Manufacturing synthetic images with continuous animation

Abstract

A method for manufacturing a synthetic image device comprises providing (S10) an array of focusing elements. An image layer is arranged (S20) near the focal length of the focusing elements in the array of focusing elements, whereby a synthetic image constituted by magnified portions of the image layer becomes perceptible to a viewer. The image layer comprises an array of image cells, each image cell being associated with a respective focusing element, and wherein the array of image cells has the same symmetry and element distance as the array of focusing elements. The arranging comprises creating (S22) continuous image objects within the image cells such that the synthetic image to be viewed exhibits a smooth continuous non-disparity change when changing viewing direction, all synthetic images having a contribution from one of the continuous image objects. The creating is performed (S30) from a digital image cell array of a digital image layer model.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to optical devices and manufacturing processes thereof, and in particular to the manufacturing of synthetic image devices. BACKGROUND

[0002] Synthetic image devices are nowadays often used to create impressive visual effects for many different purposes. Examples of uses are e.g. as security documents, security markings, tamper indications or just as an aesthetic image. Typically, the synthetic image device is intended to be provided as a label or as an integrated part in another device. Many different optical effects have been found and used, and different optical effects are often combined together to give a visual appearance that is specific to the requirements.

[0003] A typical synthetic image device presents an array of small focusing elements and image objects created in different planes of a thin foil. The focusing elements can be lenses, apertures or reflectors of different kinds. The image layer is provided with image objects. The image layer is provided relative to the array of focusing elements such that when the device is viewed from different angles, different parts of the image objects are magnified by the focusing elements and together form an integral image. Depending on the design of the image objects, the synthetic image can change in different ways when the viewing conditions, e.g. the viewing angle, change. A typical implementation of a synthetic image device is a thin polymer foil.

[0004] The actual perception of the synthetic image is done by the eyes and the brain of the user. The ability of the human brain to create a comprehensible whole out of fragmented parts of an image can be used to create a "surprising effect". This impressive effect is often used for security and / or identity verification purposes.

[0005] A simple type of "surprising effect" that is often used is to provide a perception of depth. Since the synthetic image device is typically a thin and flat device, the synthetic image appears to be positioned above or below the surface of the synthetic image device, thereby causing a "strange" experience. The synthetic image appears to float above the surface, or to exist below the surface. Such an effect is supported by providing a synthetic image that changes according to the parallax properties of the image existing above or below the surface. The effect becomes particularly striking if the image is a real 3D image, i.e. when the shown object itself has an extension in the depth direction.

[0006] Another surprising effect that is often used is that from one synthetic image to another synthetic image when the synthetic image device is tilted, i.e. by changing the viewing direction. This sudden change of synthetic image does not follow what is experienced when looking at a real object, and thus presents a surprising effect. This is e.g. demonstrated in the published international patent application WO 94 / 27254 Al, wherein, Figure 2 A and Figure 2B shows different images provided in different directions.

[0007] Even more striking effects can be gradual changes of the synthetic image. This can typically be achieved by providing a series of "sudden" changes, but with relatively small differences between each different synthetic image. This results in a stepwise animation when using the synthetic image. Different approaches have been proposed.

[0008] In published US patent US 8,739,711 B2, a micro-optic security device is presented that employs a planar arrangement of stitched icons and projects a synthetic magnified image. The synthetic magnified image constitutes an image that optionally changes to a different image as the security device is tilted, thereby giving different viewing angles. The image layer comprises slices from one or more icon designs, wherein each slice is spaced apart, abutting or slightly overlapping from an adjacent slice.

[0009] Hence, each slice represents a different image. By providing icon designs of continuously changing images, upon tilting, a series of stepwise changing images can be provided. The "smoothness" of this stepwise change of images is mainly dependent on the number of continuously changing images, which depends on the size of the slices of the icon design used. In the associated images, more slices of less change will increase the smoothness. Ultimately, the available geometric resolution of the icon provided limits this smoothness.

[0010] Furthermore, in published international patent application WO 2018 / 101881 Al, e.g. in connection with Figs. 27A-27D, 28 and 29A-29B and pages 40-43, a synthetic image device with morphing or animation properties is disclosed. In some embodiments, the image cells of the synthetic image device are divided into channels, which comprise image objects for creating a respective synthetic image. By providing synthetic images in these channels that gradually change their appearance, a stepwise morphing or animation is obtained. Also here, the size of the channels and the difference between adjacent synthetic images determines the smoothness. Due to physical limitations, channels and geometrical structures within channels cannot be produced correctly.

[0011] Nonetheless, the impression of the animation obtained by this approach is that the image behavior is rather jerky. SUMMARY

[0012] It is therefore a general object to improve the perceived quality of synthetic image animations.

[0013] The above objects are achieved by the method and device according to the independent claims. Preferred embodiments are defined in the dependent claims.

[0014] Generally, in a first aspect, a method for manufacturing a synthetic image device comprises providing an array of focusing elements. An image layer is arranged in the vicinity of the focal length of the focusing elements in the array of focusing elements, whereby a synthetic image constituted by magnified portions of the image layer becomes perceptible to a viewer. The image layer comprises an array of image cells, wherein each image cell is associated with a respective focusing element in the array of focusing elements, and wherein the array of image cells has the same symmetry and element distance as the array of focusing elements. Image points at each position within an image cell cooperate with image points at corresponding positions within other image cells to produce a synthetic image in an associated viewing direction. The arrangement comprises creating continuous image objects within the image cells such that the synthetic image to be viewed presents a smooth continuous non-parallax change when the viewing direction is changed, all synthetic images having contributions from one of the continuous image objects in at least one of the image cells. The creation of the continuous image objects is performed from a digital image cell array of a digital image layer model, wherein each digital image cell comprises a digital representation of the shape of the digital image cell and a digital description of the digital image objects within the respective digital image cell.

