Optical security element having effect regions
Patent Information
- Application Number
- EP2023787005
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-09-15
- Filing Date
- 2023-09-13
- Publication Date
- 2025-07-23
AI Technical Summary
Conventional optical security elements with multiple effect areas suffer from register fluctuations, leading to reduced anti-counterfeit security and visual attractiveness due to sharp boundaries between effect areas, making it difficult to distinguish originals from counterfeits.
An optical security element with at least two effect areas, each formed by micromirror areas or diffractive structures, featuring a dithered transition area where the pixel element share smoothly transitions from 100% to 0% along a boundary line, using dither algorithms like Floyd-Steinberg to create a continuous, monotonous transition that conceals positional deviations.
The solution provides a high level of protection against forgery while maintaining visual attractiveness by creating a smooth transition between optical effects, effectively masking register fluctuations and enhancing the ability to differentiate between originals and counterfeits.
Smart Images
Figure 1.1
Abstract
Description
[0001] Optical security element with effect areas
[0002] The invention relates to an optical security element for protecting valuables, comprising at least two effect areas for generating different optical effects. The invention also relates to a data carrier comprising such a security element, as well as a method for producing such a security element.
[0003] Data storage media, such as valuables or identification documents, but also other valuable items, such as branded goods, are often provided with security elements for security purposes. These elements allow the authenticity of the data storage media to be verified and at the same time serve as protection against unauthorized reproduction.
[0004] A combination of several different optical effects is often used to increase the counterfeit security of an optical security element. If effect areas with different optical effects border on one another, a boundary line is defined between the effect areas. This boundary line can serve as a reference for the viewer for register fluctuations that arise during other production processes. Such fluctuations can be irritating to the viewer. In addition to reducing visual appeal, the counterfeit security of the optical security element is also reduced, as counterfeits in particular often have register errors, making it more difficult to reliably distinguish between originals and counterfeits when register fluctuations occur in originals.
[0005] Based on this, the invention is based on the object of providing an optical security element of the type mentioned above with a high degree of forgery protection and an attractive visual appearance. This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.
[0006] The invention provides an optical security element for protecting valuables, comprising at least two effect regions for generating different optical effects, wherein the effect regions adjoin one another along a boundary line. In particular, at least one of the two effect regions can be formed by a micromirror region with directionally reflecting micromirrors.
[0007] The effect areas each consist of a multitude of pixel elements. A dithered transition area is formed along the boundary between a first effect area and a second effect area. In this transition area, the area proportion of the pixel elements in the first effect area decreases from 100% to 0%, while the area proportion of the pixel elements in the second effect area increases from 0% to 100%. In the transition area, the optical effect of the first effect area transitions seamlessly into the optical effect of the second effect area.
[0008] In an advantageous embodiment, the at least two effect regions are formed by micromirror regions with directionally reflecting micromirrors and different micromirror effects. In particular, one of the micromirror regions can be metallized and another of the micromirror regions can be unmetallized, for example, demetalized after metallization. In another, equally advantageous embodiment, one of the effect regions is formed by a micromirror region with directionally reflecting micromirrors, and another of the effect regions is formed by a diffractive relief structure, in particular a hologram, a holographic grating image, or a hologram-like diffraction structure.
[0009] In all designs, it can advantageously be provided that the micromirror region(s) each contain non-diffractive mirrors and preferably plane mirrors, concave mirrors and / or Fresnel-type mirrors.
[0010] Preferably, the effect areas each consist of a plurality of identically shaped pixel elements, in particular square or rectangular pixel elements. The pixel elements preferably have a maximum dimension between 1 gm and 100 gm. The pixel elements themselves are therefore not visible to the naked eye, so that despite the discrete division of the transition area into pixel elements, a smooth transition is created for the viewer.
[0011] The pixel elements advantageously fill the effect areas and the transition area without gaps, thus forming a tiling of the layer.
