EP4015228A1 - Method for manufacturing a safety device and associated safety device - Google Patents

Abstract

The invention essentially relates to a method for manufacturing a security device, comprising the following steps:- obtaining (S310) at least a first, a second, a third and/or a fourth grayscale image from of a digital color image:-- said first grayscale image comprising a plurality of pixels each having a gray level representing a first color component of the corresponding pixel of the digital color image, and-- said second grayscale image comprising a plurality of pixels each having a grayscale representing a second color component of the corresponding pixel of the digital color image,- forming (S320) said at least first and second grayscale images on a physical medium of said security device.

Description

Technical area

The present invention relates to the field of optical security devices, and relates more particularly to the manufacture of such a security device.

The invention applies in a non-exclusive manner to security and/or physical identity documents, such as a passport, an identity card, a driving licence, a residence permit, etc.

Prior technique

In known manner, a security and/or identity document can include security data making it possible to authenticate the bearer of said document, such as a photograph of the face of the authorized bearer of said document.

Such security data is printed on the document so as to be visible to an operator responsible for verifying the identity of the bearer of the document. The operator can thus check these security data. The agent can for example verify that the photograph printed on the document corresponds to the bearer of the document.

Today there is a need for a security device allowing simple and playful authentication while being difficult to counterfeit.

The document US 2018/264866 A1 describes a method of generating a mask and a printed image that are embedded in a banknote.

Disclosure of Invention

• obtention d'une image numérique en couleurs, ladite image numérique en couleurs comprenant une pluralité de pixels, la couleur de chaque pixel étant définie selon au moins une première, une deuxième et une troisième composantes de couleur d'un espace colorimétrique,
• obtention d'au moins une première et une deuxième images en niveaux de gris à partir de ladite image numérique en couleurs :
  • -- ladite première image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant la première composante de couleur du pixel correspondant de l'image numérique en couleurs, et
  • -- ladite deuxième image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant la deuxième composante de couleur du pixel correspondant de l'image numérique en couleurs,
• formation desdites au moins une première et deuxième images en niveaux de gris sur un support physique dudit dispositif de sécurité.

The present invention relates to a method of manufacturing a security device, comprising the following steps:

• obtaining a digital image in colors, said digital image in colors comprising a plurality of pixels, the color of each pixel being defined according to at least a first, a second and a third color component of a colorimetric space,
• obtaining at least a first and a second gray level image from said digital color image:
  • -- said first grayscale image comprising a plurality of pixels each having a grayscale representing the first color component of the corresponding pixel of the digital color image, and
  • -- said second gray level image comprising a plurality of pixels each having a gray level representing the second color component of the corresponding pixel of the digital color image,
• formation of said at least one first and second grayscale images on a physical medium of said security device.

The gray level of each pixel of the first gray level image represents the luminance of the first color component of the corresponding pixel of the digital color image. Additionally, the gray level of each pixel of the second gray level image represents the luminance of the second color component of the corresponding pixel of the digital color image.

The first and second images in gray levels allow simple and playful authentication, typically using a telephone equipped with a camera and the appropriate color image recomposition software, while being difficult to reproduce. The security device is thus difficult to counterfeit.

• ladite troisième image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant la troisième composante de couleur du pixel correspondant de l'image numérique en couleurs, et
• ladite quatrième image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant les première, deuxième et troisièmes composantes de couleur du pixel correspondant de l'image numérique en couleurs,
  ladite troisième image en niveaux de gris et/ou de ladite quatrième image en niveaux de gris étant formées sur le support physique dudit dispositif de sécurité.

In a particular embodiment, the method further comprises a step of obtaining a third and/or a fourth grayscale image from said digital color image:

• said third grayscale image comprising a plurality of pixels each having a grayscale representing the third color component of the corresponding pixel of the digital color image, and
• said fourth grayscale image comprising a plurality of pixels each having a grayscale representing the first, second and third color components of the corresponding pixel of the digital image in colors,
  said third grayscale image and/or said fourth grayscale image being formed on the physical medium of said security device.

In a particular embodiment, the forming step comprises, for each of said at least one first, second, third and/or fourth grayscale images, reproducing the pixels of said image so that the reproduced pixels are positioned contiguously, each of said at least one first, second, third and/or fourth grayscale images being positioned at a different location on the physical medium of the security device.

In a particular embodiment, the step of forming comprises reproducing the pixels of said at least one first, second, third and/or fourth grayscale images such that the reproduced pixels of each grayscale image are positioned in an interlaced manner with the pixels of the other images in gray levels, said at least one first, second, third and/or fourth images in gray levels thus being interlaced in the same location of the physical medium of the security device.

