Optically variable system

Abstract

Optically Variable System: A safety article comprising an optically variable system arranged to generate a sequence (S) of successive images when the viewing angle varies. The sequence of successive images generates an animation when the viewing angle varies under normal conditions of use of the article. The animation evolves symmetrically between the beginning and end of the image sequence when the viewing angle varies. The first half (S1) of the image sequence (S) and the second half (S2) of the image sequence (S1) comprise at least two different images positioned symmetrically within the sequence (S) of successive images. Figure for abbreviation: Fig. 5

Description

Title of the invention: Optically variable system

[0001] The present invention relates to a security article and a method for authenticating a security article, as well as a security document containing a security article. technical field

[0002] In many applications in the field of security elements, an optical system that provides a complete, possibly three-dimensional, synthetic image to an observer is desired. It is known to use optically variable devices, particularly parallax or lenticular grating devices, for image display in order to provide the viewer with moving images. Previous technique

[0003] Lenticular grating devices generally comprise a micro-optical system consisting of a network of microlenses, for example, hemispherical, hemispherical, or hemispherical, Fresnel or otherwise, superimposed on a network of microimages. These hemispherical lenses are capable of producing several effects depending on the microimages used. These include, in particular, translation, rotation, image change, magnification, and reduction effects.

[0004] Patent EP2707228 discloses a security device comprising an array of lenticular elements superimposed on image strips. The image strips are constructed such that the device presents a cyclically repeating sequence of images while the device is viewed from successive viewing angles.

[0005] US application 5724758 discloses a lenticular device comprising an impression representing a combination of still images with sequences of moving images.

[0006] EP 0887699 discloses a method for forming a full-frame image element comprising a set of transition frames following the last frame of an interlaced image sequence showing the first frame, intermediate frames, and the last frame successively visible by changing the viewing angle. Thus, by changing the viewing angle, the user can view an animation from the first frame to the last frame via the intermediate frames, and then from the last frame back to the first frame via the transition frames; all the frames are perceived as a loop by the observer without any visual jump between the last and first frames. The transition frames can be a gradual appearance of the first image in the last image through various transition effects. Description of the invention

[0007] There is a need to further improve security articles, in particular those incorporating lenticular or parallax barrier devices for the successive viewing of images and the corresponding authentication methods, and to increase the security provided by these articles.

[0008] The invention achieves this objective, according to a first aspect, by means of a safety article comprising an optically variable system arranged to generate a sequence of successive images when the angle of observation varies, the sequence of successive images generating an animation when the angle of observation varies under normal conditions of use of the article, the animation evolving symmetrically between the beginning and the end of the sequence of images when the angle of view varies, the first half of the sequence of images and the second half of the sequence of successive images comprising at least two different respective images positioned symmetrically within the sequence of successive images.

[0009] By "when the viewing angle varies under normal conditions of use of the article," it should be understood that the user observes the article with the naked eye, varying the viewing angle of the article continuously with a non-zero angular velocity, in particular a substantially constant one. Preferably, the viewing angle varies by rotating the viewing angle around an axis of the article, in particular parallel to a principal plane of the article. The viewing angle can be varied by rotating the eyes around said axis or by tilting the article around said axis. For example, the angular velocity of rotation of the viewing angle of the article is between 5 and 50 deg / s. The expression "with the naked eye" means observation by the unaided human eye of normal visual acuity, at a distance of 25 cm, in daylight. For example, under normal conditions of use of the item, between 2 and 20 images are seen by the observer for 1 second..

[0010] By "first half" and "second half" of the sequence of successive images, if the images of the sequence of successive images are numbered in the order of their observation when the angle of observation varies, we understand respectively: - the successive images numbered 1 to n, and n+1 to 2n, when the number of successive images N in the sequence is equal to 2n, n being an integer, or - the successive images numbered 1 to n+1, and n+1 to 2n+l, when the number of successive images N in the sequence is equal to 2n+l, n being an integer.

[0011] Preferably the image sequence comprises at least 4 successive images, i.e. N > 4.

[0012] By "two different images positioned symmetrically within the sequence of successive images", it is understood that there exists an i-th image of the sequence of successive images which is different from the image which is positioned symmetrically in the image sequence, that is to say from the (N-m+l)th image, N being the number of images in the sequence of successive images.

[0013] The animation generated by the sequence of successive images relies on at least two aspects: the apparent movement of successive images in the sequence to the eye due to changes in the viewing angle, and retinal persistence. These two aspects allow for a well-known rendering of movement, changes in shape, or changes in appearance.

[0014] In the invention, the differences between the first half, i.e., the "forward" of the sequence of successive images, and the second half, i.e., the "return" of the sequence of successive images, are such that they do not allow a user to see the difference between the "forward" and "return" with the naked eye under normal conditions of use of the article. However, it is possible to detect this difference using a higher-level authentication method, for example, by taking a video of the animation and breaking it down frame by frame, and thus concluding that the security element is authentic.It is then possible to have a so-called first-level authentication by direct visual observation of the animation, visually presenting a symmetry effect between the "going" and "return" by a continuous change of viewing angle under normal conditions of use of the item, and a higher-level authentication by more precise observation of the individual images of the sequence of successive images using an appropriate observation tool, in particular a shot by a camera with a shooting frequency appropriate for the individual viewing of the images of the image sequence and possibly a comparison of the images of the image sequence positioned symmetrically by appropriate image processing.