[0012] In an advantageous development, one of the effect regions forms an outer effect region that surrounds another of the effect regions, which forms an inner effect region, and the boundary line is formed by the outline of the inner effect region. In particular, two effect regions can be provided, with one effect region surrounding the other effect region. The width of the transition region is expediently between 50 μm and 50 mm, preferably between 50 μm and 10 mm, particularly preferably above the resolution limit of the human eye and in particular between 0.5 mm and 5 mm.
[0013] The invention also includes a data carrier with an optical security element of the type described. The data carrier can be, in particular, a value document, such as a banknote, in particular a paper banknote, a polymer banknote or a composite film banknote, a share, a bond, a certificate, a voucher, a cheque, a seal, a tax stamp, a high-value admission ticket, but also an identification card, such as a credit card, a bank card, a cash payment card, an authorization card, an identity card or a passport personalisation page.
[0014] The security elements described can be present as a separate security element applied to a data carrier to be secured, but they can also be part of the data carrier to be secured itself.
[0015] The invention further includes a method for producing an optical security element of the type described, in which at least two effect regions for generating different optical effects are generated on a carrier, which effect regions adjoin one another along a boundary line, and the effect regions are each formed from a multiplicity of pixel elements, and along the boundary line between a first effect region and a second effect region, a dithered transition region is formed, in which the area proportion of the pixel elements of the first effect region decreases from 100% to 0% and the area proportion of the pixel elements of the second effect region increases from 0% to 100%, so that in the transition region the optical effect of the first effect region merges smoothly into the optical effect of the second effect region when viewed.
[0016] Preferably, at least one of the two effect regions is formed by a micromirror region with directionally reflecting micromirrors.
[0017] In an advantageous method implementation, the dithered transition region is calculated using a dither algorithm, in particular a threshold algorithm, a random dither algorithm, a pattern dither algorithm, ordered dithering or an error diffusion algorithm.
[0018] Advantageous examples of ordered dithering methods are halftone dithering, Bayer matrix, and void-and-cluster. Advantageous examples of error diffusion algorithms are the Floyd-Steinberg algorithm, minimized average error, Stucki, Burkes, Sierra, two-row Sierra, Filter Lite, Atkinson, and gradient-based error diffusion algorithms.
[0019] Preferably, to generate the dithered transition region, a continuous progression of the size of the transition region is generated, which begins and ends with a discrete value assigned to one of the different effect regions, the continuous progression is reduced to a desired number of discrete values using a dithering algorithm, each discrete value being assigned to one of the different effect regions, and each pixel position in the transition region is assigned a pixel element of the assigned effect region in accordance with the discrete value determined for this pixel position in the dithering algorithm.
[0020] The continuous curve is advantageously monotonic, especially strictly monotonic. The continuous curve can be linear, for example, but also nonlinear, such as quadratic or following a tanh function.
[0021] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.
[0022] They show:
[0023] Fig. 1 shows a schematic representation of a banknote with a security element according to the invention with two effect areas bordering each other along a boundary line,
[0024] Fig. 2 in (a) a detailed view of a security element according to the invention with a transition region with perfect alignment of the two effect regions and in (b) a non-inventive security element without a transition region, Fig. 3 in (a) a detailed view of a security element according to the invention with a typical positional deviation of the effect regions and in (b) a non-inventive security element without a transition region,
[0025] Fig. 4 shows a detailed section of the transition area between the two effect areas, as well as even more enlarged sections of the first effect area, the transition area and the second effect area with the pixel elements,
[0026] Fig. 5 illustrates a security element in which the first effect region is formed by a metallized micromirror region and the second effect region by a demetallized micromirror region, wherein (a) the design is given, (b) as a comparative example shows a security element not according to the invention without a transition region and (c) a security element according to the invention with a transition region.
[0027] The invention will now be explained using the example of security elements for banknotes. Figure 1 shows a schematic representation of a banknote 10 with a security element 12 according to the invention.