In a particular embodiment, the method further comprises a step of obtaining an array of lenses, the array of lenses being configured to allow the viewing of each of said at least one first, second, third and/or fourth images different grayscale depending on different viewing angle.

The grayscale images, etched at different angles under the lens array, make the security device difficult to replicate.

In a particular embodiment, said at least one first, second, third and/or fourth gray level images are formed on the physical support of the security device by laser engraving.

• un support physique, et
• au moins une première et une deuxième images en niveaux de gris, obtenues à partir d'une image numérique en couleurs, et formées sur ledit support physique,
  • ladite image numérique en couleurs comprenant une pluralité de pixels, la couleur de chaque pixel étant définie selon au moins une première, une deuxième et une troisième composantes de couleur d'un espace colorimétrique,
  • ladite première image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant la première composante de couleur du pixel correspondant de l'image numérique en couleurs, et ladite deuxième image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant la deuxième composante de couleur du pixel correspondant de l'image numérique en couleurs.

The invention further relates to a security device comprising:

• a physical medium, and
• at least a first and a second gray level image, obtained from a digital color image, and formed on said medium physical,
  • said digital color image comprising a plurality of pixels, the color of each pixel being defined according to at least a first, a second and a third color component of a colorimetric space,
  • said first grayscale image comprising a plurality of pixels each having a level of gray representing the first color component of the corresponding pixel of the digital color image, and said second grayscale image comprising a plurality of pixels each having a level of gray representing the second color component of the corresponding pixel of the digital color image.

• ladite troisième image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant la troisième composante de couleur du pixel correspondant de l'image numérique en couleurs, et
• ladite quatrième image en niveaux de gris comprenant une pluralité de pixels présentant chacun un niveau de gris représentant les première, deuxième et troisièmes composantes de couleur du pixel correspondant de l'image numérique en couleurs, ladite quatrième image en niveaux de gris correspondant à l'image numérique en couleurs retraduite en niveaux de gris.

In a particular embodiment, the security device further comprises at least a third and/or a fourth grayscale image, obtained from the digital color image, and formed on said physical medium,

• said third grayscale image comprising a plurality of pixels each having a grayscale representing the third color component of the corresponding pixel of the digital color image, and
• said fourth grayscale image comprising a plurality of pixels each having a grayscale representing the first, second and third color components of the corresponding pixel of the digital color image, said fourth grayscale image corresponding to the digital color image translated back into grayscale.

• acquisition optique des au moins une première et deuxième images en niveau de gris formées sur le support physique dudit dispositif de sécurité, pour obtenir au moins une première, une deuxième, une troisième et/ou une quatrième images numériques en niveaux de gris,
• génération, à partir desdites au moins une première, deuxième, troisième et/ou quatrième images numériques en niveaux de gris, de l'image numérique en couleurs reconstituée, la couleur de chaque pixel de l'image numérique en couleurs étant obtenue à partir du niveau de gris du pixel correspondant de chacune des au moins une première, deuxième, troisième et/ou quatrième images numériques en niveau de gris, et
• affichage de ladite image numérique en couleurs reconstituée.

The invention further relates to a method for generating a digital color image reconstituted from a security device as described above, comprising the following steps:

• optical acquisition of at least one first and second grayscale images formed on the physical medium of said security device, to obtain at least a first, a second, a third and/or a fourth digital grayscale image,
• generation, from said at least one first, second, third and/or fourth digital images in gray levels, of the reconstituted digital color image, the color of each pixel of the digital image in colors being obtained from the gray level of the corresponding pixel of each of the at least one first, second, third and/or fourth digital gray level images, and
• display of said reconstructed color digital image.

In a particular embodiment, the acquisition is carried out by means of a portable device comprising a display means displaying positioning marks configured to guide the relative positioning of the portable device with respect to the security device.

In a particular embodiment, the generation method also comprises a security verification step comprising a comparison of the reconstituted digital color image with a reference image.

In a particular embodiment, the acquisition step comprises the acquisition of a video of the security device comprising said at least one first and second gray level images formed on the physical medium of said security device, and the extraction of the at least one first and second digital images in gray levels from said video.

In a particular embodiment, said video comprises the third and/or fourth gray level images formed on the physical medium of said security device, the third and/or fourth digital gray level images being extracted from said video.

In a particular embodiment, the acquisition step comprises the acquisition of the first grayscale image according to a first acquisition angle, and the acquisition of the second grayscale image according to a second angle d acquisition, and optionally the acquisition of the third grayscale image according to a third acquisition angle and/or the acquisition of the fourth grayscale image according to a fourth acquisition angle.

In a particular embodiment, in which the digital color image displayed is a 3D image, the generation step comprising a 3D reconstruction step from a 2D image obtained from said at least one first, second, third and/or fourth grayscale digital images.

