc décrivant le procédé : l'image signée obtenue par scanner est soustraite de l'image originale afin de restituer le filigrane. Le bit constituant la signature est alors calculé, optionellement, une étape supplémentaire de filtrage peut-être réalisée si des informations visibles ont été imprimées par dessus l'image uniforme signée. L'image signée 91 est préalablement filtrée 92 afin d'éliminer d'éventuels bruits (rayures, salissures, texte imprimé par dessus le filigrane, etc). L'image obtenue 93 est alors soustraite 94 de l'image originale 95 afin d'extraire le filigrane 96. La valeur du bit b est alors retrouvée selon les techniques classiques de détection de filigrane, comme décrit dans l'article [5] M. Kutter, "Watermarking resisting to translation, rotation, and scaling.", Proceedings of SPIE International Symposium on Voice, Video, and Data Communications, November 1998, et qui consiste essentiellement à inverser l'équation (2) et corréler statistiquement la valeur du bit b retrouvé 99 sur plusieurs pixels k afin de garantir une bonne robustesse aux erreurs éventuelles pouvant par exemple survenir lors du l'acquisition numérique de l'image.In the first case, the information b is then easily found insofar as o (k) = Constant, v and a (k) are all known in advance. The multiplicity of the modified points creates a redundancy making it possible to ensure the robustness of the technique to noise by statistical correlation. Figure 9 is a block diagram describing the process: the signed image obtained by scanner is subtracted from the original image in order to restore the watermark. The bit constituting the signature is then calculated, optionally, an additional filtering step can be carried out if visible information has been printed over the signed uniform image. The signed image 91 is previously filtered 92 in order to eliminate any noise (scratches, dirt, text printed over the watermark, etc.). The image obtained 93 is then subtracted 94 from the original image 95 in order to extract the watermark 96. The value of bit b is then found according to conventional watermark detection techniques, as described in article [5] M . Kutter, "Watermarking resisting to translation, rotation, and scaling.", Proceedings of SPIE International Symposium on Voice, Video, and Data Communications, November 1998, which consists essentially of reversing equation (2) and statistically correlating the value bit b found 99 on several pixels k in order to guarantee good robustness to possible errors which may for example arise during the digital acquisition of the image.
Cette méthode est généralisable à plusieurs bits b et permet alors de coder n'importe quelle information numérique comme un numéro ou une chaîne de caractères.This method can be generalized to several bits b and then makes it possible to code any digital information such as a number or a character string.
Le deuxième cas est illustré par le schéma bloc de la figure Figure 10 où l'image originale est prédite à partir de l'image signée, l'image signée est soustraite de l'image prédite afin de restituer le filigrane, le bit constituant la signature est alors calculé. Un filtre de débruitage 105, par exemple de type Wiener, est utilisé pour réaliser une prédiction 106 de l'image originale o(k) à partir de l'image signée 101. La différence 102 entre ces deux images constitue alors le filigrane 107 qui peut être décodé 103 en utilisant la clé 108 pour retrouver le bit 104 de la même manière que précédemment (Figure 9). L'erreur de prédiction étant notablement plus importante que dans le premier cas, le nombre de bits b codés de cette manière est systématiquement inférieur.The second case is illustrated by the block diagram of FIG. 10 where the original image is predicted from the signed image, the signed image is subtracted from the predicted image in order to restore the watermark, the bit constituting the signature is then calculated. A denoising filter 105, for example of the Wiener type, is used to make a prediction 106 of the original image o (k) from the signed image 101. The difference 102 between these two images then constitutes the watermark 107 which can be decoded 103 using the key 108 to find the bit 104 in the same way as before (Figure 9). The prediction error being significantly greater than in the first case, the number of bits b coded in this way is systematically lower.
