EP3931005A1

EP3931005A1 - Colour image formed from a hologram

Info

Publication number: EP3931005A1
Application number: EP20710217.9A
Authority: EP
Inventors: Benoît BERTHE; Christophe Duriez
Original assignee: Idemia France SAS
Current assignee: Idemia France SAS
Priority date: 2019-02-28
Filing date: 2020-02-13
Publication date: 2022-01-05
Also published as: CA3131622A1; FR3093302B1; CN113508040B; JP2022522135A; BR112021016558A2; WO2020174153A1; FR3093302A1; KR20210132088A; CN113508040A; JP2024102259A; AU2020228143A1; US20220184990A1; MX2021010248A

Abstract

The invention relates to a colour image (IG) comprising: a first layer (10) comprising a holographic structure forming an arrangement (29) of pixels (30) each comprising sub-pixels (32) of distinct colours; and colour modulation means configured to select the colour of the pixels (30) by modifying the colorimetric contribution of the sub-pixels (32) relative to each other in the pixels (30) so as to reveal a personalised colour image. The colour modulation means can comprise: regions of the holographic structure, called destroyed regions, that are locally destroyed by a laser; masking means positioned facing the arrangement of pixels to locally mask all or some of the sub-pixels; or even amplification means positioned facing the arrangement of pixels to locally amplify the luminosity of all or some of the sub-pixels.

Description

Title of the invention: Color image formed from a hologram

Technical area

[0001] The invention relates to a technique for forming color images and more particularly relates to a document comprising a holographic structure forming an arrangement of pixels from which a color image is formed.

Prior art

[0002] The identity market today requires increasingly secure identity documents (also known as identity documents). These documents must be easily authenticated and difficult to forge (if possible tamper-proof). This contract concerns a wide variety of documents, such as identity cards, passports, access badges, driving licenses, etc., which can be presented in different formats (cards, booklets, etc.).

[0003] Various printing techniques have been developed over time to achieve color prints. In particular, the production of identity documents such as those mentioned above requires the production of color images in a secure manner in order to limit the risks of falsification by malicious individuals. The production of such documents, in particular with regard to the identity image of the bearer, needs to be sufficiently complex to make reproduction or falsification by an unauthorized individual difficult.

[0004] Thus, a known solution consists in printing on a support a matrix of pixels composed of colored sub-pixels and of forming gray levels by laser carbonization in a lasérisable layer situated opposite the matrix of pixels, so revealing a personalized color image which is difficult to forge or reproduce. Examples of embodiment of this technique are described for example in documents EP 2 580 065 B1 (dated August 6, 2014) and EP 2 681 053 B1 (dated April 8, 2015).

[0005] Although this known technique offers good results, improvements are still possible in terms in particular of the quality of the visual rendering of the image thus formed. From this image forming technique, it is indeed difficult to achieve high levels of color saturation. In other words, the color gamut (ability to reproduce a range of colors) of this known technique may prove to be limited, which may pose a problem in certain use cases. This results in particular from the fact that the colored sub-pixels are formed by a conventional printing method, by printing of the “offset” type for example, which does not make it possible to form sufficiently rectilinear and continuous lines of sub-pixels. which generates homogeneity defects when printing sub-pixels (interruptions in the lines of pixels, irregular contours, etc.) and a degraded colorimetric rendering.

[0006] Current printing techniques also offer limited positioning accuracy due to the imprecision of printing machines, which also reduces the quality of the final image due to poor positioning of the pixels and under -pixels with respect to each other (problems of overlapping subpixels, misalignments ...) or due to the presence of a tolerance interval without printing between the subpixels.

[0007] FIG. 1 represents an example of printing 2 by offset of pixels 4 taking the form of lines 6 of sub-pixels of distinct colors. As shown, the contours of each row 6 of sub-pixels exhibit irregularities. A tolerance must be taken into account for the positioning of these lines due to positioning inaccuracies during printing.

As illustrated in Figure 1, to compensate for these defects in homogeneity and positioning of the sub-pixels of each pixel (and thus avoid possible overlaps of neighboring sub-pixels and the degradation of the desired colors), it is possible to 'print the sub-pixels so as to keep a white area 8 between each of them. This technique of adding white areas, however, has a drawback in that it limits the level of saturation that can be obtained for a given color, which prevents obtaining a satisfactory color gamut.

[0009] Today there is a need to securely form personalized color images, in particular in documents such as identity documents or others. A need exists in particular to allow flexible and secure personalization of color images, so that the image thus produced is difficult to forge or reproduce and can be easily authenticated.

[0010] No solution capable of offering an appropriate level of security and flexibility today also makes it possible today to obtain a good level of brightness of the image as well as a sufficient color gamut, in particular to obtain the shades of color necessary for the formation of certain high quality color images, for example when image areas must exhibit a highly saturated level in a given color.

Disclosure of the invention

[0011] To this end, the invention relates to a secure document comprising:

a first layer comprising a holographic structure forming an arrangement of pixels each comprising a plurality of sub-pixels of distinct colors; and

- color modulation means configured to select the

color of the pixels by modifying the colorimetric contribution of the sub-pixels relative to each other in at least part of the pixels so as to reveal a personalized color image from the arrangement of pixels combined with said modulation means,

the color modulation means comprising at least one of: o regions of the holographic structure, called destroyed regions, which are locally destroyed by laser;

o masking means positioned opposite the arrangement of pixels to locally mask all or part of the sub-pixels; and o amplification means positioned opposite the arrangement of pixels to locally amplify the brightness of all or part of the subpixels.

[0012] The invention advantageously makes it possible to create color shades so as to form a secure color image by the interaction between the color modulation means and the arrangement of pixels formed by the holographic layer. The color image is therefore formed by the combination of the means color modulation and the arrangement of pixels located opposite. Without the addition of the color modulation means for orienting or judiciously selecting the passage of the incident light, the pixels form only a blank arrangement insofar as this set is devoid of the information characterizing the color image. These are the color modulation means which are configured, depending on the arrangement of sub-pixels chosen, to personalize the visual appearance of the pixels and thus reveal the final color image.

[0013] The present invention makes it possible to produce color images exhibiting good image quality while being secure and therefore resistant to falsifications and fraudulent reproductions.

[0014] According to a particular embodiment, each sub-pixel in the pixel arrangement is formed by a respective holographic grating configured to generate by diffraction a corresponding color of said sub-pixel.

[0015] According to a particular embodiment, each pixel of said arrangement of pixels forms an identical pattern of colored sub-pixels.