[0028] The security element 12 contains two effect regions 14, 16 for generating different optical effects, which border one another along a boundary line 18. In this exemplary embodiment, the effect regions 14, 16 are formed by micromirror regions with directionally reflecting micromirrors that exhibit different micromirror effects. For example, the effect region 14 exhibits a 3D effect, while the effect region 16 exhibits a motion effect. As a special feature, a transition region 20 is formed between the two effect regions 14, 16 along the boundary line 18, in which transition region, when viewed, the optical effect of the first effect region 14 smoothly transitions into the optical effect of the second effect region 16.
[0029] The two different effect areas 14, 16 typically exhibit certain register fluctuations compared to (structural) features created in other production steps, which are, however, concealed by the transition area. As described above, conventional designs often have the problem that register fluctuations reveal weaknesses in production processes and that the visible positional deviations of the effect areas can be disconcerting to the observer.
[0030] These difficulties are overcome by providing a smooth, soft transition between the two effect areas 14, 16, as explained in more detail in Figures 2 to 4.
[0031] First, Fig. 2(a) shows a detailed view of the security element 12 with the effect regions 14, 16 and a transition region 20 formed along the boundary line 18, assuming an idealized perfect alignment of the two effect regions 14, 16, in the present case, for example, an alignment in which the boundary line 18 between the effect regions lies exactly at the height of the structural feature 22 in accordance with the design specification. For comparison, Fig. 2(b) shows a security element 12' not according to the invention without a transition region with such an idealized, perfect alignment of the boundary line 18' with the structural feature 22. Figure 3(a) then shows the security element 12 of Fig. 2(a) with a typical positional deviation A of the effect regions 14, 16 relative to the structural feature 22, which occurs due to the unavoidable register fluctuations during the production of the structural feature 22 in a separate operation.Figure 3(b) again shows, for comparison, a security element 12' not according to the invention without a transition region with the same positional deviation A.
[0032] Due to the design of the transition region 20, which is described in more detail below, the optical effect of the first effect region 14 transitions seamlessly into the optical effect of the second effect region 16. The designs of Figs. 2(a) and 3(a) therefore do not have a sharp boundary between the two optical effects, so that there is no fixed visual reference point for the correct position of the structural feature 22. The differences between the idealized, perfectly aligned position of Fig. 2(a) and a position typically occurring in reality according to Fig. 3(a) are therefore small and not distracting upon observation.
[0033] In contrast, the misalignment of the sharp boundary line 18' to the structural feature 22 in the comparative security element 12' of Fig. 3(b) is clearly perceptible due to the clearly recognizable position of the boundary line 18' compared to the perfectly aligned position of Fig. 2(b) and leads to the above-mentioned adverse effects.
[0034] The generation of the transition region 20 between the two effect regions 14, 16 is illustrated in more detail in Fig. 4, in which a detailed section 30 (see Fig. 2(a) and Fig. 3(a)) of a security element according to the invention is shown in more detail in the vicinity of the boundary line. The two effect regions 14, 16 each consist of a plurality of square pixel elements 34 and 36, respectively, wherein the pixel elements 34 of the effect region 14 produce a 3D effect as a first optical effect, and the pixel elements 36 of the effect region 16 produce a motion effect as a second optical effect. In the exemplary embodiment, each pixel element 34, 36 is formed by only a single micromirror; in other designs, however, the pixel elements can also each consist of a group of several, in particular identically aligned, micromirrors. The size of the pixel elements is below the resolution limit of the human eye, for example, 10 μm x 10 μm.
[0035] In the overview sketch of the right half of Fig. 4, for the sake of simplicity, the pixel elements 34 of the first effect area 14 are shown in white, the pixel elements 36 of the first effect area 16 in black, while the pixel elements in the more enlarged sections are shown with wide hatching (pixel elements 34, first optical effect) or with narrow hatching (pixel elements 36, second optical effect) according to the generation of the first or second optical effect.