Dans la pratique il peut également être utile d'imprimer des informations visibles par-dessus le filigrane numérique. C'est le cas par exemple d'une feuille blanche de papier qui comporte un filigrane numérique et par dessus laquelle est imprimé un texte. Ceci est réalisable en choisissant des couleurs ou des intensités distinctes pour le filigrane et pour les informations visibles. Il est ensuite possible de filtrer l'image avant la détection du filigrane (Figure 9, étape 92) pour différencier le filigrane du texte imprimé et ainsi éliminer les parties ne comportant pas le filigrane. Une méthode consiste par exemple à utiliser la composante bleu pour le filigrane et à imprimer le texte du document en noir.In practice it may also be useful to print visible information over the digital watermark. This is the case for example of a white sheet of paper which has a digital watermark and on top of which a text is printed. This can be done by choosing different colors or intensities for the watermark and for the visible information. It is then possible to filter the image before detecting the watermark (Figure 9, step 92) to differentiate the watermark from the printed text and thus eliminate the parts that do not have the watermark. One method is, for example, to use the blue component for the watermark and to print the text of the document in black.
Finalement, la mise en œuvre de la détection requiert un scanner optique capable de numériser le document sur lequel le filigrane est imprimé. Le positionnement sur le scanner n'étant jamais parfait, il est nécessaire de pouvoir retrouver l'information codé par le filigrane après d'éventuelles translations et rotations. Une technique convenable consiste à utiliser la méthode décrite par [5] qui est basée sur un filigrane auto-correllé (pour compenser les rotations) et une technique d'inter- corrélation (pour compenser les translations).Finally, the implementation of the detection requires an optical scanner capable of scanning the document on which the watermark is printed. Since positioning on the scanner is never perfect, it is necessary to be able to find the information coded by the watermark after possible translations and rotations. A suitable technique consists in using the method described by [5] which is based on an autocorrelated watermark (to compensate for rotations) and an intercorrelation technique (to compensate for translations).
Autres applicationsOther applications
Le procédé peut également être appliqué à d'autres secteurs que l'impression. Par exemple, il est possible d'utiliser un laser pour graver des surfaces métalliques, des pierres, de la céramique, etc, et encoder ainsi un filigrane digital. Les applications concernées sont alors par exemple les pièces de l'industrie automobile ou aéronautique ou des objets de luxe dans les secteurs de la joaillerie ou des objets de valeurs. On peut également imaginer de cacher des filigranes sur des CD-ROM ou CD audio, sur la face sérigraphiée ou sur la face gravée (encre ou laser). The process can also be applied to sectors other than printing. For example, it is possible to use a laser to engrave metal surfaces, stones, ceramics, etc., and thus encode a digital watermark. The applications concerned are then, for example, parts from the automobile or aeronautical industry or luxury objects in the jewelry or objects sectors. of values. We can also imagine hiding watermarks on CD-ROMs or audio CDs, on the screen-printed side or on the engraved side (ink or laser).