[0016] According to a particular embodiment, each pixel of said arrangement of pixels is configured so that each sub-pixel has a unique color in said pixel.

[0017] According to a particular embodiment, the pixel arrangement is configured so that the sub-pixels are uniformly distributed on or in a substrate.

[0018] According to a particular embodiment, the arrangement of pixels forms contiguous lines of sub-pixels.

[0019] According to a particular embodiment, said regions destroyed in the holographic structure correspond to zones destroyed by laser ablation of the holographic networks corresponding to all or part of sub-pixels in the pixel arrangement.

[0020] According to a particular embodiment, said destroyed regions comprise sub-pixels whose corresponding holographic grating is partially destroyed by laser micro-ablation. [0021] According to a particular embodiment, said masking means forming part of the color modulation means comprise at least one of:

- ink patterns printed next to the pixel arrangement to locally mask all or part of the sub-pixels; and

- laser points of different levels of gray formed in a layer, called the second layer, so as to be positioned opposite the arrangement of pixels to locally mask all or part of the sub-pixels.

According to a particular embodiment, said amplification means forming part of the color modulation means comprise at least one of:

- an array of lenses arranged opposite the arrangement of pixels so as to generate the personalized color image by focusing or diverging light incident through the lenses on at least part of the subpixels; and

an optical amplification device comprising a transparent lasérisable layer, called the third layer, and a transparent separating layer placed between the first layer and the third layer, said third layer comprising areas opacified locally with the laser facing the first layer so causing an amplification of the brightness of subpixels in said pixel array in regions corresponding to said opacified areas.

According to a particular embodiment, each lens of the lens array is positioned, relative to an associated pixel located opposite, to focus or diverge an incident light on at least one of the sub-pixels of said associated pixel so as to modify the contribution of the respective colors of the sub-pixels of the associated pixel, in a region of the personalized color image generated through said lens, relative to the pattern intrinsically formed by the associated pixel independently of said lens.

[0024] According to a particular embodiment, the document further comprises a transparent lasérisable layer, said fourth layer, facing the first layer, said fourth layer being at least partially carbonized by laser radiation so as to include opacified regions locally in subpixel look of the pixel arrangement to produce grayscale in the custom color image.

[0025] According to a particular embodiment, the first layer comprises:

- a first under-layer of varnish forming the reliefs of a holographic network; and

a second sub-layer deposited on the reliefs of the first sub-layer, said second sub-layer having a refractive index greater than that of the first sub-layer.

[0026] The invention also relates to a corresponding manufacturing process. More particularly, the invention relates to a process for manufacturing a document, comprising the following steps:

- Creation in a first layer of a holographic structure forming an arrangement of pixels each comprising a plurality of sub-pixels of distinct colors;

- formation of color modulation means to select the color of the pixels by modifying the colorimetric contribution of the sub-pixels relative to each other in at least part of the pixels so as to reveal a personalized color image from the arrangement pixels combined with said color modulation means,

the color modulation means comprising at least one of:

o regions of the holographic structure, called destroyed regions, which are locally destroyed over all or part of the sub-pixels by a single first laser radiation;

[0027] According to a particular embodiment, said formation of the color modulation means comprises at least one of: - local destruction, by means of a single first laser radiation (at a single wavelength), by laser ablation of regions of the holographic structure in order to eliminate all or parts of sub-pixels in the pixel arrangement;

- printing ink patterns next to the first layer to locally mask all or part of the subpixels in the pixel arrangement;

- formation, by means of a single second laser radiation (at a single wavelength), of an array of lenses arranged opposite the arrangement of pixels so as to generate the personalized color image by focusing or divergence light incident through the lenses on at least a portion of the subpixels of the pixel array; and

- Formation of an optical amplification device comprising a transparent lasérisable layer, said third layer, and a transparent separating layer disposed between the first layer and the third layer, said third layer comprising locally opacified areas, by means of a single third laser radiation (at a single wavelength), facing the first layer so as to cause an amplification of the brightness of sub-pixels in said arrangement of pixels in regions corresponding to said opacified areas.

Brief description of the drawings

[0028] [Fig. 1] Figure 1, already described above, schematically represents the printing of lines of colored subpixels on a support.

[0029] [Fig. 2] Figure 2 schematically shows a color image according to a particular embodiment of the invention;

[0030] [Fig. 3] Figure 3 shows schematically a secure document according to a particular embodiment of the invention;

[0031] [Fig. 4] FIG. 4 schematically represents a holographic layer of a secure image according to a particular embodiment of the invention; [0032] [Fig. 5] FIG. 5 schematically represents the reliefs of a holographic layer according to a particular embodiment of the invention;

[0033] [Fig. 6A-6B] Figures 6A and 6B schematically represent a pixel formed by a region of a holographic structure, according to a particular embodiment of the invention;

[0034] [Fig. 7A-7B-7C] Figures 7A, 7B and 7C schematically show an arrangement of pixels and sub-pixels, according to particular embodiments of the invention;

[0035] [Fig. 8] Figure 8 schematically shows a color image according to a particular embodiment of the invention;

[0036] [Fig. 9] Figure 9 schematically illustrates the partial destruction of subpixels, according to a particular embodiment of the invention;

[0037] [Fig. 10] Figure 10 schematically shows a color image according to a particular embodiment of the invention;

[0038] [Fig. 1 1] Figure 1 1 shows schematically a color image according to a particular embodiment of the invention;

[0039] [Fig. 12] Figure 12 schematically shows a color image according to a particular embodiment of the invention;

[0040] [Fig. 13] Figure 13 shows schematically a color image according to a particular embodiment of the invention; and

[0041] [Fig. 14] Figure 14 shows schematically a manufacturing process according to a particular embodiment of the invention.

Description of embodiments

[0042] As indicated above, the invention relates generally to the formation of a color image and relates in particular to a secure document comprising such an image.

The invention proposes to form a color image in a secure manner from a holographic layer comprising a hologram forming an arrangement of pixels, these pixels themselves comprising a plurality of sub- colored pixels, and from color modulation means which are configured to select the color of the pixels in the holographic layer by modifying the relative color contribution of the subpixels with respect to each other in at least part of the pixels. As described in more detail below, various embodiments are possible. In particular, the aforementioned color modulation means can take various forms as explained below with reference to the figures.

[0044] The color modulation means modify the colorimetric contribution (or weight) of sub-pixels relative to neighboring sub-pixels in the corresponding pixels, so as to reveal a personalized color image from the combination of the arrangement of pixels and said modulation means.

