Optically variable system

Abstract

Security article comprising an optically variable system ((10), with microlenses (20) and an array of images (30) having sections (31, 32, 33, 34) and contours (21, 41)) arranged to generate a sequence (S) of successive images when the angle of observation varies, wherein the sequence of successive images generates an animation when the angle of observation varies under normal conditions of use of the article, the animation changing symmetrically between the start and the end of the sequence of images when the angle of view varies, and the first half (S1) of the sequence (S) of images and the second half (S2) of the sequence (S1) of images comprising at least two different respective images positioned symmetrically within the sequence (S) of successive images.

Description

[0001] Description

[0002] Title: Optically Variable System

[0003] 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.

[0004] technical field

[0005] In many security applications, an optical system that provides a complete, possibly three-dimensional, synthetic image to an observer is desired. Optically variable devices, such as parallax or lenticular gratings, are known to be used for image display to provide the viewer with moving images.

[0006] Previous technique

[0007] Lenticular grating devices generally comprise a micro-optical system consisting of an array of microlenses, for example, hemispherical, hemispherical, or hemispherical, Fresnel or otherwise, superimposed on an array of microimages. These hemispherical lenses are capable of producing various effects depending on the microimages used. These effects include translation, rotation, image transformation, magnification, and reduction.

[0008] 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 as the device is viewed from successive viewing angles.

[0009] US5724758 discloses a lenticular device comprising an impression representing a combination of still images with sequences of moving images.

[0010] EP 0887699 discloses a method for forming a seamless image element comprising a set of transition images following the final image of an interlaced image sequence. This sequence presents the first image, intermediate images, and the final image successively by changing the viewing angle. Thus, by changing the viewing angle, the user can view an animation from the first image to the last image via the intermediate images, and then from the last image back to the first image via the transition images. All images are perceived as a loop by the observer without any visual jump between the last and first images. The transition images can be a gradual appearance of the first image within the last image through various transition effects.

[0011] Description of the invention

[0012] There is a need to further improve security articles, particularly 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.

[0013] 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.

[0014] By "when the viewing angle varies under normal conditions of use of the article," it is understood that the user observes the article with the naked eye, continuously varying the viewing angle with a non-zero, and in particular substantially constant, angular velocity. 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" refers to 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.

[0015] Preferably, the animation progresses between the beginning and end of the image sequence in such a way that a symmetrical effect is perceived by the user. However, the individual symmetrical images within the animation may not be perfectly identical, even if the perceived animation is indeed symmetrical. This is because, as mentioned earlier, there are at least two symmetrically positioned images within the sequence that are different.

[0016] By "first half" and "second half" of the sequence of successive images, if we number the images of the sequence of successive images 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.

[0017] Preferably the image sequence comprises at least 4 successive images, i.e. N > 4.

[0018] By "two different images positioned symmetrically within the sequence of successive images," we understand that there is a m iemeimage of the sequence of successive images which is different from the image which is positioned symmetrically in the image sequence, that is to say of the (N-m+l) ieme image, N being the number of images in the sequence of successive images.

[0019] The animation generated by the sequence of successive images relies on at least two aspects: the way the successive images of the sequence appear 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.

[0020] In the invention, the differences between the first half, i.e., the "outward movement" of the sequence of successive images, and the second half, i.e., the "return movement" of the sequence of successive images, are such that they do not allow a user to see the difference between the "outward movement" and the "return movement" with the naked eye under normal conditions of use of the item. 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 "going" and "returning" by a continuous change of viewing angle under normal conditions of use of the article 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.

[0021] The invention enables the creation of visually appealing 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. Specifically, the difference between two symmetrically positioned images within a sequence of successive images is configured to be detectable under visible light.

[0022] In one variant, the difference between two distinct images positioned symmetrically within the sequence of successive images is configured to be detectable under a specific illumination, namely non-visible illumination, i.e., outside the visible spectrum, specifically under UV and / or IR illumination. For example, the two images differ in that at least a portion of only one of them is detectable under a particular illumination, such as UV. Authentication could then consist of using this specific illumination and verifying that the affected portion only appears when viewing that image.