[0015] The invention makes it possible to produce visually attractive security items that enhance security against counterfeiting, as they are difficult to imitate due to their high level of authentication, which can be achieved without requiring an additional light source or excitation. In particular, the difference between two distinct images positioned symmetrically within a sequence of successive images is configured to be detectable under visible light.

[0016] In one embodiment, the difference between two distinct images positioned symmetrically within the sequence of successive images is configured to be detectable under a particular illumination, in particular a non-visible illumination, specifically under UV and / or IR illumination. For example, the two distinct images differ in that at least a portion of only one of the two images is detectable under a particular illumination, for example, under UV. Authentication can therefore consist of using this particular illumination and verifying that said portion appears only when viewing this image.

[0017] Preferably, the entire image sequence is observed by varying the viewing angle in a single direction, i.e., without changing the direction of rotation. In particular, the optically variable system is configured so that it is not necessary to rotate the optically variable system in one direction to observe the first half of the sequence and then in the opposite direction to observe the second half of the sequence.

[0018] The invention can allow the observation of a single sequence of successive images in its entirety by changing the observation angle of the article continuously in the same direction.

[0019] In one embodiment, the invention allows for the successive observation of two or more successive image sequences in their entirety by continuously changing the viewing angle of the article in the same direction. The successive image sequences may be identical, such that the article is configured to allow the observation of the same repeating image sequence by continuously changing the viewing angle of the article in the same direction. Two successive image sequences may be dissociated from each other, that is, formed from different image components, particularly printed ones. Alternatively, two successive image sequences may partially overlap, in particular by having at least one image in common, with the first image of the second image sequence constituting the last image of the first image sequence. This allows, in particular, for visual continuity between the successive image sequences.

[0020] Each image in the sequence of successive images may include one or more elements, including a landscape, one or more objects, one or more people, one or more shapes, one or more signs, including alphanumeric, one or more marks and / or one or more animals, the element or at least one of the elements being animated in the animation.

[0021] Each image in the sequence of successive images can present, with the image positioned symmetrically within the sequence of successive images, a superposition area of ​​the corresponding elements of the two images, greater than or equal to 80%, preferably greater than or equal to 85%, and more preferably greater than 90% of the cumulative surface area of ​​the elements in said image has a color difference AE*94 according to CIE 1994 of 4 or less, preferably 2 or less. From this characteristic, it is understood that two different images positioned symmetrically in the symmetrical image sequence also meet this criterion. This ensures that the different images differ by a sufficiently small difference that it is not perceptible when viewing the animation by changing the viewing angle under normal conditions of use.

[0022] When two images positioned symmetrically within the sequence of successive images are different, they may present at least a part of their corresponding surfaces of different colors between the two images with a colorimetric difference between the two corresponding parts of between 4 and 2 so that the difference is visible to the naked eye by comparison of the two images but is not discernible to the naked eye when scrolling through the sequence of successive images under normal conditions of use.Alternatively, when two symmetrically positioned images within the sequence of successive images are different, they may have at least a portion of their corresponding surfaces in different colors between the two images, with a non-zero color difference between the two corresponding parts less than or equal to 2, such that the difference is visible using a special tool by comparing the two images but is not discernible to the naked eye. The two respective different images positioned symmetrically within the image sequence may differ from each other by the color of one or more portions of their surface, by a difference in the shape of one or more portions of their surface, by a different positioning of one or more elements in a portion of the images, and / or by one or more elements present in one of the two images and absent in the other.

[0023] The invention also relates, according to a second aspect, to a safety article comprising an optically variable system, arranged to generate a sequence of successive images when the angle of observation varies, each image of the sequence of successive images having, with the image positioned symmetrically within the sequence of successive images, a superposition area of ​​the corresponding elements of the two images greater than or equal to 80%, preferably greater than or equal to 85% and more preferably greater than 90%, of the cumulative area of ​​the elements of said image with a colorimetric deviation AE*94 according to CIE 1994 less than 4, preferably less than or equal to 2, the first half of the sequence and the second half of the sequence comprising at least two respective different images positioned symmetrically within the sequence of images.

[0024] By "a superposition area of ​​the corresponding elements of the two images greater than or equal to 80%, preferably greater than 85% and more preferably "Greater than 90% of the cumulative area of ​​the elements in said image with a color difference AE*94 according to CIE 1994 of less than 4, preferably less than or equal to 2," it is understood that the images positioned symmetrically in the sequence contain corresponding elements, including identical or distorted ones, and that these corresponding elements have an overlapping area with colorimetric identity or a small colorimetric difference, in particular less than 4, representing more than 80% of the total area of ​​these elements in each of the two images positioned symmetrically in the sequence. "Cumulative area of ​​the elements" of an image is understood to be the sum of the areas of the elements composing the image. "Area of ​​an element" is understood to be an area defined by an edge of the element.If the outline of an element within the image is not continuous, for example, an element with a dashed outline, it must be understood as a surface defined by lines connecting adjacent points on the element's outline. It should be understood that if an image contains an element defined by a dashed outline, these points are not considered individually as elements within the image for the purposes of defining the aforementioned surfaces.