In a particular embodiment, the different steps of the generation method as described above are determined by computer program instructions.

Consequently, the invention also relates to a computer program on an information medium (or recording medium), this program being capable of being implemented by a server or more generally in a computer, this program comprising instructions suitable for implementing the steps of a generation method as described above.

This program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in specially compiled form, or in any other desirable form.

The invention also relates to an information medium (or recording medium) readable by a server or more generally by a computer, and comprising instructions of a computer program as mentioned above.

The information carrier can be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a rewritable non-volatile memory (of the “EEPROM” or “NAND Flash” type for example), or such as a “ROM”, for example a “CD ROM or a microelectronic circuit “ROM”, or else a magnetic recording medium, for example a floppy disk or a hard disk.

On the other hand, the information medium can be a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded from an Internet-type network.

Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

Brief description of the drawings

• [Fig. 1] La figure 1 représente, de manière schématique, un dispositif de sécurité optique conforme à un exemple de mode de réalisation de l'invention ;
• [Fig. 2A] La figure 2A représente, de manière schématique, un dispositif de sécurité optique conforme à un autre exemple de mode de réalisation de l'invention ;
• [Fig. 2B] La figure 2B représente, de manière schématique, une coupe selon l'axe c-c du dispositif de la figure 2A ;
• [Fig. 3] La figure 3 représente, sous forme d'un organigramme, les principales étapes d'un procédé de fabrication conforme à un exemple de mode de réalisation de l'invention ;
• [Fig. 4] La figure 4 représente, de manière schématique, un exemple d'image source en couleurs utilisée lors de la mise en œuvre du procédé de la figure 3 ;
• [Fig. 5] La figure 5 représente, de manière schématique, un exemple d'image source en couleurs utilisée lors de la mise en œuvre du procédé de la figure 3, l'image source filtrée selon les composantes de couleur, et les images en niveaux de gris représentant les composantes de couleur ;
• [Fig. 6] La figure 6 représente, sous forme d'un organigramme, les principales étapes d'un procédé de génération d'une image numérique en couleurs, conforme à un exemple de mode de réalisation de l'invention.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof which is devoid of any limiting character. In the figures:

• [ Fig. 1 ] The figure 1 schematically represents an optical security device according to an exemplary embodiment of the invention;
• [ Fig. 2A ] The figure 2A schematically represents an optical security device according to another exemplary embodiment of the invention;
• [ Fig. 2B ] The figure 2B schematically represents a section along the cc axis of the device of the figure 2A ;
• [ Fig. 3 ] The picture 3 represents, in the form of a flowchart, the main steps of a manufacturing method in accordance with an exemplary embodiment of the invention;
• [ Fig. 4 ] The figure 4 schematically represents an example of a color source image used during the implementation of the method of the picture 3 ;
• [ Fig. 5 ] The figure 5 schematically represents an example of a color source image used during the implementation of the method of the picture 3 , the source image filtered according to the color components, and the grayscale images representing the color components;
• [ Fig. 6 ] The figure 6 represents, in the form of a flowchart, the main steps of a method for generating a digital color image, in accordance with an exemplary embodiment of the invention.

Description of embodiments

The invention proposes an optical security device 100 comprising n images IM1-IMn in gray levels formed on a physical medium 110, n being a natural integer greater than or equal to 2 (see figure 1 and 2A-2B , described below). The invention further relates to the manufacture of such an optical security device 100 and the generation of a color image from such an optical security device 100.

The optical security device 100 is typically intended to be incorporated into a physical security and/or identity document 160, such as a passport, identity card, driver's license, etc.

The term “identity document” refers to any document containing information (photograph, surname, first name, etc.) enabling the authorized bearer of the document to be identified more or less securely. This identity information appears physically on the body of the document so as to be visually verifiable by a person or a control machine. In addition to the identity information visually accessible on the body of the identity document, it is possible to store identity information in a memory contained in the body of the identity document (in a chip for example), this information being accessible if necessary. electronically by suitable means to verify the identity of the data subject.

The picture 3 depicts a method of manufacturing an optical security device 100, the method being in accordance with an exemplary embodiment of the invention.

The manufacturing method is typically implemented by a manufacturing system comprising digital data processing means and printing means.

The data processing means typically takes the form of a computer, executing a computer program stored in a computer readable medium (or memory).

In a step S300, a digital color image 400, called source color image 400 is obtained by the data processing means, this digital color image 400 generally being transmitted by a digital camera or by a color scanner having digitized a printed color image to obtain the digital color image 400. The figure 4 schematically represents an example of source image 400 in colors.

