EP0178232A1 - Identity document protected against falsification and method for manufacturing the same - Google Patents

Abstract

The document includes graphical indications with at least two levels of light absorption, comprising alphanumeric information carried in clear, specific to the holder and / or to the document and possibly a figurative part, the indications appearing on a screen background, the surface of the document is broken down into a network of macropixels each having a determined average absorption level, and each macropixel is in turn constituted by a matrix of micropixels each having an absorption chosen from at least two levels and distributed so as to maintain the absorption average of each macropixel and to constitute the frame which reproduces at microscopic scale at least part of the specific indications.

Description

The invention relates to identity documents of the type comprising alphanumeric information carried in clear, specific to the holder and / or to the document, as well as frequently a figurative part, on a screen background. A particularly important application is constituted by documents, such as identity card and credit card, bearing specific information to the bearer, some of which are alphanumeric (name and first names, etc.) and generally represented by signs materialized by two levels of absorption or reflection of light, that is to say a single contrast (black on white for example) and others are figurative (photography for example) and represented by a number of levels much greater than two.

A screen background is commonly used to complicate the falsification of documents by scraping and substitution of indications. However, known screening techniques have drawbacks either the frame is simple and clearly visible and, in this case, can be reconstructed, or else it has a level of complexity which makes it practically impossible to verify its state by simple visual examination of the document. .

The invention aims to provide an identity document of the type defined above, the frame, repetitive and covering the entire document, has, with at least part of the alphanumeric indications, a correlation preventing modification of said part without a disappearance of the correlation which can be detected by a short visual examination.

To this end, the invention provides a document of the type defined above, comprising graphical indications and generally, graphs with at least two levels of light absorption, the surface of the document. being broken down into a network of macroscopic pixels (or macropixels) each having a determined average level of absorption, characterized in that each macropixel is constituted in turn by a matrix of elementary pixels or micropixels each having an absorption chosen from at least two (and generally 2 ^p ) levels and distributed so as to maintain the average absorption of each macropixel and to constitute a frame reproducing on a microscopic scale at least part of the indications specific to the document.

We see that any falsification will destroy the correlation: if the date of birth is modified on an identity document, it is enough to detect fraud either to examine the frame under the falsified characters, or to compare information (the date by example) represented by the macropixels with the corresponding information (which must be identical) reproduced by the micropixels in the frame. This verification can be done by examination with a magnifying glass, the micropixels being able to form alphanumeric indications which are then visible, in the form of 5 × 7 matrices of micropixels of 20 _N m × 20 μm for example.

When the identity document only contains alphanumeric indications, it is generally sufficient to have 4 levels of light absorption for micropixels, since a letter or a number always occupies less than half of the matrix of micropixels which represented. A single contrast (black on white or vice versa) may even be sufficient in some cases. On the other hand, the figurative parts and in particular the photographs require between 16 and 64 levels of absorption (gray levels) to be acceptable. It is then necessary to have a contrast quantization scale, for micropixels, having a number of levels much greater than 2.

We see that the invention involves being able to represent each macropixel of an alphanumeric element visible to the naked eye by a microscopic alphanumeric character whose average absorption is the same as that of the macropixel represented in contrast between two absorption levels only . For this to be possible it is necessary that, among the levels available to constitute the micropixels, at least two correspond respectively to stronger and weaker light absorptions than those which belong to the absorption range which the macropixels can take. This implies that, for a black to white impression of micropixels, macropixels only take gray values: in other words, the inscriptions will appear in dark gray on light gray, the dark gray being the same on all graphemes. of the same frame character.

In the case of graphic indications, such as a photograph, comprising a very wide absorption dynamic, going from black to white, it will be necessary in a first processing step to compress the absorption dynamic according to an arbitrary law, chosen however so as not to distort the images.

In an advantageous mode, because it is relatively simple, of implementing the invention, each macropixel contains a microscopic alphanumeric element and constitutes the basic "block" for the constitution of the alphanumeric characters. In return, the definition of these characters is then limited by the size of the macropixels, which will each represent for example 6 × 8 = 48 micropixels. Another solution, more complicated to implement but making it possible to improve the definition, consists in decomposing each macropixel containing an alphanumeric character of frame in micropixel having absorptions determined so as to improve the definition of the document.

