Color image formed from hologram

Abstract

The invention relates to a color image (CI) comprising: a first layer (10) having a holographic structure forming an arrangement (29) of pixels (30), each comprising sub-pixels (32) of distinct colors; and color modulation means configured to select the color of the pixels (30) by modifying the colorimetric contribution of the sub-pixels (32) relative to each other within the pixels (30) so as to reveal a customized color image. The color modulation means include amplification means positioned opposite the pixel arrangement to locally amplify the brightness of all or part of the sub-pixels.

Description

Domaine Technique

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

[0002] The identity market today demands increasingly secure identity documents. These documents must be easily authenticated and difficult to counterfeit (ideally, impossible to forge). This market encompasses a wide variety of documents, such as identity cards, passports, access badges, driver's licenses, etc., which can come in different formats (cards, booklets, etc.).

[0003] Various printing techniques have been developed over time to produce color prints. The production of identity documents, such as those mentioned above, requires secure color image creation to minimize the risk of falsification by malicious individuals. The manufacturing of such documents, particularly the bearer's identity image, must be sufficiently complex to make reproduction or falsification by an unauthorized person difficult.

[0004] One known solution involves printing a pixel matrix composed of colored sub-pixels onto a substrate and then creating grayscale levels by laser carbonization in a laser-etched layer adjacent to the pixel matrix. This reveals a customized color image that is difficult to falsify or reproduce. Examples of this technique are described, for instance, in documents EP 2 580 065 B1 (dated August 6, 2014) and EP 2 681 053 B1 (dated April 8, 2015).

[0005] Although this well-established technique offers good results, improvements are still possible, particularly in terms of the visual quality of the resulting image. Achieving high levels of color saturation with this image formation technique is indeed difficult. In other words, the color gamut (the ability to reproduce a range of colors) of this technique can be limited, which can be problematic in certain use cases. This stems primarily from the fact that the color subpixels are formed using a conventional printing method, such as offset printing, which does not allow for the creation of sufficiently straight and continuous lines of subpixels. This leads to inconsistencies in the printing of the subpixels (breaks in the pixel lines, irregular edges, etc.) and a degraded color 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 pixels and sub-pixels relative to each other (sub-pixel overlap problems, misalignments...) or due to the presence of a tolerance interval without printing between sub-pixels.

[0007] There figure 1 This represents an example of offset printing of 4 pixels, taking the form of 6 lines of sub-pixels in distinct colors. As shown, the outlines of each 6 line of sub-pixels exhibit irregularities. A tolerance must be allowed for the positioning of these lines due to positioning inaccuracies during printing.

[0008] As illustrated in figure 1 ,To compensate for these imperfections in the homogeneity and positioning of the subpixels within each pixel (and thus avoid potential overlaps of neighboring subpixels and the degradation of desired colors), it is possible to print the subpixels in such a way as to maintain a white area between each of them. However, this technique of adding white areas has a drawback in that it limits the level of saturation that can be achieved for a given color, preventing the creation of a satisfactory color gamut.

[0009] Today, there is a need for secure creation of personalized color images, particularly in documents such as identity documents and others. Specifically, there is a need for flexible and secure personalization of color images, making the resulting image difficult to falsify or reproduce and easily authenticated.

[0010] Furthermore, no solution capable of offering an appropriate level of security and flexibility currently allows for a good level of image brightness and a sufficient color gamut, particularly to obtain the color nuances necessary for the formation of certain high-quality color images, for example when image areas need to exhibit a highly saturated level in a given color. Exposé de l'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 pixel comprising a plurality of sub-pixels of distinct colors; and color modulation means configured to select the color of pixels by modifying the colorimetric contribution of the sub-pixels relative to each other in at least a portion of the pixels so as to reveal a customized color image from the pixel arrangement combined with said modulation means, color modulation means including at least one of the following: • regions of the holographic structure, called destroyed regions, which are destroyed locally by laser; • masking means positioned opposite the pixel arrangement to locally mask all or part of sub-pixels; and • amplification means positioned opposite the pixel arrangement to locally amplify the brightness of all or part of sub-pixels.

[0012] The invention advantageously enables the creation of color nuances to form a color image secured by the interaction between the color modulation means and the pixel arrangement formed by the holographic layer. The color image is thus formed by the combination of the color modulation means and the opposite pixel arrangement. Without the addition of color modulation means to orient or judiciously select the passage of incident light, the pixels form only a blank arrangement, as this set lacks the information characterizing the color image. It is the color modulation means that are configured, according to the chosen sub-pixel arrangement, to customize the visual appearance of the pixels and thus reveal the final color image.

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

[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 pixel arrangement is configured such that each sub-pixel exhibits 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 destroyed regions in the holographic structure correspond to areas destroyed by laser ablation of the holographic arrays 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 array is partially destroyed by laser micro-ablation.

[0021] According to a particular embodiment, said masking means, which are part of the color modulation means, include at least one of the following: ink patterns printed alongside the pixel arrangement to locally mask all or part of sub-pixels; and laser points of different shades of grey formed in a layer, called the second layer, so as to be positioned alongside the pixel arrangement to locally mask all or part of sub-pixels.

[0022] According to a particular embodiment, said amplification means forming part of the color modulation means comprise at least one of the following: a lens array arranged opposite the pixel arrangement so as to generate the personalized color image by focusing or diverging incident light through the lenses onto at least a portion of the sub-pixels; and an optical amplification device comprising a laserizable transparent layer, called the third layer, and a transparent separating layer disposed between the first layer and the third layer, said third layer comprising areas locally laser-opacified opposite the first layer so as to cause amplification of the brightness of sub-pixels in said pixel arrangement in regions corresponding to said opacified areas.