[0015] One advantage with the proposed technology is that it provides synthetic image animations with improved smoothness. Further advantages will appear from the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0016] The application can best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

[0017] Figures 1A-1C is a schematic illustration of a synthetic image device utilizing different focusing elements;

[0018] Figure 2 is a schematic illustration showing views from different angles;

[0019] Figures 3A-3B illustrates the formation of synthetic images for two different viewing angles;

[0020] Figures 4A-4C illustrates the idea of forming an integrated synthetic image device;

[0021] Figure 5 illustrates another example of an integrated synthetic image device;

[0022] Figure 6 illustrates an example of how a three-dimensional image can be created;

[0023] Figures 7A-7D illustrates schematically the creation of animated synthetic images;

[0024] Figure 8Apart of an embodiment of a digital image layer model for animated composite images is shown;

[0025] Figure 8B part of an embodiment of a digital image layer model for animated composite images is shown; Figure 8A an enlarged portion of

[0026] Figure 9 is a flowchart of steps of an embodiment of a method for manufacturing a composite image device;

[0027] Figure 10 is a flowchart of part steps of an embodiment of step S22 in Figure 9

[0028] Figure 11A schematically shows how another embodiment of creating a digital image layer model for animated composite images operates;

[0029] Figure 11B part of an embodiment of a digital image layer model for animated composite images is shown; Figure 11A an enlarged portion of

[0030] Figure 11C part of an embodiment of a digital image layer model for animated composite images is shown; Figure 11A an enlarged portion of

[0031] Figure 12 schematically shows how another embodiment of creating a digital image layer model for animated composite images operates;

[0032] Figure 13 schematically shows how another embodiment of creating a digital image layer model for animated composite images operates;

[0033] Figures 14A-14D different embodiments of digital image cells are shown; and

[0034] Figures 15A-15C different embodiments of image cell parts are shown. DETAILED DESCRIPTION

[0035] In all the figures, like reference numerals are used for similar or corresponding elements.

[0036] For a better understanding of the proposed technology, it can be useful to start with a brief overview of a composite image device. This preliminary overview is provided in order to understand the basic nature of composite images. However, the simplest type of composite image mentioned here (e.g. a pure ripple image) cannot be used for the purposes of the present invention.

[0037] Figure 1A ​One example of a synthetic image device 1 is schematically illustrated. The synthetic image device 1 comprises a focusing element array 20 of focusing elements 22. In this example, the focusing elements are lenses 24. In typical cases where the synthetic image is intended to be substantially the same in different surface directions, the lenses 24 are usually spherical lenses. In applications where there is a difference between the image properties in different surface directions, biconvex lenses can be used. Depending on the application, it can also be advantageous to use other types of lenses, such as polygonal lenses, zone plate lenses, etc.

[0038] The synthetic image device 1 further comprises an image layer 10 comprising image objects 12. The image objects 12 are optically distinguishable from the parts 14 of the image layer 10 not covered by the image objects 12. The image objects 12 can for example be constituted by printed product microfeatures 11 and / or embossed microstructures. The image layer 10 is arranged in the vicinity of the focal length d of the focusing elements 22 in the focusing element array 20. This means that a parallel light beam 6 incident on a focusing element 22 will be refracted 5 and focused at one small area at the image layer 10, here denoted an image point 4. Likewise, light emanating from one image point 4 at the image layer 10 will result in a parallel light beam 6 when passing through a focusing element 22. Thus, when a viewer looks from a distance in the direction of the resulting parallel light beam 6, which is schematically illustrated by the eye of the viewer 2, the image point 4 at the image object 12 will appear to fill the entire surface of the focusing element 22. The material 9 between the image layer 10 and the focusing element array 20 is at least partly transparent and is usually constituted by a thin polymer foil.

[0039] The distance d does not have to be exactly equal to the focal distance of the focusing elements 22. Firstly, there is always a certain degree of aberration which in any case widens the area from which optical information in the parallel light beam 6 is collected. This is more pronounced at shallower angles and in order to have a more uniform general level of resolution, it can be beneficial to select a distance in the vicinity of the focal length but not exactly equal to the focal length. Furthermore, since the focusing element surface has a certain two-dimensional extension, this surface can also be used to create fine objects of the entire synthetic image. In this case, fine objects of small areas on the image layer 10 can beneficially be magnified to cover the surface of the focusing elements, which means that in this case the actually selected distance d is also selected to be in the vicinity of the focal length but not exactly equal to the focal length. Such cases are well known in the field of synthetic images.

[0040] By arranging the image objects 12 of the image layer 10 in a suitable manner, the partial images created at each individual focusing element 22 surface will be collectively perceived by the viewer 2 as a synthetic image. When the synthetic image device 1 is viewed in different directions, different images can be displayed for the viewer, which opens up the way for creating different kinds of optical effects, as will be further described below.