The invention also provides a method of manufacturing identity documents comprising clear alphanumeric information, and possibly a figurative part, on a screen background, characterized in that the contrast dynamics of the graphic information to be reproduced for compression are compressed. reduce to a contrast range lower than that which can be obtained at the micropixel level; we decompose the graphic indications into macropixels having a dimension greater than or equal to that of micropixels, we determine, in each macropixel, the optical density to be given to each micropixel to represent at the microscopic scale a raster character in each macropixel and leave unchanged its overall contrast, and we print the micropixels on the document.

• Les figures 1 à 4 sont des schémas montrant respectivement des indications graphiques à reproduire sur un document constitué par 5 macropixels accolés ; un exemple de trame à insérer dans le document ; les indications macroscopiques après compression de dynamique de contraste ; et la représentation tramée des indications macroscopiques sur le document.
• La figure 5 est un graphique montrant une échelle de détermination du type de représentation à adopter pour un caractère de trame.
• La figure 6 montre, à grande échelle une représentation possible de la lettre M après tramage.
• La figure 7 montre un fragment de la lettre A représentée par tramage suivant une variante de réalisation de l'invention.
• La figure 8 est un schéma synoptique de principe d'un appareil de saisie de données en vue de la mise en oeuvre du procédé suivant l'invention.
• La figure 9 est un schéma synoptique d'un appareil de génération de pixels et d'impression utilisable pour la mise en oeuvre de l'invention.

The invention will be better understood on reading the following description of particular embodiments of the invention, given by way of non-limiting example. The description refers to the accompanying figures in which:

• Figures 1 to 4 are diagrams respectively showing graphical indications to be reproduced on a document consisting of 5 adjoining macropixels; an example of a frame to insert in the document; macroscopic indications after compression of dynamic contrast; and the raster representation of the macroscopic indications on the document.
• FIG. 5 is a graph showing a scale for determining the type of representation to be adopted for a frame character.
• FIG. 6 shows, on a large scale, a possible representation of the letter M after screening.
• FIG. 7 shows a fragment of the letter A represented by screening according to an alternative embodiment of the invention.
• Figure 8 is a block diagram of a data entry apparatus for the implementation of the method according to the invention.
• Figure 9 is a block diagram of a pixel generation and printing apparatus usable for the implementation of the invention.

Before giving a complete description of the representation used by the invention in the most general case, we will consider a simple case, that where the macroscopic indications to be reproduced on the document are constituted by five adjoining macropixels having a regularly increasing light absorption , from white to black. These five macropixels 10 ₁ , 10 ₂ , 10 ₃ , 10 ₄ , 10 can be considered as the initial image. They have been shown in FIG. 1 by adjacent rectangles, increasingly tight points indicating the successive levels of gray. Each of them will be represented on the document by a matrix of 6 x 8 micropixels, each matrix representing an alphanumeric character of the frame, on 5 x 7 micropixels. These characters in the frame reproduce part of the alphanumeric indications represented by the macropixels on the document and therefore visible to the naked eye. In the case shown in Figure 2, it is the word MATRA, which will be given by the frame repeatedly.

The image which will appear with the naked eye on the document cannot be the initial image (figure 1) going from white to black but a corrected image (figure 3) presenting a reduced dynamic, going from very light gray (macropixel 12 ₁ ) very dark gray (macropixel 12 ₅ ). With a magnifying glass, the macropixels 14 will appear, due to the screening, with the constitution shown in FIG. 4. Each matrix of micropixels 14 will have the same average absorption as the corresponding macropixel 12 of the corrected image and will be made up of micropixels each having a absorption chosen from n values which, in the cases represented, are five in number, this time going from white to black.

We will now describe in detail first a possible mode of compression of the light absorption contrast scale, then the determination of the gray levels of the micropixels as a function of the alphanumeric character to be represented by the macropixel and of the quantification levels. available, ranging from white to black. It should also be understood that the words white, black and gray are used here only for the convenience of the disclosure and that the invention would also be applicable to a color document.