The color source image 400 can visually represent a security datum, such as for example a personal datum of an authorized bearer of the document 160, such as the face V or the irises of the authorized bearer. The color source image 400 is thus typically a digital photograph of the V face or irises of the authorized wearer. As a variant, the security datum may be a datum relating to the document 160.

The color source image 400 comprises a plurality of P1-Pp pixels, the color of each P1-Pp pixel being typically defined according to at least three color components of a colorimetric space.

Also, the color of each pixel P1-Pp is typically defined according to a first, a second and a third color component of a colorimetric space.

The colorimetric space is for example the RGB space (acronym for “Red Green Blue”, in English terminology), so that the three color components are a red component, a green component and a blue component. As a variant, the colorimetric space can be the CYM space (acronym for “Cyan Yellow Magenta”, in English terminology), so that the three color components are a Cyan component, a yellow component and a magenta component. Any triplet of colors orthogonal to each other in the colorimetric space can be used.

The terms "first", "second" and "third" of the expressions "first color component", "second color component" and "third color component" are introduced to distinguish the different color components of the same colorimetric space . Also, the expression “first color component” designates one of the color components of the colorimetric space different from the other color components (for example the red component, the green component or the blue component in the RGB space).

Furthermore, the position of each pixel P1-Pp in the color source image 400 is defined according to at least two spatial dimensions, typically according to two directions perpendicular by X and Y, the first direction X being typically the abscissa axis, parallel to a first side of the source color image 400 and the second direction Y being typically the ordinate axis, parallel to a second side of the source color image 400.

In a step S310, the digital data processing means obtain the n images in gray levels IM1-IMn from the source color image 400.

Each of the n grayscale images IM1-IMn comprises the same number p of pixels as the source color image 400, the source color image 400 and each grayscale image IM1-IMn having the same size, c i.e. the same height H and the same width L.

Each of the n images in gray levels IM1-IMn thus comprises a plurality of pixels, and each of these pixels has a level of gray representing a color component of the corresponding pixel P1-Pp of the source color image 400. p is a natural number greater than or equal to two.

The term "corresponding pixel" designates the pixel of the source color image 400 having the same position (according to the spatial dimensions) in the image as the pixel of the grayscale image IM1-IMn, typically the same abscissa and the same ordinate.

For each of the n grayscale images IM1-IMn, the gray level of each pixel is determined according to the brightness level (also called luminance level or brightness level) of the color component represented by the gray level . The lower the brightness level of the color component, the darker the gray level, the correspondence between the brightness level and the gray level being linear. For example, the luminosity obtained according to the red component corresponds to the luminosity of the source image in colors 400 observed through a red filter.

At least a first grayscale image IM1 and a second grayscale image IM2 are thus obtained in step S310.

The first image in gray levels IM1 comprises a plurality of pixels each having a level of gray representing the first color component of the corresponding pixel P1-Pp of the source image in colors 400, and the second image in gray levels IM2 comprising a plurality of pixels each having a gray level representing the second color component of the corresponding pixel P1-Pp of the source color image 400.

The number n of grayscale images is typically equal to three, where three is the number of dimensions of the color space, so that each color component is represented by the grayscales of the pixels of a leveled image of gray IM1-IMn different.

Also, when the color of each pixel P1-Pp of the color source image 400 is defined according to the three color components, a third grayscale image IM3 is typically obtained at step S310, each pixel of the third grayscale image IM3 having a grayscale representing the third color component of the corresponding pixel of the source color image 400.

In addition, a so-called global grayscale image IM4 can be obtained in step S310, each pixel of the global grayscale image IM4 having a gray level representing the M color components of the corresponding pixel P1-Pp of the source image in 400 colors.

The overall grayscale image IM4 and the grayscale images IM1, IM2 and IM3 are linked by an equation. Thus, by knowing three of these four images, it is possible to calculate the fourth image. It is for this reason that two images among the images in gray levels IM1 IM2 and IM3 suffice on condition of knowing the image IM4.

When the color space is RGB space, the equation used for a given pixel of the global image seen through a video screen is typically NGg = 0.299 NGr + 0.587 NGv + 0.114 NGb, where NGg is the level of gray of said pixel of the global image IM4, NGr is the gray level of the corresponding pixel of the gray level image representing the red component, NGv is the gray level of the corresponding pixel of the gray level image representing the green component, NGb is the gray level of the corresponding pixel of the gray level image representing the blue component. The aforementioned coefficients are related to the sensitivity of the human eye to the colors red, green and blue (the human eye is more sensitive to green than to red, and more sensitive to red than to blue, a bright green thus contributing more than other colors to overall brightness). However, these coefficients are only examples and different coefficients can be considered.

In the case where the image is observed directly, the equation used is for example NGg=0.2125 NGr+0.7154 NGv+0.0721 NGb.