[0023] Preferably, the entire image sequence is observed by varying the viewing angle in a single direction, that is, without changing the direction of rotation. Specifically, the optically variable system is configured so that it is not necessary to rotate it in one direction to observe the first half of the sequence and then in the opposite direction to observe the second half.

[0024] 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.

[0025] In one embodiment, the invention allows for the successive viewing of two or more successive image sequences in their entirety by continuously changing the viewing angle of the item in the same direction. The successive image sequences may be identical, such that the item is configured to allow the viewing of the same repeating image sequence by continuously changing the viewing angle of the item 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.

[0026] Each image in the sequence of successive images may contain 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 characters, one or more marks, and / or one or more animals, with one or more of these elements being animated. In particular, the element(s) of an image must be viewed from the same angle. In this application, where the images contain a single element, for example, a single object, the terms "image," "image element," or "image element" are used interchangeably.

[0027] Each image in the sequence of successive images can, with the image positioned symmetrically within the sequence of successive images, have an overlap 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 color difference AE*94 according to CIE 1994 less than or equal to 4, preferably less than or equal to 2. From this characteristic, it is understood that each image in the sequence of successive images can, with the image positioned symmetrically within the sequence of successive images, have an overlap 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 each of the two symmetrically positioned images, i.e.The image in the image sequence under consideration and its symmetrical counterpart within the sequence of successive images, with an AE*94 color difference according to CIE 1994 of 4 or less, preferably 2 or less, between the corresponding elements of the two images under consideration. It is also understood that two different images positioned symmetrically within the symmetrical image sequence also meet this criterion. In other words, the at least two symmetrically positioned and different images must have an overlap 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 each of the two different and symmetrical images, with an AE*94 color difference according to CIE 1994 of 4 or less, preferably 2 or less, between the corresponding elements of the two different and symmetrical images.This allows the different images to differ by a difference small enough that it is not perceptible when viewing the animation by changing the viewing angle under normal conditions of use.

[0028] The term "overlap area" refers to the common surface defined by the element(s) of the two images when they are superimposed and positioned to maximize this overlap area. Specifically, the overlap area of ​​the images can be determined, for example, by capturing these two symmetrical images in the image sequence using an image capture device and then superimposing them, for example, using a computer. The superposition is performed in such a way as to maximize this overlap area.

[0029] 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 such 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 some of their corresponding surfaces in different colors between the two images, with a non-zero color difference between the two corresponding parts that is 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.

[0030] 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.

[0031] By "an overlap area of ​​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 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 overlap 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. By "cumulative area of ​​elements" of an image is understood to be the sum of the areas of the elements composing the image.The term "surface of an element" refers to a surface defined by the contour of the element. If the contour of an element composing the image is not continuous, for example, an element with a dashed line contour, it refers to a surface defined by lines connecting adjacent points on the element's contour. It should be understood that if an image contains an element defined by a dashed line contour, these points are not considered individually as elements composing the image for the purpose of defining the aforementioned surfaces. From this characterization of the invention, it is understood that the two different images positioned symmetrically in the sequence of successive images also satisfy the criterion mentioned above for each image.This ensures that the different images differ by a sufficiently small amount that it is imperceptible when viewing the animation by changing the viewing angle under normal conditions of use. Indeed, above 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 previously in connection with the first aspect of the invention also apply to the second aspect of the invention.

[0032] Each image in the sequence of successive images can be as described previously.

[0033] The features below can be applied independently to the first or second aspect of the invention above.

[0034] The successive images in the sequence of successive images can represent different stages of the animation.

[0035] The animation may involve a continuous change in appearance of one or more elements of successive images, including 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.

[0036] For example, a change in appearance can involve a change in shape, color, and / or size—for instance, an object might expand in the first half of the image sequence and contract in the second half, or vice versa. Only a portion of the image may grow or shrink. In one variation, the entire image may grow or shrink. A change in shape refers to a change in the image's outline, specifically a local change in the curvature of that outline. The size of an image can change without a change in its shape.

[0037] The animation may involve 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. Only a portion of the image may be animated as shown. In a variation, the entire image may be animated as shown. The animation may also involve the appearance or disappearance of an object, animal, and / or person. Only a portion of the image may appear or disappear. In a variation, the entire image may appear or disappear.

[0038] Alternatively, each image in the sequence of successive images is a flat color, either solid or not, with the animation being a color change of part or all of the image.