[0023] According to a particular embodiment, each lens of the lens array is positioned, relative to an associated pixel located opposite it, to focus or diverge incident light on at least one of the sub-pixels of said associated pixel so as to modify the respective color contribution of the sub-pixels of the associated pixel, in a region of the custom color image generated through said lens, relative to the pattern formed intrinsically by the associated pixel independently of said lens.

[0024] According to a particular embodiment, the document further comprises a laserizable transparent layer, referred to as the fourth layer, opposite the first layer, said fourth layer being at least partially carbonized by laser radiation so as to comprise locally opacified regions opposite sub-pixels of the pixel arrangement to produce gray levels in the custom color image.

[0025] According to a particular embodiment, the first layer comprises: a first undercoat of varnish forming the reliefs of a holographic network; and a second undercoat deposited on the reliefs of the first undercoat, said second undercoat having a refractive index higher than that of the first undercoat.

[0026] The invention also relates to a corresponding manufacturing method. More specifically, the invention relates to a method 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 for selecting the color of pixels by modifying the colorimetric contribution of the sub-pixels relative to each other in at least a portion of the pixels so as to reveal a personalized color image from the pixel arrangement combined with said color modulation means, color modulation means including at least one of the following: • regions of the holographic structure, called destroyed regions, which are destroyed locally on all or part of sub-pixels by a single first laser beam; • masking means positioned opposite the pixel arrangement to locally mask all or part of sub-pixels; and • amplification means positioned opposite the pixel arrangement to locally amplify the brightness of all or part of sub-pixels.

[0027] According to a particular embodiment, said color modulation means formation comprises at least one of the following: local destruction, by means of a single first laser beam (at a single wavelength), by laser ablation of regions of the holographic structure to eliminate all or parts of sub-pixels in the pixel arrangement; printing of ink patterns opposite the first layer to locally mask all or part of sub-pixels in the pixel arrangement; formation, by means of a single second laser beam (at a single wavelength), of a lens array arranged opposite the pixel arrangement so as to generate the personalized color image by focusing or diverging incident light through the lenses onto at least some of the sub-pixels of the pixel arrangement;and the formation of an optical amplification device comprising a laserizable transparent layer, called the third layer, and a transparent separating layer disposed between the first layer and the third layer, said third layer comprising areas locally opacified by means of a single third laser beam (at a single wavelength), opposite the first layer so as to cause an amplification of the brightness of sub-pixels in said pixel arrangement in regions corresponding to said opacified areas. Brève description des dessins

[0028] [ Fig. 1 ] There figure 1 The process, already described above, schematically represents the printing of lines of colored sub-pixels onto a substrate. Fig. 2 ] There figure 2 schematically represents a color image according to a particular embodiment of the invention; Fig. 3 ] There figure 3 schematically represents a secure document according to a particular embodiment of the invention; [ Fig. 4 ] There figure 4 schematically represents a holographic layer of a secure image according to a particular embodiment of the invention; [ Fig. 5 ] There figure 5 schematically represents the reliefs of a holographic layer according to a particular embodiment of the invention; [ Fig. 6A-6B ] THE figures 6A et 6B schematically represent a pixel formed by a region of a holographic structure, according to a particular embodiment of the invention; [ Fig. 7A-7B-7C ] THE figures 7A, 7B et 7C schematically represent an arrangement of pixels and sub-pixels, according to particular embodiments of the invention; [ Fig. 8 ] There figure 8 schematically represents a color image according to a particular embodiment of the invention; Fig. 9 ] There figure 9 schematically illustrates the partial destruction of sub-pixels, according to a particular embodiment of the invention; [ Fig. 10 ] There figure 10 schematically represents a color image according to a particular embodiment of the invention; Fig. 11 ] There figure 11 schematically represents a color image according to a particular embodiment of the invention; Fig. 12 ] There figure 12 schematically represents a color image according to a particular embodiment of the invention; Fig. 13 ] There figure 13 schematically represents a color image according to a particular embodiment of the invention; and [ Fig. 14 ] There figure 14 schematically represents a manufacturing process according to a particular embodiment of the invention. Description des modes de réalisation

[0029] As previously stated, the invention relates generally to the formation of a color image and in particular to a secure document containing such an image.

[0030] The invention aims to securely form a color image from a holographic layer comprising a hologram forming an arrangement of pixels, these pixels themselves comprising a plurality of colored sub-pixels, and from color modulation means configured to select the color of pixels in the holographic layer by modifying the relative colorimetric contribution of the sub-pixels to each other in at least a portion 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.

[0031] The color modulation means modify the colorimetric contribution (or weight) of subpixels relative to neighboring subpixels in corresponding pixels, so as to reveal a custom color image from the combination of the pixel arrangement and said modulation means.

[0032] The invention also relates to a method for forming such a color image.

[0033] Other aspects and advantages of the present invention will become apparent from the embodiments described below with reference to the aforementioned drawings. In the remainder of this document, examples of implementations of the invention are described for a document containing a color image according to the principle of the invention. This document can be any type of document, referred to as a secure document, such as a booklet, card, or other. The invention finds particular applications in the creation of identity images in identity documents such as: identity cards, credit cards, passports, driver's licenses, secure access badges, etc. The invention also applies to security documents (banknotes, notarized documents, official certificates, etc.) containing at least one color image.

[0034] In general, the image according to the invention can be formed on any suitable medium.

[0035] Similarly, the implementation examples described below aim to create an identity image. It is understood, however, that the color image used can be of any kind. It could be, for example, an image representing the portrait of the document holder, although other implementations are possible.