[0025] From this characterization of the invention, it is understood that the two different images positioned symmetrically in the sequence of successive images also meet the criterion mentioned above for each image. This ensures that the different images differ by a sufficiently small difference that it is not perceptible when viewing the animation by changing the viewing angle under normal conditions of use. Indeed, below the overlap area value mentioned above, it is generally difficult to perceive the difference between two different images during normal use of the device. The advantages described above in connection with the first aspect of the invention also apply to the second aspect of the invention.

[0026] Each image in the sequence of successive images can be as described above.

[0027] The features below can be applied independently to the first or second aspect of the invention above.

[0028] The successive images of the sequence of successive images can represent different stages of the animation.

[0029] The animation may include a continuous change of appearance of one or more elements of successive images, in particular of a scene, an object, an animal and / or a person from a first appearance to a second appearance and then from the second appearance to the first appearance.

[0030] For example, the change in appearance may involve a change in shape, color, and / or size, for example, an object expanding during the first half of the image sequence and contracting during the second half, or vice versa. Only a portion of the image may enlarge or shrink. In one variation, the image may enlarge or shrink globally. A change in shape is understood to mean a change in the image's contour, in particular a local change in the curvature of the image's contour. The size of an image may change without a change in its shape.

[0031] The animation may consist of the continuous movement of an object, animal, or character from a first state to a second state and then from the second state back to the first state. Only a portion of the image may exhibit animation as described. In a variant, the entire image may be animated as described.

[0032] The animation may include the appearance or disappearance of an object, an animal, and / or a person. Only a part of the image may appear or disappear. In a variant, the entire image may appear or disappear.

[0033] Alternatively, each image in the sequence of successive images is a flat color, whether solid or not, the animation being a color change of part or all of the image.

[0034] The first and last images in the sequence of successive images can be identical. The animation can thus be cyclical between the beginning and the end of the image sequence.

[0035] The two different images positioned symmetrically within the sequence of successive images may differ in the appearance of the image, in particular by the presence or absence, color, size and / or shape of at least one of their elements.

[0036] The at least two different images positioned symmetrically within the image sequence may have an overlap area of ​​the corresponding elements of the two images strictly less than 100%, preferably less than 95%, of the cumulative area of ​​the elements of at least one of the two images with a color deviation AE*94 according to CIE 1994 less than 4, preferably less than or equal to 2. The two different images positioned symmetrically may then have at least one element having a significant difference in shape and / or size between the two images or having a significant difference in color, to allow the authentication of the article.

[0037] The at least two different images positioned symmetrically within the image sequence may be of identical color and may have an overlap area of ​​the corresponding elements of the two images strictly less than 100%, preferably less than 95%, of the cumulative area of ​​the elements of at least one of the two images. Preferably, each image of the sequence of successive images presents, with the image positioned symmetrically within the sequence of successive images, corresponding colors between the two identical images and a superposition area of ​​the corresponding elements of the two images greater than or equal to 80%, preferably greater than 85% and more preferably greater than 90%, of the cumulative area of ​​the elements of said image.

[0038] For example, the at least two different images positioned symmetrically within the image sequence may have an overlap area of ​​the corresponding elements of the two images strictly less than 100%, preferably less than 95% of the cumulative area of ​​the elements of at least one of the two images. The two different images positioned symmetrically may then have at least one element with a significant difference in shape and / or size between the two images.

[0039] Alternatively, the at least two different images positioned symmetrically within the image sequence may have an overlapping area of ​​the corresponding elements of the two images substantially equal to 100% of the cumulative area of ​​the elements of each image, with at least a portion of the overlapping area having an AE*94 color difference according to CIE 1994 of less than 4, preferably less than or equal to 2, but preferably greater than 0.5 to allow for authentication of the item by a color difference. The two different images positioned symmetrically may then have elements of identical shapes and sizes between the two images but a color difference with an AE*94 color difference according to CIE 1994 of less than 4, preferably less than or equal to 2.

[0040] At least one of the elements in the two different images positioned symmetrically in the image sequence may differ in shape in the two images, the difference in shape representing less than 10%, preferably less than 5%, of the cumulative surface area of ​​the elements in each image. For example, the element may differ in the two images in the shape of its outline, in particular its local curvature, thickness, and / or pattern. For example, the lines of part of its outline may be continuous in one of the two images and dashed in the other. An element in the two respective different images positioned symmetrically within the image sequence may have outlines of different lengths.

[0041] At least one of the elements in the two different images positioned symmetrically in the image sequence may differ in size in the two images, the size difference representing less than 10%, preferably less than 5%, of the cumulative surface area of ​​the elements in each image.

[0042] At least one of the elements in the two different images positioned symmetrically in the image sequence may differ in its position in the two images, the difference in position, characterized by the distance between the two positions in the image, being less than 10%, preferably less than 5%, of the dimension of the image in the direction of movement of the element between the two images, the dimension of the image being defined by the distance between two extreme points of the image along the direction in which the element was moved between the two different images positioned symmetrically in the image sequence.By "direction of displacement of the element between the two different images positioned symmetrically in the image sequence", we understand the direction formed by the shortest line connecting the centroid of the two corresponding elements when the different images positioned symmetrically in the sequence of successive images are superimposed.

[0043] At least one of the elements in the two different images positioned symmetrically in the image sequence may differ in its colorimetric appearance, in particular its color, gloss, or matte finish. The AE*94 color difference according to CIE 1994 between the two images for the element with the different appearance may be less than 4, preferably less than or equal to 2, but greater than 0.5.

