Document capable of generating a colour image and method of generating a color image

Abstract

The invention relates to a document (2) capable of generating a colour image (6), comprising: a set of pixels (20) printed on or in a substrate (2), each pixel (20) forming a pattern comprising an arrangement of sub-pixels (22) of at least two different colours; and an array of lenses (LN) disposed facing the set of pixels so as to generate the colour image (6) by focusing or diverging an incident light through the lenses on at least one part of the sub-pixels (22), each lens (LN) being positioned, relative to an associated pixel (20) located opposite, to focus or diverge the incident light on at least one of the sub-pixels (22) of said associated pixel so as to modify the contribution of the respective colours of the sub-pixels (22) of the associated pixel (20), in a region of the colour image (6) generated through said lens, relative to the pattern intrinsically formed by the associated pixel (20) independently of said lens (LN).

Description

Arrière-plan de l'invention

[0001] The invention relates to the field of color image formation and more particularly relates to a document capable of generating a personalized color image and a method of generating a color image.

[0002] The invention finds particular applications in the formation of identity images in identity documents such as official documents: identity cards, credit cards, passports, driving licenses, secure entry badges, 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 the secure production of color images to limit the risk of falsification by malicious individuals. The production of such documents, particularly with regard to the bearer's identity image, must be sufficiently complex to make reproduction or falsification by an unauthorized individual difficult.

[0004] Thus, as is well known, some official documents contain, for example, guilloches representing a pattern using a complex set of printed lines, which are difficult to reproduce without sophisticated equipment and adequate expertise. Various security features (hologram, security inks, etc.) have been developed, but these are not always sufficient to prevent fraud, particularly given the significant resources available to some forgers today.

[0005] Furthermore, color imaging techniques used today, particularly in secure identity documents, do not always provide satisfactory visual rendering quality. Problems arise, in particular, when the imaging techniques used are limited in their ability to saturate certain colors. In other words, the color gamut (ability to reproduce a range of colors) of known color imaging techniques is sometimes limited.

[0006] When, for example, an identity image is created on a document, it is generally composed of a face surrounded by a light, or even white, area, constituting the image background. It is not always possible to obtain sufficiently saturated colors on the face area or on the background, so that this same face placed on a monochrome background for example, and not sufficiently light, presents a satisfactory contrast between this face and the background fully satisfactory for the observer.

[0007] There is a need today to securely form personalized color images, for example in identity documents, such as those mentioned above in particular. In particular, there is a need to enable flexible and secure personalization of color images in documents or the like, so that, even if a document is illicitly obtained by an individual, the latter cannot personalize the color image at will without this being detectable during proper inspection.

[0008] Furthermore, no solution capable of offering an appropriate level of security and flexibility currently makes it possible to obtain a sufficient color gamut, in particular to obtain the color nuances necessary for the formation of certain high-quality color images, in particular when image areas must have a highly saturated level in a given color, or even a very light identity image background for example, i.e. totally desaturated and bright.

[0009] Document FR 3 030 851 A1 discloses a security device and a method for manufacturing such a security device comprising a first color pattern visible along an associated vision axis Δα and at least one second color pattern visible along an associated vision axis Δβ, comprising the following steps: assembling an image layer capable of forming at least one color pattern by laser engraving, above a support, - laser engraving in the image layer of the first color pattern, along its associated vision axis, in such a way that it can be seen through a lenticular network, - for each of said at least one second color pattern, laser engraving in the image layer, of said at least one second color pattern, along its associated vision axis, in such a way that it can be seen through a lenticular network.

[0010] EP 2 727742 A1 discloses a secure element for securing documents, the secure element comprising a lenticular image for representing two or more target images without changing scale. GB 2 553 104 describes the formation of multiple images using masks and lens arrays. Objet et résumé de l'invention

[0011] The invention is defined in the attached set of claims.

[0012] The invention aims in particular to remedy the drawbacks and inadequacies of the state of the art mentioned above.

[0013] To this end, the present invention relates to a document capable of generating a color image, as defined in claim 1.

[0014] The invention advantageously makes it possible, thanks to the lenses, to create shades of color so as to form a color image by the interaction between the lens array and the set of pixels. The color image is therefore formed by the combination of the lens array and the set of pixels located opposite. Without the addition of the lenses to judiciously direct the incident light, the set of pixels constitutes only a blank arrangement of color pixels insofar as this set is devoid of the information characterizing the color image. It is the lens array which is configured, according to the chosen arrangement of sub-pixels, to customize the visual appearance of the pixels and thus generate, by juxtaposition of the visual appearances of the pixels, the final color image.

[0015] In particular, it is possible to configure the lenses (shape, positioning, etc.) so as to select certain colors from among the different colors present in the set of pixels. Conversely, it is possible to mask or reduce the color contribution of certain sub-pixels in the visual rendering of the final color image 6.

[0016] The invention makes it possible in particular to generate a highly saturated color zone in the desired color or even desaturated in the particular case where the targeted sub-pixel is white.

[0017] The invention thus makes it possible to form monochrome image areas of good quality, while ensuring a high level of complexity guaranteeing the security of the image against fraud. The invention makes it possible, for example, to produce a highly saturated or desaturated image background in a given color, such as white for example.

[0018] By implementing the principle of the invention, it is possible to easily detect fraud when the image has been falsified or illicitly reproduced. Furthermore, this level of complexity and security of the image achieved thanks to the invention is not at the expense of the quality of the visual rendering of the image. This does not prevent in particular the formation of color images comprising areas requiring significant contrast as in the case of a face vis-à-vis an image background. The invention makes it possible to form quality color images from a wide color gamut.

[0019] According to a particular embodiment, each pixel of said set of pixels forms an identical pattern of color sub-pixels.

[0020] According to a particular embodiment, the set of pixels is configured such that the sub-pixels are uniformly distributed on or in the substrate.

[0021] According to the invention, each pixel of said set of pixels is configured such that each sub-pixel has a unique color in said pixel.

[0022] According to a particular embodiment, the lens array is formed from a layer comprising surface deformations defining the microlenses, said layer being the substrate or a layer laminated with the substrate.

[0023] According to a particular embodiment, the subpixels in the pixel array comprise a reflective surface positioned beneath the subpixels to reflect incident light through the lens array.

[0024] According to a particular embodiment, at least one lens in the lens array is a converging lens configured to focus the received incident light so as to accentuate the color contribution of at least one sub-pixel of the associated pixel, in the corresponding region of the color image generated through said lens, relative to the respective color contribution of each other sub-pixel of said associated pixel.

[0025] According to a particular embodiment, at least one lens in the lens array is a converging lens configured to focus the received incident light onto only one of the sub-pixels of the associated pixel so as to mask the color of each other sub-pixel of said associated pixel in the corresponding region of the color image generated through said lens.

[0026] According to a particular embodiment, in a monochrome region of the color image, each lens of the lens array is a converging lens configured to focus the incident light received onto a single sub-pixel of the same predetermined color in the associated pixel, so as to make the predetermined color appear as a single color in said monochrome region of the color image.

[0027] According to the invention, at least one first lens of the lens array is a converging lens configured to focus the incident light received onto at least two sub-pixels of the associated pixel so as to cause a hybrid color resulting from a combination of the colors of said at least two sub-pixels to appear in a corresponding region of the color image, wherein said first lens has, in its smallest dimension, a smallest maximum dimension of 150 µm.