[0041] Figure 1B Another example of a synthetic image device 1 is schematically illustrated. In this example, the focusing elements 22 are constituted by concave mirrors 26. The image layer 10 is here located on the front surface with respect to the viewer 2, and the focusing element array 20 is located behind the image layer 10. The light rays 5 propagating from the image object to the viewer 2 pass twice through the material 9 of the synthetic image device.

[0042] Figure 1C Yet another example of a synthetic image device 1 is schematically illustrated. In this example, the focusing elements are pinholes 28, which restrict the light coming from the image layer 10 and passing to the viewer 2. In this example, the synthetic image is established by a narrow beam of light passing through the pinholes 28, and typically only provides “light” or “dark”. Since the pinholes 28 do not have any magnifying effect, most of the viewing surface does not contribute to the synthetic image.

[0043] Figure 2 The selection of different partial areas or image points 4 of the image layer 10 is schematically illustrated. The image layer 10 comprises image objects 12. When the synthetic image device 1 is viewed in a viewing direction 3 perpendicular to the main surface of the synthetic image device 1 as illustrated in the left part of the figure, the image point 4 that is magnified by the focusing element 22 is located at the center line of the focusing element 22, which is illustrated by a dashed line in the figure. If there is an image object 12 at this position, a magnified version is presented at the surface of the synthetic image device 1. However, as in the case of Figure 2 , there is no image object present, and there will be no magnified image at the surface of the synthetic image device 1.

[0044] When the synthetic image device 1 is viewed at another angle, e.g. as illustrated in the right part of the figure, the image point 4 that is focused on by the focusing element 22 is offset to the side. In the illustrated case, the image point 4 overlaps with at least a part of the image object 12, and a magnified version can be seen at the surface of the synthetic image device 1. In this way, the image presented at the surface of the synthetic image device 1 can change for different viewing angles, which can be used to implement different kinds of optical effects of the synthetic image. Thus, there is a correlation between the position of the image point 4 and the viewing direction 3 at which the image point 4 contributes to the synthetic image.

[0045] One type of synthetic image is the so-called moire image. The moire magnification effect is well known for many years and is based on the cooperation of two slightly mismatched arrays. These basic findings are disclosed, for example, in “The moire magnifier”, M C Hutley et al., Pure Appl. Opt. 3 (1994), pages 133-142. Figure 3AIn the upper part, an example is schematically illustrated in which a portion of the image layer 10 is shown. The image layer 10 comprises a repeating pattern 15 of image objects 12. In this example, the image objects 12 are chosen to be the letter “K”. The focusing elements 22 associated with the shown portion of the image layer 10 are shown by the dashed circles to indicate the relative lateral position. Both the repeating pattern 15 of image objects 12 and the array of focusing elements 20 have hexagonal symmetry. However, the distance between two adjacent image objects 12 is slightly shorter than the distance between two adjacent focusing elements 22 in the same direction.

[0046] Also marked are the image points 4, which correspond to the focusing area of each focusing element 22 when viewed in the associated viewing direction. In the shown case, the image points 4 correspond to the direction of direct viewing from the front. The portion of the image object 12 that is present within each image point 4 will thus be present in an enlarged version on the surface of the corresponding focusing element 22, which is here denoted as the projected image 25. In the case of the letter “K”, the projected image 25 is a part of the letter “K”. Figure 3A In the lower part, the corresponding array of focusing elements 20 is shown, which comprises the projected images 25 of the image objects 12 of the image points 4. The dashed lines from one of the image points 4 in the upper part to one of the focusing elements 22 in the lower part show this association. The different projected images at the focusing elements 22 together form a composite image 100. In this case, the composite image 100 is a part of a large “K”. If the structures are small enough, the human eye will typically fill in the blank areas between the focusing elements 22, and the viewer will perceive the complete “K”. The reason for the K is that there is a slight period mismatch between the repeating pattern 15 of image objects 12 and the array of focusing elements 20. In this example, the mismatch between the repeating image pattern 15 and the array of focusing elements 22 is used to call the composite image 100 a moire image 105.

[0047] But when viewed in another viewing direction, Figure 3B the same composite image device 1 as in Figure 3A is schematically illustrated. This corresponds to the composite image device 1 being tilted slightly to the left. The image points 4 that correspond to the focusing areas of the focusing elements 22 in this direction are thus slightly shifted to the left. This results in another image point 4 of the image object 12 being projected to the focusing elements 22, as seen in the lower part of Figure 3B . The result of the tilt is that the composite image 100, i.e. the large “K”, is shifted to the right.

[0048] The viewer will interpret this motion as a result of the position of the large “K” at some imaginary or apparent depth below the surface of the composite image device 1. In other words, a depth sensation is achieved. Both the magnification and the experienced depth depend on the relationship between the array of focusing elements 20 and the repeating pattern 15 of image objects 12. It has been shown in the prior art that the obtained magnification M is determined as:

[0049]

[0050] wherein

[0051] wherein P o is the period of the repeating pattern 15 of the image object 12, and P l is the period of the array of focusing elements 20. For P o < P l , the magnification is positive, for P o > P l , the magnification becomes negative, i.e. the synthetic image 100 becomes inverted compared to the image object 12.

[0052] When using spherical microlenses, the apparent image depth d i of the moire image can also be determined as:

[0053] d i = (d - R l ) / (1 - F) + R l , (2)

[0054] wherein d is the thickness of the synthetic image device, and R l is the radius of curvature of the spherical microlenses. It can be noted here that for P o < P l , the apparent depth is generally positive, while for P o > P l , the apparent depth becomes negative, i.e. the moire image 105 seems to float above the surface of the synthetic image device 1.