[0044] At least one of the elements in one of the two symmetrically positioned images may be a mark that is present in one of the two images and absent in the other. In particular, the mark is different from the element(s) of the image that is the subject of the animation. This mark may be in the form of letters, alphanumeric characters, ideograms, or symbols. The area of ​​the mark preferably represents less than 10%, preferably less than 5%, of the area of ​​the image containing the mark, and in particular less than 10%, preferably less than 5%, of the cumulative area of ​​the elements (90) of at least one of the two images.

[0045] At least one of the elements in the two different symmetrically positioned images may differ in two characteristics chosen from its colorimetric appearance, its shape, its size and its position.

[0046] The safety feature of the present invention can be made machine-readable by introducing machine-detectable materials into any one of the layers or by introducing separate machine-readable layers. Machine-detectable materials that react to an external stimulus include, but are not limited to, luminescent, fluorescent, phosphorescent, X-ray absorbing or emitting, infrared or ultraviolet, thermochromic, photochromic, magnetic, electrochromic, conductive, and piezochromic materials.

[0047] The safety article of the present invention may also include additional safety features such as desired printed images, Metallic layers that can be opaque, semi-transparent, or textured. Such metallic layers may contain negative or positive indices created by known demetallization processes.

[0048] Additional optically variable materials may be included in the safety device, such as thin-film interference elements, liquid crystal materials, and photonic crystal materials. Such materials may be in the form of film layers or pigmented materials suitable for application by printing.

[0049] Preferably, the optically variable system is a parallax barrier system or a lenticular grating system.

[0050] The parallax barrier or lenticular grating system may comprise a grid of developing elements, including a developing frame, a microlens array, for example hemicylindrical, hemispherical, or hemispherical, or a micromirror array, and an associated array of image components arranged respectively on opposite sides of a transparent substrate. The developing elements, particularly the microlenses, may be arranged to visualize a section of an associated image component such that a synthetic integral image is perceived when viewed by an observer positioned at a distance from the grid of developing elements at a predetermined viewing angle. The developing elements and image components may be located, in particular with precision.

[0051] The associated network of image components may have the same periodicity or an integer multiple of the periodicity of the network of revealing elements

[0052] Image components can be in the form of bands or pixels.

[0053] Image components can be in the form of nested images or intertwined.

[0054] The width in the direction of the change in viewing angle of each image component may be less than or equal to 50 pm, preferably less than or equal to 20 pm, preferably in the range of 1 to 10 pm. The width may be greater than or equal to 1 pm.

[0055] The image sequence(s) can be formed by successively viewing, through the lenticular lens, by varying the viewing angle under normal operating conditions of the device, sections of the image components. The image sequence(s) can be formed by sections of a single image component. Alternatively, the image sequence(s) can be formed by sections of one image component and a section of an adjacent image component. Thus, the first or last section of each image component can be visible by two revealing elements at two different respective angles to form the first and last image of the or a sequence of images.

[0056] The image sequence may consist of at least five images.

[0057] According to another aspect, the invention relates to a method for authenticating a security article according to the invention in either the first or second aspect, comprising the steps of: • a) verification that the article generates, when the viewing angle varies, an animation that is perceived under normal conditions of use of the article as evolving symmetrically between the beginning and the end of the image sequence, • b) verification that the first half of the image sequence and the second half of the image sequence each contain at least two different images positioned symmetrically within the overall sequence, • c) generation of information on the authenticity of the item at least on the basis of these checks.

[0058] Step b) may include capturing the image sequence. This capture may be done by capturing successive individual images of the image sequence from different viewing angles.

[0059] Step b) is, for example, carried out with a device that enlarges the images to be observed, for example, using a magnifying glass or an image capture tool, and then the images can be displayed on a display medium such as a screen. Step b) may include video recording of the animation and its frame-by-frame decomposition to determine the authenticity of the security feature. In particular, two respective images positioned symmetrically within the overall sequence can be displayed simultaneously on the display medium, for example, superimposed on the screen, to be compared, for example, by a human, to see if they contain the difference(s) sought in order to determine the authenticity of the item.In one variant, the detection of differences between two respective images positioned symmetrically within the overall sequence can be achieved with a computer program for comparing symmetrically positioned images in the captured image sequence.

[0060] Step b) may include, for each image, calculating the ratio of the overlap area of ​​the corresponding elements of the two images positioned symmetrically in the image sequence to the cumulative area of ​​the elements of said image and calculating the AE*94 color difference according to CIE 1994 of the overlap area of ​​the corresponding elements of the two images positioned symmetrically in the image sequence, particularly in the case where the ratio is different from 100%, in particular strictly less than 95%, for example less than 90%.

[0061] Step c) may include the generation of authenticity information when, on the one hand, a symmetrical animation is observed, and on the other hand, the ratio calculated for at least two symmetrically positioned images in the image sequence is different from 100% or the colorimetric difference of at least two symmetrically positioned images in the image sequence is non-zero.

[0062] According to another aspect, the invention also relates to a security document comprising a security article according to the invention.

[0063] The security document can be chosen from among the secure documents, for example a means of payment, such as a banknote, a bank card, a check or a restaurant voucher, an identity document such as an identity card, a visa, a passport or a driving licence, a secure card, a lottery ticket, a transport ticket or even an entry ticket to events, or a secure label.