[0036] 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.

[0037] There figure 2 schematically represents a color image IG conforming to a particular embodiment of the invention.

[0038] As illustrated in this figure, the color image IG includes a holographic layer (also called the "first layer") 12 coupled to, or comprising, color modulation means 10. The holographic layer 12 includes a holographic structure forming an arrangement 29 of pixels 30, each pixel comprising a plurality of sub-pixels 32 of distinct colors.

[0039] As described below, the holographic layer 12 inherently forms a blank arrangement 29 of pixels, in the sense that the pixels 30 do not contain the information defining the pattern of the desired IG image. It is by combining this arrangement 29 of pixels with the color modulation means 10 that a pattern of a custom color image is revealed. To achieve 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 a portion of the pixels 30 formed by the holographic layer 12, so as to reveal a custom IG color image from the arrangement 29 of pixels combined with the color modulation means 10.

[0040] In other words, the color modulation means 10 are configured to cause a selective (or modified, by masking, amplification or otherwise) passage of light from the holographic layer 12 to an observation point external to the IG image. These modulation means 10 thus generate color nuances in the pixels 30 by modifying the contribution of certain sub-pixels to the visual rendering of the final IG image.

[0041] The color modulation means 10 allow in particular the modulation of the passage of light so that, for at least part of the pixels 30, one or more sub-pixels have an increased or decreased contribution compared to that of at least one other sub-pixel near the pixel concerned.

[0042] As already mentioned, the IG color image can be formed on any medium. As shown in figure 3 , we will subsequently consider a secure document 20 comprising a document body 14 in or on which a secure image IG is formed as described above with reference to the figure 2 .

[0043] The following implementation examples assume that the secure document 20 is an identity document, such as a card like an identity card, identification badge, or similar. In these examples, the image IG is a color image whose design corresponds to the portrait of the document holder. As already mentioned, other examples are possible.

[0044] In general, the holographic layer 12 has a holographic structure such that it produces 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. Some elements are recalled below for reference. Examples of the realization of holographic structures are described, for example, in document EP 2 567 270 B1.

[0045] There figure 4 represents, 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 represented here in its intrinsic form, that is to say without the presence of the color modulation means 10 (which will be described later).

[0046] The holographic layer 12 comprises a layer (or sublayer) 22 and reliefs (or relief structures) 24, containing three-dimensional information, which are formed from the layer 22 serving as a support. These reliefs 24 form protruding portions (also called "mountains") separated by indentations (also called "valleys").

[0047] The holographic layer 22 further comprises a layer (or sub-layer) 28, called the "high refractive index layer," which has a refractive index 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 those skilled in the art understand, the reliefs 24, in combination with the layer 28, form a holographic structure 27 that produces a hologram (a holographic effect).

[0048] The reliefs 24 of the holographic structure 27 can be formed, for example, by embossing a layer of stamping varnish (included in layer 22 in this example) in a manner known for producing diffring structures. The embossed surface of the reliefs 24 thus exhibits a periodic lattice shape whose depth and period can be on the order of hundreds to hundreds of nanometers, respectively, in this example. This embossed surface is coated with layer 28, for example, by vacuum deposition of a transparent dielectric material (with a high refractive index) and / or a metallic material. The holographic effect results from the combination of the reliefs 24 and layer 28, forming the holographic structure 27.

[0049] 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.

[0050] Layer 28 has a high refractive index ( figure 4 ) can be formed from at least one of the following materials: aluminium, silver, copper, zinc sulfide, titanium oxide...

[0051] In the embodiments described in this document, the holographic layer 12 is transparent, so that the holographic effect revealing the color image IG is visible by diffraction, reflection, and refraction. However, other arrangements are conceivable in which the holographic layer 12 is opaque, so that the color image IG is visible only by reflection of incident light on the holographic structure 27.

[0052] The holographic structure 12 is produced by any suitable process known to a person skilled in the art.

[0053] The reliefs 24 have a refractive index noted n1, of the order of 1.56 at a wavelength λ = 656 nm for example.

[0054] In the example considered here ( figure 4 ), Layer 22 is a transparent varnish layer. The holographic structure 27 is coated with a thin layer 28, for example, of aluminum or zinc sulfide, having a high refractive index n2 (relative to n1), for example, 2.346 at a wavelength λ = 660 nm for zinc sulfide. The thin layer 28 has, for example, a thickness between 30 and 200 nm.

[0055] Layer 22 can be a thermoformable layer, allowing the reliefs 24 of the holographic structure 27 to be formed by embossing onto the layer 22, which serves as a substrate. Alternatively, the reliefs 24 of the holographic structure 27 can be produced using an ultraviolet (UV) curing technique. Since these manufacturing techniques are known to those skilled in the art, they are not described in further detail for the sake of simplicity.

[0056] There figure 5 represents examples of reliefs 24 of a holographic structure 27, comprising protruding portions and recesses.

[0057] Still referring to the figure 4 ,The holographic layer 12 can be encapsulated or assembled with various other layers. Furthermore, as already mentioned, 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.

[0058] An OB observer can thus visualize, according to a particular observation direction, the arrangement 29 of pixels from light refracted, reflected and / or diffracted from the holographic structure 27 of the holographic layer 12.

[0059] As illustrated later, the 29-pixel arrangement can appear in various forms.

[0060] THE figures 6A et 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 specifically, it is considered here that the reliefs 24 of the holographic structure 27 ( figure 4 ) form parallel lines 34 of sub-pixels, although 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 sub-pixel.