[0055] It should be noted that Figure 3A and Figure 3B the exhibited period difference is relatively large, which gives a relatively low magnification and a relatively small apparent depth. This is done for illustrative purposes. In a typical moire synthetic image device, the relative period difference can generally be much smaller. Period differences of less than 1% and even less than 0.1% are not uncommon.

[0056] However, moire images have certain limitations. Firstly, they can only produce repeating images. Furthermore, the size of the image object 12 is limited to the size of the focusing elements. In Figure 4A , an image object 13 to be repeated is schematically shown. If this image object is repeated with almost the same period as the focusing elements 22 of Figure 4B , the repeating pattern of the repeated image object 13 will overlap. A moire image from such a structure is almost impossible to resolve for the human brain, because the parts of the image object associated with adjacent focusing elements 22 will interfere.

[0057] Figure 4C In this, the image cells 16 of the image layer 10 are exclusively associated with each focusing element 22. The image layer 10 thus comprises an array 7 of image cells 16, wherein each image cell 16 is associated with a respective focusing element of the array of focusing elements. Within each image cell 16, only the part of the original repeating image object that belongs to one copy of the repeating image object is retained as a truncated image object 17 of that image cell 16, and the other interfering repeating image objects are removed. The different truncated image objects 17 of the different image cells 16 will now not be identically repeated on the image layer 10, but the truncated image objects 17 change continuously in shape. By using these cut-out parts or fractions as truncated image objects 17, a synthetic image will also be created. The synthetic image based on the non-identical subdivided image objects 17 within the image cells 16 associated with the focusing elements 22 is referred to in this disclosure as an integral synthetic image.

[0058] Figure 5 In this, an example of a part of the image layer 10 of an integral synthetic image device that produces an image of the number “5” is shown.

[0059] As long as the focus area of the associated focusing element, i.e. the image point, remains within the image cell 16, a synthetic image similar to a moire image is created. However, when the focus area of the associated focusing element enters an adjacent cell 16, the synthetic image will suddenly disappear and will instead appear in another location; a flip occurs in the synthetic image.

[0060] The idea of having different image objects per image cell can be further pushed. A moire synthetic image can be given an apparent depth, but in principle only to one depth. It is difficult to achieve a real three-dimensional appearance using a moire synthetic image. However, when considering an integral synthetic image, the freedom to change the image object from one image cell to another image cell can also be used, for example, to provide a more realistic three-dimensionality of the produced image.

[0061] In Figure 6 In this, the image cells 16 of the image layer 10 are shown. Four different image points 4 per image cell 16 are shown, which correspond to the focus area of the associated focusing element when viewed in four different directions. The image object of the central image point 4 in each image cell corresponds to the viewing angle achieved when viewing the synthetic image device in a perpendicular manner. Such an image object can then be designed such that it produces an integral synthetic image 110B, as Figure 6Fig. 4 shows the lower middle part of the top surface of the box as exhibited. The image objects of the uppermost image points 4 in each image cell correspond to the viewing angles achieved when the synthetic image device is tilted away from the viewer. Such image objects can then be designed so that they produce the integral synthetic image 110A, as Figure 6 Fig. 5 shows the lower left part of the top surface and the front surface of the box as exhibited. The image objects of the leftmost image points 4 in each image cell correspond to the viewing angles achieved when the synthetic image device is tilted to the left with respect to the viewer. Such image objects can then be designed so that they produce the integral synthetic image 110C, as Figure 6 Fig. 6 shows the lower right part of the top surface and the side surface of the box as exhibited. The image objects of the lower right part of the image points 4 in each image cell correspond to the viewing angles achieved when the synthetic image device is tilted to the right and to the right with respect to the viewer. Such image objects can then be designed so that they produce the integral synthetic image 110D, as Figure 6 Fig. 7 shows the bottommost part of the top surface, the side surface and the back surface of the box as exhibited. These integral synthetic images 110A-D and further integral synthetic images emanating from other image points of these cells together give a three-dimensional impression of the rotating box. This variation of the synthetic image thus follows the expected parallax rules. In this case, the image properties thus achieved are a simulation of "real" optical properties, for example a real three-dimensional image with a parallax variation.

[0062] In a similar manner, different kinds of optical phenomena can be achieved by modifying the image content in each image cell, respectively. By adjusting each part of the image cell in the corresponding viewing direction according to the requested image appearance, the integral synthetic image can be given almost any appearance. Thus, the image properties thus achieved can be designed to show optical effects that do not exist in "real" systems, i.e. with non-parallax characteristics. This is the type of synthetic image device that is the object of the present technology.

[0063] A simple effect is to switch between different synthetic images in different angular sectors. This is for example demonstrated in the published international patent application WO 94 / 27254 A1. In this case, the image layer is provided with more than one image cell associated with a single focusing element. Within each of these image cells, image objects are provided that result in a specific synthetic image. Since the area of each image cell is limited, the angular direction in which the synthetic image is visible is also limited. Another typical example of such an arrangement can be found in Fig. 47 of the US patent 7,738,175 B2. Here, a plurality of image cells are provided that are divided into sectors in the azimuthal direction. This means that different synthetic images are viewable in limited azimuthal viewing directions.

[0064] In an alternative representation, all image objects can be considered to be contained in one common image cell, but divided in different image cell portions, each composite image being for one image cell portion.