[0064] The safety article may be in the form of a safety wire.

[0065] The safety article may be a film, a lamination strip, a patch and / or a foil appearing on the safety document. The film, lamination strip, patch and / or foil may contain metallizations and / or demetallizations, for example in aluminium or copper, or any type of printing.

[0066] The term "patch" means an element smaller than the secure article and which may not extend to the edge of the article. The patch may have a polygonal, circular, oval outline or form a more complex pattern, including a pattern representing text, an alphanumeric symbol, an ideogram, an object, a person, a plant, a monument and / or an animal.

[0067] The term "foil" or "lamination strip" refers to an element applied, in particular by heat, for example by transfer onto the article secured, notably from a supporting structure. This element can extend continuously from one edge of the article to the opposite edge.

[0068] The film, lamination strip, patch and / or foil may include holographic prints and / or liquid crystals.

[0069] The safety article may be a safety wire, in particular incorporated on the surface or in window(s) in the secure article.

[0070] The safety feature can be incorporated as a window in the safety document. The window can be formed in the safety document during its manufacture. The window can be formed by a lack of material, for example, a local absence of paper, above or below the optically variable system, the window preferably being at least partially transparent or translucent on the side of the optically variable system opposite the lack of material. The window can The window must not have any material gaps. For example, the window may be at least partially transparent or translucent above and below the optically variable system, with the transparent or translucent areas overlapping to allow observation of both opposite sides of the security item. The window may also be pass-through. In this case, the window may have overlapping material gaps on either side of the optically variable system. Two sides of the optically variable system can thus be directly observed, rather than through transparent or translucent areas. The optically variable system may be fully or partially incorporated into the window.

[0071] The safety document and / or one or more of its elements such as a substrate, a safety wire, a patch and / or a foil, may include one or more additional safety elements such as fibers, strips, bands, threads, particles or tracers, these safety elements being visible to the naked eye or detectable only with a relatively simple device, such as a lamp emitting in the ultraviolet (UV) or infrared (IR) range, or requiring a more sophisticated detection device for their detection.

[0072] The additional security features present within the security document may have first, second or third level security characteristics. Brief description of the drawings

[0073] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the accompanying drawing on which:

[0074] [Fig-1] Fig. 1 schematically represents a cross-sectional view of a optically variable system.

[0075] [Fig.2] The [Fig.2] schematically represents a cross-sectional view of a variant of the system of the [Fig.1].

[0076] [Fig.3] represents an example of a semicylindrical microlens array.

[0077] [Fig.4A] to [Fig.4C] represent an example of an optically variable system comprising a parallax barrier grating.

[0078] [Fig.5] illustrates an example of an image sequence generated by a security article according to the invention.

[0079] [Fig.5A] [Fig.5A] represents the superposition of two respective images positioned symmetrically within the image sequence of [Fig.5] which are different.

[0080] [Fig.5B] The [Fig.5B] illustrates an example of two successive image sequences generated by a safety article according to the invention.

[0081] [Fig.6] Fig.6 represents an example of an image sequence generated by a security article according to the invention.

[0082] [Fig.6A] The [Fig.6A] represents the superposition of two respective images 4, 6 positioned symmetrically within the sequence of images of the [Fig.6] which are different.

[0083] [Fig.6B] The [Fig.6B] represents the superposition of two other respective images 3, 7 positioned symmetrically within the sequence of images of the [Fig.6].

[0084] [Fig.6C] The [Fig.6C] represents the superposition of two respective images 2, 8 positioned symmetrically within the image sequence of the [Fig.6].

[0085] [Fig.7] Fig.7 represents a variant of an image sequence generated by a safety article according to the invention.

[0086] [Fig.7A] The [Fig.7A] represents the superposition between two respective images positioned symmetrically within the image sequence of the [Fig.7].

[0087] [Fig.8] Fig.8 represents a variant of an image sequence generated by a safety article according to the invention.

[0088] [Fig.9] Fig.9 represents a variant of an image sequence generated by a safety article according to the invention.

[0089] [Fig. 10] The [Fig. 10] schematically represents a method of authenticating the security article according to the invention. Detailed description

[0090] Figure 1 shows a cross-section of an optically variable system 10 comprising a microlens array 20 and an associated array of image components 30 arranged respectively on opposite sides of a transparent substrate 50.

[0091] In the embodiment illustrated in [Fig. 2], each microlens 20 is arranged to magnify a section 31, 32, 33, or 34 of an associated image component 30 such that a synthetic integral image is perceived when viewed by an observer positioned at an appropriate distance from the microlens array 20 at a given viewing angle. By changing the viewing angle, different images can be seen. Consequently, when the system is tilted by a user gradually from a first viewing angle to a second viewing angle, a succession of different images forming a sequence of successive images will pass before the user's eye. The image sequence then generates an animation so that the image appears to move.The transition from one image to another can result in complex animations, for example, parts of the image changing almost continuously, morphing in which one image transforms into another, or zooming in which an image becomes larger or smaller in stages. Microlens arrays are known to be able to... generating a sequence of images producing an animation effect when the system is tilted, and their manufacturing process, are disclosed for example in applications EP2536564 and WO2005052650.