Compression of the absorption scale.

• 0 = point noir
• 1 = point blanc

• on doit modifier la dynamique des niveaux de gris afin que l'échelle ne s'étende qu'entre deux valeurs intermédiaires, par exemple
• I'i = 0,05, se substituant à Ii mini = 0 min
• I'i = 0,95, se substituant à Ii maxi = 1 max

The first step in processing graphic information, when the latter is available in a black-to-white scale, consists in modifying the dynamics of the image to allow writing of raster characters with non-zero contrast inside. the lightest and darkest macropixels. If we assume that the light reflection (gray level) Ii of each micropixel is between 0 and 1:

• 0 = black point
• 1 = white point

• we must modify the gray level dynamics so that the scale only extends between two intermediate values, for example
• I'i = 0.05, replacing Ii mini = 0 min
• I'i = 0.95, replacing Ii max = 1 max

The law matching the gray level i in the transformed scale to the original level Ii can be:

Each macropixel, whether it belongs to an image or to an alphanumeric character, will thus have a level of gray which will never reach white or black, which can on the contrary be printed on the scale of the micropixel.

Macropixel screening

• - le niveau de gris commun des graphèmes du caractère,
• - le niveau de gris du fond sur lequel apparaissent les graphèmes.

Each macropixel, of determined level of reflection or optical density, is then represented by a character formed by a matrix of micropixels having one or the other of the two levels of optical reflection. These micropixels are so large that they are not visible to the naked eye. The plot character plot being imposed, the available parameters are:

• - the common gray level of the character graphemes,
• - the gray level of the background on which the graphemes appear.

The condition to be fulfilled is that the mean value of optical reflection is equal to i.

We will consider the particular case where each macropixel consists of m = 6 x 8 micropixels and where this macropixel contains an alphanumeric character.

We must first determine what is the gray level of the macropixel, that is to say of the character to be represented which can be written in dark on light (positive contrast) or in light on dark (negative contrast).

If the graphemes have n micropixels and the latter are black, the average gray level will be:

In negative contrast, the graphemes being written in white on black, the average gray level will be:

In the case for example of the letter A (figure 2) the graphemes represent n = 18 micropixels in a matrix of m = 48 micropixels.

For each frame character to represent, we can therefore establish a scale of the type shown in figure 5, on which appear the average gray levels 0.05 and 0.95 which correspond to the gray limits of the macropixels to be represented, and the values Ii and Ii characterizing the frame character to be placed in the macropixel.

The mode of representation of the frame character, using two levels among several which are available (and go from black to white) will then depend on that of the ranges 18, 20, 22 and 24 (figure 5) in which is found the average gray level of the macropixel to represent.

1st case: range 18 (very dark macropixel)

c'est-à-dire pour la lettre A :

We then start from the character written in negative contrast (on a black background) and we lighten the graphemes in order to bring the average gray level of this screened macropixel to the value I'i. In the case of a matrix of n = 48 micropixels, we obtain a contrast I of the character on a black background, by giving the gray level of the graphemes the value:

that is to say for the letter A:

We thus have a representation of the letter A of the genus shown for the last letter of the word MATRA in FIG. 4.

2nd case: track 20

We start again from the character written in negative contrast and we lighten the background, to which we give a gray level defined by the formula

The character contrast is then 1 - 1

3rd case range 22

This time we start from the character written in positive contrast and we darken the background to darken the macropixel.

The gray level of the elementary background pixels will be chosen to the value:

4th case: range 24 (very clear macropixel)

We start from the written character in positive contrast by clarifying the graphemes. The gray level of the elementary pixels of the character is chosen equal to:

The character contrast is then 1 -1

The representation is then of the kind shown for the first letter A in FIG. 4.