[0061] In the example considered here, the pixels 30 thus comprise 3 sub-pixels of distinct colors, although other examples are possible. We assume that each sub-pixel 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 modified at a different viewing angle. For example, we assume that the sub-pixels 32 of each pixel 30 each exhibit a distinct primary color (e.g., green / red / blue or cyan / yellow / magenta) at a predetermined viewing angle.

[0062] As represented in figures 6A et 6B ,The holographic gratings corresponding to the three lines 34, which form the sub-pixels 32 of the same pixel 30, have particular geometric specifications in order to generate a distinct desired 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 grating denoted p.

[0063] Thus, in the example considered where each pixel 30 is composed of 4 sub-pixels 32, the maximum theoretical saturation capacity S in one of the colors of the sub-pixels in the same pixel can be stated as follows: S = 25 100 × l l + p

[0064] As an example, we can consider that I = 60 µm and p = 10 µm which leads to a maximum theoretical saturation capacitance S = 0.21.

[0065] It is possible to form the holographic networks forming the sub-pixels 32 so that the step p tends towards zero, which makes it possible to increase the maximum theoretical saturation capacity in a color of a sub-pixel (S then tending towards 0.25).

[0066] In one particular example, the step size is set to p = 0, which allows for a maximum theoretical saturation capacity S of 0.25. In this case, the 34 sub-pixel lines are as represented in figures 6A et 6B are contiguous (no space or white area is present between the sub-pixel lines).

[0067] The invention thus makes it possible to form lines of sub-pixels that are contiguous, that is, adjacent to each other, without the need for separating white areas between each line, or possibly by maintaining separating white areas of limited size between the lines of sub-pixels (with a small pitch p). As will become clearer from the following embodiments, this particular configuration of holographic arrays significantly improves the quality of the final IG image (better color saturation). This is possible in particular because the formation of holographic structures allows for greater sub-pixel positioning accuracy and homogeneity than conventional sub-pixel printing (by offset or other methods).

[0068] As already mentioned, the arrangement of pixels 29 and 30 formed by the holographic layer 12 ( figure 2 ) It can take various forms. Examples of implementation are described below.

[0069] 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 a hexagonal (Bayer type) array, other examples being possible.

[0070] The 32 sub-pixels can, for example, form an orthogonal matrix.

[0071] The pixels 30 can be evenly distributed in the arrangement 29 so that the same pattern of sub-pixels 32 is repeated periodically in the holographic layer 12.

[0072] Furthermore, each pixel 30 in the arrangement of pixels 29 can be configured so that each subpixel 32 displays a unique color within that pixel. In a particular example, each pixel 32 in the arrangement of pixels 29 forms an identical pattern of colored subpixels.

[0073] Specific examples of pixel arrangements (or tiling) 29 that can be implemented in the secure document 20 ( figure 3 ) are now described with reference to figures 7A, 7B et 7C It should be noted that these implementations are presented only as non-limiting examples, as many variations are possible, particularly in terms of the arrangement and shape of pixels and sub-pixels, as well as the colors assigned to these sub-pixels.

[0074] According to a first example represented in figure 7A The 30 pixels of the 29 pixel arrangement are rectangular (or square) and comprise 3 sub-pixels 32a, 32b, and 32c (collectively denoted as 32) of distinct colors. As already described with reference to figures 6A-6B , the sub-pixels 32 can each be formed by a portion of a row 34 of sub-pixels. In this example, the tiling 29 thus forms a matrix of rows and columns of pixels 30, orthogonal to each other.

[0075] There figure 7B is a top view representing another example of a regular tiling in which each pixel 30 is composed of 3 sub-pixels 32, labeled 32a to 32c, each of a distinct color. The sub-pixels 32 are hexagonal in shape here.

[0076] There figure 7C is a top view representing another example of a regular tiling in which each pixel 30 is composed of 4 sub-pixels 32, labeled 32a to 32d, each of a distinct color. The sub-pixels 32 are triangular in shape here.

[0077] For each of the pixel arrangements considered, it is possible to adapt the shape and dimensions of each pixel 30 and also the dimensions of the white separating areas present, if any, between the sub-pixels, so as to achieve the desired maximum color saturation level and the desired brightness level.

[0078] As already described, the 10 color modulation means included in the IG image ( figures 2-3 ) can take various forms. Generally, the means of color modulation 10 can include at least one of the following: regions of the holographic structure 12, called destroyed regions, which are destroyed locally 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.

[0079] Examples of specific implementation of the secure document 20, including a color IG image as described previously with reference to figures 2-7C , are described below. In these examples, the IG image (more precisely noted as IG1 to IG5, respectively) thus includes a holographic layer 12 and color modulation means 10 as already described in general terms.

[0080] More specifically, a first particular implementation method of the secure document 2 ( figure 1 )is described with reference to the figures 8 et 9 . In this example, the holographic layer 12 is interposed between transparent layers 40 and 42. In the examples considered here, these two layers are made of polycarbonate, or any other suitable material to cover the holographic layer 12.

[0081] The holographic layer 12 contains RG1 regions of the holographic structure 27, called destroyed regions, which are locally destroyed by laser. This selective destruction of the holographic structure 27 leads to the partial or total destruction of one or more subpixels 32 in at least some of the pixels 30, resulting in a modification of the holographic effect in the affected regions. Thus, the holographic effect is eliminated, or reduced, in the destroyed regions of the holographic structure 27, which diminishes (or even completely eliminates) the relative color contribution of one or more subpixels 32, located opposite the destroyed RG1 regions, compared to at least one other neighboring subpixel 32 of the affected pixels 30.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 noted here as IG1, compared to at least one other sub-pixel 32 near the pixels 30 concerned.