[0092] The microlenses 20 can be formed by embossing in the substrate 50, in a layer, not shown here, such as a layer of embossable resin, applied to the substrate 50, or by a curing process by casting in a separate layer, not shown here, on the substrate 50. The microlenses can be hemispherical or hemicylindrical, or even hemispherical.

[0093] Here, sections 31 to 34 of the image components 30 are shown as being joined. However, they could overlap at least partially or be separated from each other by a non-zero distance.

[0094] In the embodiment of [Fig. 2], the images formed by sections 31 and 34 can correspond, in particular be identical, to form the beginning and end of an image sequence according to the invention, as will be seen later. The image sequence is then formed by four successive images formed respectively by sections 31, 32, 33, and 34, visible at different viewing angles. In this case, the image components 30 could be joined or separated.

[0095] Alternatively, the images formed by sections 31 and 34 may not correspond; the image formed by section 34 may correspond to that formed by section 32. In this case, the beginning and end of an image sequence according to the invention may be formed by sections 31, each viewed from different angles by each lens of the lenticular array. The image sequence is then formed by five successive images formed respectively by sections 31, 32, 33, 34, and 31 again. Sections 31 are then visible by each developing element at different viewing angles, in particular at the first and last viewing angles. In this case, it is preferable that the image components be joined or that the spaces between sections 31 to 34 and between image components 30, i.e. between section 34 of an image component and section 31 of the adjacent image component, be substantially identical.This allows for visual continuity of the image sequence by changing the viewing angle under normal conditions of use.

[0096] In the embodiment illustrated in [Fig. 3], the combination of sections 32 of the image components 30 and the combination of sections 34 of the image components 30 form two different synthetic images positioned symmetrically in the sequence of successive images generated by the change in the viewing angle. The combination of sections 31 of the image components 30 can form the first image at a first viewing angle and the last image of the sequence successive images at a final viewing angle during the change of viewing angle, under normal conditions of use of the item.

[0097] The image components 30 can be printed directly onto the substrate 50 as shown in [Fig. 1], and optionally protected by a protective layer. In one embodiment, the image components 30 can be printed onto one or more surface layers 60 arranged on the substrate 50 as shown in [Fig. 2]. The surface layer 60 is, in particular, arranged on the substrate 50 without pre-structuring the substrate sheet 50, or the surface layer, for infill. The surface layer 60 preferably comprises a polymeric material. Preferably, the surface layer comprises a curable material, in particular a varnish. The curable layer 60 may also include non-curable components.The surface layer 60 or protective layer may be transparent, translucent, tinted, pigmented, opaque, metallic, magnetic, optically variable, or any combination thereof that provides desirable optical effects and / or additional functionality for security and authentication purposes, including support for automatic authentication, verification, tracking, counting and detection systems, which rely on optical effects, electrical conductivity or electrical capacitance, magnetic field detection.

[0098] In one variant, the optically variable system 10 can be parallax effect, for example as disclosed in application WO2011007344.

[0099] An optically variable system 10 comprising a parallax barrier is shown in [Fig. 4A] at AC. The system 10 comprises a non-opaque substrate 50, for example perfectly transparent, having a first face 2a bearing image components 30. Image components comprise, for example, a plurality of nested coded images Ib I2,.... In. The constituent elements 300 of these images are, for example, in the form of continuous or discontinuous lines, most often discontinuous. The set of coded images L,.... L forms a combined image I, as can be seen in [Fig. 3].

[0100] The second face 2b of the substrate 2, opposite to the first, carries a development grid 25 (also called a decomposition filter) in the form of a parallax barrier network. The development grid comprises opacifying bands 55 (or lines).

[0101] The development frame 25 can be composed of a periodic pattern, in this case the opacifying band 55, of constant period p, as can be seen in [Fig. 4B]. The periodicity is observed parallel to the direction of the relative displacement X between the optical system and the observer, allowing the different coded images to be observed.

[0102] The simplest embodiment of the development screen 25 is a succession of opacifying bands 25 of constant width at regular intervals w, as illustrated in [Fig.4B]. The period p corresponds to the sum of the width of an opacifying band 55 and a transparent interval between two consecutive opacifying bands 55.

[0103] An example of an image sequence S generated by changing the viewing angle of a safety device according to the invention is illustrated in [Fig. 5]. The sequence S comprises five images, here numbered 1, 2, 3, 4, and 1, where the first image 1 of the sequence S corresponds to the beginning of the sequence S and the last image 5 of the sequence S corresponds to the end of the sequence. The first half S1 of the sequence S comprises three images 1, 2, 3 forming the "outward" part of the sequence, and the second half S2 of the sequence S comprises three images 3, 4, 1 forming the "return" part of the sequence. The first 1 and the last 1 images of the sequence S are identical in order to create a cyclical animation. They have also been numbered identically to illustrate this. The successive images are in the form of a butterfly flapping its wings and represent successive stages of the butterfly's wing flapping.Preferably, the complete S sequence is observed by tilting the system in a single direction between two observation angles. In particular, it is not necessary to rotate the system in one direction to observe the first half of the S1 sequence and then in a second, opposite direction to observe the second half of the S2 sequence.