[0028] According to a particular embodiment, at least one lens of the lens array is a diverging lens configured to diverge incident light received by the lens so as to reduce the color contribution of at least one sub-pixel of the associated pixel, in the corresponding region of the color image generated through said lens, relative to the respective color contribution of each other sub-pixel of said associated pixel.

[0029] According to a particular embodiment, the document further comprises: a laserable transparent layer arranged opposite the set of pixels, said laserable transparent layer being at least partially carbonized by laser radiation so as to comprise locally opacified regions opposite sub-pixels to produce gray levels in the color image generated through the lenses.

[0030] According to a particular embodiment, the probability density of the presence of each sub-pixel color is constant in the set of pixels.

[0031] The invention also relates to a method for generating an image in a document as defined in claim 9.

[0032] It will be noted that the various embodiments mentioned above in relation to the document of the invention as well as the associated advantages apply in a similar manner to the generation method of the invention.

[0033] According to a particular embodiment, the method comprises: providing a first transparent layer; and projecting onto the first transparent layer a first laser radiation so as to form the lenses by surface deformation of said first transparent layer.

[0034] According to a particular embodiment, the method comprises: providing a first transparent layer; and producing a projection of transparent material on the first transparent layer using a 3D printer head so as to form lenses on the surface of the first transparent layer.

[0035] According to a particular embodiment, during the formation step, each lens is positioned relative to the associated pixel located opposite independently of the positioning of the other lenses of said lens array.

[0036] According to the invention, at least one first lens of the lens array is a converging lens configured to focus the incident light received onto at least two sub-pixels of the associated pixel so as to cause a hybrid color resulting from a combination of the colors of said at least two sub-pixels to appear in a corresponding region of the color image, wherein said first lens is formed so that it has, in its smallest dimension, a smallest maximum dimension of 150 µm.

[0037] The method also comprises determining respective weights assigned to each of said at least two sub-pixels, said weights representing respective contributions of each sub-pixel in the combination of colors producing the hybrid color; said first lens being configured relative to the associated pixel in accordance with said respective weights assigned to said at least two sub-pixels. Brève description des dessins

[0038] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not in any limiting nature. In the figures: there figure 1 schematically represents a document according to a particular embodiment of the invention; the figure 2 is a sectional view schematically representing a document according to a particular embodiment of the invention; the figures 3A à 3D schematically represent sets of pixels according to particular embodiments of the invention; the figure 4 is a sectional view along IV schematically representing a document according to a particular embodiment of the invention; the figure 5 is a perspective view schematically representing the document of the figure 4 , according to a particular embodiment of the invention; the figures 6 And 7 are top views schematically representing the set of pixels of the document of the figure 4 , according to a particular embodiment of the invention; the figure 8 is a top view schematically representing the visual appearance of an image generated by the document of the figure 4 , according to a particular embodiment of the invention; the figure 9 is a sectional view along IX schematically representing a document according to a particular embodiment of the invention; the figure 10 is a perspective view schematically representing the document of the figure 9 , according to a particular embodiment of the invention; the figure 11 is a top view schematically representing the set of pixels of the document of the figure 9 , according to a particular embodiment of the invention; the figure 12 is a top view schematically representing the visual appearance of an image generated by the document of the figure 9 , according to a particular embodiment of the invention; the figure 13 is a sectional view schematically representing a document according to a particular embodiment of the invention; the figure 14 is a sectional view schematically representing a document according to a particular embodiment of the invention; the figure 15 is a sectional view schematically representing a document according to a particular embodiment of the invention; the figure 16 represents, in the form of a diagram, the steps of a method for generating a color image, according to a particular embodiment of the invention; and the figure 17 represents, in the form of a diagram, the steps of a method for generating a color image, according to a particular embodiment of the invention. Description détaillée de plusieurs modes de réalisation

[0039] As indicated above, the invention relates to the formation of color images and in particular aims at a device or object, such as a document for example, capable of generating a personalized color image from color pixels.

[0040] The device within the meaning of the invention can take various forms and have various functions, one characteristic being that it is capable of generating a color image according to the principle of the invention as set out in the claims.

[0041] In the remainder of this document, examples of implementations of the invention are described in the case of a document capable of generating a color image according to the principle of the invention. This document may be any document, such as a booklet, card or other, in particular an identity document such as, for example: an identity card, a credit card, a passport, a driving license, a secure entry badge, etc.

[0042] It is understood, however, that the invention is not limited to documents, but also applies to other objects configured to generate a color image according to the principle of the invention.

[0043] Similarly, the examples described below aim to generate an identity image. However, it is understood that the image considered can be any. In particular, the image can be (or include a region of) monochrome or multi-color.

[0044] The invention proposes to manufacture personalized color images that are highly secure and that have good image quality. To this end, the invention, according to various embodiments, implements a device capable of generating a color image, comprising: a set of pixels printed on or in a substrate, each pixel forming a pattern comprising an arrangement of sub-pixels of at least two different colors; and a lens array arranged opposite the set of pixels so as to generate the color image by focusing or divergence of incident light through the lenses onto at least some of the sub-pixels.

[0045] Each lens can be positioned (or configured), relative to a pixel (called "associated pixel") located opposite, to focus or diverge the 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 color image generated through the lens, relative to the pattern formed intrinsically by the associated pixel independently of (or without) said lens.

[0046] In other words, each lens can be positioned (or configured), relative to an associated pixel located opposite, to focus or diverge the incident light on at least one of the sub-pixels of said associated pixel so as to modify the contribution of the respective color of at least one sub-pixel of the associated pixel, in a region of the color image corresponding to said pixel, relative to the respective color contribution of each other sub-pixel of said associated pixel.

[0047] The lenses thus make it possible to create shades of color so as to form (or generate) a color image by the interaction between the lens array and the set of pixels. More particularly, each lens array makes it possible to create shades of color, so as to form a unique color image, specific to each array and distinct from the pattern of pixels. The invention also relates to a corresponding method for producing (or generating) a color image.

[0048] Other aspects and advantages of the present invention will emerge from the exemplary embodiments described below with reference to the drawings mentioned above.

[0049] 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.

[0050] There figure 1 schematically represents a device 2 according to an exemplary embodiment of the invention. In this example, the device 2 is a document comprising an identity image 6 formed in or on a device body (or substrate) 4. In this example, the document 2 takes the form of a card although other embodiments are possible.

[0051] The color image 6 represents in this example a face 8 surrounded by a background image 6 which is monochrome, white or pale blue for example.

[0052] There figure 2 is a sectional view schematically representing the color image 6 formed in the document 2 shown in figure 1 , according to a particular embodiment. More particularly, document 2 comprises a substrate 12 in or on which is arranged an array (or arrangement) of LN lenses.

[0053] A set of pixels 20, also called a tiling (or pixel tiling), is printed in the substrate 12, each pixel 20 forming a pattern comprising an arrangement of sub-pixels 22 of at least two different colors. Examples of sub-pixel patterns, the possible configurations of which are multiple, are described later with reference in particular to figures 3A-3D .