[0045] The invention also relates to a method of forming such a color image.

Other aspects and advantages of the present invention will emerge from the embodiments described below with reference to the drawings mentioned above.

[0047] In the remainder of this document, examples of implementations of the invention are described in the case of a document comprising a color image according to the principle of the invention. This document can be any document, called a secure document, of the booklet, card or other type. The invention finds particular applications in the formation of identity images in identity documents such as: identity cards, credit cards, passports, driver's licenses, secure entry badges, etc. The invention also applies to security documents (banknotes, notarial documents, official certificates, etc.) comprising at least one color image.

[0048] In general, the image according to the invention can be formed on any suitable medium.

Likewise, the exemplary embodiments described below aim to form an identity image. It is understood, however, that the color image considered can be any. For example, it may be an image representing the portrait of the holder of the document concerned, other implementations are however possible.

Unless otherwise indicated, elements common or similar to several figures bear the same reference signs and have identical or similar characteristics, so that these common elements are generally not described again for the sake of simplicity.

[0051] Figure 2 schematically shows a color image IG according to a particular embodiment of the invention.

As illustrated in this figure, the color image IG comprises a holographic layer (also called "first layer") 12 coupled to, or comprising, color modulation means 10. The holographic layer 12 comprises a holographic structure forming an arrangement 29 of pixels 30, each of the pixels comprising a plurality of sub-pixels 32 of distinct colors.

As described below, the holographic layer 12 intrinsically forms an arrangement 29 of pixels which is blank, in the sense that the pixels 30 do not include the information defining the pattern of the image IG that is desired. form. It is by combining this arrangement 29 of pixels with the color modulation means 10 that a pattern of a personalized color image is revealed. To do this, the color modulation means 10 are configured to select the color of the pixels 30 by modifying the colorimetric contribution of the sub-pixels 32 relative to each other in at least part of the pixels 30 formed by the holographic layer 12. , so as to reveal a personalized color image IG from the arrangement 29 of pixels combined with the color modulation means 10.

In other words, the color modulation means 10 are configured to cause a selective passage (or modified, by masking, amplification or other) of the light from the holographic layer 12 to an observation point external to the image IG. These modulation means 10 thus generate color nuances in the pixels 30 by modifying the contribution of certain sub-pixels in the visual rendering of the final IG image.

The color modulation means 10 make it possible more particularly to modulate the passage of light so that, for at least part of the pixels 30, one or more sub-pixel has an increased or decreased contribution relative to that of at least one other neighboring sub-pixel of the pixel concerned.

[0056] As already indicated, the color image IG can be formed on any medium. As shown in FIG. 3, a secure document 20 comprising a document body 14 in or on which is formed a secure image IG as described above with reference to FIG. 2 will be considered below.

It is assumed in the following exemplary embodiments that the secure document 20 is an identity document, for example in the form of a card, such as an identity card, identification badge or the like. In these examples, the GI image is a color image with a pattern that matches the portrait of the document holder. As already indicated, however, other examples are possible.

[0058] In general, the holographic layer 12 has a holographic structure so as to produce the arrangement 29 of pixels in the form of a hologram by diffraction, refraction and / or reflection of incident light. The principle of the hologram is well known to those skilled in the art. Certain elements are recalled below for reference. Examples of embodiments of holographic structures are described, for example, in document EP 2 567 270 B1.

FIG. 4 shows, according to a particular embodiment, the holographic layer 12 of the color image IG mentioned above. To facilitate the description of the invention, the holographic layer 14 is shown here in its intrinsic form, that is to say without the presence of the color modulation means 10 (which will be described later).

The holographic layer 12 comprises a layer (or sub-layer) 22 as well as reliefs (or structures in relief) 24, containing three-dimensional information, which are formed from the layer 22 serving as a support. These reliefs 24 form projecting portions (also called “mountains”) separated by recesses (also called “valleys”).

The holographic layer 22 further comprises a layer (or sub-layer) 28, called a "high refractive index layer", which has an index of refraction n2 greater than the refractive index n1 of the reliefs 24 (it is assumed here that the reliefs 24 are an integral part of the layer 22 serving as a support, so that the reliefs 24 and the layer 22 have the same refractive index n1) . This layer 28, which can be a metallic and / or dielectric layer, covers the reliefs 24 of the holographic layer 12. As a person skilled in the art understands, the reliefs 24 form, in combination with the layer 28, a holographic structure 27 which produces a hologram (a holographic effect).

The reliefs 24 of the holographic structure 27 can be formed, for example, by embossing a layer of stamping varnish (included in the layer 22 in this example) in a known manner for producing different structures. The embossed surface of the reliefs 24 thus has the shape of a periodic lattice whose depth and period can be respectively of the order of a hundred to a few hundred nanometers, for example. This stamped surface is coated with layer 28, for example by means of vacuum deposition of a transparent dielectric material (with a high optical index) or / and of a metallic material. The holographic effect results from the combination of reliefs 24 and layer 28 forming the holographic structure 27.

[0063] The holographic layer 12 may optionally include other sub-layers (not shown) necessary to maintain the optical characteristics of the hologram and / or to ensure mechanical and chemical resistance of the assembly.

[0064] The high refractive index layer 28 (Figure 4) can be formed from at least one of the following materials: aluminum, silver, copper, zinc sulphide, titanium oxide ...

[0065] In the embodiments described in this document, the holographic layer 12 is transparent, so that the holographic effect revealing the IG color image is visible by diffraction, reflection and refraction. However, other arrangements are possible in which the holographic layer 12 is opaque so that the color image IG is only visible by reflection of light incident on the holographic structure 27.

The holographic structure 12 is produced by any suitable method known to those skilled in the art. The reliefs 24 have a refractive index denoted n1, of the order of 1.56 at a wavelength l = 656 nm for example.

In the example considered here (Figure 4), the layer 22 is a transparent varnish layer. The holographic structure 27 is coated with a thin layer 28, for example of aluminum or zinc sulphide, exhibiting a high refractive index n2 (relative to n1), for example of 2.346 at a wavelength l = 660 nm for zinc sulphide. The thin layer 28 has, for example, a thickness of between 30 and 200 nm.

Layer 22 may be a thermoformable layer thus allowing reliefs 24 of holographic structure 27 to be formed by embossing on layer 22 serving as a support. As a variant, the reliefs 24 of the holographic structure 27 can be produced using an ultraviolet (UV) crosslinking technique. Since these manufacturing techniques are known to those skilled in the art, they are not described in more detail for the sake of simplicity.