[0036] Along the boundary line 18, a transition region 20 of width B is formed in the effect regions 14, 16, in which transition region 20, by means of a dithering process, the area proportion of the pixel elements 34 of the first effect region 14 decreases from 100% to 0% in a direction 32 perpendicular to the boundary line 18, and the area proportion of the pixel elements 36 of the second effect region 16 increases from 0% to 100%. Due to the small dimensions of the pixel elements 34, 36, they cannot be separately identified upon observation. Rather, the optical effect of the first effect region 14 merges smoothly into the optical effect of the second effect region 16 for the observer along the direction 32. The width B of the transition region 20 can, for example, be a few tenths of a millimeter or even a few millimeters.
[0037] To decrease or increase the area proportion of the pixel elements in the transition region as described, a dithering method originally derived from image processing is used, which controls the allocation of each pixel position in the area of the security element 12 with one of the pixel elements 34, 36 of the first or second effect region, respectively. The procedure is explained in detail below using the Floyd-Steinberg algorithm as an example; however, it is understood that other dithering algorithms can also be used accordingly.
[0038] Specifically, for example, the size of the finished security element should be 10 mm x 10 mm and the size of the pixel elements 34, 36 should each be 10 gm x 10 |µm, so that the security element consists of 1000 x 1000 pixel elements. A horizontal boundary line at y = 5 mm should separate a first effect area 14, which extends from y = 0 to the boundary line, from a second effect area 16, which extends from the boundary line to y = 10 mm. To conceal register fluctuations, a transition area with a width of B = 2 mm should be created around the boundary line, in which a smooth transition between the optical effects of the effect areas 14, 16 is recognizable.
[0039] The security element 12 then contains 1000 pixel elements each in the x- and y-direction, whereby the transition area in the y-direction, expressed in pixel elements, should extend from ymin = 400 to ymax = 600. For the sake of simplicity, a linear transition is created here. Specifically, a default field V(x,y) is initialized in pseudocode as follows: for y = 1 to 1000 for x = 1 to 1000 if y < 400 then V(x,y) = 0; else if y > 600 then V(x,y) = 1; else V (x, y) = (y-400) / 200;
[0040] The preset field is thus initialized for all 1000 x 1000 pixel elements so that it is 0 in the first effect area when y < 400, 1 in the second effect area when y > 600, and increases linearly from 0 to 1 in a transition area that has a width of 200 pixels (equivalent to 2 mm) in the y direction. For example, V(x, 450) = (450-400) / 200 = 0.25, V(x, 500) = (500-400) / 200 = 0.5, and V(x, 550) = (550-400) / 200 = 0.75, each for all values x = 1...1000.
[0041] To obtain only the discrete values 0 and 1 in the transition range between 400 and 600, a dithering method, in this case the Floyd-Steinberg algorithm, is applied to the specified field V(x,y). In the pseudocode: for y = 1 to 1000 for x = 1 to 1000 initialV alue = V (x,y ) ; newValue = findClosestValue (initialValue);
[0042] V(x,y) = newValue; quantizationError = initialValue - newValue;
[0043] V(x+l,y) = V(x+l,y) + quantizationError x 7 / 16;
[0044] V(x-1, y+1) = V(xl,y+l) + quantizationError * 3 / 16; V(x, y+1) = V(x, y+1) + quantizationError * 5 / 16;
[0045] V(x+1, y+1) = V(x+l,y+l) + quantizationError * 1 / 16; where findClosestV alue(val) = 1 if val > 0.5
[0046] = 0, otherwise.
[0047] As can be seen from the pseudocode, in the Floyd-Steinberg algorithm all 1000 x 1000 pixels in the security element are traversed and by applying the function findClosestV alue() each pixel is set to either the value 0 or the value 1 according to the value of initialValue.