[0104] In the illustrated example, the two respective images 2 and 4, positioned symmetrically within the image sequence S, are different, as can be seen on a superposition of images 2 and 4 shown in [Fig. 5A]. These are different on a part of their contour 21 and 4L. In the illustrated example, the image contains a single animated element 90, i.e. a butterfly, and the difference in the contour is located at the level of the butterfly's wings, the butterfly's body being identical.

[0105] Preferably, an overlay area A of the butterfly, i.e., the corresponding element 10 of the two images, is greater than or equal to 80% of the total area A2, A4 of element 90 in each image. In other words, the area corresponding to the difference between the two images, relative to the total area A2 or A4 of element 90 of each image, is less than 0.2. Furthermore, the two images 2 and 4 represent slightly different moments of wingbeat, so that the human eye will perceive a continuity of movement as the images in the image sequence are viewed. Thus, under normal conditions of use of the article, it is difficult to perceive the difference between these two images 2 and 4, especially when viewed within the context of the animation by changing the viewing angle.The user will therefore perceive a perfectly symmetrical animation by changing the viewing angle, and the different images 2 and 4 can be identified as different by more complex means of comparison. image, in particular a superposition of the two images 2 and 4 as illustrated in [Fig.5A].

[0106] In the example in [Fig. 5], we have illustrated a single sequence of images obtained by observation from successive viewing angles. However, the article can be configured to generate two successive identical image sequences S and S' by continuously varying the viewing angle of the article in the same direction, as shown in [Fig. 5B]. In this case, the two image sequences S and S' can be superimposed, sharing a common image for improved continuity between the two sequences. The last image 1 of the first image sequence S can be the first image 1 of the second image sequence S'. Thus, the cyclical animation of the butterfly's wingbeats can be repeated twice by continuously varying the viewing angle of the article in the same direction, resulting in a continuous visual appearance between the two sequences.

[0107] In an unillustrated variant, the two identical image sequences could be disjointed from each other by repeating image 1, an image 1 for the last image of sequence S and an image 1 for the first image of sequence S'.

[0108] In the image sequences of Figures 6 and 7, each sequence S comprises nine images. The first half S1 of sequence S comprises five images 1, 2, 3, 4, 5 forming the "forward" part of the sequence, and the second half S2 of sequence S comprises five images 5, 6, 7, 8, 1 forming the "return" part of the sequence. The images each contain a geometric figure. The change in the shape of the figure exhibits a "morphing" effect. During the "forward" part of the sequence, the shape of the images changes successively from a square to a circle, with the corners of the square becoming rounded, while during the "return" part of the sequence, the shape of the images returns successively from a circle to a square.

[0109] In the example in [Fig. 6], each of the three pairs of images 2 and 8, 3 and 7, 4 and 6, comprises two respective images positioned symmetrically within the overall sequence S, which are different, as can be seen in Figures 6A to 6C representing their respective superpositions. In the example in [Fig. 7], the sequence comprises only one pair of images 3 and 7, whose two respective images positioned symmetrically within the overall sequence S are different, as can be seen in [Fig. 7A].

[0110] To verify that the first half of the sequence and the second half of the sequence each contain at least two distinct images positioned symmetrically within the overall sequence, the sequence can be videotaped and broken down frame by frame. The respective images positioned symmetrically within the overall sequence can be compared, for example by being displayed simultaneously on a screen side by side or superimposed. The existence verification The desired difference can be achieved by a human by looking at the images on the screen, or by a computer program, for example allowing the automatic identification of the difference between two images.

[0111] Figure 8 illustrates an example in which the corresponding element 90 of two different images positioned symmetrically in the sequence of successive images differs in its position in the two images m and m'. In the illustrated example, the animation can be a back-and-forth movement of the element along the directions F indicated by the arrows. It should be noted that even though the edges 70 of the image are not shown, it is clearly observable by an observer. The difference d in position between the two positions of the element 90 in the image is less than 10% of the dimension D of the image in the direction of movement F of the element between the two images m and m'.

[0112] In the aforementioned examples, the corresponding element 90 of the two different images positioned symmetrically in the sequence of successive images is represented with a difference in color level when the two images are superimposed, to allow for better distinction between this element 90 in the two images. It should nevertheless be understood that they have a color difference AE*94 according to CIE 1994 equal to 0, being of the same color.

[0113] In the example of [Fig. 9], the corresponding element 90 of two different images positioned symmetrically in the sequence of successive images is shown. These images differ by a color difference AE*94 according to CIE 1994. The color difference AE*94 according to CIE 1994 between the corresponding element 90 of these two images is less than or equal to 1 so as to be imperceptible to the human eye in an animation but identifiable during the verification of the authenticity of the invention as described below. This difference is perceptible, for example, by capturing the two images and bringing them together during a comparison step.

[0114] The authentication of a security article comprising an image sequence as described above can be carried out in several steps as illustrated in [Fig. 10]. A first step 100 is performed by observing a symmetrical animation by changing the viewing angle while rotating the security article under normal viewing conditions, for example, by observing the article with the naked eye at a distance of 25 cm in white light while rotating the article at a speed of approximately 20 deg / s. A second step 105 consists of identifying two different images positioned symmetrically in the image sequence by comparing the images as described above. Observing symmetry in the animation and a difference in at least two symmetrically positioned images in the image sequence can lead to a conclusion regarding the authentication of the security article according to step 110.