[0054] The substrate 12 is transparent here in order to allow at least partial passage of incident light through the lenses LN so as to reach the color pixels 20. The pixels 20, and more particularly their sub-pixels 22, comprise in this example a reflective surface 23 located under the sub-pixels to reflect (at least partially) the incident light received through the array of lenses LN. This reflective surface is for example a white surface.

[0055] As represented in figure 2 , the lens array LN is arranged opposite the set of pixels 20 so as to generate the color image 6 ( figure 1 )by focusing or diverging incident light through the LN lenses onto at least a portion of the sub-pixels 22. As described below, the lenses may be configured in different ways and, in particular, may be convergent and / or divergent depending on the specific case. In the example considered, the LN lenses are convergent to converge the incident light onto at least one of the sub-pixels 22 of the associated pixels 20 located opposite each other.

[0056] More particularly, each lens LN is positioned, relative to a pixel 20 located opposite, called the “associated” pixel, to focus or diverge the incident light onto at least one of the sub-pixels 22 of the associated pixel 20 so as to modify the contribution of the respective colors of the sub-pixels 22 of the associated pixel 20, in a region of the corresponding color image 6 (i.e. generated through this lens LN), relative to the pattern formed intrinsically by the associated pixel 20 independently of said lens LN.

[0057] In other words, the LN lenses are configured so as to converge or diverge the incident light on certain sub-pixels 22 so as to make appear (reveal) the color image 6, from the set of pixels 20, by favoring the color contribution of certain sub-pixels compared to others.

[0058] The LN lenses thus make it possible to create shades of color so as to form a color image 6 by the optical interaction between the LN lens array and the set of pixels 20. The color image 6 is therefore formed by the combination of the LN lens array and the set of pixels 20 located opposite. Without the addition of the LN lenses to judiciously orient the incident light, the set of pixels 20 constitutes only a blank arrangement of color pixels insofar as this set is devoid of the information characterizing the color image 6. It is the LN lens array which is configured, according to the arrangement of sub-pixels 22 chosen, to customize the visual appearance of the pixels 20 and thus generate, by juxtaposition of the visual appearances of the pixels, the final color image 6.

[0059] How the lenses can guide incident light to change the color contribution of some subpixels 22 relative to other subpixels in the final color image 6 is described in more detail later.

[0060] It is in particular possible to configure the LN lenses (shape, positioning, etc.) so as to select certain colors from among the different colors present in the set of pixels 20. Conversely, it is possible to mask or reduce the color contribution of certain sub-pixels 22 in the visual rendering of the final color image 6.

[0061] As described below, it is possible to further add opacifying elements (black or dark, for example) opposite certain sub-pixels 22 in order to create gray levels of the resulting color image 6, and thus generate contrast in the color image after the alignment of the lenses on the appropriate sub-pixels has selected an appropriate tint.

[0062] The LN lenses arranged opposite the set of pixels 20 may have various shapes, dimensions and configurations (magnifying power, convergent or divergent, etc.). Depending on the specific case, the LN lenses may, for example, be spheroidal or cylindrical, for example.

[0063] Furthermore, the set of pixels 20 within the meaning of the invention may be in different shapes, configurations, dimensions, etc. In particular, each pixel of the set of pixels 20 may form an identical pattern of color sub-pixels 22. In this case, the set of pixels consists of a single pattern of sub-pixels which is repeated a plurality of times. This arrangement of sub-pixels is said to be “virgin” in the sense that it does not intrinsically form (i.e. without the addition of the LN lenses and / or the opacifying elements) the color image 6.

[0064] According to a particular example, each pixel 20 has an identical pattern of sub-pixels 22 in the same orientation across the set of pixels 20. It is thus possible to distribute the color sub-pixels identically in the set of pixels (as illustrated for example in figure 3A ), which makes lens formation easier as the same frame of reference (or arrangement) is used in each pixel.

[0065] According to a particular example, each pixel 20 has an identical pattern of sub-pixels 22, variations in the orientation of this pattern being however made between certain pixels relative to each other, across the set of pixels 20. In other words, the same pattern of sub-pixels 22 of color is then found in all the pixels 20 of said set but following at least two different orientations (for example by applying rotations of 90° and / or 180° on the same pattern which is repeated across the set of pixels 20). figure 3C thus illustrates an example in which the same pattern of color sub-pixels 22a-22d is found in two different orientations (180° rotation) in the set of pixels 20. This variant thus makes it possible to form a blank set of color sub-pixels offering the flexibility necessary to generate any image through the LN lenses, while making it possible to incorporate the same pattern in variable orientations to form, for example, a signature or a secure element, specific to each color image, which is difficult to reproduce and easily detectable in the event of fraud.

[0066] The pixel array 20 may be configured such that the sub-pixels are uniformly distributed on or in the substrate 12. In other words, the pixel array may form a regular or periodic arrangement of pixels 22, forming identical or non-identical sub-pixel patterns as appropriate.

[0067] The set of pixels 20 can form a matrix of pixels, consisting of rows and columns of sub-pixels 22. These rows and columns can be rectilinear and possibly orthogonal to each other.

[0068] According to a particular example, each pixel 20 forms a pattern composing an arrangement of sub-pixels 22 of at least two different colors, the probability density of the presence of each sub-pixel color being constant in the pixels 20 of the pixel arrangement. In other words, if we consider pixels 20 of n color sub-pixels (n being an integer), the surface proportion of each color (formed by one or more sub-pixels) is identical in each pixel 20 of the set of pixels. By way of example, we can find in each pixel 20 the following densities: 30% yellow, 20% magenta, 40% cyan and 10% white).In this particular example, each pixel 20 can thus present an identical pattern of sub-pixels 22 of color in the same orientation across the arrangement of pixels 20 or, possibly, in an orientation which varies in the arrangement of pixels 20 (according to random variations or according to regular or other variations).

[0069] In particular, in more complex examples, a random arrangement of the pixels 20 is possible. It is in particular possible to organize the distribution of the sub-pixels 22 randomly but in such a way that the probability density of the presence of each sub-pixel color is constant in the pixels 20 of the set of pixels. In this case, it is necessary that, in a given area of ​​the pixel arrangement 20, it is possible to select using the lenses LN the desired color(s) even if the corresponding sub-pixels are not located exactly at their assumed theoretical coordinates.

[0070] According to the invention, each pixel 20 of the set of pixels is configured so that each of the sub-pixels 22 has a unique color in said pixel 20. A pixel 20 can thus be composed of a plurality of sub-pixels 22, all of a distinct color. Alternatively, it is possible to define the pixels 20 so that they comprise at least two sub-pixels 22 of the same color among all their sub-pixels (for example, 2 sub-pixels in each primary color), provided that each pixel comprises at least two sub-pixels 22 of a different color.

[0071] The colors of the sub-pixels 22 may vary depending on the case and may constitute primary colors from which the color image 6 is generated in combination with the lens array LN. In a particular example, each pixel 20 comprises sub-pixels 22 in the primary colors red / green / blue (RGB), possibly with white, or in the primary colors yellow / magenta / cyan, possibly with white. A white area may optionally be provided in the pixel arrangement 22 between the rows and columns of sub-pixels 22 to avoid color overlap.