[0039] The first and last images in the sequence of successive images can be identical. The animation can thus be cyclical between the beginning and end of the image sequence.

[0040] 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.

[0041] 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 difference 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 item.

[0042] The at least two different images positioned symmetrically within the image sequence may be of identical colors 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 in the sequence of successive images has, with the image positioned symmetrically within the sequence of successive images, corresponding colors between the two identical images and an overlap 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.

[0043] For example, the at least two different images positioned symmetrically within the image sequence may have an overlap area of ​​corresponding elements in both images strictly less than 100%, preferably less than 95% of the cumulative area of ​​the elements in at least one of the two images. The two different images positioned symmetrically may then contain at least one element with a significant difference in shape and / or size between the two images.

[0044] 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 that is 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.

[0045] At least one element in the two symmetrically positioned images within the image sequence may differ in shape, with the difference representing less than 10%, preferably less than 5%, of the cumulative area of ​​the elements in each image. For example, the element may differ in the shape of its outline, including its local curvature, thickness, and / or pattern. For instance, the lines of its outline may be solid in one image and dashed in the other. An element in the two symmetrically positioned images within the image sequence may have outlines of different lengths.

[0046] 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 area of ​​the elements in each image.

[0047] 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 image dimension in the direction of movement of the element between the two images, the image dimension 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 movement of the element between the two different images positioned symmetrically in the sequence of images", 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.

[0048] At least one of the elements in the two different images positioned symmetrically in the image sequence may differ in its colorimetric appearance, specifically 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.

[0049] At least one element in one of the two symmetrically positioned images may be a trademark that is present in one image and absent in the other. Specifically, the trademark is distinct from the element(s) in the image that is the subject of the animation. This trademark may be in the form of letters, alphanumeric characters, ideograms, or symbols. The trademark's area preferably represents less than 10%, and preferably less than 5%, of the area of ​​the image containing the trademark, and specifically less than 10%, and preferably less than 5%, of the combined area of ​​the elements (90) in at least one of the two images.

[0050] At least one of the elements in the two symmetrically positioned different images may differ in two characteristics chosen from its colorimetric appearance, its shape, its size and its position.

[0051] 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.

[0052] The security feature of the present invention may also include additional security elements such as desired printed images, metallic layers that may be opaque, semi-transparent, or halftone. Such metallic layers may contain negative or positive indices created by known demetallization processes.

[0053] Additional optically variable materials can be included in the security device, such as thin-film interference elements, liquid crystal materials, and photonic crystal materials. Such materials can be in the form of film layers or pigmented materials suitable for printing.

[0054] Preferably, the optically variable system is a parallax barrier or lenticular grating system.

[0055] The parallax barrier or lenticular grating system may include an array of developing elements, such as a developing frame, a microlens array (e.g., hemispherical, hemispherical, or hemispherical), or a micromirror array, and an associated array of image components arranged 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 so that a synthetic integral image is perceived when viewed by an observer positioned at a distance from the developing element array at a predetermined viewing angle. The developing elements and image components may be pinpointed, including with precision.

[0056] The associated network of image components may exhibit the same periodicity or an integer multiple of the periodicity of the network of revealing elements.

[0057] Image components can be in the form of bands or pixels.

[0058] Image components can be in the form of nested or interlaced images.

[0059] 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.

[0060] The image sequence(s) can be formed by successively viewing sections of image components through the lenticular lens, varying the viewing angle under normal operating conditions. Each image sequence can be formed from sections of a single image component. Alternatively, each image sequence can be formed from 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 viewed by two different viewing angles to form the first and last images of the image sequence(s).

[0061] The image sequence can contain at least five images.

[0062] 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:

[0063] - a) verification 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,

[0064] - 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,

[0065] - c) generation of information on the authenticity of the item at least on the basis of these checks.

[0066] Step b) may involve capturing the image sequence. This capture can be done by capturing successive individual images of the image sequence from different viewing angles.

[0067] Step b) is, for example, carried out using a device that magnifies the images to be observed, such as a magnifying glass or an image capture tool. The images can then be displayed on a display device such as a screen. Step b) may involve recording the animation and decomposing it frame by frame to determine the authenticity of the security feature. In particular, two images positioned symmetrically within the overall sequence can be displayed simultaneously on the display device, for example, superimposed on the screen, to be compared, for example, by a human, to see if they contain the difference(s) being 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 global sequence can be achieved with a computer program for comparing images positioned symmetrically in the captured image sequence.