FIG. 5 represents examples of reliefs 24 of a holographic structure 27, comprising projecting portions and recesses.

Still with reference to Figure 4, the holographic layer 12 can be encapsulated or assembled with various other layers. Moreover, as already indicated, the holographic layer 12 forms an arrangement 29 of pixels 30. Each pixel 30 comprises a plurality of color sub-pixels 32, namely 3 sub-pixels 32 in the example considered here.

An OB observer can thus visualize, according to a particular direction of observation, the arrangement 29 of pixels from a light refracted, reflected and / or diffracted from the holographic structure 27 of the holographic layer 12.

As illustrated below, the arrangement 29 of pixels can take various forms.

FIGS. 6A and 6B represent, according to a particular embodiment, a pixel 30 formed by a region of the holographic structure 27 present in the holographic layer 12. More particularly, it is considered here that the reliefs 24 of the holographic structure 27 (figure 4) form lines 34 parallels of subpixels, however other implementations are possible. For each pixel 30, its constituent sub-pixels 32 are thus formed by a portion of a respective line 30, this portion constituting a respective holographic grating (or portion of a holographic grating) configured to generate by diffraction and / or reflection a corresponding color of said subpixel.

In the example considered here, the pixels 30 thus comprise 3 sub-pixels of distinct colors, other examples being however possible. Assume that each subpixel 32 is monochromatic. Each holographic grating is configured to generate a color in each sub-pixel 32 corresponding to a predetermined viewing angle, this color being changed to a different viewing angle. It is assumed, for example, that the sub-pixels 32 of each pixel 30 respectively have a distinct fundamental color (for example green / red / blue or cyan / yellow / magenta) according to a predetermined viewing angle.

As shown in Figures 6A and 6B, the holographic gratings corresponding to the three lines 34, which form the subpixels 32 of a single pixel 30, have particular geometric specifications so as to generate a desired distinct color. In particular, the holographic gratings forming the 3 sub-pixels 32 in this example have a width denoted I and a pitch between each holographic array denoted p.

Thus, in the example considered where each pixel 30 is composed of 4 subpixels 32, the maximum theoretical saturation capacity S in one of the colors of the subpixels in a same pixel can be stated from the as follows:

[0078] [Math. 1]

For example, we can consider that I = 60 pm and p = 10 pm which leads to a maximum theoretical saturation capacity S = 0.21.

It is possible to form the holographic networks forming the sub-pixels 32 so that the pitch p tends towards zero, which makes it possible to increase the capacitance. of maximum theoretical saturation in a color of a sub-pixel (S then tending towards 0.25).

According to a particular example, the pitch is set at p = 0, which makes it possible to achieve a maximum theoretical saturation capacity S equal to 0.25. In this case, the lines 34 of sub-pixels as shown in FIGS. 6A and 6B are contiguous (no space or white area being present between the lines of sub-pixels).

The invention thus makes it possible to form lines of sub-pixels which are contiguous, that is to say adjacent to each other without it being necessary to leave separating white areas between each line, or possibly by keeping white separating areas but of limited size between the lines of sub-pixels (with a low pitch p). As will appear more clearly in the light of the exemplary embodiments which follow, this particular configuration of the holographic networks makes it possible to significantly improve the quality of the final image IG (better color saturation). This is possible in particular because the formation of holographic structures makes it possible to achieve better positioning precision of the sub-pixels and better homogeneity than by conventional printing of the sub-pixels (by offset or other).

[0083] As already indicated, the arrangement 29 of pixels 30 formed by the holographic layer 12 (FIG. 2) can take various forms. Exemplary embodiments are described below.

In general, the arrangement 29 of pixels can be configured so that the sub-pixels 32 are uniformly distributed in the holographic layer 12. The sub-pixels 32 can for example form parallel lines of sub-pixels or another network in the form of a hexagon (of the Bayer type), other examples being possible.

The sub-pixels 32 can for example form an orthogonal matrix.

The pixels 30 can be uniformly distributed in the arrangement 29 so that the same pattern of sub-pixels 32 is periodically repeated in the holographic layer 12. Furthermore, each pixel 30 of the array 29 of pixels can be configured so that each sub-pixel 32 has a unique color in said pixel considered. According to a particular example, each pixel 32 in the array 29 of pixels forms an identical pattern of colored sub-pixels.

Particular examples of arrangements (or tiling) 29 of pixels that can be implemented in the secure document 20 (Figure 3) are now described with reference to Figures 7A, 7B and 7C. It should be noted that these implementations are presented only by way of nonlimiting examples, many variations being possible in terms in particular of the arrangement and shape of the pixels and sub-pixels, as well as the colors assigned to these. subpixels.

According to a first example shown in Figure 7A, the pixels 30 of the array 29 of pixels are rectangular (or square) in shape and include 3 sub-pixels 32a, 32b and 32c (collectively denoted 32) of distinct colors. As already described with reference to Figures 6A-6B, the subpixels 32 may each be formed by a portion of a line 34 of subpixels. In this example, the tiling 29 thus forms a matrix of rows and columns of pixels 30, orthogonal to one another.

FIG. 7B is a top view showing another example of regular tiling in which each pixel 30 is made up of 3 sub-pixels 32, denoted 32a to 32c, each of a distinct color. The sub-pixels 32 are here of hexagonal shape.

FIG. 7C is a top view showing another example of regular tiling in which each pixel 30 is composed of 4 sub-pixels 32, denoted 32a to 32d, each of a distinct color. The sub-pixels 32 are here triangular in shape.

For each of the pixel arrangements considered, it is possible to adapt the shape and the dimensions of each pixel 30 and also the dimensions of the separating white zones present, where appropriate, between the sub-pixels, so as to achieve the desired maximum color saturation level and the desired brightness level.

As already described, the color modulation means 10 included in the image IG (Figures 2-3) can be in different forms. Of generally, the color modulation means 10 can comprise at least one of:

- regions of the holographic structure 12, called destroyed regions, which are locally destroyed by laser;

- masking means positioned opposite the arrangement 29 of pixels 30 to locally mask all or part of sub-pixels 32; and

- Amplification means positioned opposite the arrangement 29 of pixels 30 to locally amplify the brightness of all or part of sub-pixels 32.

Examples of particular implementation of the secure document 20, comprising a color image IG as described previously with reference to FIGS. 2-7C, are described below. In these examples, the image IG (denoted more precisely IG1 to IG5, respectively) thus comprises a holographic layer 12 and color modulation means 10 as already described in general.