[0072] Particular examples of tiling (arrangement) of pixels 20, which can be implemented in a device of the invention such as document 2 represented in figures 1-2 , are now described with reference to figures 3A, 3B, 3C And 3D .It should be noted that these implementations are presented only as non-limiting examples, with numerous variations being possible in terms of, in particular, the arrangement and shape of the pixels and sub-pixels, as well as the colors assigned to these sub-pixels.

[0073] There figure 3A is a top view showing a set of pixels 20 according to a particular embodiment. In this example, the tiling forms a matrix of rows and columns of pixels, orthogonal to each other. Each pixel 20, of square shape, forms a pattern composed of 4 sub-pixels 22, denoted 22a to 22d, also of square shape. In this example, the sub-pixels 22 all have a single color in the pixel 20 considered. The pixels 20 are uniformly distributed so that the same pattern of sub-pixels 22 is repeated periodically in a region of the substrate 12.

[0074] There figure 3B is a top view showing another example of a regular tiling in which each pixel 20 is composed of 3 sub-pixels 22, denoted 22a to 22c, each of a distinct color. The sub-pixels 22 are here hexagonal in shape.

[0075] There figure 3C is a top view showing another example of a regular tiling in which each pixel 20 is composed of 4 sub-pixels 22, denoted 22a to 22d, each of a distinct color. The sub-pixels 22 are here triangular in shape.

[0076] There figure 3D is a top view showing another example of regular tiling in which each pixel 20 is composed of 4 sub-pixels 22, denoted 22a to 22d, each of a distinct color. The sub-pixels 22 are here rectangular in shape and are arranged in a line, that is to say arranged parallel to each other in order to form rectilinear columns of sub-pixels.

[0077] Examples of specific implementation of the device 2 described previously with reference to the figures 1, 2 And 3A -3D are now described below. More specifically, a first particular implementation of document 2 ( figure 1 ) is described with reference to figures 4 à 8 .

[0078] The device 2 comprises in this example a substrate 12 in which a set of pixels 20 is arranged, each pixel comprising a plurality of sub-pixels 22. A lens array, here denoted LN1, is arranged opposite the set of pixels 20 so as to generate the color image 6 ( figure 1 ) by focusing incident light 30 on certain sub-pixels 22.

[0079] More particularly, as illustrated in figures 4 And 5 ,the substrate 12 comprises in this example a transparent upper layer 12a arranged on a white lower layer 12b. The set of pixels 20 is printed on the upper face of the lower layer 12b or on the lower face of the upper layer 12a, so as to be located at the interface between the layers 12a and 12b, inside the substrate 12. According to a variant, the set of pixels 20 is printed on the upper face of the substrate 12.

[0080] As already indicated, each pixel 20 forms a pattern comprising an arrangement of sub-pixels 22 of at least two different colors. The sub-pixels 22 can be produced according to any color printing technique that the person skilled in the art can choose depending on the specific case. The set of pixels 20 used in this example is described later with reference to the figure 6 .

[0081] In this example, LN1 lenses are formed in a layer 14 comprising surface deformations defining the lenses. This layer 14 covers the substrate 12, the layer 14 and the substrate 12 being for example laminated together. The layer 14 may be for example made of silica glass or polycarbonate, or any transparent material with a density different from that of air so that there is refraction of light and therefore a lens effect. According to a variant, the array of LN1 lenses is formed directly in the substrate 12 which then comprises surface deformations defining the lenses, no additional layer 14 then being necessary.

[0082] As illustrated in figures 5-6 , The LN1 lenses here are cylindrical in shape and extend parallel to each other.

[0083] The lenses LN1 are in this example converging lenses. The array (or arrangement) of lenses LN1 is arranged opposite the set of pixels 20 so as to generate the color image 6 by focusing an incident light 30 through the lenses onto at least a portion of the sub-pixels 22. Each lens LN1 is positioned, relative to an associated pixel 20 located opposite, to focus the incident light 30 onto at least one of the sub-pixels 22 of the associated pixel 20 so as to modify (or modulate) the contribution of the respective colors of the sub-pixels 22 of the associated pixel 20, in a region of the color image 6 generated through said lens LN1, relative to the pattern formed intrinsically by the associated pixel 20 independently of said lens LN1.

[0084] In this document, the term "pattern formed intrinsically by a pixel" means a pattern formed by the colors of the sub-pixels of said pixel, this pattern being considered as such, without taking into account the modulation effect resulting from the positioning of a lens opposite it.

[0085] As already explained, the substrate 12 and the layer 14 are transparent in order to allow at least partial passage of the incident light through the lenses LN1 until it reaches the color pixels 20. The pixels 20, and more particularly their sub-pixels 22, comprise in this example a reflective surface 23, located under the sub-pixels, to reflect (at least partially) the incident light 30 received through the lens array LN1. The layers 12 and 14 are for example made of polycarbonate. The reflective layer 23 may be a white surface located under the pixels.

[0086] As represented in figure 4 ,each lens LN1 comprises an incidence surface (or lens surface) S1, capable of receiving an incident light 30, and further defines, on the surface of the set of pixels 20, a useful surface S2 on which the lens LN1 converges (guides) the incident light 30. Each lens LN1 is positioned opposite a pixel 20 associated with it, the lens LN1 being arranged so that its useful surface S2 is positioned on at least a part of one or more of the sub-pixels 22 of the associated pixel 20.

[0087] The LN1 lenses thus focus the received incident light 30 so as to accentuate the color contribution of at least one sub-pixel 22 of the associated pixel 20, in the corresponding region of the color image generated through said lens, relative to the respective color contribution of each other sub-pixel 22 of the associated pixel 20. This modulation of the colorimetric contributions of the sub-pixels is described in more detail below with reference to figures 6 , 7 e 8 .

[0088] The set of pixels 20 used in the example considered here is illustrated in figure 6 .The pixels 20 are rectangular and composed of 4 sub-pixels 22a-22d themselves rectangular in shape. Each sub-pixel 22a-22d of the same pixel 20 has a single color denoted respectively CLa-CLd. The sub-pixels 22 are uniformly distributed so that the colors CLa to CLd are repeated periodically in the substrate 12. This rectangular configuration has the advantage of being relatively simple to produce by color printing.

[0089] Alternatively, thin white lines, for example less than 30 µm wide, are provided between the different color sub-pixels CLa, CLb, CLc and CLd.

[0090] Alternatively, one of the colors CLa, CLb, CLc, and CLd is white.

[0091] There figure 7 represents in dotted lines the useful surface S2 defined by each lens LN1 on an associated pixel 20. In this example, the outline of the useful surfaces S2 corresponds to the sub-pixels 22c of color CLc. In a variant, the useful surface S2 is smaller than the corresponding sub-pixel so that the observed color does not vary when the observer looks at the surface of the lenses with an angle that is not exactly perpendicular (oblique observation).

[0092] There figure 7 further represents, in superposition, the outline of the incidence surfaces (or lens surfaces) S1 defining the location of the lenses LN1 situated opposite the pixels 20. In this example, each lens LN1 is positioned in correspondence with the sub-pixels 22b, 22c and 22d of the associated pixel 20 and further covers a part of the sub-pixel 22a of the associated pixel 20 (as well as a part of the sub-pixel 22a of a neighboring pixel 20).