[0082] 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 ( figures 2-3 ), as already described above.

[0083] Laser destruction causes localized elimination (or deformation) of the geometry of the holographic structure 27, and more specifically of the reliefs 24 and / or the layer 28 covering said reliefs. These localized destructions result in a modification of the behavior of light (i.e., the reflection, diffraction, and / or refraction of light) in the corresponding pixels and sub-pixels.

[0084] According to a specific example, these destroyed regions RG1 in the holographic structure 27 correspond to areas destroyed by laser ablation in the holographic gratings corresponding to all or part of sub-pixels 32 in the pixel arrangement 29. Thus, it is possible to perform partial laser ablation of a sub-pixel 32, as illustrated as an example in figure 9 , so as to reduce the colour contribution of said sub-pixel in the relevant pixel 30.

[0085] Laser ablation ( figures 8-9 ) can be achieved using LS1 laser radiation, for example of the Nd:YAG type with a single wavelength, for example on the order of 1064 nm.

[0086] A second specific embodiment of the secure document 2 ( figure 1 ) is now described with reference to the figure 10 . In this example, the holographic layer 12 previously described with reference to figures 2-7C is also interposed between a layer 40 and a layer 42, as already described with reference to the figure 9 .

[0087] A pattern 50 is further printed opposite the holographic structure 27, i.e. opposite the arrangement 29 of pixels 30, so as to locally mask all or part of sub-pixels 32. This pattern 50 is formed from an ink (or equivalent material) which makes it possible to at least partially mask certain regions of the holographic structure 27.

[0088] Adding this printed pattern 50 to the overall structure reduces (or even completely eliminates) the relative color contribution of one or more subpixels 32, located opposite the printed pattern 50, compared to at least one other neighboring subpixel 32 in the relevant pixels 30. In other words, this selective masking of the holographic structure 27 leads to a modification of the color weight of certain subpixels 32 in the final color image, here denoted IG2, compared to at least one other neighboring subpixel 32 of the relevant pixels 30.

[0089] This printed pattern 50 thus forms means of color modulation 10 which are configured, in combination with the holographic layer 12, to reveal the personalized color image IG2 ( figures 2-3 ),as already described above. Insofar as this pattern 50 aims to locally mask certain sub-pixels, it constitutes more particularly masking means within the meaning of the invention.

[0090] 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 arrangement 29 of pixels.

[0091] In particular, it is possible to produce a print, such as an inkjet print, so as to mask only a portion of a sub-pixel 32 (or even the entire sub-pixel 32), which makes it possible to reduce the relative color contribution of said sub-pixel 32 in the pixel 30 concerned.

[0092] In the example shown in figure 10 , lePattern 50 is printed on the upper surface of the holographic layer 12, opposite the holographic structure 27. However, other embodiments are possible. For example, pattern 50 can be printed on another layer opposite the holographic layer 12, such as layer 40, layer 42, or an additional layer not shown. Printing pattern 50 is also possible on the lower surface of the holographic layer 12.

[0093] A third specific embodiment of the secure document 2 ( figure 1 ) is now described with reference to the figure 11 . In this example, the holographic layer 12 already described in reference to figures 2-7C is also interposed between transparent layers 40 and 42, as already described with reference to the figure 9 .

[0094] In this example, a laser-sensitive transparent layer 60, called the "laserizable" layer, is further disposed at the interface between the holographic layer 12 and the layer 40. This laserizable layer 60 is capable of being locally opacified by means of laser radiation LS2 in order to block at least partially the passage of light, which makes it possible to at least partially mask one or a plurality of sub-pixels.

[0095] As illustrated, the laser-sealable layer 40 comprises areas (or volumes) 62, referred to as "opaque zones," which are locally opacified by laser radiation LS2. These opaque zones are positioned opposite the holographic structure 27 so as to locally mask all or part of the sub-pixels 32. More specifically, these opaque zones 62 constitute laser points of varying shapes and opacities, which are formed by local carbonization of the laser-sealable layer 60. By adjusting the power of the laser LS2 and / or 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 laser radiation LS2.

[0096] The opaque areas 60 (non-reflective) are formed opposite certain sub-pixels 32 so as to produce grey levels in the final colour image noted here as IG3.

[0097] The addition of these opaque areas 62 makes it possible to reduce (or even completely eliminate) the relative color contribution of one or more subpixels 32, located opposite each other, compared to at least one other subpixel 32 near the pixels 30 in question. In other words, this selective masking of the holographic structure 27 leads to a modification of the color weight of certain subpixels 32 in the final color image IG1, compared to at least one other subpixel 32 near the pixels 30 in question.

[0098] These opaque areas 62 thus collectively form color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the customized color image IG3 ( figures 2-3 ), as already described above. Insofar as these opaque areas 62 are intended to locally mask certain sub-pixels, they constitute more specifically masking means within the meaning of the invention.

[0099] In the example shown in figure 11 , The laserizable layer 60 is located below the holographic layer 12, on the side of the holographic structure 27. However, other implementations are possible. In particular, the laserizable layer 60 can be positioned above the holographic layer 12, on the opposite side from the holographic structure 27. Alternatively, several laserizable layers with opaque areas can be placed above and below the holographic layer 12.

[0100] Laserizable materials that can be used to form the laserizable layer(s) described in this document include, but are not limited to, polycarbonates, certain treated polyvinyl chlorides, treated acrylonitrile-butadiene-styrenes, or treated polyethylene terephthalates.