[0065] When passing through the viewing angle associated with the border between two image cell portions, a flip will occur between the two composite images seen. If the difference between the individual composite images is small between successive adjacent image cell portions, a continuous change in image appearance can be obtained. In other words, an animation can be created. Such a gradual change can be of different types, such as, but not limited to, shape, size, orientation, position, color, or a combination of several of these parameters.

[0066] This can be illustrated schematically by the following figures. In Figure 7A a similar setup as in Figure 3A is shown. However, in this case, the composite image device 1 is not a moire device, since the content of the different image cells will be different. The image layer 10 is divided into image cells 16 in the array 7 of image cells. Each image cell 16 is associated with a focusing element 22. In order to create the "K" image, only parts of the image objects within the image points 4 are needed, forming truncated image objects 17. Whatever is outside these image points 4, when viewing the device from the top, will in any way see the large composite image 100 of the "K", however, in this case, a unitary image 106 is seen, since it is based on the non-repeating truncated image objects 17.

[0067] In Figure 7B the viewing angle has changed and, as a consequence, the image points 4 are shifted within the image cells 16. In this case, the content of the truncated image objects 17 in this position is changed in order to alternatively create the letter "Y". If the intermediate image points between the image points of the composite image in these two figures are designed to form an intermediate design between the letter "K" and the letter "Y", an animation of the letter K gradually changing into the letter Y can be achieved.

[0068] In Figure 7C a further viewing angle is shown. In the image points 4 associated with this viewing angle, there are truncated image objects 17 that create a severely distorted "Y". Also here, only the image object features contained within the image points will contribute to the composite image 100 seen.

[0069] In Figure 7D a further viewing angle is shown. In the image points 4 associated with this viewing angle, there are truncated image objects 17 that create a severely distorted "Y". Also here, only the image object features contained within the image points will contribute to the composite image 100 seen. Figures 7A-7CThe case is assembled in an illustration. Within the marked image point 4, there is enough image information to provide a "K", a "Y" and a "twisted Y" in three different directions, as schematically demonstrated at the bottom of the figure. The remaining part of the image layer 10 outside the marked image point 4 can now be provided with image objects that produce other composite images. For example, if an animation is requested, the area of the image layer 10 between the marked image points 4 can be populated with image objects that produce a composite image somewhere in between the "K", the "Y" and the "twisted Y".

[0070] In this way, the entire image cell 16 can be populated with cut-off image objects 17 that will produce different composite images 100 in different directions, so that an animation effect can be given, beyond the expected three-dimensional parallax behavior.

[0071] In order for such an animation to be pleasant to watch, the change between successive composite images should be small, which means that a large number of image objects giving a composite image must be provided within the respective image cell part within the image cell. Since the total available space of the image cell is limited, more steps between successive composite images result in smaller individual image cell parts.

[0072] When manufacturing a composite image device, the image layer is usually provided by printing or embossing on a polymer film, which polymer film also comprises or is attached to the array of focusing elements. When the image layer has been formed on the polymer film, it is almost impossible to adapt any structures in this image layer. This means that, whether it is a basic image design, an advanced image effect or an appearance enhancement measure, any structure that is intended to be included in the image layer of the final product must be provided at the time of printing / embossing. This also means that the definition of the structure to be printed / embossed must also include any appearance enhancement modifications or advanced image effects of the original designed composite image or composite image animation. The definition of the image layer to be provided can be demonstrated by a digital image layer model comprising an array of digital image cells.

[0073] In Figure 8A , a digital image layer model 101 is demonstrated that shows an example of a simple animation with 4 steps. When the composite image device to be manufactured is tilted in the vertical direction, the composite image that is intended to be produced by the image objects is a circle that increases in size with a factor of 2 and decreases again to the initial value. In a preferred embodiment, the number of steps is of course larger to achieve a smoother transition, but in order to show the principle in an illustrative way, the number of steps is kept small. The digital image layer model 101 is also demonstrated at a very high magnification. The typical size of the distance between adjacent focusing elements in the final product can be in the range of 15-150 micrometer, which means that the associated size of the digital image cells 116 should be the same.

[0074] The digital image layer model 101 comprises an array 107 of digital image cells 116, only a few of which are labeled in the figure for reasons of legibility. Each digital image cell 116 is divided into 4 digital image cell portions 118. In the present embodiment, the digital image cell portions 118 have the shape of horizontal bands or stripes. The digital image layer model 101 is established using a method similar to the one described in published US patent US 8,739,711 B2. Within each digital image cell portion 118, a digital cutout image object 117 is provided. Since the intended composite image is an animation, the digital cutout image objects 117 in each digital image cell portion 118 are not registered with each other. The variation of the digital cutout image objects 117 over the area of the illustrated portion of the digital image layer model 101 is a feature connected to the integral image device.

[0075] Figure 8B A close-up of some structures of the digital image layer model 101 is shown. Here it can be seen that at the border between two consecutive digital image cell portions 118, there is sometimes a very sharp structure of the cutout digital image objects 117, i.e. there is a discontinuity between the cutout digital image objects 117 of one digital image cell portion 118 and the cutout digital image objects 117 of the other digital image cell portion 118. This discontinuity reduces the smoothness of the animation when the final composite image device is tilted in the vertical direction. Since the size is small, such sharp structures can also be difficult to reproduce in reality when the actual image layer is to be made as a "copy" of the digital image layer model 101. In published US patent US 8,739,711 B2, it is mentioned that the image objects of different stripes can be slightly overlapping or can be slightly separated. However, such an arrangement typically produces strange or jumping optical effects at the viewing angles associated with the borders.