Also, in addition to the first grayscale image IM1 and the second grayscale image IM2, it is possible to obtain at step S310 the third grayscale image IM3 and/or the overall image in IM4 grayscale.

The overall grayscale image allows natural black and white viewing of the image with the naked eye, while grayscale images representing a single color component distort the source image more.

The figure 5 shows a source image 400 in colors, the global image in gray levels IM4, as well as the source image filtered according to the red component 520, the green component 530 and the blue component 540, and the image in gray levels IM1 representing the red component, the grayscale image IM2 representing the green component and the grayscale image IM3 representing the blue component, determined according to the filtered source images.

In a step S320, the N images in gray levels IM1-IMn obtained in step S310 are formed on the physical medium 110 of the security device 100, by the printing means of the manufacturing system.

IM1-IMn grayscale images are typically formed by laser etching. As a variant, the images in gray level are formed by printing, the printing typically being digital printing, for example by inkjet or thermal transfer, or else by retransfer or any other equivalent digital process.

The training step S320 can comprise, typically for each image in gray levels IM1-IMn obtained in step S310, a reproduction S322 of the pixels of the image in gray levels IM1-IMn so that the pixels reproduced from the image are positioned contiguously, with no space being formed between two adjacent pixels of the image.

Each of the grayscale images IM1-IMn obtained in step S310 is thus positioned at a different location on the physical medium 110 of the security device 100.

Moreover, each of these images in gray levels IM1-IMn is directly fully visible to a user, without the aid of an additional element such as an array of lenses.

The figure 1 schematically represents an optical security device 100, in accordance with an exemplary embodiment of the invention and comprising images in gray levels IM1-IM4 formed according to step S322 of contiguous reproduction of the pixels.

In this example, the images in gray levels IM1-IM4 are positioned side by side at the level of a lower part of the support 110. However, another configuration could be envisaged.

The pixels of each image having been reproduced on the support 110 so as to be positioned contiguously, each image formed in its entirety at a different location E1-E4 of the support 110.

Furthermore, the pixels P1-Pp of the source color image 400 from which the grayscale images IM1-IM4 of this example were obtained are typically defined according to three color components.

Also, the pixels of the first image IM1 in gray levels each have a level of gray representing the first color component of the corresponding pixels of the source image in colors 400, the pixels of the second image IM2 in gray levels each have a gray level representing the second color component of the corresponding pixels of the source color image 400, the pixels of the third gray level image IM3 each have a gray level representing the third color component of the corresponding pixels of the The source color image 400 and the pixels of the fourth grayscale image IM4 each have a gray level representing the first, second and third color components of the corresponding pixels of the source color image 400.

Alternatively, the forming step S320 may comprise the reproduction S324 of the pixels of the grayscale images IM1-IMn obtained in the step S310 so that the reproduced pixels of each grayscale image IM1-IMn are positioned in an interlaced manner with the pixels of the other grayscale images IM1-IMn, typically along a distribution direction DR.

More precisely, each image in gray levels IM1-IMn can be divided into q rows of pixels, the pixels of a same row having the same abscissa (or the same ordinate).

The lines of the images in gray levels IM1-IMn are then interlaced along the distribution direction DR periodically. More precisely, the first line of the first image is followed by the first line of the second image and so on until the first line of the n-th image so as to form a first series of lines, the first line of the n-th image being followed by the second line of the first image which is followed by the second line of the second image, and so on until the last (q-th) line of the n-th image. A number q of series of lines is thus formed.

The grayscale images IM1-IMn thus formed are interlaced in the same location E of the physical support 110 of the security device 100. Such a configuration thus makes it possible to reduce the space necessary for the formation of the grayscale images IM1- IMn, which is advantageous in the context of security and/or identity documents whose size is restricted.

When the grayscale images IM1-IMn are formed to be interlaced, a lens array 200 is typically obtained (step S326).

Lens array 200 is typically affixed to physical medium 110 or created by hot rolling the surface of physical medium 110.

The lens array 200 is configured to allow each of the different grayscale images IM1-IMn to be viewed from a different viewing angle.

Also, each lens 202 of the lens array 200 typically has the shape of a half-cylinder, the length of each lens 202 being equal to the length of a pixel line (and therefore to the height of the grayscale images IM1-IMn) and the width of each lens 202 being equal to the width of a pixel multiplied by the number n of images in gray levels IM1-IMn.

The lenses 202 of the array of lenses 200 are positioned contiguously along the distribution direction DR, each lens 202 being positioned above a series of lines.