[0101] A fourth specific embodiment of the secure document 2 ( figure 1 )is now described with reference to the figure 12 . In this example, the holographic layer 12 already described in reference to figures 2-7C is also interposed between transparent layers 40 and 42a. Layers 40 and 42a can be made of polycarbonate or any other suitable material.

[0102] In this example, a lenticular array 68 comprising a plurality of LN lenses is arranged opposite the arrangement 29 of pixels formed by the holographic layer 12, so as to generate the custom color image - noted here as IG4 - by focusing or diverging incident light through the LN lenses onto at least a part of the sub-pixels 32.

[0103] The lenticular grating 68 is formed in this example on the surface of the upper layer 42a, although other implementations are possible. The LN lenses can be formed, for example, by projecting LS3 laser radiation. A CO2 or other type of laser radiation can be used to create surface deformations defining the LN lenses of the lenticular grating 68. Layer 42a is itself laminated onto the holographic layer 12, or possibly onto an intermediate layer located between layer 42a and holographic layer 12.

[0104] Each lens can be positioned (or configured), relative to a pixel 30 (called "associated pixel") located opposite it, 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 color contribution of the sub-pixels of the associated pixel, in a region of the color image IG4 generated through the lens, with respect to the pattern formed intrinsically by the associated pixel 30 independently of (or without) said lens.

[0105] In other words, each LN lens can be positioned (or configured), relative to an associated pixel 30 located opposite it, to focus or diverge the incident light on at least one of the subpixels 32 of said associated pixel so as to modify the respective relative color contribution of at least one subpixel of the associated pixel, in a region of the color image corresponding to said pixel, relative to the respective color contribution of the other neighboring subpixel(s) of said associated pixel.

[0106] The LN lenses thus make it possible to amplify the brightness of some sub-pixels 32 and to decrease the brightness of other sub-pixels 32, which produces shades of color which reveal the final color image IG4 by the interaction between the lenticular network 68 and the arrangement 29 of pixels formed by the holographic structure 27. From the same empty arrangement 29 of pixels 30, it is thus possible to adapt the configuration of the LN lenses so as to generate various color images IG4.

[0107] The lenticular array 68 thus forms color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the customized color image IG4 ( figures 2-3 ),as already described above. Insofar as this lenticular network 68 aims in particular to amplify the brightness of certain sub-pixels relative to others, it constitutes more particularly amplification means within the meaning of the invention.

[0108] According to a particular example, LN lenses (or at least a part of them) are converging lenses configured to focus the received incident light so as to accentuate the relative color contribution of at least one subpixel 32 of the associated pixel (opposite pixel), in the corresponding region of the color image IG4 generated through said lens, relative to the respective color contribution of each other subpixel 32 neighboring said associated pixel 30.

[0109] According to a particular example, the LN lenses are configured to focus light on a single subpixel 32 of the associated pixel 30 so as to mask the color of each other subpixel 32 neighboring the associated pixel 30 in the corresponding region of the color image IG4 generated through said lens.

[0110] It is also possible to configure LN lenses in the lenticular array 68 so that they focus light on sub-pixels 32 of the same color in the pixels 30 of a given region of the holographic structure 27, so as to make a monochrome region appear in the custom color image IG4.

[0111] Alternatively, 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 neighbors of the associated pixel 30, thus causing a hybrid color to appear in a corresponding region of the color image IG4 resulting from a combination of the colors of said at least two sub-pixels 32 neighbors.

[0112] According to a particular example, at least some of the diverging LN lenses are configured to diverge incident light received by the lens so as to reduce the color contribution of at least one subpixel 32 of the associated pixel 30, in the corresponding region of the color image IG4 generated through said lens, relative to the respective color contribution of the other subpixel(s) 32 neighboring the associated pixel 30.

[0113] The arrangements above are described only as examples; other implementations of the lenticular 68 network are possible. In the example shown in figure 12 , The lenticular network 68 is located above the holographic layer 12. Alternatively, the lenticular network 68 can be formed on a laminated layer (for example layer 40) below the holographic layer 12 (on the side of the holographic structure 27).

[0114] A fifth specific embodiment of the secure document 2 ( figure 1 ) is now described with reference to the figure 13 . In this example, the holographic layer 12 already described in reference to figures 2-7C is also interposed between transparent layers 40 and 42 as already described previously.

[0115] The color image, here denoted IG5, is formed by the combination of the holographic layer 12 described above and an optical amplification device 74 comprising a laser-serizable transparent layer and a transparent separating layer 70 located between the holographic layer 12 and the laser-serizable transparent layer. The laser-serizable transparent layer and the transparent separating layer 70 are situated beneath the holographic layer 12, that is, 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 maintains a gap, denoted e1, between the holographic layer 12 and the laser-serizable transparent layer.

[0116] In the example considered here, the laserizable transparent layer mentioned above is layer 40 located below the holographic layer 12, although other arrangements are possible.

[0117] In this example, the laserizable layer 40 includes areas 72 that are locally opacified by means of laser radiation LS4, opposite the holographic layer 12, so as to cause an amplification of the brightness of subpixels 32 in the pixel arrangement 30 in regions of the final color image IG5 corresponding to the opacified areas 72. The technique for forming the opaque areas 72 is identical to the technique described previously with reference to the figure 11 to form the opaque areas 62. The laser-sealable layer 40 can be identical to the laser-sealable layer 60 described with reference to the figure 11 . In particular, the opaque areas 72, partially or totally blocking light, are produced by laser carbonization of certain regions of the laserizable layer 40.