[0093] Also, in this particular example, each lens LN1 focuses the received incident light 30 ( figure 4 ) on sub-pixel 22c of the associated pixel 20, which has the consequence of strongly accentuating the color contribution of sub-pixel 22c, in the corresponding region of the color image 6 ( figure 1 ) generated through said lens LN1, relative to the respective color contribution of each other sub-pixel 22a, 22b and 22d of the associated pixel 20.

[0094] There figure 8 represents the visual rendering, in regions R1 and R2, of the color image 6 observable by an observer OB ( figure 4 ) . As shown, regions R1 and R2 are observable in the single color CLc due to the focusing of the incident light 30 by the lenses LN1 onto the subpixels 22c.

[0095] By preferentially converging the incident light 30 onto certain appropriately chosen sub-pixels 22, it is thus possible to generate (or reveal) the desired color image 6. The lenses LN1 make it possible to select certain colors so as to form the final color image 6 by the interaction between the lens array LN1 and the set of pixels 20.

[0096] The color image 6 is therefore formed by the combination of the lens array LN1 and the set of pixels 20 located opposite. Without the addition of the lenses LN1 to judiciously orient the incident light, the set of pixels 20 constitutes only a blank arrangement of color pixels insofar as this set is devoid of the information characterizing the color image 6. It is the lens array LN1 which is configured, according to the arrangement of sub-pixels 22 chosen, to customize the visual appearance of the pixels 20 and thus generate the final color image 6.

[0097] In the example considered here, the lenses LN1 each converge the incident light 30 towards a single sub-pixel 22c of the same predetermined color CLc in the associated pixel 20, so as to make the color CLc appear as a single color in a monochrome region (for example the image background 10) of the color image 6 ( figure 1 ).

[0098] According to a particular example, the smallest dimension of the LN1 lenses is less than or equal to 350.10 -6< m, or 350 µm. In the case where the LN1 lenses are cylindrical in shape as shown in figures 5-7 , the smallest dimension of the lenses corresponds to the smallest side of the rectangle formed by the intersection of the cylinder portion of the lens with the plane on which it rests.

[0099] According to a particular example, the pixel arrangement 20 in the document 2 shown in figure 4 à 8 is such that the initial color contribution of a sub-pixel 22 in its pixel 20 (i.e. the intrinsic color contribution of this sub-pixel 22, independently of the lenses) is 25% and its contribution in the corresponding region (corresponding to the incidence surface of the associated lens) of the final color image 6 is 100%.

[0100] The invention therefore advantageously makes it possible to generate a highly saturated color zone in the desired color CLc or even desaturated in the particular case where the targeted sub-pixel is white. Each lens LN1 masks the colors CLa, CLb, CLd of the other sub-pixels 22a, 22b and 22d of the associated pixel 20 in the corresponding region (R1 and R2) of the color image 10 generated through the lens. This masking is preferably visible when the card is not inclined relative to the observer OB, that is to say, when one is in an observation normal to the plane in which the pixels extend. The observation may not be constrained to exact normality if the convergence of the lenses makes it possible to have a smaller useful surface centered on the targeted sub-pixel.

[0101] The invention thus makes it possible to form good quality monochrome image areas, while ensuring a high level of complexity guaranteeing the security of the image against fraud. The invention makes it possible, for example, to produce an image background 10 ( figure 1 ) highly saturated or desaturated in a given color, such as white for example.

[0102] By inspecting the color image 6, it is possible, thanks to the invention, to easily detect fraud when the image has been falsified or illicitly reproduced. The configuration of the lenses is only adapted to the set of pixels 20 which has been printed and is therefore fixed in the image. Furthermore, this level of complexity and security of the image achieved thanks to the invention is not at the expense of the quality of the visual rendering of the image. This does not prevent in particular the formation of color images comprising areas requiring significant contrast, as in the case of a face against an image background. The invention makes it possible to form quality color images from a wide color gamut.

[0103] Alternatively, it is possible to configure the lenses LN1 so that they each focus the incident light 30 onto a single sub-pixel 22 of the associated pixel 20, these sub-pixels 22 not necessarily always being of the same color. Various color combinations are thus possible.

[0104] Furthermore, in the example shown in figures 4-8 , the lenses LN1 each focus the incident light onto a single sub-pixel 22 of an associated pixel 20 located opposite. Other embodiments are however possible in which the lenses focus the incident light onto at least two sub-pixels of the same pixel, as described below.

[0105] A second particular implementation of the device 2, as previously described with reference to the figures 1, 2 And 3A -3D, is now described with reference to the figures 9 à 13 .

[0106] The device 2 here comprises a substrate 12 in which a set of pixels, denoted 40, is arranged, each pixel comprising a plurality of sub-pixels denoted here 42. A network of lenses, denoted here LN2, is arranged opposite the set of pixels 40 so as to generate the color image 6 ( figure 1 ) by focusing incident light 30 onto some of the sub-pixels 42.

[0107] More particularly, the substrate 12 comprises an upper layer 12a arranged on a lower layer 12b, in a manner identical to the embodiment of the figures 4- 5. The set of pixels 40 is printed on the upper face of the lower layer 12b or on the lower face of the upper layer 12a, so as to be located at the interface between the layers 12a and 12b, inside the substrate 12. According to a variant, the set of pixels 40 is printed on the upper face of the substrate 12.

[0108] As already described in the previous examples, each pixel 40 forms a pattern comprising an arrangement of sub-pixels 22 of at least two different colors. The sub-pixels 22 can be produced according to any color printing technique that the person skilled in the art can choose depending on the specific case. The set of pixels 20 used in this example is described later with reference to the figure 11 .

[0109] In this example, LN2 lenses are formed in a layer 14 having surface deformations defining the lenses, in a manner identical to the embodiment of the figures 4-5 .This layer 14 covers the substrate 12, the layer 14 and the substrate 12 being for example laminated together. The layer 14 can be made of silica glass, polycarbonate or any other transparent material. According to a variant, the LN2 lens array is formed directly in the substrate 12 which then comprises surface deformations defining the lenses, no additional layer 14 then being necessary.

[0110] As illustrated in figure 9-10 , The LN2 lenses here are spheroidal in shape and together form an LN2 lens matrix, composed for example of orthogonal rows and columns. However, it is possible to arrange the LN2 lenses in a non-orthogonal arrangement, or even in a non-regular manner, depending on the visual effect that is sought.

[0111] The LN2 lenses are in this example converging lenses. The array (or arrangement) of LN2 lenses is arranged opposite the set of pixels 40 so as to generate the color image 6 by focusing an incident light 30 through the LN2 lenses onto at least a portion of the sub-pixels 42. Each LN2 lens is positioned, relative to an associated pixel 40 located opposite, to focus the incident light 30 onto at least one of the sub-pixels 22 of the associated pixel 20 so as to modify (or modulate) the contribution of the respective colors of the sub-pixels 22 of the associated pixel 20, in a region of the color image 6 generated through said LN2 lens, relative to the pattern formed intrinsically by the associated pixel 40 independently of said LN2 lens (i.e. without taking into account the modulation effect of said lens).