[0076] It was found that if the image objects are given a smoother shape as a whole, a more attractive appearance will be achieved. The idea of the present invention is not to divide the image structures in the image cells into narrow strips, but rather to point in the opposite direction, i.e. with the final goal of creating continuous image objects that can cover a large part of the image cells.

[0077] In other words, Figure 9Embodiments of a method for manufacturing a synthetic image device are shown in Fig. 10. In step S10, an array of focusing elements is provided. In step S20, an image layer is arranged in the vicinity of the focal length of the focusing elements in the array of focusing elements. Thereby, a synthetic image composed of magnified portions of the image layer becomes perceptible to a viewer. The image layer comprises an array of image cells, wherein each image cell is associated with a respective focusing element in the array of focusing elements. The array of focusing elements has the same symmetry and element distance as the array of focusing elements. Thereby, image points at each position within an image cell cooperate with image points at corresponding positions within other image cells to produce a synthetic image in an associated viewing direction. The arranging step S20 comprises a step S22 of creating continuous image objects within the image cells such that the synthetic image to be viewed exhibits a smooth continuous non-parallax change when changing the viewing direction, all synthetic images having a contribution from one of the continuous image objects in at least one of the image cells.

[0078] The above method thus produces a synthetic image device. The synthetic image device comprises an array of focusing elements and an image layer. The image layer is arranged in the vicinity of the focal length of the focusing elements in the array of focusing elements, thereby a synthetic image composed of magnified portions of the image layer becomes perceptible to a viewer. The image layer comprises an array of image cells, wherein each image cell is associated with a respective focusing element in the array of focusing elements, and wherein the array of focusing elements has the same symmetry and element distance as the array of focusing elements. Thereby, image points at each position within an image cell cooperate with image points at corresponding positions within other image cells to produce an image in an associated viewing direction. The image cells comprise continuous image objects, wherein these continuous image objects are arranged such that the synthetic image to be viewed exhibits a smooth continuous non-parallax change when changing the viewing direction, all synthetic images having a contribution from one of the continuous image objects in at least one of the image cells.

[0079] Since it is difficult to modify the image layer once it has been printed or embossed, it is preferred that any definition of the requested animated composite image and possible modifications thereof are performed prior to forming the actual image objects, as mentioned before and as will be further discussed below. In other words, in a preferred embodiment, in step S23, the requested animated composite image to be produced by the composite image device is designed and defined. The definition of the requested animated composite image is typically performed by using mathematical geometric definitions, and typically has a view angle dependency. In step S24, an array of digital image cells of a digital image layer model is derived, wherein each of the digital image cells comprises a digital representation of a digital image cell shape and a digital description of a digital image object within the respective digital image cell. The digital description of the digital image object is derived from the definition of the requested animated composite image, which is transformed by the operation of the array of focusing elements. The transformation comprises mapping the angular dependency of the requested appearance of the surface of the focusing elements to a positional dependency of the requested appearance of the surface of the focusing elements at the corresponding digital image cells.

[0080] In step S30, continuous image objects are created from the array of digital image cells of the digital image layer model. This step is typically performed according to processes known in the art. Typically, such a process can comprise manufacturing an embossing tool having a structure defined according to the array of digital image cells of the digital image layer model, and embossing the image layer of the composite image device by the embossing tool. Alternatively, such a process can comprise manufacturing a printing tool having a structure defined according to the array of digital image cells of the digital image layer model, and printing the image layer of the composite image device by the printing tool. A further alternative can comprise controlling a print head in a laser printer based on the content of the array of digital image cells. All these processes of transferring an array of digital image cells defined by mathematical or other digital means into a physical structure at the image layer at the composite image device are known to any person skilled in the art and are not discussed further.

[0081] In other words, in one embodiment, creating a continuous image object in each image cell comprises embossing a continuous image object in a polymer layer on a polymer substrate presenting the focusing elements, or printing a continuous image object on the polymer substrate.

[0082] In one embodiment, creating a continuous image object in each image cell comprises forming a tool for embossing or printing, the tool having a recess formed according to the continuous image object to be created.

[0083] In one embodiment, printing comprises controlling a print head to print the continuous image object to be created.

[0084] Thus, the basic procedure starts with the definition of the requested composite image animation. This requested composite image animation is thus a design related input to the manufacturing process. The design can be provided by any external or internal process and is thus the goal of the composite image produced by the composite image device. Once the design is set, a number of process steps are performed which are not related to the design of the image but to the problems required to provide a composite image as clear and easy to view as possible. The first of these steps is the mathematical or digital transformation of the composite image animation into a digital definition of the image structure, resulting in the requested composite image animation as an array of digital image cells of a digital image layer model. When the array of digital image cells of the digital image layer model is defined, the physical image layer is created from the digital image layer model. Thus, the overall transformation and possible adaptation of the image structure is preferably performed in the digital scheme before any physical counterpart structure is created.

[0085] A method comprises defining the requested composite image animation digitally, wherein the shape is represented as a function of the viewing angle in a digital image model. The digital image model can thus continuously change its appearance for different viewing directions. In one embodiment, the digital image layer model can then be a mathematical focusing element array transformation of the digital image model. Thereby, each position within the digital image object is a part transformation of the respective viewing angle of the smooth continuous non-parallax variation of the composite image.