The result of the screening of the document appears on figure 6, which shows on a large scale the representation obtained of the letter M which, from black on white that it was in the original document is transformed into a letter where the graphemes appear in dark gray on a light gray background, at least with the naked eye. Each of the macropixels in the 6 x 8 matrix occupied by the letter and by the space between two successive letters contains a raster character, in dark gray on a black background in the case of graphropic macropixels, in very light gray on a white background for the background. The characters in the frame reproduce, on a microscopic scale, those which will appear on the document as a whole. We see in particular the word "MATRA" reappear and fragments of address.

FIG. 7 shows a fragment of the letter A as it is represented by screening according to an alternative embodiment of the invention. In the embodiment of FIG. 7, the macropixels are reduced to the size of the micropixels, instead of being each made up of an example of 48 micropixels such as that indicated at 48. The definition is then very improved, which is particularly interesting for the reproduction of figurative parts. It can in particular be noted that each letter intended to be visible to the naked eye is coded on 30 × 48 micropixels.

On the other hand, it becomes more difficult to calculate the gray levels of the micropixels after screening, if it is desired that the average gray levels, calculated by groups of pixels, remain unchanged after screening.

To avoid excessive complication in this case, it is then possible to content ourselves with modifying the gray level of the points constituting the frame (micropixels) by adding or subtracting from the gray level of the corresponding pixel, in the initial image, a constant value. The operation is an addition or a subtraction depending on whether the gray level of the pixel of the initial image is less than 0.5 or more than 0.5.

As an example of an embodiment, it can be indicated that satisfactory results are obtained when the document (identity card for example) consists of micropixels of 20 x 20 p, each macropixel consisting of 6 x 8 micropixels and each character alphanumeric readable occupying 6 x 8 macropixels. In general, an alphanumeric or graphic height between 1 and 5 mm will be satisfactory.

To avoid unauthorized reproduction of the document by photography, watermarked paper can be used as a support or a watermark can be included inside a plastic protection for the document, insofar as this protection cannot be removed from the document without irreversible damage to the latter.

In addition, colored documents can be obtained by various techniques, in particular the use of a medium sensitive to color, the use of a document pre-printed with colored pads or patterns and the use of plastic protection. on which are transparent colored areas.

• - établissement d'un bordereau contenant les indications alphanumériques et fourniture d'une photo par le candidat, ou bien introduction directe des données alphanumériques par l'opérateur et prise de photographie sur place, l'ensemble des données étant de toute façon numérisé et stocké sur le même support de mémorisation
• - génération des micropixels par un calculateur rapide qui doit calculer la valeur moyenne des pixels macroscopiques, générer la trame et calculer la valeur des pixels élémentaires en temps réel suivant un algory- thme déterminé, et commander l'impression
• - impression par un système rapide, qui sera généralement à prisme tournant et faisceau laser modulé par des moyens acousto-optiques.

The production of the document which has just been described can be carried out by various methods. However, these processes will generally include a series of common steps:

• - establishment of a list containing the alphanumeric indications and supply of a photo by the candidate, or else direct introduction of the alphanumeric data by the operator and taking of photographs on the spot, all the data being in any case digitized and stored on the same storage medium
• - generation of micropixels by a fast calculator which must calculate the average value of macroscopic pixels, generate the frame and calculate the value of elementary pixels in real time according to a determined algorithm, and order printing
• - Printing by a fast system, which will generally be with a rotating prism and a laser beam modulated by acousto-optical means.

Given the high cost of the printing apparatus itself, it will often be useful to divide the manufacturing device into two parts. The first part is made up of a device for entering data, digitizing information and storing on a transportable medium. The second part consists of the calculation and printing apparatus. This latter device, operating in deferred time, can process the storage media from a large number of data entry devices.

FIG. 8 shows, by way of example, a possible constitution of an apparatus for entering and recording data, usable in particular for the establishment of identity cards.

The device, the basic structure of which is shown in FIG. 8, constitutes an autonomous terminal, a copy of which can be installed in each center. administrative in order to collect information at the source.

The apparatus of FIG. 8 comprises a management member 30 comprising a microprocessor 32 and a character generator 34, connected to input / output members. In general, these organs will notably include those which will now be described.