[0112] In other words, each lens LN2 is positioned (or configured), relative to an associated pixel 40 located opposite, to focus the incident light 30 on at least one of the sub-pixels 22 of the associated pixel 20 so as to modify (or modulate) the contribution of the respective color of at least one sub-pixel 22 of the associated pixel 20, in a corresponding region of the color image 6 generated through said lens LN2, relative to the respective color contribution of each other sub-pixel 22 of said associated pixel 20.

[0113] As such, each lens can be uniquely offset from the position of the pixels 20 according to the perfectly regular organization shown as an example in the figure 10 .

[0114] As already explained, the substrate 12 and the layer 14 are transparent in order to allow the incident light 30 to pass at least partially through the lenses LN2 until it reaches the color pixels 40. The pixels 40, and more particularly their sub-pixels 42, comprise in this example a reflective surface 23, positioned under the sub-pixels 42, to reflect (at least partially) the incident light 30 received through the array of lenses LN2. The layers 12 and 14 are for example made of polycarbonate.

[0115] As represented in figure 9 , and as already explained with reference to the figure 4 ,each lens LN2 comprises an incidence surface S1, capable of receiving an incident light 30, and further defines, on the surface of the set of pixels 40, a useful surface S2 on which the lens LN2 converges the incident light 30. Each lens LN2 is positioned opposite a pixel 40 which is associated with it, the lens LN2 being arranged so that its useful surface S2 is positioned on at least a part of two sub-pixels 42 of the associated pixel 40.

[0116] The LN2 lenses thus focus the received incident light 30 so as to accentuate the color contribution of at least two sub-pixels 42 of the associated pixel 20, in the corresponding region of the color image generated through said lens, relative to the respective color contribution of each other sub-pixel 42 of the associated pixel 40. This modulation of the colorimetric contributions of the sub-pixels is described in more detail below with reference to figures 11 et 12 .

[0117] The set of pixels 40 used in the example considered here is illustrated in figure 11 . The pixels 40 are here composed of 4 sub-pixels 42a-42d of hexagonal shape. Each sub-pixel 42a-42d of the same pixel 40 has a single color denoted respectively CLa-CLd in the pixel considered. The sub-pixels 42 are uniformly distributed so that the colors CLa to CLd are repeated periodically in the substrate 12. This hexagonal configuration offers great flexibility in the range of colors that it is possible to produce. Other exemplary embodiments are possible with only 3 sub-pixels 42 of distinct color in each pixel 40 (see for example the variation represented in figure 3B ).

[0118] There figure 11 represents in dotted lines the useful surface S2 defined by each lens LN2 on an associated pixel 40. In this example, the useful surface S2 of each lens LN2 defines an area straddling two sub-pixels 42 of the associated pixel 40 located opposite each other. According to other variants, it is possible to configure lenses so that they focus the incident light on 3 sub-pixels or more.

[0119] The incidence surfaces S1 define in particular the location of the lenses LN2 situated opposite the pixels 40. These incidence surfaces S1 are dependent on the shape, the position, and more generally the configuration of the lenses LN2. In this example, each lens LN2 is positioned in correspondence with a part of certain sub-pixels 42 of an associated pixel 40 and may, if necessary, also cover a part of one or more neighboring pixels 40.

[0120] More specifically, we consider here the case of two LN2 lenses respectively defining incidence surfaces S11 and S12, and useful surfaces S21 and S22.

[0121] Also, in this particular example, each LN2 lens focuses the received incident light 30 ( figure 9 ) on two sub-pixels 42 of the associated pixel 40 which has the consequence of strongly accentuating the color contribution of these sub-pixels, in the corresponding region of the color image 6 ( figure 1 ), corresponding to the incidence surface S11, S12, generated through said lens LN2, relative to the respective color contribution of each other sub-pixel 42 of the associated pixel 20.

[0122] So, in the example shown in figure 11 ,the area defined by the useful surface S21 is such that the colors CLc and CLd of the respective sub-pixels 42c and 42d are accentuated relative to the colors of the other sub-pixels 42 of the pixel 40 considered. Similarly, the area defined by the useful surface S22 is such that the colors CLa and CLb of the respective sub-pixels 42a and 42b are accentuated relative to the colors of the other sub-pixels 42 of the pixel 40 considered. By adapting the configuration of the lenses LN2, it is possible to control the shape and dimensions of the useful surfaces and thus to choose which colors are favored in each region of the image 6, and in what proportions the colorimetric contributions of each sub-pixel 42 are modified.

[0123] There figure 12 represents the visual rendering, in regions R1 and R2, of the color image 6 observable by an observer OB ( figure 9 ). As shown, the regions R1 and R2, corresponding respectively to the incidence surfaces S11 and S12 of two lenses LN2, are observable in hybrid colors CL1 and CL2 obtained by mixing colors from the sub-pixels on which the incident light 30 is focused.

[0124] Thus, region R1 presents the hybrid color CL1 resulting from an addition of the weighted contributions of the colors CLc and CLd of subpixels 42c and 42d. Similarly, region R2 presents the hybrid color CL2 resulting from an addition of the weighted contributions of the colors CLa and CLb of subpixels 42a and 42b.

[0125] By preferentially converging the incident light 30 onto certain appropriately chosen sub-pixels 22, it is thus possible to generate (or reveal) the desired color image 6. The LN2 lenses make it possible to generate complex colors from the colors of the sub-pixels located opposite the lenses. It is possible to generate a hybrid color from 2, 3 or 4 distinct sub-pixels for example, depending on the tiling used. As already explained, the color image 6 is therefore formed by the combination of the LN2 lens array and the set of pixels 40 located opposite. Without the addition of the LN2 lenses to judiciously orient the incident light, the set of pixels 40 constitutes only a blank arrangement of color pixels insofar as this set is devoid of the information characterizing the color image 6.It is the LN2 lens array that is configured, depending on the chosen sub-pixel arrangement 42, to customize the visual appearance of the pixels 40 and thus generate the final color image 6.

[0126] Note that different types of visual rendering can be obtained when a lens converges incident light onto at least two subpixels. In the example considered above, we assume that the regions R1 and R2 of the color image 6 ( figure 12 )as they appear to an observer OB are monochrome. In other words, these regions R1 and R2 appear as areas with a single uniformly distributed color, namely the respective hybrid colors CL1 and CL2 in this example. To achieve this, it is necessary that the dimensions of the lenses LN2 be sufficiently small with respect to the distance between the image and the observer so that the intrinsic resolving power of the human eye cannot discern the different primary colors constituting the hybrid colors CL1 and CL2, respectively. When the combination of distinct colors is carried out beyond the resolving power of the human eye, only the hybrid color resulting from the additions of the constituent colors is perceived by an observer.

[0127] There figure 13 represents an observer OB observing from a point I a portion of image projected onto a lens LN2. According to a particular embodiment, the smallest dimension D of the lenses LN2 is such that: D < tan αlim 2 ⋅ 2 L where αlim corresponds to the maximum limiting angle of observation beyond which the human eye cannot discern two distinct colors, and L is the distance between the observation point I and the image. Note that the smallest dimension of D is included in a plane in which the LN2 lens considered extends.