[0086] In other words, the transformation transforms the viewing angle dependency of the digital image model into a position dependency within each digital image cell of the digital image layer model, thereby creating the requested continuous image object.

[0087] Such a mathematical transformation can be performed for simple designs of the requested composite image animation. However, for more complex images and animation sequences, the pure mathematical approach can be extremely complex and not practically implementable. In this case, a slightly different approach can be used to derive the definition of the array of digital image cells of the digital image layer model. It was surprisingly found that in many cases the smoothness of the image object is more important for the pleasant perception of the composite image animation than the exactness of the requested shape of the image object. If small adaptations to the actual shape of the image object are performed which contribute to the formation of a smooth continuous image object, the defects in the perception of the composite image caused by these adaptations are in most cases smaller than the defects in the perception of the composite image caused by sharp structures at the borders of the cell parts. In other words, in many cases, a more pleasant appearance of the composite image animation can be obtained if the smoothness of the image object is performed, even if it interferes with the original intended shape of the image object.

[0088] In practice, any such adaptation has to be performed in the digital image layer model before the actual creation of the real image layer, i.e. before step S30.

[0089] Figure 10 One preferred embodiment of the step S22 of creating a continuous image object is illustrated. The step S24 of deriving an array of digital image cells of a digital image layer model comprises a step S25 in which each digital image cell is divided into a plurality of digital image cell portions. In a step S26, digital image objects are created for these digital cell portions, which together with the digital image objects of the corresponding digital cell portions of other digital image cells, when they are transformed to be viewed via the associated focusing elements, produce a composite image corresponding to the digital image model, thereby continuously changing its appearance for different viewing directions. This particular sub-step can have some similarities with some prior art methods.

[0090] However, contrary to any prior art method, the present method is directed to a continuous image object. To this end, in a step S27, the digital image objects of each digital cell portion within each digital image cell are fused into a digital continuous image object of the digital image cell, whereby the digital continuous image object extends over the plurality of digital cell portions. The creation of the continuous image object in the image layer in step S30 is then performed from the digital continuous image object of the digital image cell.

[0091] This digital continuous image object is a smooth object, without sharp structures resulting from the division by any digital cell portion. Except when the design of the composite image that the viewer is to see includes sharp edges, the digital continuous image object has a border in the mathematical description that has a tangent direction that is obtainable at all points. In other words, there is no sharp edge at the image object as a result of any cell portion division. The digital continuous image object is thus continuous in the sense that the associated composite image animation occurs continuously, without any abrupt transition between the various steps.

[0092] In one embodiment, each digital cell portion is associated with a respective associated viewing direction.

[0093] If returning to the digital image layer model, Figure 11A and Figure 11B One example of such a method is illustrated. In Figure 11A the solid line associated with the image object represents the digital truncated image object 117, i.e. the digital image object precursor, of each digital cell portion 118. Note the sharp edges present at many of the borders between digital cell portions 118. The digital continuous image object 119 is marked with shading and extends over several digital image cell portions 118. The digital continuous image object 119 has a more rounded shape than the shape provided by the digital truncated image objects 117. Once the digital continuous image object 119 is provided, the digital image cell portion borders are irrelevant and can be omitted.

[0094] In one embodiment, interpolation of the precursor (i.e. the digital cutout image object 117 in the interpolation zone 121 near the border between adjacent digital image cell portions 118) is performed. The method used for interpolation can for example be a spline approximation of the vertices present in the interpolation zone 121. Of course other mathematical methods for approximation or interpolation can be used as well. Figure 11B A close-up view of Figure 11A is shown in Fig. 4. This is the digital model to be transferred into the physical image layer. In other words, the resulting digitally continuous image object 119 of the digital image cell 116 of the digital image layer model 101 is used to control the creation of the actual physical image layer. Figure 11C An enlarged portion of such an image layer 10 is shown in Fig. 5. One of the image cells 16 marked in the figure comprises a continuous image object 19. Thus, in the physical image layer 10, there are no image cell portions and no cutout image objects.

[0095] For example, returning to Figure 11B , the width of the interpolation zone 121 is one parameter that can be used to optimize the shape of the digital continuous image object 119. A very narrow interpolation zone 121 will typically result in a digital continuous image object 119 with a relatively abrupt curvature. A very wide interpolation zone 121 can alternatively lead to a large change in the main shape of the digital continuous image object 119. Thus, the interpolation zone 121 width is preferably chosen in accordance with the actual design of the requested composite image animation (i.e. how fast and how large the differences in shape are). A suitable interpolation zone 121 width can be chosen in which there is a reasonable compromise between abruptness in the digital continuous image object 119 and the shape change. Since these changes are performed digitally, it is even possible to test different interpolation zone 121 widths in order to be able to conclude which one gives the most promising results. In a typical case, the interpolation zone 121 width of the edge-to-edge placed cutout image objects is chosen in the range of 5% - 60% of the width of the digital cell portions in the direction under consideration.

[0096] In other words, in one embodiment, the method for manufacturing a composite image device comprises: if two digital cell portions have a common edge and a border of the respective digital image objects at the common edge, removing the border portions of the respective digital image objects at the common edge facing each other, thereby merging the digital image objects. The border of the merged digital image object is smoothed at least near the common edge, thereby giving a digital continuous image object extending over the plurality of digital cell portions.