Claims

Revendications claims
1. Procédé destiné à prévenir la contrefaçon ou l'altération d'une surface imprimée ou gravée, caractérisé par l'incorporation d'une signature sous la forme d'un filigrane numérique dans une partie ou dans l'ensemble du document.1. Method for preventing counterfeiting or alteration of a printed or engraved surface, characterized by the incorporation of a signature in the form of a digital watermark in part or in the whole of the document.
2. Procédé selon la revendication 1 , caractérisé en ce que l'on incorpore un filigrane numérique dit "fragile".2. Method according to claim 1, characterized in that one incorporates a digital watermark called "fragile".
3. Procédé selon l'une des revendications 1 ou 2, caractérisé en ce que l'on incorpore un filigrane numérique à modulation asymétrique de l'amplitude d'une composante lumineuse visible ou invisible.3. Method according to one of claims 1 or 2, characterized in that one incorporates a digital watermark with asymmetrical modulation of the amplitude of a visible or invisible light component.
4. Procédé selon la revendication 3, caractérisé en ce que pour détecter la présence ou non de la signature sur la surface, on prend en compte l'hypothèse que la surface est de couleur uniforme.4. Method according to claim 3, characterized in that to detect the presence or not of the signature on the surface, the assumption is made that the surface is of uniform color.
5. Procédé selon la revendication 4, caractérisé en ce l'on effectue un prétraitement de l'image afin d'éliminer des informations visibles imprimées ou gravées et ne comportant pas le filigrane.5. Method according to claim 4, characterized in that a preprocessing of the image is carried out in order to eliminate visible information printed or engraved and not comprising the watermark.
6. Procédé selon la revendication 3, caractérisé en ce que lors de la recherche de la signature, l'image définissant la surface originale est prédite à partir de l'image de la surface signée.6. Method according to claim 3, characterized in that during the search for the signature, the image defining the original surface is predicted from the image of the signed surface.
7. Procédé selon la revendication 3, caractérisé en ce que des informations liées à la signature sont également imprimées de manière visible sur la surface.7. Method according to claim 3, characterized in that information related to the signature is also visibly printed on the surface.
8. Procédé selon la revendication 3, caractérisé en ce que lors de la recherche de la signature, on digitalise le filigrane numérique au moyen d'un scanner. 8. Method according to claim 3, characterized in that when searching for the signature, the digital watermark is digitized by means of a scanner.
9. Procédé selon la revendication 6, caractérisé en ce que lors de la recherche de la signature, on digitalise le filigrane numérique au moyen d'un détecteur portable.9. Method according to claim 6, characterized in that during the search for the signature, the digital watermark is digitized by means of a portable detector.
10. Procédé selon la revendication 3, caractérisé en ce l'on utilise une propriété non visible de l'encre pour réaliser la modulation asymétrique.10. Method according to claim 3, characterized in that a non-visible property of the ink is used to carry out the asymmetrical modulation.
11. Procédé selon l'une des revendication précédentes, caractérisé en ce que l'on cache des signatures différentes dans différentes régions de la surface.11. Method according to one of the preceding claim, characterized in that different signatures are hidden in different regions of the surface.
12. Procédé selon l'une des revendication précédentes, caractérisé en ce que la surface est un document et en ce que l'on cache des signatures différentes sur les faces du document.12. Method according to one of the preceding claim, characterized in that the surface is a document and in that different signatures are hidden on the faces of the document.
13. Application du procédé selon la revendication 2, éventuellement combinée avec les caractéristiques de l'une des revendications 3 à 12 en vue de permettre l'authentification du dit papier-valeur.13. Application of the method according to claim 2, optionally combined with the features of one of claims 3 to 12 in order to allow the authentication of said value paper.
14. Application du procédé selon l'une des revendications 1 à 12 pour prévenir l'altération d'une surface imprimée ou gravée, telle qu'un emballage, un certificat, un contrat, un chèque ou un objet de luxe, et permettre le cas échéant la détection d'une telle altération.14. Application of the method according to one of claims 1 to 12 to prevent alteration of a printed or engraved surface, such as a packaging, a certificate, a contract, a check or a luxury item, and allow the if necessary, the detection of such an alteration.
15. Procédé pour cacher et/ou retrouver une signature sous la forme d'un filigrane numérique, caractérisé par l'utilisation d'une modulation asymétrique de l'amplitude d'une composante lumineuse visible ou invisible.15. Method for hiding and / or finding a signature in the form of a digital watermark, characterized by the use of asymmetrical modulation of the amplitude of a visible or invisible light component.
16. Procédé selon la revendication 15, caractérisé en ce que la modulation asymétrique est réalisée par impression du filigrane.16. Method according to claim 15, characterized in that the asymmetric modulation is carried out by printing the watermark.
17. Procédé selon la revendication 15, caractérisé en ce que pour rechercher la signature le filigrane numérique est digitalisé. 17. The method of claim 15, characterized in that to search for the signature the digital watermark is digitized.
EP01964793A 2000-09-20 2001-09-17 Method for preventing counterfeiting or alteration of a printed or engraved surface Expired - Lifetime EP1319219B1 (en)

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CH183200 2000-09-20
CH18322000 2000-09-20
PCT/CH2001/000560 WO2002025599A1 (en) 2000-09-20 2001-09-17 Method for preventing counterfeiting or alteration of a printed or engraved surface

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CN1252653C (en) 2006-04-19
US7684088B2 (en) 2010-03-23
CN1475001A (en) 2004-02-11
EP1319219B1 (en) 2010-11-17
ATE488822T1 (en) 2010-12-15
US20040013285A1 (en) 2004-01-22
EP2261867A3 (en) 2012-12-19
EP2261867A2 (en) 2010-12-15
DK1319219T3 (en) 2011-02-21
WO2002025599A1 (en) 2002-03-28
EP2261867B1 (en) 2018-07-18
DE60143487D1 (en) 2010-12-30
ES2356598T3 (en) 2011-04-11

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