More particularly, a first particular embodiment of the secure document 2 (FIG. 1) is described with reference to FIGS. 8 and 9. In this example, the holographic layer 12 is interposed between transparent layers 40 and 42. In this example. the examples considered here, these two layers are made of polycarbonate, or any other suitable material for covering the holographic layer 12.

The holographic layer 12 comprises regions RG1 of the holographic structure 27, called destroyed regions, which are locally destroyed by laser. This selective destruction of the holographic structure 27 leads to a destruction, partial or total, of one or a plurality of sub-pixels 32 in at least part of the pixels 30, which causes a modification of the holographic effect in the regions concerned. Thus, the holographic effect is eliminated, or reduced, in the destroyed regions of the holographic structure 27, which decreases (or even completely eliminates) the relative contribution in color of one or a plurality of sub-pixels 32, located facing the destroyed regions RG1, with respect to at least one other neighboring sub-pixel 32 of the pixels 30 concerned. In other words, this selective destruction of the holographic structure 27 leads to a modification of the colorimetric weight of certain sub-pixels 32, in the final color image denoted here IG1, relative to at least one other sub-pixel 32 neighboring the pixels 30 concerned.

These destroyed regions RG1 thus collectively form color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the personalized color image IG1 (FIGS. 2-3), as already described above. .

Destruction by laser causes local elimination (or deformation) of the geometry of the holographic structure 27, and more particularly of the reliefs 24 and / or of the layer 28 covering said reliefs. These local destructions lead to a modification of the behavior of light (i.e. reflection, diffraction and / or refraction of light) in the corresponding pixels and sub-pixels.

According to a particular example, these destroyed regions RG1 in the holographic structure 27 correspond to areas destroyed by laser ablation in the holographic networks corresponding to all or part of sub-pixels 32 in the arrangement 29 of pixels. Thus, it is possible to achieve a partial laser ablation of a sub-pixel 32, as illustrated by way of example in FIG. 9, so as to reduce the color contribution of said sub-pixel in the pixel 30 concerned.

[0100] Laser ablation (Figures 8-9) can be carried out by means of LS1 laser radiation, for example of the Nd: YAG type having a single wavelength, for example of the order of 1064 nm. .

[0101] A second particular embodiment of the secure document 2 (FIG. 1) is now described with reference to FIG. 10. In this example, the holographic layer 12 previously described with reference to FIGS. 2-7C is also interposed between a layer 40 and a layer 42, as already described with reference to FIG. 9.

A pattern 50 is also printed facing the holographic structure 27, that is to say facing the arrangement 29 of pixels 30, so as to locally mask all or part of the sub-pixels 32. This pattern 50 is formed from a ink (or an equivalent material) which makes it possible to at least partially mask certain regions of the holographic structure 27.

The addition of this printed pattern 50 in the overall structure makes it possible to reduce (or even completely eliminate) the relative contribution in color of one or a plurality of sub-pixels 32, located opposite the printed pattern. 50, relative to at least one other neighboring sub-pixel 32 in the pixels 30 concerned. In other words, this selective masking of the holographic structure 27 leads to a modification of the colorimetric weight of certain sub-pixels 32, in the final color image denoted here IG2, relative to at least one other sub-pixel 32 adjacent to the pixels 30 concerned.

[0104] This printed pattern 50 thus forms color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the personalized color image IG2 (FIGS. 2-3), as already described above. Insofar as this pattern 50 aims to locally mask certain sub-pixels, it more particularly constitutes masking means within the meaning of the invention.

[0105] The ink used to form this printed pattern 50 can be black, white or any other color, depending on the desired masking effect, so as to modulate the color of the pixels 30 in the array 29 of pixels.

It is in particular possible to carry out printing, of inkjet type for example, so as to mask only a portion of a sub-pixel 32 (or even all of the sub-pixel 32), which allows to decrease the relative contribution in color of said sub-pixel 32 in the pixel 30 concerned.

[0107] In the example shown in Figure 10, the pattern 50 is printed on the upper face of the holographic layer 12, opposite the holographic structure 27. Other embodiments are however possible. One can for example print the pattern 50 on another layer facing the holographic layer 12, such as for example on the layer 40, on the layer 42 or on an additional layer not shown. Printing of the pattern 50 is also possible on the underside of the holographic layer 12.

[0108] A third particular embodiment of the secure document 2 (FIG. 1) is now described with reference to FIG. 11. In this example, the holographic layer 12 already described with reference to FIGS. 2-7C is also interposed between transparent layers 40 and 42, as already described with reference to FIG. 9.

In this example, a transparent layer 60 sensitive to the laser, called a “laserisable” layer, is also placed at the interface between the holographic layer 12 and the layer 40. This laserable layer 60 is capable of being locally opacified by means of LS2 laser radiation in order to at least partially block the passage of light, thereby making it possible to at least partially mask one or a plurality of sub-pixels.

[01 10] As illustrated, the lasérisable layer 40 thus comprises zones (or volumes) 62, called “opaque zones”, locally opacified by laser radiation LS2, these opaque zones being positioned opposite the holographic structure 27 so as to locally masking all or part of the sub-pixels 32. More particularly, these opaque zones 62 constitute laser points, of variable shapes and opacities, which are formed by local carbonization of the lasérisable layer 60. By playing in particular on the power of the laser LS2 and / or over the duration of the impact, the desired opaque zones 62 can be formed. Thus, the degree of blackening is a function of the energy applied by the LS2 laser radiation.

[01 11] The opaque (non-reflective) zones 60 are formed opposite certain sub-pixels 32 so as to produce gray levels in the final color image denoted here IG3.

[01 12] The addition of these opaque areas 62 makes it possible to reduce (or even completely eliminate) the relative contribution in color of one or a plurality of sub-pixels 32, located opposite, with respect to at least another sub-pixel 32 neighboring the pixels 30 concerned. In other words, this selective masking of the holographic structure 27 leads to a modification of the colorimetric weight of certain sub-pixels 32, in the final color image IG1, relative to at least one other sub-pixel 32 neighboring the pixels 30 concerned.

[01 13] These opaque zones 62 thus collectively form color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the personalized color image IG3 (FIGS. 2-3), as already described above. before. Insofar as these opaque zones 62 aim to locally masking certain sub-pixels, they more particularly constitute masking means within the meaning of the invention.

[01 14] In the example shown in FIG. 11, the laserisable layer 60 is located under the holographic layer 12, on the side of the holographic structure 27. Other implementations are however possible. In particular, the lasérisable layer 60 can be positioned above the holographic layer 12, on the side opposite the holographic structure 27. As a variant, several lasérisable layers comprising opaque zones can be provided above and below the layer. holographic 12.