[0068] Step b) may include, for each image, the calculation of the ratio of the overlap area of ​​the corresponding elements of the two images positioned symmetrically in the image sequence with the cumulative area of ​​the elements of said image and the calculation of the AE*94 color deviation according to CIE 1994 of the overlap area of ​​the corresponding elements of the two images positioned symmetrically in the image sequence, in particular in the case where the ratio is different from 100%, in particular strictly less than 95%, for example less than 90%.

[0069] 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 calculated ratio 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.

[0070] According to another aspect, the invention also relates to a security document comprising a security article according to the invention.

[0071] 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.

[0072] The safety device may be in the form of a safety wire.

[0073] The safety article may be a film, lamination strip, patch, and / or foil shown on the safety document. The film, lamination strip, patch, and / or foil may have metallization and / or demetallization, for example in aluminum or copper, or any type of printing.

[0074] A "patch" is defined as an element smaller than the security item and which may not extend to the edge of the item. The patch may have a polygonal, circular, oval, or more complex shape, including a design representing text, an alphanumeric symbol, an ideogram, an object, a person, a plant, a monument, and / or an animal. A "foil" or "lamination strip" is defined as an element applied, for example, by heat transfer onto the security item from a carrier structure or by lamination. This element may extend continuously from one edge of the item to the opposite edge.

[0075] The film, lamination strip, patch and / or foil may contain holographic prints and / or liquid crystals.

[0076] The security item may be a security wire, in particular incorporated into the surface or window(s) of the secured item.

[0077] The security feature may be incorporated as a window within the security document. The window may be formed within the security document during its manufacture. The window may 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. Alternatively, the window may not have a lack of material. The window may, for example, be at least partially transparent or translucent above and below the optically variable system, the transparent or translucent areas being superimposed so that both opposite sides of the security feature can be observed. The window may also be pass-through. The window may have superimposed lacks of material on either side of the optically variable system.Two sides of the optically variable system can thus be observed directly, rather than through transparent or translucent areas. The optically variable system can be fully or partially incorporated into the window.

[0078] The safety document and / or one or more of its components, such as a substrate, safety wire, patch, and / or foil, may include one or more additional safety features such as fibers, strips, tapes, threads, particles, or tracers. These safety features may be visible to the naked eye or detectable only with a relatively simple device, such as an ultraviolet (UV) or infrared (IR) lamp, or may require a more sophisticated detection device. The additional safety features within the safety document may have first, second, or third-level safety characteristics.

[0079] Brief description of the drawings

[0080] 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 attached drawing on which:

[0081] [Fig 1] Figure 1 schematically represents a cross-sectional view of an optically variable system.

[0082] [Fig 2] Figure 2 schematically represents a cross-sectional view of a variant of the system in Figure 1.

[0083] [Fig 3] represents an example of a hemicylindrical microlens array.

[0084] [Fig 4A] to [Fig 4C] represent an example of an optically variable system featuring a parallax barrier grating.

[0085] [Fig 5] illustrates an example of an image sequence generated by a security article according to the invention.

[0086] [Fig 5A] Figure 5A represents the superposition of two respective images positioned symmetrically within the image sequence of Figure 5 which are different.

[0087] [Fig 5B] Figure 5B illustrates an example of two successive image sequences generated by a safety article according to the invention.

[0088] [Fig 6] Figure 6 represents an example of an image sequence generated by a security article according to the invention.

[0089] [Fig 6A] Figure 6A represents the superposition of two respective images 4, 6 positioned symmetrically within the sequence of images in Figure 6 which are different.

[0090] [Fig 6B] Figure 6B represents the superposition of two other respective images 3, 7 positioned symmetrically within the image sequence of Figure 6.

[0091] [Fig 6C] Figure 6C represents the superposition of two respective images 2, 8 positioned symmetrically within the image sequence of Figure 6. [Fig 7] Figure 7 represents a variant of an image sequence generated by a safety article according to the invention.