The management body is connected to two video cameras 36 and 38 respectively provided to provide an image of the face and the fingerprint of the applicant. A video multiplexer 40 makes it possible to display, on a television monitor 42, one or the other of the images supplied by the cameras 36 and 38. A second multiplexer 44 makes it possible to orient towards a storage member 48, represented under form of a video recorder, the information supplied by the cameras and that which comes from an operator console 50 provided with a data entry keyboard. If a video recorder is used, the images are advantageously recorded on the video channel, while the alphanumeric information coded by the character generator 34 is recorded simultaneously on the soundtrack.

The device can be supplemented by a printer which provides a copy of the information recorded by the operator and which can be validated by the requester, for example by opposition of a signature or a fingerprint. A badge reader can also be provided, authorizing the entry of data only by an operator who has previously introduced his identification badge and typed a password known to him alone.

The recording thus produced can then be transported for use by the pixel generation and printing apparatus.

This device can have the general constitution shown in Figure 9, many other constitutions being possible. The device shown diagrammatically in FIG. 9 comprises a bus 52 to which input-output members and processor members are connected. When the apparatus is intended to receive the information in the form of videotape recording, the apparatus comprises a videotape interface 54 connected to the videotape recorder 56. A microprocessor card 58 also connected to the bus processes the data entered using a operator keyboard 60 and restores the information to be stored on a display member, such as a printer 62. The information concerning a document to be produced read by the video recorder 56 is stored in a random access memory 64. A capacity of 256 k.bytes is generally sufficient to store all of the information corresponding to an identity card.

The means for determining the frame, that is to say the gray level to be given to each micropixel, comprises an address sequencer 66 comprising a random access memory. This buffer memory will store the text which must be reproduced repeatedly in the frame, consisting of a maximum of 256 bytes, coded in binary, and the available levels of gray going from black to white, coded on 8 bits for example.

The sequencer receives, this time from the microprocessor 58, on the one hand the row and column indications of each micropixel, in succession, and on the other hand the parameters chosen for the production. The sequencer is controlled by a clock which gives the printing rate of successive dots and determines the content of the frame associated with each line of micropixels in turn. A correspondence table addressable by the sequencer will make it possible to supply the value of the micropixels corresponding to each line to the restitution device 70 which may be either of the direct printing on paper type or of the photographic type.

• - l'échelle des niveaux de gris,
• - les dimensions de la matrice de définition des caractères de la trame (c'est-à-dire le nombre de micropixels dans un macropixel, dans le sens horizontal et le sens vertical)
• - les commandes nécessaires au séquenceur,
• - le préchargement du compteur de texte de trame, permettant de piloter l'organisation de la trame dans le sens horizontal et le sens vertical.

The process implemented is then as follows: each time that the elements of a new card to be produced appear, the microprocessor card loads the characters of the text to be inserted in the form of a frame into the random access memory of 256 alphanumeric characters, at the same time as the value of a parameter indicating the length of the frame text. The operation will then take place at a rate fixed by a clock incorporated in the restorer 70. This clock supplies pulses at the rate of printing of the dots of a line and of line return pulses. Line return pulses are deviated by a value such that only part of the line time is used for the transmission of information concerning the micropixels to be printed. During this line length time, the data transmitted to the restorer 70 are transcribed on the support, for example paper. The rest of the time is ignored by the dispatcher. It is used by the microprocessor card which manages the system. During this duration of the line period, the microprocessor card loads into the sequencer:

• - the grayscale scale,
• - the dimensions of the matrix for defining the characters of the frame (that is to say the number of micropixels in a macropixel, in the horizontal direction and the vertical direction)
• - the commands necessary for the sequencer,
• - the preloading of the frame text counter, making it possible to control the organization of the frame in the horizontal direction and the vertical direction.

• - la police de caractères, avec la définition associée (nombre de micropixels dans un macropixel),
• - la dimension de la carte d'identité à réaliser,
• - la définition de l'image, puisque les niveaux de gris qui la constituent sont mis à jour à chaque ligne de micropixels,
• - la définition des caractères visibles à l'oeil nu, indépendamment de la police de caractère constituant la trame.