[01 15] The laserisable materials that can be used to form the laserisable layer (s) described in this document are, by way of nonlimiting examples, polycarbonates, certain treated polyvinyl chlorides, treated acrylonitrille-butadiene-styrenes, or treated polyethylene terephthalates.

[01 16] A fourth particular embodiment of the secure document 2 (Figure 1) is now described with reference to Figure 12. In this example, the holographic layer 12 already described with reference to Figures 2-7C is also interposed between transparent layers 40 and 42a. The layers 40 and 42a can be made of polycarbonate or any other suitable material.

[01 17] In this example, a lenticular array 68 comprising a plurality of lenses LN is placed opposite the arrangement 29 of pixels formed by the holographic layer 12, so as to generate the personalized color image - denoted here IG4 - by focusing or diverging light incident through the LN lenses on at least part of the subpixels 32.

[01 18] The lenticular array 68 is formed in this example on the surface of the upper layer 42a, although other implementations are possible. LN lenses can be formed, for example, by projecting LS3 laser radiation. One can for example use a laser radiation of C0 ₂ or other type to create surface deformations defining the lenses LN of the lenticular array 68. The layer 42a is itself laminated on the holographic layer 12, or possibly on an intermediate layer located between layer 42a and holographic layer 12. [01 19] Each lens can be positioned (or configured), relative to a pixel 30 (called an “associated pixel”) located opposite, to focus or diverge the incident light on at least one of the sub- pixels 32 of said associated pixel so as to modify the contribution of the respective colors of the sub-pixels of the associated pixel, in a region of the color image IG4 generated through the lens, relative to the pattern intrinsically formed by the independently associated pixel 30 of (or without) said lens.

[0120] In other words, each lens LN can be positioned (or configured), relative to an associated pixel 30 located opposite, to focus or diverge the incident light on at least one of the sub-pixels 32 of said. associated pixel so as to modify the respective relative contribution in color of at least one sub-pixel of the associated pixel, in a region of the color image corresponding to said pixel, with respect to the respective contribution in color of the other sub-pixel (s) neighboring pixels of said associated pixel.

LN lenses thus make it possible to amplify the luminosity of certain sub-pixels 32 and to reduce the luminosity of other sub-pixels 32, which produces color nuances making it possible to reveal the final color image IG4 by the 'interaction between the lenticular array 68 and the arrangement 29 of pixels formed by the holographic structure 27. From the same arrangement 29 blank of pixels 30, it is thus possible to adapt the configuration of the lenses LN so as to generate various color images IG4.

[0122] The lenticular array 68 thus forms color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the personalized color image IG4 (Figures 2-3), as already described above. Insofar as this lenticular array 68 aims in particular to amplify the brightness of certain sub-pixels relative to others, it more particularly constitutes amplification means within the meaning of the invention.

[0123] According to a particular example, the LN lenses (or at least part of them) are converging lenses configured to focus the incident light received so as to accentuate the relative contribution in color of at least one sub-pixel. 32 of the associated pixel (pixel located opposite), in the corresponding region of the color image IG4 generated through said lens, by relative to the respective color contribution of each other neighboring sub-pixel 32 of said associated pixel 30.

[0124] According to a particular example, the LN lenses are configured to focus the light on a single sub-pixel 32 of the associated pixel 30 so as to mask the color of each other neighboring sub-pixel 32 of the associated pixel 30 in the corresponding region of the color image IG4 generated through said lens.

[0125] It is also possible to configure LN lenses in the lenticular array 68 so that they focus the light on subpixels 32 of the same color in the pixels 30 of a given region of the holographic structure. 27, so that a monochrome region appears in the custom color image IG4.

[0126] As a variant, it is possible to configure LN lenses in the lenticular array 68 so that they focus the light on at least two sub-pixels 32 neighboring the associated pixel 30, thus showing in a corresponding region of the color image IG4, a hybrid color resulting from a combination of the colors of said at least two neighboring sub pixels 32.

[0127] According to a particular example, at least part of the divergent LN lenses are configured to diverge an incident light received by the lens so as to reduce the color contribution of at least one sub-pixel 32 of the associated pixel 30, in the corresponding region of the color image IG4 generated through said lens, with respect to the respective contribution in color of the other sub-pixel (s) 32 neighboring the associated pixel 30.

[0128] The above arrangements are described only by way of example, other implementations of the lenticular array 68 being possible. In the example shown in Figure 12, the lenticular array 68 is located above the holographic layer 12. Alternatively, the lenticular array 68 may be formed on a laminated layer (eg, layer 40) below the holographic layer 12. (on the side of the holographic structure 27).

[0129] A fifth particular embodiment of the secure document 2 (FIG. 1) is now described with reference to FIG. 13. In this example, the holographic layer 12 already described with reference to FIGS. 2-7C is also interposed between transparent layers 40 and 42 as already described above.

The color image denoted here IG5 is formed by the combination of the holographic layer 12 already described above and of an optical amplification device 74 comprising a transparent laserable layer and a transparent separating layer 70 disposed between the layer. holographic 12 and the transparent laser layer. The transparent laserisable layer and the transparent separating layer 70 are located under the holographic layer 12, that is to say on the side of the holographic structure 27 formed by the reliefs 24 and the high refractive index layer 28. As explained below, the transparent separating layer 70 makes it possible to maintain a gap noted e1 between the holographic layer 12 and the transparent laserisable layer.

[0131] In the example considered here, the transparent laserisable layer mentioned above is the layer 40 located under the holographic layer 12, although other arrangements are possible.

Still in this example, the laserisable layer 40 comprises locally opacified areas 72, by means of laser radiation LS4, opposite the holographic layer 12 so as to cause an amplification of the brightness of sub-pixels 32 in the arrangement 30 of pixels in regions of the final color image IG5 corresponding to the opaque areas 72. The technique for forming the opaque areas 72 is identical to the technique described previously with reference to FIG. 11 for forming the opaque areas 62. The laserisable layer 40 may be identical to the laserisable layer 60 described with reference to FIG. 11. In particular, the opaque zones 72, partially or totally blocking the light, are produced by laser carbonization of certain regions of the laserable layer 40.