The periodicity of the interlacing and of the network of lenses 200, as well as the positioning of the network of lenses 200 with respect to the interlacing implies, when the security device 100 is oriented according to a given orientation (and therefore viewed according to an angle of given visualization), the focusing, by the array of lenses 200, of the incident light rays on the rows of pixels of the same image among the images in gray levels IM1-IMn.

Each image in gray levels IM1-IMn is thus associated with a given viewing angle and, when the security device 100 is oriented according to this viewing angle, each lens 202 of the lens array 200 focuses the light rays on the line of pixels of the associated image of the series of lines on which the lens 202 is positioned.

Each image in gray level IM1-IMn can thus be viewed in its entirety according to the associated viewing angle.

The formation of the gray level images (step S324) is typically implemented by laser etching after the creation or attachment of the lens array 200, the laser etching (step S326) being performed through the lens array 200.

The figure 2A and 2B schematically represent an optical security device 100, in accordance with an exemplary embodiment of the invention and comprising images in gray levels IM1-IM4 formed according to step S324 of interlaced reproduction of the pixels.

The security device 100 comprises in this example four images in interlaced gray levels IM1-IM4.

Furthermore, the pixels of the source color image 400 from which the grayscale images IM1-IM4 of this example were obtained are typically defined according to three color components, such that the pixels of the first image IM1 in grayscale each have a grayscale representing the first color component of the corresponding pixels of the color source image 400, the pixels of the second grayscale image IM2 each have a gray level representing the second color component of the corresponding pixels of the color source image 400, the pixels of the third image IM3 in grayscale each have a level of gray representing the third color component of the corresponding pixels of the source color image 400 and the pixels of the fourth image IM4 in grayscale each have a level of gray representing the first, second and third color components of the corresponding pixels of the color source image 400.

The interlacing of grayscale images IM1-IM4 forms three series S1-S3 of rows of pixels. Each lens 202 of lens array 200 is positioned on a different series S1-S3 of pixel lines. The invention is described in the case where the number of series is equal to three, but the invention nevertheless remains applicable when a greater number of series is used.

A simple and playful authentication of the security document 100 or of the bearer of the security document 100 can be carried out from the images in gray levels IM1-IMn formed on the physical support 110 of the security document 100 manufactured according to the method of the picture 3 .

The figure 6 represents a method for generating a digital color image, called a reconstituted image, from a security device 100 manufactured according to the method for manufacturing the picture 3 , the generating method being in accordance with an exemplary embodiment of the invention.

The generation method is typically implemented by a generation device, having the conventional architecture of a computer and comprising digital data processing means, an optical sensor, such as a camera, and a display means such as a screen.

The data processing means typically takes the form of a computer, executing a computer program stored in a computer readable medium (or memory).

The generation device is typically a portable device, such as a “smartphone” type terminal or a tablet.

In a step S600, at least two images in gray levels IM1-IMn formed on the physical medium 110 of the security device 100 are acquired optically, by means of the optical sensor of the generation device. For example, each grayscale image IM1-IMn formed on the physical medium 110 is optically acquired at step S600. Alternatively, each grayscale image associated with a single color component of the source color image 400 is optically acquired. Alternatively, two grayscale images associated with a single color component of the source color image 400 and the overall grayscale image IM4 are acquired optically. As a variant, two grayscale images associated with a single color component of the source color image 400 are optically acquired as well as the source color image, an overall grayscale image IM4 being obtained from the acquisition of the source image in colors. A digital grayscale image is thus created by the generation device for each grayscale image IM1-IMn acquired.

Several digital images in gray levels can thus be obtained, typically one digital image for each image in gray levels associated with a single color component of the source image, or two digital images for two images in gray levels associated with a single color component and a digital image for the overall grayscale image IM4. Alternatively, a video is obtained by means of the sensor, then digital images are extracted from the video.

In order for this acquisition to be implemented, an operator positions the optical sensor of the generation device and/or the security device so that the optical sensor can successively acquire each image in gray levels IM1-IMn.

The relative positioning of the sensor of the generation device with respect to the safety device 100 can be guided by means of positioning marks displayed by the display means of the generation device.

The positioning marks are more precisely superimposed on the image displayed by the display means, this image representing in real time the environment captured by the optical sensor. The operator can thus modify the relative positioning so that the grayscale image to be captured is superimposed on the positioning marks. The positioning marks are thus configured to guide the relative positioning of the generation device with respect to the security device, and the digital images acquired or extracted from the acquired video have a size suitable for the generation of the reconstituted image.

When the grayscale images IM1-IMn are formed so as to be interlaced and the security device 100 comprises an array of lenses 200, the acquisition step comprises the acquisition of each image according to an acquisition angle different, the acquisition angles corresponding to the different viewing angles, which is the viewing angle associated with the image in gray levels IM1-IMn. As a variant, a video is acquired according to several acquisition angles, then the digital images are extracted from the video.