[0118] The transparent separating layer 70 maintains a gap e1 between the holographic structure 27 and the opaque areas 72. The formation of the opaque areas 72 in the laserizable layer 40, at a distance from the holographic structure 27, generates a local amplification of the brightness of the sub-pixels 32 located opposite these opaque areas 72. To obtain this optical amplification effect, the thickness e1 of the transparent separating layer 70 must be greater than or equal to half the longest wavelength – denoted λmax – in the visible spectrum. In other words, it is necessary that: e 1 ≥ 1 2 × λ max = 375 nm où λ max = 750 nm

[0119] According to a particular example, the thickness e1 is between 0.375 µm and 100 µm (inclusive terminals), and preferably between 0.375 µm and 5 µm (inclusive terminals).

[0120] Each opaque area 72 in the laserizable 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 compared to at least one other sub-pixel 32 near the pixel 30 under consideration.

[0121] The optical amplification device 74 thus forms color modulation means 10 which are configured, in combination with the holographic layer 12, to reveal the customized color image IG ( figures 2-3 ), as already described above. Insofar as this optical amplification device 74 aims to amplify the brightness of certain sub-pixels relative to others, it constitutes more particularly amplification means within the meaning of the invention.

[0122] In general, with reference to each of the embodiments described above, it is possible to generate additional contrast in the resulting IG color image by incorporating a laserizable layer into the overall structure, if such a layer is not already present in said structure. This laserizable layer can be locally carbonized by laser in the same way as described above with reference to the laserizable layer 60 ( figure 11 ) or to the 40 laser-coated layer ( figure 13 ), in order to create contrast in the final color image and thus improve the quality of its visual rendering.

[0123] More specifically, the overall structure of the color image may further include such a laserizable transparent layer opposite the holographic layer 12, this laserizable layer being at least partially carbonized by laser radiation so as to include locally opacified regions opposite subpixels 32 of the arrangement 29 of pixels to produce grey levels in the customized color image.

[0124] In general, the invention advantageously allows for the creation of color nuances to form a color image secured by the interaction between the color modulation means and the pixel arrangement formed by the holographic layer. The color image is thus formed by the combination of the color modulation means and the opposite pixel arrangement. Without the addition of color modulation means to judiciously direct or select the passage of incident light, the pixels form a blank arrangement, as this set lacks the information characterizing the color image. It is the color modulation means that are configured, according to the chosen sub-pixel arrangement, to customize the visual appearance of the pixels and thus reveal the final color image.

[0125] The present invention makes it possible to produce color images with good image quality while being secure and therefore resistant to falsification and fraudulent reproduction.

[0126] More specifically, the invention enables enhanced image quality, namely improved overall brightness of the final image (greater brightness, more vibrant colors) and greater color saturation. In other words, the invention makes it possible to produce a high-quality color image with an improved color gamut compared to a printed image.

[0127] Using a holographic structure to form the pixel arrangement is advantageous because this technique offers high precision in positioning the resulting pixels and sub-pixels. This technique helps avoid overlaps or misalignments between sub-pixels, thus improving the overall visual rendering.

[0128] As already described with reference to figures 6A-6B , Due to the increased positioning accuracy compared to conventional printing techniques, the invention makes it possible to reduce, or even eliminate, the white separator areas that would otherwise be necessary between subpixels (for example, between subpixel lines) to prevent potential overlaps. Thanks to the invention, it is no longer necessary to maintain white separator lines between subpixels to preserve subpixel positioning tolerance, thus increasing the maximum color saturation of each subpixel (less white per pixel and therefore more primary colors).

[0129] However, white subpixels, possibly small, can be retained in the pixel arrangement to achieve the desired brightness level. It is even possible to remove white subpixels altogether, as holograms inherently possess high brightness and, in particular, allow for greater luminosity than printed inks. This makes it possible to retain only subpixels of the primary color in the pixel arrangement, resulting in increased color saturation. For example, pixels can be formed from just three subpixels (using a hexagonal pattern, for instance), allowing for a theoretical maximum color saturation of 33% for each primary color.

[0130] By implementing the principle of the invention, it is possible to easily detect fraud when an image has been falsified or illegally reproduced. Furthermore, this level of complexity and image security achieved through the invention does not compromise the quality of the image's visual rendering.

[0131] 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 can, however, comprise any combination, or subcombination, 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)).

[0132] A method for manufacturing a color IG image as described previously is now described with reference to the figure 14 , according to a particular embodiment. For example, we assume that we are forming a color image IG in a document 20 as illustrated in figure 3 .

[0133] During a creation step S2, a holographic structure 27 is fabricated in a holographic layer 12, forming an arrangement 29 of pixels 30, as described previously. Each pixel 30 comprises a plurality of sub-pixels 32 of distinct colors according to one of the examples already described.

[0134] Layer 22 ( figure 4 )This could be a thermoformable layer, allowing the reliefs 24 of the holographic structure 27 to be formed by embossing onto the support layer 22. Alternatively, the reliefs 24 of the holographic structure 27 can be produced using a UV curing technique, as already mentioned. Since these manufacturing techniques are known to those skilled in the art, they are not described in further detail for the sake of simplicity.

[0135] An adhesive layer and / or glue (not shown) may also be used to ensure adhesion of the holographic layer 12 to a substrate (for example, to a layer 42 or 42a already described previously).

[0136] During a training step S4, color modulation means 10 are trained as already described previously, to select the color of pixels 30 by modifying the relative colorimetric contribution of sub-pixels 32 to each other in at least a part of pixels 30 so as to reveal a custom color image IG from the arrangement 29 of pixels combined with the color modulation means 10.