With this software-based command, you can easily modify:

• - the font, with the associated definition (number of micropixels in a macropixel),
• - the size of the identity card to be produced,
• - the definition of the image, since the gray levels which constitute it are updated with each line of micropixels,
• - the definition of the characters visible to the naked eye, independently of the typeface constituting the frame.

• - le niveau de gris moyen de la carte à un emplacement déterminé, c'est-à-dire pour macropixels donnés,
• - les paramètres de définition des caractères de la trame (c'est-à-dire les dimensions de ces caractères en micropixels),
• - le type de caractères à imprimer.

The correspondence table 68 is provided for determining the video of the renderer 70 as a function of several parameters which are:

• - the average gray level of the map at a determined location, that is to say for given macropixels,
• - the parameters for defining the characters of the frame (that is to say the dimensions of these characters in micropixels),
• - the type of characters to be printed.

This table must therefore have a large dimension, if at least a high number of gray levels and a large number of different characters are desired. If for example one wishes to have 64 gray levels, in order to have a good reproduction of the figurative parts and to be able to restore both Latin characters and other characters (for example Arabic), a table of 500 k.mots could be necessary. This table could be constituted by a programmable read only memory, receiving as input a code representative of the character (7 bits), a code representing the average gray level (6 bits) and a code representative of the font (6 bits). At the output, the table provides in sequence, on 6 bits in case 64 gray levels are available, a signal representative of the absorption of successive micropixels.

The invention is susceptible of numerous variants. It makes it possible to produce documents in characters other than Latin (the same machine can alternately print several types of characters or multiple fonts). The document produced may have a frame coded according to a simple code allowing very rapid verification using a calculator containing the decoding key.

Claims (7)

1. Identity document that is difficult to falsify and includes graphical indications with at least two levels of light absorption, comprising alphanumeric or more generally graphical information, shown in clear, specific to the holder and / or to the document and possibly a figurative part, the indications appearing on a screen background, characterized in that the surface of the document is broken down into a network of macropixels each having a determined average level of absorption and in that each macropixel is in turn constituted by a matrix of micropixels each having an absorption chosen from at least two levels and distributed so as to maintain the average absorption of each macropixel and to constitute the frame which reproduces at microscopic scale at least part of the specific indications. 2. Document according to claim 1, characterized in that each macropixel is constituted by a matrix of micropixels in sufficient number to allow to represent an alphanumeric or graphic character of frame in each macropixel. 3. Document according to claim 1 or 2, characterized in that the alphanumeric and graphic information are formed from macropixels decomposed into micropixels having light absorptions determined so as to improve the definition of the alphanumeric and graphic indications. 4. Document according to claim 1, 2 or 3, characterized in that each alphanumeric or graphic character of frame is produced on a matrix of several micropixels and in that each alphanumeric or graphic character carried in clear and visible to the naked eye corresponds to the surface occupied by several alphanumeric characters or raster graphics, with a height between 1 mm and 5 mm. 5. Document according to claim 1, characterized in that each alphanumeric character of frame is represented in a macropixel by graphemes having a determined absorption on a background having another determined absorption, so that each macropixel contains only two levels of absorption from light. 6. Document according to claim 5, characterized in that the absorption levels available to constitute the macropixels are between 4 and 64, the extreme levels being constituted by white and black, the graphic indications carried by the document then appearing in a range from very light gray to very dark gray. 7. Method for manufacturing an identity document comprising graphical indications with at least two levels of light absorption consisting of alphanumeric information carried in clear, specific to the holder or to the document, and possibly by a figurative part, on a screen background, characterized in that the contrast dynamic of the graphic information to be reproduced is compressed in order to reduce it to a range of contrast less than that which can be obtained at the level of micropixels; we decompose the graphic indications into macropixels having a dimension greater than or equal to that of micropixels, we determine, in each macropixel, the optical density to be given to each micropixel to represent at the microscopic scale a raster character in each macropixel and leave unchanged its overall contrast, and we print the micropixels on the document.

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