In a step S610, the reconstituted image is generated, from the images in gray levels IM1-IMn acquired in step S600, by the digital data processing means of the generation system.

The color component(s) represented by the gray levels of the pixels of each gray level image IM1-IMn acquired is retrieved by means of a component location information element.

The location information element is for example represented on the physical medium 110 of the security device 100 or coded in a coding element represented on the physical medium 110, the coding element being typically a 2D barcode or 3D.

Alternatively, when the grayscale images IM1-IMn are formed so as to be interlaced, the location information item is typically the acquisition angle of the grayscale image. The lines of the grayscale images IM1-IMn are indeed typically interlaced so that each grayscale image IM1-IMn is associated with a predetermined viewing angle, a correspondence table between the grayscale images and the viewing angles being accessible by the generating device.

The color of each pixel of the reconstructed digital color image is typically obtained from the gray level of the pixel of each digital image whose gray levels correspond to a single color component of the source color image 400. More specifically, for each digital image whose gray levels are associated with a single component, the associated component is determined by means of the component location information element, then, for each pixel of the digital image, the The component's brightness level is determined from the gray level of the pixel.

The color of each pixel of the reconstituted digital color image is then obtained from the luminosity levels of each component, associated with the corresponding pixels of the digital images in gray levels.

Alternatively, when a grayscale image associated with the first red color component, a grayscale image associated with the second green color component and the overall grayscale image IM4 are acquired optically, the level of gray of the third blue color component is determined for each pixel by means of the aforementioned equation NGg = 0.299 NGr + 0.587 NGv + 0.114 NGb, then the brightness level of each component is determined from the gray level of the pixel associated, the color of each pixel of the reconstituted digital color image then being obtained from the brightness levels of each component, associated with the corresponding pixels of the digital images in gray levels.

The image obtained from the images in gray levels IM1-IMn acquired at step S600 is typically a two-dimensional (2D) image. The generation step S610 can then include a three-dimensional (3D) reconstruction step from the 2D image obtained.

When the color source image 400 is a digital photograph of the face V of the authorized wearer, and therefore the 2D image obtained is the face V of the authorized wearer, the 3D reconstruction comprises a measurement of at least one distance on 2D image, such as the pupillary distance and/or the distance between the two ears.

The 2D photo is then projected onto a 3D volume in the form of a white head, the 3D volume being further deformed according to the distance measurement(s) made. Alternatively, the head volume is encoded in an information item represented or encoded on the physical medium 110.

In a step S620, the reconstituted color image is displayed by the display means of the generation device. This color display makes it possible to authenticate the security device 100 and/or the bearer of the document 160 incorporating the security device 100 in a simple and playful manner, using images in gray levels.

A security check can further be implemented in a step S630, from the color digital image generated in step S610. This security check typically includes a comparison of the generated color digital image with a reference image.

The reference image is typically an image stored in a database accessible by the generation device, this image typically being the color source image 400.

As a variant, the reference image corresponds to the acquisition in step S600 of the global image in gray levels IM4, or of a color image formed on the physical medium 110 of the security device 100 (typically the 400 color source image).

As a variant, when the color source image 400 represents personal data of an authorized holder of the document 160, the reference image is acquired at the time of a security check during which the generation method is implemented, typically by filming or photographing the personal data of the bearer of the document 160 (for example the face or the irises).

When the reconstructed color image displayed is a 3D image reconstructed in step S610, the display angle of the 3D image can be determined based on the viewing angle of the document 160.

More precisely, the viewing angle can be equal to the viewing angle of the document 160. This viewing angle can be determined from an image of the document 160 acquired by the optical sensor. For example, when document 160 includes rectangular faces, the viewing angle can be determined based on the distortion of a rectangular face in the image of document 160.

It is thus possible to display the reconstructed color image in augmented reality, the 3D image being displayed at a display angle depending on the relative position of the document 160 with respect to the optical sensor of the generation device. Also, when the reconstituted image is the face of the authorized bearer, the operator has the impression that he is turning around a color 3D face when he moves his generation device relative to the document 160.