[0137] As already described, the color modulation means 10 thus formed may include at least one of the following: regions (RG1) of the holographic structure, called destroyed regions, which are locally destroyed on all or part of sub-pixels 32 by a single first laser beam LS1 ( figure 8 ) ; masking means (50; 60-62) positioned opposite the pixel arrangement 29 to locally mask all or part of sub-pixels 32 ( figures 10-11 ) ; and amplification means (68; 70-72) positioned opposite the pixel arrangement 29 to locally amplify the brightness of all or part of sub-pixels 32 ( figures 12-13 ).

[0138] Thus, the destroyed regions RG1 represented in figure 8 are formed by local destruction, by means of a single laser beam LS1, by laser ablation of regions of the holographic structure to eliminate all or parts of sub-pixels in the pixel arrangement.

[0139] The 50 masking methods represented in figure 10 are formed by printing ink patterns opposite the holographic layer 12 obtained in step S2, so as to locally mask all or part of sub-pixels in the pixel arrangement.

[0140] The lenticular network 68 represented in figure 12 is formed by deforming the surface of a layer 42a using a single laser beam LS3, this lenticular array being positioned opposite the pixel arrangement 29 so as to generate the customized color image by focusing (or diverging) incident light through the lenses onto at least some of the sub-pixels of the pixel arrangement. Alternatively, a transparent material is projected using a 3D printer head to form lenses on the surface of the transparent layer 42a.

[0141] The optical amplification device 74 shown in figure 13is formed so as to comprise a laserizable transparent layer 40 and a transparent separating layer 70 disposed between the holographic layer 12 and the laserizable transparent layer 40. Opaque areas 72 are further formed locally, by means of a single laser beam LS4, by carbonization in the laserizable layer 40 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 corresponding to said opaque areas.

[0142] It is thus possible to form the color modulation means 10 using a single laser beam, namely one of LS1, LS2, LS3, and LS4, depending on the type of color modulation means 10 that one wishes to form. In other words, the color modulation means 10 can be formed using a single laser beam from among: the LS1 laser radiation required to produce RG1 destroyed regions as already described ( figure 8 ) ; the LS2 laser radiation needed to form opaque areas 62 as already described ( figure 11 ) ; the LS3 laser radiation required to form a lenticular grating 68 as already described ( figure 12 ) ; and the LS4 laser radiation needed to form opaque areas 72 as already described ( figure 13 ).

[0143] According to a particular example, the color modulation means 10 can be formed using at most two distinct laser beams, from among the LS1 and LS4 beams described above.

[0144] In one particular example, the laser radiations LS2 and LS4 are identical.

[0145] The invention thus makes it possible to securely generate a high-quality, personalized color image from a relatively simple manufacturing process.

[0146] A person skilled in the art will understand that the embodiments and variations described in this document are merely non-limiting examples of how the invention can be implemented. In particular, a person skilled in the art may consider any adaptation or combination of the features and embodiments described above to meet a specific need.

Claims

1. Secure document (2) comprising: - a first layer having 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 to each other in at least a 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 amplification means positioned opposite the arrangement of pixels to locally amplify the brightness of all or part of the sub-pixels.

2. Document according to claim 1, wherein 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.

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

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

5. Document according to any one of claims 1 to 4, wherein the pixel arrangement is configured so that the sub-pixels are uniformly distributed on or in a substrate.

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

7. A document according to any one of claims 1 to 6, wherein said amplification means forming part of the color modulation means comprise at least one of: - a lens array arranged opposite the pixel arrangement so as to generate the personalized color image by focusing or diverging incident light through the lenses onto at least a portion of the sub-pixels; and - an optical amplification device comprising a laserizable transparent layer, referred to as the third layer, and a transparent separating layer disposed between the first layer and the third layer, said third layer comprising areas locally laser-opacified opposite the first layer so as to cause amplification of the brightness of sub-pixels in said pixel arrangement in regions corresponding to said opacified areas.

8. Document according to claim 7, wherein each lens of the lens array is positioned, relative to an associated pixel located opposite it, to focus or diverge incident light on at least one of the sub-pixels of said associated pixel so as to modify the respective color contribution of the sub-pixels of the associated pixel, in a region of the custom color image generated through said lens, relative to the pattern formed intrinsically by the associated pixel independently of said lens.

9. Document according to any one of claims 1 to 8, wherein the document further comprises a laserizable transparent layer, referred to as the fourth layer, opposite the first layer, said fourth layer being at least partially carbonized by laser radiation so as to comprise locally opacified regions opposite sub-pixels of the pixel arrangement to produce grey levels in the customized color image.

10. Document according to any one of claims 1 to 9, wherein the first layer comprises: - a first undercoat of varnish forming the reliefs of a holographic network; and - a second undercoat deposited on the reliefs of the first undercoat, said second undercoat having a refractive index higher than that of the first undercoat.

11. A method for manufacturing a document, comprising: - the 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; - the formation (S4) of color modulation means for selecting the color of the pixels by modifying the colorimetric contribution of the sub-pixels to each other in at least a 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 amplification means positioned opposite the arrangement of pixels to locally amplify the brightness of all or part of the sub-pixels.

12. A method according to claim 11, wherein said color modulation means formation comprises at least one of: - the formation, by means of a single second laser beam, of a lens array arranged opposite the pixel arrangement so as to generate the personalized color image by focusing or diverging incident light through the lenses onto at least a portion of the sub-pixels of the pixel arrangement; and - the formation of an optical amplification device comprising a laserizable transparent layer, said third layer, and a transparent separating layer disposed between the first layer and the third layer, said third layer comprising areas locally opacified, by means of a single third laser beam, opposite the first layer so as to cause amplification of the brightness of sub-pixels in said pixel arrangement in regions corresponding to said opacified areas.

Images