[0092] [Fig 7A] Figure 7A represents the superposition between two respective images positioned symmetrically within the image sequence of Figure 7.

[0093] [Fig 8] Figure 8 represents the superposition of two different images positioned symmetrically within a variant of an image sequence generated by a safety article according to the invention.

[0094] [Fig 9] Figure 9 represents the colorimetric difference between two different images positioned symmetrically within a variant of an image sequence generated by a safety article according to the invention.

[0095] [Fig 10] Figure 10 schematically represents a method for authenticating the security article according to the invention.

[0096] Detailed description

[0097] Figure 1 illustrates 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.

[0098] In the embodiment illustrated in Figure 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 the system is 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 progressively 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 such that the image appears to move or be modified, in particular to transform or undergo enlargement and / or reduction.The transition from one image to another can result in complex animations, such as 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 known to generate 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 W02005052650.

[0099] 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.

[0100] Here, sections 31 to 34 of image components 30 are shown as joined. However, they could overlap at least partially or be separated from each other by a non-zero distance.

[0101] In the embodiment shown in Figure 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 from different viewing angles. In this case, the image components 30 could be joined or separated.

[0102] 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, particularly 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 the image components 30—that is, between section 34 of one image component and section 31 of the adjacent image component—be substantially identical.This allows visual continuity of the image sequence by changing the viewing angle under normal conditions of use.

[0103] In the embodiment illustrated in Figure 3, the combination of sections 32 of image components 30 and the combination of sections 34 of image components 30 form two different synthetic images positioned symmetrically in the sequence of successive images generated by the change in viewing angle. The combination of sections 31 of image components 30 can form the first image at a first viewing angle and the last image of the sequence of successive images at a final viewing angle during the change in viewing angle, under normal operating conditions of the device.

[0104] The image components 30 can be printed directly onto the substrate 50 as shown in Figure 1, and optionally protected by a protective layer. Alternatively, the image components 30 can be printed onto one or more surface layers 60 arranged on the substrate 50 as shown in Figure 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.

[0105] In one variant, the optically variable system 10 can have a parallax effect, for example as disclosed in application WO2011007344.

[0106] Figures 4A to 4C illustrate an optically variable system 10 comprising a parallax barrier. The system 10 includes a non-opaque substrate 50, for example, perfectly transparent, having a first face 2a bearing image components 30. Image components include, for example, a plurality of nested coded images Ii, h, ..., 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, ..., I n forms a combined image I, as can be seen in Figure 4C. The second face 2b of the substrate 2, opposite the first, carries a development grid 25 (also called a decomposition filter) in the form of a parallax barrier grating. The development grid has opacifying bands 55 (or lines).

[0107] The development grid 25 can be composed of a periodic pattern, in this case the opacifying band 55, of constant period p, as can be seen in Figure 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.

[0108] The simplest realization of the development grid 25 is a succession of opacifying bands 25 of constant width at regular intervals w, as illustrated in figure 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.

[0109] An example of an image sequence S generated by changing the viewing angle of a safety device according to the invention is illustrated in Figure 5. The sequence S comprises five images, here numbered 1, 2, 3, 4, and 1, with the first image 1 of the sequence S corresponding to the beginning of the sequence and the last image 5 of the sequence S corresponding 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 and last images 1 of the sequence S are identical 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 wingbeat.Preferably, the complete S sequence is observed by tilting the system in a single direction between two observation angles. Specifically, 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.

[0110] In the illustrated example, the two respective images 2 and 4, positioned symmetrically within the image sequence S, are different, as can be seen in the superposition of images 2 and 4 shown in Figure 5A. These images differ along a portion of their contours 21 and 41. In the illustrated example, the image contains a single animated element 90, i.e., a butterfly, and the difference in the contour lies at the butterfly's wings, the butterfly's body being identical. Preferably, a superposition 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 in each image, is less than 0.2.Furthermore, images 2 and 4 represent slightly different moments of wingbeat, so the human eye will perceive a continuity of movement as the image sequence scrolls before it. Thus, under normal conditions of use, it is difficult to discern 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 using more complex image comparison methods, such as superimposing the two images 2 and 4, as illustrated in Figure 5A.

[0111] In the example in Figure 5, we illustrated a single image sequence 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 in the same direction, as shown in Figure 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 in the same direction, resulting in a continuous visual appearance between the two sequences.