[0133] The transparent separating layer 70 makes it possible to maintain a distance e1 between the holographic structure 27 and the opaque zones 72. The formation of the opaque zones 72 in the laserable layer 40, at a distance from the holographic structure 27, makes it possible to generate a phenomenon of local amplification of the luminosity of the sub-pixels 32 situated opposite said opaque zones 72. To obtain this optical amplification effect, it is necessary that the thickness e1 of the transparent separating layer 70 is greater than or equal to half of the longest wavelength - denoted A _max - in the visible spectrum. In other words, it is necessary that:

[0134] [Math. 2]

or A _max ⁼ 750 nm

[0135] According to a particular example, the thickness e1 is between 0.375 pm and 100 pm (limits included), and preferably between 0.375 pm and 5 pm (limits included).

[0136] Each opaque zone 72 in the laserisable layer 40 is positioned opposite at least one sub-pixel 32 so as to amplify its relative colorimetric contribution in the region of the final color image IG5 with respect to at least one other sub-pixel 32 neighboring the pixel 30 considered.

[0137] The optical amplifying device 74 thus forms color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the personalized color image IG (FIGS. 2-3), as already described herein. -before. Insofar as this optical amplifying device 74 aims to amplify the luminosity of certain sub-pixels relative to others, it more particularly constitutes amplification means within the meaning of the invention.

In general, with reference to each of the embodiments described above, it is possible to further generate contrast to the color image IG thus obtained by incorporating in the overall structure a laserisable layer, if such a layer n 'is not already present in said structure. This laserisable layer can be carbonized locally with the laser in an identical manner to what is described above with reference to the laserisable layer 60 (FIG. 11) or to the laserisable layer 40 (FIG. 13), in order to create contrast in the color image. finish and thus improve the quality of its visual rendering.

[0139] More particularly, the overall structure of the color image may further comprise such a transparent laserisable layer facing the holographic layer 12, this lasérisable layer being at least partially carbonized by laser radiation so as to comprise regions opacified locally next to subpixels 32 of the pixel array 29 to produce grayscale in the custom color image.

[0140] In general, the invention advantageously makes it possible to create shades of colors so as to form a secure color image by the interaction between the color modulation means and the arrangement of pixels formed by the holographic layer. The color image is therefore formed by the combination of color modulation means and the arrangement of pixels located opposite each other. Without the addition of the color modulation means to orient or judiciously select the passage of the incident light, the pixels only form a blank arrangement as this set is devoid of the information characterizing the color image. These are the color modulation means that are configured, depending on the chosen subpixel arrangement, to customize the visual appearance of the pixels and thus reveal the final color image.

[0141] The present invention makes it possible to produce color images having good image quality while being secure and therefore resistant to falsifications and fraudulent reproductions.

[0142] More particularly, the invention makes it possible to obtain an increased image quality, namely a better overall brightness of the final image (more brilliance, more vivid colors) and a better capacity for color saturation. In other words, the invention achieves a high quality color image with an improved color gamut compared to a printed image.

[0143] The use of a holographic structure to form the arrangement of pixels is advantageous in that this technique offers high positioning precision of the pixels and sub-pixels thus formed. This technique makes it possible in particular to avoid overlaps or misalignments between sub-pixels, which improves the overall visual rendering.

[0144] As already described with reference to FIGS. 6A-6B, due to the increased positioning precision compared to the case of a conventional printing technique, the invention makes it possible to reduce, or even eliminate, the white areas. separator that would otherwise be necessary to provide between the sub-pixels (for example between the lines of sub-pixels) to avoid possible overlaps between subpixels. Thanks to the invention, it is therefore no longer necessary to keep separating white lines between the sub-pixels in order to maintain a positioning tolerance of the sub-pixels, which makes it possible to increase the maximum color saturation of each sub-pixel. pixel (less white per pixel and therefore more fundamental colors).

[0145] However, white sub-pixels, possibly of reduced size, can be kept in the pixel arrangement in order to obtain the desired level of brightness. It is even possible to remove white subpixels because the hologram is inherently very glossy and in particular allows for greater brightness than with printed inks. It is thus possible to keep only fundamental color subpixels in the pixel arrangement, which allows for increased color saturation capability. It is for example possible to form the pixels from only 3 subpixels (according to a hexagonal pattern for example), which makes it possible to achieve a theoretical maximum color saturation of 33% for each fundamental color.

[0146] By implementing the principle of the invention, it is possible to easily detect fraud when the image has been falsified or illegally reproduced. Furthermore, this level of complexity and security of the image achieved by the invention is not at the expense of the quality of the visual rendering of the image.

[0147] The color modulation means according to the principle of the invention can take various forms: (1) destroyed regions of the holographic structure,

(2) masking means or (3) amplification means, as described above. The color image IG according to the invention may however comprise any combination, or under combination, of at least two of the forms (1), (2) and (3) indicated above (for example (1) and (2), or (1) and

(3), or (2) and (3)).

A method for manufacturing a color image IG as described above is now described with reference to FIG. 14, according to a particular embodiment. Suppose, for example, that a color image IG is formed in a document 20 as illustrated in FIG. 3. During a creation step S2, a holographic structure 27 is produced in a holographic layer 12 which forms an arrangement 29 of pixels 30, as described above. Each pixel 30 comprises a plurality of sub-pixels 32 of distinct colors according to one of the examples already described.

[0150] Layer 22 (FIG. 4) may be a thermoformable layer thus allowing reliefs 24 of holographic structure 27 to be formed by embossing on layer 22 serving as a support. As a variant, the reliefs 24 of the holographic structure 27 can be produced using a UV crosslinking technique, as already indicated. Since these manufacturing techniques are known to those skilled in the art, they are not described in more detail for the sake of simplicity.

[0151] A layer of adhesive and / or glue (not shown) can also be used to ensure adhesion of the holographic layer 12 on a support (for example on a layer 42 or 42a already described above).

During a training step S4, color modulation means 10 are formed as already described previously, to select the color of the pixels 30 by modifying the relative colorimetric contribution of the sub-pixels 32 with respect to each other. others in at least part of the pixels 30 so as to reveal a personalized color image IG from the arrangement 29 of pixels combined with the color modulation means 10.

[0153] As already described, the color modulation means 10 thus formed can comprise at least one of:

- regions (RG1) of the holographic structure, called destroyed regions, which are locally destroyed over all or part of the sub-pixels 32 by a single first laser radiation LS1 (FIG. 8);

- masking means (50; 60-62) positioned opposite the arrangement 29 of pixels to locally mask all or part of sub-pixels 32 (FIGS. 10-11); and - amplification means (68; 70-72) positioned opposite the arrangement 29 of pixels to locally amplify the brightness of all or part of sub-pixels 32 (FIGS. 12-13).