[0048] The quantization error generated by this discretization is proportionally distributed among four neighboring, as yet unprocessed pixels. The mean value of the pixels thus remains essentially unchanged. After running through the Floyd-Steinberg algorithm, the preset field V(x,y) contains only the values 0 and 1. In the transition region, the areal density of the pixels decreases linearly from 100% to 0% with V(x,y) = 0, while the areal density of the pixels increases linearly from 0% to 100% with V(x,y) = 1.
[0049] Then, in a further step, all 1000 x 1000 pixel positions of the security element 12 are scanned, and at a pixel position (x,y), a pixel element 34 with the first optical effect is generated when V(x,y) = 0, and a pixel element 36 with the second optical effect is generated when V(x,y) = 1. The dither algorithm ensures that, after application of the dither algorithm, V(x,y) is either 0 or 1 for each pair of values (x,y). In the first effect region 14, V(x,y) is always 0, in the second effect region 16, V(x,y) is always 1, and in the transition region, the density of the pixel elements with V(x,y) = 0 decreases from 100% to 0%, while the density of the pixel elements with V(x,y) = 1 increases accordingly from 0% to 100%.
[0050] Accordingly, in the finished security element, the area proportion of the pixel elements 34 of the first effect region 14 in the transition region decreases from 100% to 0%, while the area proportion of the pixel elements 36 of the second effect region increases from 0% to 100%, as illustrated in Fig. 4.
[0051] Unlike image processing, where dithering simulates grayscale as real intermediate tones between white and black, the present designs do not have intermediate levels between the first and second optical effects whose appearance could be simulated. The two optical effects may even be completely dissimilar and even incompatible. Rather, the dithering process creates a smooth transition between two different, discrete optical effects.
[0052] Figure 5 shows a further embodiment in which the first effect region is formed by a metallized micromirror region 54 and the second effect region by a demetallized micromirror region 56. For illustration, Fig. 5(a) shows the design specification of an idealized, star-shaped demetallization 46 within a surrounding metallized region 44. Figure 5(b) shows, as a comparative example, a security element 52' not according to the invention without a transition region, i.e. with a sharp boundary 58' and with a certain register fluctuation of the demetallization 56' within the metallized region 54'. As illustrated in Fig. 5(b), the occurrence of the register fluctuations is clearly perceptible to an observer due to the irregular star shape and the sharply defined boundary 58'.
[0053] Figure 5(c) finally shows a security element 52 according to the invention, in which a dithered transition region 60 is formed at the boundary line between the demetallized micromirror region 56 and the metallized micromirror region 54.
[0054] The dithered transition region can, for example, have a width of 1 mm and, as described above, can be calculated from a linear transition using the Floyd-Steinberg algorithm. In this case, the pixel elements of the first and second effect regions are formed by metallized micromirror elements and demetallized micromirror elements, respectively.
[0055] In this way, a soft, flowing transition is achieved between the metallized region 54 and the demetallized region 56, which conceals the presence of register fluctuations, as illustrated in Fig. 5(c).
[0056] List of reference symbols
[0057] 10 banknotes
[0058] 12 Security element
[0059] 12' Comparison example
[0060] 14, 16 effect areas
[0061] 18 boundary line
[0062] 18' boundary line in comparison example
[0063] 20 Transition area
[0064] 22 Structural feature
[0065] 30 Detail section
[0066] 32 Direction perpendicular to the boundary line
[0067] 34, 36 pixel elements
[0068] 44 metallized areas in design specification
[0069] 46 Demetallization in design specification
[0070] 52 security element
[0071] 52' Comparison example
[0072] 54 metallized micromirror area
[0073] 54' metallized area in the comparison example
[0074] 56 demetallized micromirror area
[0075] 56' Demetallization in comparison example
[0076] 58' sharply defined boundary in the comparison example
[0077] 60 transition area
Claims
Patent claims 1. Optical security element for securing valuables, with at least two effect regions for generating different optical effects, wherein the effect regions border one another along a boundary line, characterized in that the effect regions each consist of a multiplicity of pixel elements and that along the boundary line between a first effect region and a second effect region a dithered transition region is formed, in which the area proportion of the pixel elements of the first effect region decreases from 100% to 0% and the area proportion of the pixel elements of the second effect region increases from 0% to 100%, so that in the transition region when viewed the optical effect of the first effect region merges smoothly into the optical effect of the second effect region.