Claims (13)

Method of manufacturing a security device (100), comprising the following steps: - obtaining (S300) a digital color image (400), said digital color image (400) comprising a plurality of pixels (P1-Pp), the color of each pixel (P1-Pp) being defined according to at least a first, a second and a third color component of a color space, - obtaining (S310) at least a first and a second grayscale image (IM1-IMn) from said digital color image (400): -- said first gray level image (IM1) comprising a plurality of pixels each having a gray level representing the first color component of the corresponding pixel of the digital color image (400), and -- said second gray level image (IM2) comprising a plurality of pixels each having a gray level representing the second color component of the corresponding pixel of the digital color image (400), - obtaining (S310) a third and/or a fourth grayscale image (IM1-IMn) from said digital color image (400): - said third gray level image (IM3) comprising a plurality of pixels each having a gray level representing the third color component of the corresponding pixel of the digital color image (400), and - said fourth gray level image (IM4) comprising a plurality of pixels each having a gray level representing the first, second and third color components of the corresponding pixel of the digital color image (400), - formation (S320) of said at least one first and second grayscale images (IM1-IMn) on a physical medium (110) of said security device (100), and forming said third grayscale image and/or said fourth grayscale image on the physical medium (110) of said security device (100), said at least one first, second, third and/or fourth gray level images (IM1-IMn) being formed on the physical support (110) of the security device (100) by laser engraving. A manufacturing method according to claim 1, wherein the step of forming (S320) comprises, for each of said at least one first, second, third and/or fourth grayscale images (IM1-IMn), reproducing (S322 ) pixels of said image (IM1-IMn) such that the reproduced pixels are positioned contiguously, each of said at least one first, second, third and/or fourth grayscale images (IM1-IMn) being positioned at a different location (E1-E4) of the physical support (110) of the security device (100). A manufacturing method according to claim 1, wherein the step of forming (S320) comprises reproducing (S324) the pixels of said at least one first, second, third and/or fourth grayscale images (IM1-IMn) of so that the reproduced pixels of each grayscale image (IM1-IMn) are positioned interlaced with the pixels of the other grayscale images (IM1-IMn), said at least one first, second, third and/or fourth images in gray levels (IM1-IMn) thus being interlaced in the same location (E) of the physical medium (110) of the security device (100). A manufacturing method according to claim 3, further comprising a step of obtaining (S326) an array of lenses (200), the array of lenses (200) being configured to allow the visualization of each of said at least one first, different second, third and/or fourth grayscale images (IM1-IMn) according to a different viewing angle. Security device (100) comprising: - a physical medium (110), and - at least a first and a second gray level image (IM1-IMn), obtained from a digital color image (400), and formed on said physical medium (110), said digital color image (400) comprising a plurality of pixels (P1-Pp), the color of each pixel (P1-Pp) being defined according to at least first, second and third color components of a color space , said first grayscale image (IM1) comprising a plurality of pixels each having a grayscale representing the first color component of the corresponding pixel of the digital color image (400), and said second grayscale image (IM2) comprising a plurality of pixels each having a grayscale representing the second color component of the corresponding pixel of the digital color image (400) - at least a third and/or a fourth grayscale image (IM1-IMn) obtained from said digital color image (400), and formed on said physical medium (110): - said third gray level image (IM3) comprising a plurality of pixels each having a gray level representing the third color component of the corresponding pixel of the digital color image (400), and - said fourth gray level image (IM4) comprising a plurality of pixels each having a gray level representing the first, second and third color components of the corresponding pixel of the digital color image (400). A method of generating a reconstructed digital color image from a security device (100) according to claim 5, comprising the following steps: - optical acquisition (S600) of gray level images (IM1-IMn) formed on the physical medium (110) of said security device (100), to obtain at least a first, a second, and a third or a fourth image digital grayscale, - generation (S610), from said at least one first, second, third and/or fourth digital grayscale images, of the image reconstructed digital color, the color of each pixel of the digital color image being obtained from the gray level of the corresponding pixel of each of the at least one first, second, third and/or fourth digital gray level image, and - display (S620) of said reconstituted digital color image. A generation method according to claim 6, wherein the acquisition (S600) is performed by means of a portable device comprising display means displaying positioning marks configured to guide the relative positioning of the portable device with respect to the security. Generation method according to claim 6 or 7, further comprising a security verification step (S630) comprising a comparison of the reconstructed digital color image with a reference image. A generation method according to any of claims 6 to 8, wherein the step of acquiring (S600) comprises acquiring a video of the security device including said at least first and second grayscale images formed on the physical medium of said security device, and the extraction of at least one first and second digital images in gray levels of said video. A generation method according to any of claims 6 to 9, wherein the acquiring step (S600) comprises acquiring the first grayscale image at a first acquisition angle and acquiring the second image in gray levels according to a second acquisition angle. Generation method according to any one of claims 6 to 10, in which the digital color image displayed is a 3D image, the generation step (S610) comprising a step of 3D reconstruction from a 2D obtained from said at least one first, second, third and/or fourth digital grayscale images. Computer program comprising instructions for the execution of the steps of the generation method according to any one of Claims 6 to 11 when the said program is executed by a computer. A computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the generation method according to any one of Claims 6 to 11.

Images