[0115] The invention is not limited to the embodiment described. For example, although embodiments of the invention are illustrated with microlenses, it should be understood that other elements capable of focusing on a section and / or restricting the view of an associated image element can be used to obtain a complete representation. Examples of such focusing elements are apertures, micromirrors, or lenticular lenses. Similar effects can be obtained, for example, using a mirror array in a manner similar to the microlens array, or by parallax effect, for example, using a developing grid and an associated array of image components arranged respectively on opposite sides of a transparent substrate or on different parts of one or more safety articles, as described in applications WO2010 / 073225 and WO2011 / 007344.

[0116] For example, the difference between two symmetrically positioned images may be other than that illustrated, in particular the presence of an element on one of the two images that is not present on the other image, a variation in color, or any other difference that would not be perceptible to the human eye in the context of a slideshow of images to form an animation but would be detectable by more complex means of image comparison. In particular, a color difference with a color deviation AE*94 according to CIE 1994 less than or equal to 4 would not be perceptible to the human eye in an animation.

[0117] The images represented here are quite simple, notably consisting of a single figurative element representing a shape or an animal. However, they could be more complex and represent a scene with several elements, one or more characters, one or more objects, and / or one or more alphanumeric characters. They could also be colored images forming a solid or non-solid color animation. The differences between the outward and return journeys could be more complex, including a combination of color differences and differences in shape or size.

[0118] In one embodiment, the difference between two distinct images positioned symmetrically within the image sequence can be configured to be undetectable under white light, even when superimposed. For example, two distinct images positioned symmetrically within the overall sequence may appear identical under visible light but different under infrared or ultraviolet illumination. For example, the aforementioned mark may contain a machine-detectable material, such as an ultraviolet or infrared ink that is undetectable under visible light. In another variant, one of the two distinct images positioned symmetrically within the within the overall sequence may have identical shapes under visible light but different shapes under infrared or ultraviolet illumination.

Claims

Demands

1. A safety article comprising an optically variable system arranged to generate a sequence (S) of successive images when the viewing angle varies, the sequence of successive images generating an animation when the viewing angle varies under normal conditions of use of the article, the animation evolving symmetrically between the beginning and the end of the image sequence when the viewing angle varies, the first half (S1) of the image sequence (S) and the second half (S2) of the image sequence (S1) comprising at least two different respective images positioned symmetrically within the sequence (S) of successive images.

2. Article according to claim 1, each image of the sequence (S) of successive images comprising one or more elements (90), the or at least one of the elements (90) being animated in the animation.

3. A safety article comprising an optically variable system, arranged to generate a sequence (S) of successive images when the viewing angle varies, each image in the sequence (S) of successive images having, with the image positioned symmetrically within the sequence of successive images, an overlap area of ​​the corresponding elements (90) of the two images greater than or equal to 80% of the cumulative area of ​​the elements (90) of said image with a color deviation AE*94 according to CIE 1994 less than or equal to 4, the first half (S1) of the sequence (S) and the second half (S2) of the sequence (S) comprising at least two respective different images positioned symmetrically within the sequence of images.

4. Article according to any one of the preceding claims, the animation comprising a continuous change in appearance of one or more elements (90) of successive images, including a change in shape, color and / or size.

5. Article according to one of the preceding claims, the two different images positioned symmetrically within the sequence of images differing in the appearance of the image, in particular by the presence or absence, color, size and / or shape of at least one of their elements (90).

6. Article according to any one of the preceding claims, the at least two different images positioned symmetrically within the image sequence having an overlap area of ​​the corresponding elements (90) of the two images strictly less than 100%, in particular less than 95% of the cumulative area of ​​the elements (90) of at least one of the two images.

7. Article according to any one of the preceding claims, at least one of the elements in one of the two symmetrically positioned different images comprising a mark which is present on one of the two images and absent on the other, the mark being different from the element(s) (90) of the animated image in the animation.

8. Article according to the preceding claim, the area of ​​the mark representing less than 10% of the area of ​​the image bearing the mark.

9. Article according to any one of the preceding claims, being in the form of a security thread, a film, a lamination strip, a patch and / or a foil, and preferably in the form of a security thread.

10. Article according to any one of the preceding claims, the optically variable system (10) being a parallax effect or lenticular grating system.

11. Article according to the preceding claim, the parallax effect or lenticular array system comprising an array of revealing elements, in particular a revealing frame, an array of microlenses, in particular hemicylindrical, hemispherical or hemispherical, or an array of micromirrors, and an associated array of image components (30) arranged respectively on opposite sides of a transparent substrate (50).

12. Article according to any one of the preceding claims, the sequence (S) of images comprising at least four successive images.

13. A method for authenticating a security article according to any one of the preceding claims, comprising the steps of: • a) verifying that the article generates, when the viewing angle varies, an animation which is perceived under normal conditions of use of the article, as evolving symmetrically between the beginning and the end of the image sequence,

14.

15.

16. • b) verification that the first half of the sequence and the second half of the sequence each contain at least two different images positioned symmetrically within the overall sequence, • c) generation of information on the authenticity of the item at least on the basis of these checks. Method according to the preceding claim, step a) comprising varying the observation angle of the article continuously in the same direction to observe the sequence of successive images. Method according to claim 13 or 14, step b) comprising video recording of the animation and decomposing it frame by frame to conclude on the authenticity of the security element. Safety document comprising a safety article according to any one of claims 1 to 12.

Images