2. Optical security element according to claim 1, characterized in that at least one of the two effect regions is formed by a micromirror region with directionally reflecting micromirrors.
3. Optical security element according to claim 2, characterized in that the at least two effect regions are formed by micromirror regions with directionally reflecting micromirrors and different micromirror effects.
4. Optical security element according to claim 3, characterized in that one of the micromirror regions is metallized and another of the micromirror regions is not metallized, in particular demetallized.
5. Optical security element according to claim 2, characterized in that one of the effect regions is formed by a micromirror region with directionally reflecting micromirrors and another of the effect regions is formed by a diffractive relief structure, in particular a hologram, a holographic grating image or a hologram-like diffraction structure.
6. Optical security element according to at least one of claims 2 to 5, characterized in that the micromirror region(s) each contain non-diffractive mirrors and preferably plane mirrors, concave mirrors and / or Fresnel-type mirrors.
7. Optical security element according to at least one of claims 1 to 6, characterized in that the effect regions each consist of a plurality of pixel elements of the same shape, in particular of square or rectangular pixel elements.
8. Optical security element according to at least one of claims 1 to 7, characterized in that the pixel elements fill the effect regions and the transition region each without gaps.
9. Optical security element according to at least one of claims 1 to 8, characterized in that the pixel elements have a maximum dimension which lies between 1 gm and 100 gm.
10. Optical security element according to one of claims 2 to 9, characterized in that each pixel element of the at least one by a micromirror area with directionally reflecting micromirrors, the effect area consists of a single micromirror or a group of several micromirrors.
11. Optical security element according to at least one of claims 1 to 10, characterized in that one of the effect regions forms an outer effect region which surrounds another of the effect regions which forms an inner effect region, and the boundary line is formed by the outline of the inner effect region.
12. Optical security element according to at least one of claims 1 to 11, characterized in that the width of the transition region is between 50 μm and 50 mm, preferably between 50 μm and 10 mm, particularly preferably above the resolution limit of the human eye and in particular between 0.5 mm and 5 mm.
13. A data carrier with an optical security element according to one of claims 1 to 12.
14. A method for producing an optical security element according to one of claims 1 to 12, in which at least two effect regions for producing different optical effects are produced on a carrier, which effect regions adjoin one another along a boundary line, and the effect regions are each formed from a multiplicity of pixel elements and along the boundary line between a first effect region and a second effect region a dithered transition region is formed, in which the area proportion of the pixel elements of the first effect region decreases from 100% to 0% and the area proportion of the pixel elements of the second effect area increases from 0% to 100%, so that in the transition area the optical effect of the first effect area flows smoothly into the optical effect of the second effect area when viewed 15. The method according to claim 14, characterized in that at least one of the two effect regions is formed by a micro-mirror region with directionally reflecting micro-mirrors.
16. The method according to claim 14 or 15, characterized in that the dithered transition region is calculated using a dither algorithm, in particular a threshold algorithm, a random dither algorithm, a pattern dither algorithm, ordered dithering or with an error diffusion algorithm.
17. Method according to at least one of claims 14 to 16, characterized in that to generate the dithered transition region, a continuous progression of the size of the transition region is generated, which begins and ends with a discrete value that is assigned to one of the different effect regions, the continuous progression is reduced to a desired number of discrete values using a dither algorithm, each discrete value being assigned to one of the different effect regions, and each pixel position in the transition region is assigned a pixel element of the assigned effect region in accordance with the discrete value determined for this pixel position in the dither algorithm.