[0128] So that a human eye cannot separately discern the different colors of the sub-pixels 40 in an image area defined by a useful surface S1 ( figure 11 ), it is necessary that the observation angle α be such that: α < αlim

[0129] Here we consider that αlim = 1' (minute) = 3.10 -4< rad.

[0130] According to a particular example, assuming that the observation distance L = 0.5 m (meter), it is necessary that the smallest dimension D of the LN2 lenses is less than 150.10 -6< m, or 150 µm. In the case where the LN2 lenses are spheroidal in shape, the smallest dimension D corresponds to the diameter of the circle formed by the intersection of the sphere portion of the lens with the plane on which it rests.

[0131] It will be noted that in the embodiments described above, the lenses used are convergent, although other embodiments are possible. Thus, it is possible to apply the principle of the invention using divergent lenses. For example, in document 2 shown in figure 2 ,the lens array LN may comprise at least one diverging lens configured to diverge an incident light received by the lens so as to reduce the color contribution of at least one sub-pixel 22 of the associated pixel 20, in the corresponding region of the color image 6 generated through said lens, relative to the respective color contribution of each other sub-pixel 22 of said associated pixel 20.

[0132] There figure 13 represents in sectional view the document 2 according to a variant of the embodiment represented in figure 2 . Document 2 differs from the implementation of the figure 2 in that the lenses, here denoted LN3, are divergent so that they diverge the incident light onto the corresponding sub-pixels 22. It is thus possible to position the diverging lenses LN3 in correspondence with certain sub-pixels 22 so as to reduce the color contribution of these sub-pixels in the regions of the color image 6 generated through these lenses. With reference to the figure 11 , we can consider an exemplary embodiment where S21 and S22 define the incidence surfaces of diverging LN3 lenses, and S11 and S22 define the useful surfaces of these lenses.

[0133] According to this variant, it is also possible to modify (modulate) the color contribution of certain sub-pixels compared to others in the rendering of the final color image 6, according to the principle of the invention.

[0134] Furthermore, as already indicated, it is possible to give contrast to a color image 6 ( figure 1 ) generated according to the principle of the invention by adding opacifying elements (black or dark) opposite certain sub-pixels in order to create gray levels of the color image 6, as described below.

[0135] There figure 15 represents a particular embodiment that differs from the embodiment of the figure 2 in that the document 2 further comprises opaque (or opacifying) or non-reflective zones (or volumes) 60, which may be dark, gray or black for example, located opposite certain sub-pixels 22 so as to create gray levels in the final color image 6. To do this, the substrate 12 comprises for example a transparent laserizable layer 65 (corresponding for example to the layer 12a shown in figures 4 And 9). Here, the term “laserable” layer means a layer sensitive to laser radiation.

[0136] The laserable transparent layer 65 is arranged opposite the set of pixels 20, this laserable transparent layer being at least partially carbonized by laser radiation LR1 so as to comprise regions 60 locally opacified opposite sub-pixels 20 to produce gray levels (or contrast) in the color image 6 generated through the lenses LN.

[0137] The opaque regions 60 partially or totally mask some of the sub-pixels 22 (a subset of the sub-pixels 22) thus forming the gray levels of the color image 6. These opaque regions can also partially or totally mask the lenses, thus making it possible to modulate, that is to say to vary, the brightness of composite colors, created by the alignment of the lenses and the sub-pixels.

[0138] By combining this technique of local opacification of a laserizable layer with the principle of the invention based on the use of lenses arranged opposite color sub-pixels, it is possible to obtain personalized color images of good quality, while guaranteeing a high level of security against fraud due to the particularly advanced complexity of the image.

[0139] In the example shown in figure 15 , the opaque areas 60 are formed so as to cover the entirety of a corresponding sub-pixel 22, although other embodiments are possible where, for example, at least some of these opaque areas 60 only cover a part of the corresponding sub-pixel 22. It is thus possible to adapt very finely the gray levels in the image 6 ( figure 1 ).

[0140] According to a particular example, one or more opaque regions 60 are configured so as to partially (or even totally) mask a respective area of ​​the pixel arrangement 20 visible through an associated LN lens located opposite. All of the opaque regions 60 can form a general pattern such as an inscription (characters or symbols for example, such as a name or other) or an image. This general pattern is then visible through the LN lenses.

[0141] The invention also relates to a method for generating (or forming) a color image according to the principle of the invention. This generation method can be configured to produce a device (or a document) according to any of the embodiments described in this document.

[0142] A method of generating (or forming) the document 2 represented in figure 2 is now described with reference to the figure 16 .

[0143] The process includes the following steps: printing (step E2) a set of pixels 20 on or in the substrate 12, each pixel 20 forming a pattern comprising an arrangement of sub-pixels 22 of at least two different colors; and forming (step E4) a lens array LN arranged opposite the set of pixels 20 so as to generate the color image 6 ( figure 1 ) by focusing or divergence of incident light through the lenses onto at least part of the sub-pixels 22. In the example shown in figure 2 , LN lenses are converging, so they focus incident light onto 22 subpixels.

[0144] The forming step E4 is such that each lens LN is positioned, relative to an associated pixel 20 located opposite, to focus (or, alternatively, to diverge) the incident light onto at least one of the sub-pixels 22 of said associated pixel 20 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 6 generated through said lens, relative to the pattern formed intrinsically by the associated pixel 20 independently of said lens 20.

[0145] In a particular example, step E4 of forming the LN lenses comprises: a provision of a first transparent layer; and a projection onto this first transparent layer of laser radiation (distinct from the LR1 radiation represented in figure 15 ) so as to form the LN lenses by surface deformation of said first transparent layer.

[0146] According to one variant, a projection of transparent material is carried out on the first transparent layer using a 3D printer head so as to form lenses on the surface of the first transparent layer.

[0147] This first transparent layer may correspond for example to layer 14 shown in figures 4 And 9 , or even to the substrate 12 itself in the case where the LN lenses are formed directly in the substrate.

[0148] For example, CO2 laser radiation can be used to create the surface deformations necessary to form the LN lens array.

[0149] According to a particular example, during the E4 training step, each lens LN ( figure 2 )is positioned relative to the associated pixel 20 independently of the positioning of the other lenses LN of the lens array. This positioning is for example carried out using a camera capable of identifying, for each lens, the adapted position with respect to the associated pixel 20.

[0150] The method may further comprise a step E5 of forming opaque zones 60 to create gray levels in the final image, as already explained with reference to the figure 15 .

[0151] As represented in figure 17 , the method may further comprise, before the forming step E4, a calculating step E6 whether at least one of the lenses LN must be configured to focus the incident light onto at least two sub-pixels, as represented for example in the figures 11 et 12 , to create a hybrid color.

[0152] During this calculation step E6, carried out by a calculation unit such as a computer for example, the respective weights (or respective proportions, or respective weighting coefficients) of each color constituting a hybrid color that one wishes to obtain are determined and, from these weights, the positioning of the corresponding LN lens (and in particular the position of its useful surface) relative to the sub-pixels of the associated pixel is determined.