[0154] Thus, the destroyed regions RG1 shown in FIG. 8 are formed by local destruction, by means of a single laser radiation LS1, by laser ablation of regions of the holographic structure in order to eliminate all or parts of sub-pixels in the pixel arrangement.

The masking means 50 shown in FIG. 10 are formed by printing ink patterns facing the holographic layer 12 obtained in step S2, so as to locally mask all or part of the sub-pixels in the pixel arrangement.

The lenticular array 68 shown in FIG. 12 is formed by deforming at the surface a layer 42a by means of a single laser radiation LS3, this lenticular array being arranged opposite the arrangement 29 of pixels so as to generate the A personalized color image by focusing (or diverging) light incident through the lenses onto at least a portion of the subpixels of the pixel array. As a variant, a projection of transparent material is made using a 3D printer head so as to form lenses on the surface of the transparent layer 42a.

[0157] The optical amplification device 74 shown in FIG. 13 is formed so as to include a transparent lasérisable layer 40 as well as a transparent separating layer 70 disposed between the holographic layer 12 and the transparent lasérisable layer 40. Opaque zones 72 are further formed locally, by means of a single laser radiation LS4, by carbonization in the laserisable layer 40 opposite the holographic layer 12 so as to cause an amplification of the brightness of subpixels 32 in the array 30 of pixels in regions corresponding to said opaque areas.

[0158] It is thus possible to form the color modulation means 10 using a single laser radiation, namely one of LS1, LS2, LS3 and LS4 depending on the type of color modulation means 10. that we want to train. In other words, the color modulation means 10 can be formed using a single laser radiation among:

- LS1 laser radiation necessary to produce destroyed regions RG1 as already described (Figure 8); the LS2 laser radiation necessary to form opaque zones 62 as already described (FIG. 11);

the LS3 laser radiation necessary to form a lenticular array 68 as already described (FIG. 12); and

the LS4 laser radiation necessary to form opaque zones 72 as already described (FIG. 13).

[0159] According to a particular example, the color modulation means 10 can be formed using at most two distinct laser radiations, from among the LS1 and LS4 radiations described above.

[0160] According to a particular example, the laser radiation LS2 and LS4 are identical.

[0161] The invention thus makes it possible to securely generate a high-quality personalized color image, from a relatively uncomplicated manufacturing process.

[0162] A person skilled in the art will understand that the embodiments and variants described in this document constitute only non-limiting examples of implementation of the invention. In particular, a person skilled in the art will be able to envisage any adaptation or combination of the characteristics and embodiments described above in order to meet a very specific need.

Claims

1. Secure document (2) comprising:

- color modulation means configured to select the color of the pixels by modifying the colorimetric contribution of the subpixels relative to each other in at least part of the pixels so as to reveal a personalized color image from the arrangement pixels combined with said modulation means,

The document of claim 1, wherein each subpixel in the pixel array is formed by a respective holographic grating configured to diffractively generate a corresponding color of said subpixel.

3. Document according to claim 1 or 2, wherein each pixel of said arrangement of pixels forms an identical pattern of color subpixels.

4. Document according to any one of claims 1 to 3, wherein each pixel of said arrangement of pixels is configured such that each sub-pixel has a unique color in said pixel.

A document according to any one of claims 1 to 4, wherein the pixel arrangement is configured such that the subpixels are evenly distributed on or in a substrate.

6. A document according to any one of claims 1 to 5, wherein the arrangement of pixels forms contiguous sub-pixel lines.

7. Document according to any one of claims 1 to 6, wherein said destroyed regions in the holographic structure correspond to areas destroyed by laser ablation of holographic gratings corresponding to all or part of sub-pixels in the pixel arrangement.

8. Document according to claim 7, wherein said destroyed regions comprise sub-pixels whose corresponding holographic grating is partially destroyed by laser micro-ablation.

9. Document according to any one of claims 1 to 8, wherein said masking means forming part of the color modulation means comprise at least one of:

10. Document according to any one of claims 1 to 9, wherein said amplification means forming part of the color modulation means comprise at least one of:

an array of lenses arranged opposite the arrangement of pixels so as to generate the personalized color image by focusing or diverging light incident through the lenses on at least part of the sub-pixels; and an optical amplification device comprising a transparent lasérisable layer, called the third layer, and a transparent separating layer arranged between the first layer and the third layer, said third layer comprising locally opacified areas with the laser facing the first layer so causing an amplification of the brightness of subpixels in said pixel arrangement in regions corresponding to said opacified areas.

1 1. Document according to claim 10, wherein each lens of the lens array is positioned relative to an associated pixel located vis-à-vis, to focus or diverge incident light on at least one of the sub-pixels of said associated pixel so as to modify the contribution of the respective colors of the sub-pixels of the associated pixel, in a region of the personalized color image generated through said lens, with respect to the pattern intrinsically formed by the associated pixel independently of said lens .

12. Document according to any one of claims 1-1 1, wherein the document further comprises a transparent lasérisable layer, said fourth layer, facing the first layer, said fourth layer being at least partially carbonized by laser radiation. so as to include locally opacified regions opposite subpixels of the pixel arrangement to produce gray levels in the custom color image.

13. Document according to any one of claims 1 to 12, wherein the first layer comprises:

14. A method of manufacturing a document, comprising:

- Creation (S2) in a first layer of a holographic structure forming an arrangement of pixels each comprising a plurality of sub-pixels of distinct colors;

- formation (S4) of color modulation means for selecting the color of the pixels by modifying the colorimetric contribution of the subpixels relative to each other in at least part of the pixels so as to reveal a personalized color image from the arrangement of pixels combined with said color modulation means,

the color modulation means comprising at least one of: o regions of the holographic structure, called destroyed regions, which are locally destroyed on all or part of the sub-pixels by a single first laser radiation;

15. The method of claim 14, wherein said forming of the color modulation means comprises at least one of:

- local destruction, by means of a single first laser radiation, by laser ablation of regions of the holographic structure to eliminate all or parts of subpixels in the pixel arrangement;

- formation, by means of a single second laser radiation, of an array of lenses arranged opposite the arrangement of pixels so as to generate the personalized color image by focusing or divergence of an incident light through the lenses on at least part of the subpixels of the pixel array; and - Formation of an optical amplification device comprising a transparent lasérisable layer, said third layer, and a transparent separating layer disposed between the first layer and the third layer, said third layer comprising locally opacified areas, by means of a single third laser radiation, facing the first layer so as to cause an amplification of the brightness of sub-pixels in said arrangement of pixels in regions corresponding to said opacified areas.