[0112] In an unillustrated variant, the two identical image sequences could be disjointed from each other by repeating image 1, one image 1 for the last image of sequence S and one image 1 for the first image of sequence S'.

[0113] In the image sequences of Figures 6 and 7, each sequence S comprises nine images. The first half S1 of sequence S contains five images 1, 2, 3, 4, 5, forming the "forward" part of the sequence, and the second half S2 of sequence S contains five images 5, 6, 7, 8, 1, forming the "return" part of the sequence. The images contain a geometric figure. The change in the figure's shape 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.

[0114] In the example in Figure 6, each of the three pairs of images 2 and 8, 3 and 7, and 4 and 6, comprises two distinct images positioned symmetrically within the overall sequence S, as can be seen in Figures 6A to 6C, which represent their respective superpositions. In the example in Figure 7, the sequence comprises only one pair of images, 3 and 7, whose two distinct images, positioned symmetrically within the overall sequence S, are also distinct, as can be seen in Figure 7A.

[0115] To verify that the first half and 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. These distinct images can then be compared, for example, by being displayed simultaneously on a screen side-by-side or superimposed. The verification of the desired difference can be performed by a human viewing the images on the screen, or by a computer program, for example, one that automatically identifies the difference between two images.

[0116] 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, they are clearly observable. The difference d in position between the two positions of 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'.

[0117] In the examples above, the corresponding element 90 in 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. This allows for a clearer distinction between this element 90 in the two images. It is important to understand, however, that they have a color difference (AE*94) according to CIE 1994 equal to 0, as they are the same color.

[0118] In the example in Figure 9, the corresponding element 90 of two different images is shown. These images are positioned symmetrically in a sequence of successive images and 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 invention's authenticity as described below. This difference is perceptible, for example, by capturing the two images and bringing them together during a comparison step.

[0119] The authentication of a security item containing an image sequence as described above can be carried out in several steps, as illustrated in Figure 10. A first step, 100, is performed by observing a symmetrical animation by changing the viewing angle while rotating the security item under normal viewing conditions, for example, by observing the item with the naked eye at a distance of 25 cm in white light while rotating it at a speed of approximately 20 deg / s. A second step, 105, consists of identifying two different images positioned symmetrically within 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 within the image sequence can lead to a conclusion regarding the authentication of the security item, according to step 110.

[0120] 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 achieved, for example, using a mirror array in a manner similar to the microlens array, or by parallax effect, for example, using a development 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 W02010 / 073225 and WO2011 / 007344.For example, the difference between two symmetrically positioned images may be something other than what is illustrated. This could include the presence of an element in one image that is not present in the other, a variation in color, or any other difference that would not be perceptible to the human eye in a slideshow of images to create an animation but would be detectable by more complex image comparison methods. In particular, a color difference with a color deviation AE*94 according to CIE 1994 of 4 or less would not be perceptible to the human eye in an animation.

[0121] The images shown here are quite simple, often consisting of a single figurative element representing a shape or an animal. However, they could be more complex, depicting a scene with multiple 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 intricate, including a combination of color differences and differences in shape or size.

[0122] 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 instance, 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 overall sequence may have identical shapes under visible light but different shapes under infrared or ultraviolet illumination.

Claims

Demands 1. 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 sequence of images when the viewing angle varies, the first half (S1) of the sequence (S) of images and the second half (S2) of the sequence (S1) of images 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 of the sequence (S) of successive images having, with the image positioned symmetrically within the sequence of successive images, a superposition 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 each of the two symmetrically positioned images, with a color difference AE*94 according to CIE 1994 less than or equal to 4 between the corresponding elements (90) of these two images, 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, in particular 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 one of the preceding claims, the at least two different images positioned symmetrically within the image sequence presenting a superposition area of ​​corresponding elements (90) of the two images strictly less than 100%, in particular less than 95% of the cumulative area of ​​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 system or lenticular array comprising an array of revealing elements, in particular a revealing frame, an array of microlenses, in particular hemicylindrical, hemispherical or hemi-aspherical, 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) verification 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, - 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.

14. 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.

15. 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.

16. Safety document comprising a safety article according to any one of claims 1 to 12.

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