[0153] Thus, in a particular mode, at least one lens LN, called the first lens, of the lens array is a converging lens configured to focus the incident light received onto at least two sub-pixels 42 of the associated pixel 40 ( figures 9-12 ) so as to cause a hybrid color CL1, CL2 to appear in a corresponding region R1, R2 of the color image 6 resulting from a combination of the colors of said at least two sub-pixels, wherein said first lens LN is formed so that it has, in its smallest dimension, a smallest maximum dimension of 150 µm. The generation method then comprises a determination (E6) of respective weights assigned to each of said at least two sub-pixels 42, these weights representing respective contributions of each sub-pixel 42 in the combination of colors producing the hybrid color; the first lens being positioned relative to the associated pixel 40 in accordance with said respective weights assigned to said at least two sub-pixels 42.

[0154] As already indicated, the process ( figure 17 ) may further comprise a step E5 of forming opaque zones 60 to create gray levels in the final image, as already explained with reference to the figure 15 .

[0155] As indicated in the various embodiments considered above, numerous variants and adaptations are possible within the scope of the invention. In particular, those skilled in the art can envisage numerous configurations of the lenses. Similarly, numerous pixel arrangements are possible depending on the specific case.

[0156] The order in which the steps are performed in the figures 16 et 17 can be adapted according to the specific case.

[0157] According to a particular embodiment, each lens of the document of the invention is associated with a single pixel. Image 6 ( figure 1 ) is thus formed by n lens / associated pixel pair(s), n being an integer greater than or equal to 1.

[0158] A person skilled in the art will understand that the embodiments and variants described above constitute only non-limiting examples of implementation of the invention. In particular, a person skilled in the art may envisage any adaptation or combination among the characteristics and embodiments described above in order to meet a very specific need.

[0159] Thus, it is possible to use, for example, diverging lenses in the embodiments of the figures 4 And 9 or spheroidal lenses in the embodiment of the figure 4 or cylindrical lenses in the embodiment of the figure 9, within the scope of the appended claims. Different pixel tilings are possible in each of the embodiments described herein within the scope of protection of the appended claims. The different variations described with reference to each embodiment may be applied to the other embodiments within the scope of protection of the appended claims.

Claims

1. Document (2) capable of generating a colour image (6), comprising: - a set of pixels (20) printed on or in a substrate (2), each pixel forming a pattern comprising an arrangement of sub-pixels (22) of at least two different colours, each pixel (20) of said set of pixels being configured so that each sub-pixel has a distinct colour in said pixel; and - an array of lenses (LN) placed facing the set of pixels so as to generate the colour image by focusing incident light or causing incident light to diverge through the lenses (LN) onto at least some of the sub-pixels (22), each lens (LN) being positioned, relative to an associated pixel (20) located opposite, to focus incident light or cause incident light to diverge onto at least one of the sub-pixels (22) of said associated pixel so as to modify the contribution of the respective colours of the sub-pixels of the associated pixel, in a region of the colour image (6) generated through said lens, with respect to the pattern formed intrinsically by the associated pixel (20) independently of said lens (LN), in which at least one lens (LN1, LN2) in the array of lenses is a convergent lens configured to focus the received incident light so as to accentuate the colour contribution of at least one sub-pixel (22) of the associated pixel (20), in the corresponding region of the colour image generated through said lens (LN1, LN2), with respect to the respective colour contribution of each other sub-pixel (22) of said associated pixel (20), and in which at least a first lens (LN2) of the array of lenses (LN) is a convergent lens configured to focus the received incident light onto at least two sub-pixels (22) of the associated pixel so as to make appear, in a corresponding region of the colour image, a hybrid colour (CL1, CL2) resulting from a combination of the colours of said at least two sub-pixels, characterized in that said convergent first lens (LN2) being configured relative to the associated pixel in accordance with respective weights assigned to each of said at least two sub-pixels, said weights representing respective contributions of each sub-pixel in the combination of colours producing the hybrid colour; and in that said first lens has, in respect of its smallest dimension, a maximum smallest dimension of 150 µm.

2. Document according to Claim 1, wherein each pixel (20) of said set of pixels forms an identical pattern of colour sub-pixels (22).

3. Document according to Claim 1 or 2, wherein the set of pixels (20) is configured so that the sub-pixels are evenly distributed over or in the substrate.

4. Document according to any one of Claims 1 to 3, wherein the probability density of the presence of each sub-pixel colour remains constant throughout the set of pixels.

5. Document according to any one of Claims 1 to 4, wherein the array of lenses (LN) is formed from a layer comprising surface deformations defining the microlenses, said layer being the substrate or a layer laminated with the substrate.

6. Document according to any one of Claims 1 to 5, wherein the sub-pixels (22) in the set of pixels have a reflective surface (23) positioned under the sub-pixels to reflect the incident light through the array of lenses.

7. Document according to any one of Claims 1 to 6, wherein at least one lens of the array of lenses is a divergent lens configured to make incident light received by the lens diverge so as to reduce the colour contribution of at least one sub-pixel of the associated pixel, in the corresponding region of the colour image generated through said lens, with respect to the respective colour contribution of each other sub-pixel of said associated pixel.

8. Document according to any one of Claims 1 to 7, further comprising: a transparent laserable layer (65) placed facing the set of pixels (20), said transparent laserable layer being at least partially carbonised by laser radiation so as to comprise locally opacified regions facing sub-pixels to produce shades of grey in the colour image generated through the lenses.

9. Process for generating a colour image (6), comprising: - printing (E2) a set of pixels (20) on or in a substrate, each pixel forming a pattern comprising an arrangement of sub-pixels (22) of at least two different colours, each pixel (20) of said set of pixels being configured so that each sub-pixel (22) has a distinct colour in said pixel; and - forming (E4) an array of lenses (LN) placed facing the set of pixels so as to generate the colour image by focusing incident light or causing incident light to diverge through the lenses onto at least some of the sub-pixels, each lens being positioned, relative to an associated pixel located opposite, to focus incident light or cause incident light to diverge onto at least one of the sub-pixels of said associated pixel so as to modify the contribution of the respective colours of the sub-pixels of the associated pixel, in a region of the colour image generated through said lens, with respect to the pattern formed intrinsically by the associated pixel independently of said lens, in which at least a first lens (LN2) of the array of lenses is a convergent lens configured to focus the received incident light onto at least two sub-pixels (22) of the associated pixel so as to make appear, in a corresponding region of the colour image, a hybrid colour (CL1, CL2) resulting from a combination of the colours of said at least two sub-pixels, characterized in that said convergent lens being configured relative to the associated pixel in accordance with respective weights assigned to each of said at least two sub-pixels, said weights representing respective contributions of each sub-pixel in the combination of colours producing the hybrid colour, the first lens being configured relative to the associated pixel in accordance with said respective weights assigned to said at least two sub-pixels; and in that said first lens has, in respect of its smallest dimension, a maximum smallest dimension of 150 µm.

10. Process according to Claim 9, comprising: - providing a transparent first layer; and - projecting onto the transparent first layer first laser radiation so as to form the lenses by deforming a surface of said transparent first layer.

11. Process according to Claim 9, comprising: - providing a transparent first layer; and - spraying, onto the transparent first layer, transparent material using a 3D-printing head so as to form lenses on a surface of the transparent first layer.

12. Process according to any one of Claims 9 to 11, wherein, in the forming step, each lens is positioned relative to the associated pixel located opposite independently of the position of the other lenses of said array of lenses.

Images