[0097] Another close-up Figure 12Another example of a method of merging digital cutout image objects 117 of different digital image cell portions 118 is shown. Here, digital cutout image objects 117 are provided in overlapping digital image cell portions 118. The solid lines 117 represent digital cutout image objects 117 formed in different digital image cell portions 118. Digital continuous image objects 119 are marked with hatching and extend over several digital image cell portions 118. The digital continuous image objects 119 have circular shapes which are compromises between overlapping portions of digital cutout image objects 117. Once digital continuous image objects 119 are provided, the boundaries of digital image cell portions 118 are irrelevant and can be omitted.

[0098] In one embodiment, an interpolation of digital cutout image objects in an interpolation zone 121 at least surrounding the overlap between adjacent digital image cell portions 118 is performed. The method for interpolation can for example be a spline approximation from the vertices of the two digital cutout image objects 117 present in the interpolation zone 121. Other mathematical methods for approximation or interpolation can of course also be used.

[0099] In other words, in one embodiment, a method for manufacturing a synthetic image device comprises, if two digital cell portions overlap and have boundaries of respective digital image objects at the edges of the overlap, removing the boundary portions of the respective digital image objects of the overlap, thereby merging the digital image objects. The boundaries of the merged digital image objects are smoothed at least in an interpolation zone in the vicinity of the overlap, thereby giving a digital continuous image object extending over the plurality of digital cell portions.

[0100] Yet another close-up Figure 13 Yet another example of a method of merging digital cutout image objects 117 of different digital image cell portions 118 is shown. Here, digital cutout image objects 117 are provided in digital image cell portions 118 which are separated from each other by a separation distance 122. Within this distance, no information about any requested shape is available. The solid lines represent digital cutout image objects 117 formed in different digital image cell portions 18. The separate digital cutout image objects 117 are connected to each other, thereby forming digital continuous image objects 119. The digital continuous image objects 119 are marked with hatching and extend over several digital image cell portions 118. The digital continuous image objects 119 have circular shapes which adapt the edges of the digital cutout image objects 117 to each other. Once digital continuous image objects 119 are provided, the boundaries of digital image cell portions are irrelevant and can be omitted.

[0101] In one embodiment, an interpolation of the digital cutout image objects 117 in an interpolation zone 121 that at least encompasses a part of the separate adjacent digital image cell parts 118 is performed. The method used for the interpolation can for example be a spline approximation from the vertices of the two digital cutout image objects 117 on each side of the separation distance 122. Preferably, additional information, for example about the slope of the digital image objects at these locations, is also used for the interpolation, or, as shown, the interpolation zone 121 can also include a part of the digital image cell part 118. Of course other mathematical methods for the approximation or interpolation can also be used.

[0102] In other words, in one embodiment, a method for manufacturing a synthetic image device comprises, if two digital cell parts have a separating edge facing each other and a respective digital image object border at the separating edge facing each other, removing the border part of the respective digital image object at the separating edge facing each other and connecting the respective digital image objects at the separating edge facing each other, thereby merging the digital image objects. The border of the merged digital image object is smoothed at least in an interpolation zone near the separating edge facing each other, thereby giving a digital continuous image object extending over the plurality of digital cell parts.

[0103] It can be noted that a synthetic image device with image layers manufactured according to any of Figures 8A-8B , Figures 11A-11C , Figure 12 and Figure 13 will give essentially the same synthetic image animation. In other words, all these examples belong to the same design of a synthetic image animation. However, the differences in details in the image objects will give the animation different degrees of smoothness and pleasure when watching the animation. Thereby, the adaptation of the digital image objects is not related to the design of the requested synthetic image animation, but is a pure technical measure for obtaining a better quality experience animation.

[0104] As indicated above, one small drawback of using the general one-piece image method is that there can be a discontinuity when the viewing angle becomes large enough to pass the border of an image cell. This is also relevant for animations. When the viewing angle reaches the image cell border and moves to the adjacent image cell, it can cause a discontinuity in the animation. However, if the animation belongs to a type that can be repeated, this situation can be mitigated. In this case, the start image and the end image are the same. By choosing the associated viewing angles such that the start angle is associated with a position in the image cell that is absolutely near the image cell border and the end angle is associated with a position in the image cell that is absolutely near the opposite image cell border, a continuous animation over the image cell border can be obtained.

[0105] If the animation is short, there can of course be several such animation loops within a single image cell.

[0106] In other words, in one embodiment, creating a continuous image object in each image cell comprises creating a continuous image object that repeats in at least one direction. The distance between adjacent focusing elements in the first distance is equal to an integer multiple of the repetition distance of the continuous image object in the first direction.

[0107] In the above example, the digital image cells are shown as rectangles. However, other geometrical shapes can also be used. Figure 14A A case is shown in which the image cells 16 cover the entire surface of the image layer. The focusing elements 22 are here assumed to have a circular shape and are also closely packed. The array of image cells 16 thereby has the same symmetry and element distance as the array of focusing elements 22, even though the shapes of the elements in the different arrays are different.

[0108] Figure 14B Another example is shown in which the image cells 16 have a rectangular shape. Nonetheless, the array itself has a common symmetry and element distance. This means that corresponding points within different image cells have the same relationship to the respective focusing elements 22.

[0109] Figure 14C is still another example. Here, the image cells 16 have a hexagonal shape and are not perfectly centered compared to the focusing elements 22. However, the property that corresponding points within different image cells have the same relationship to the respective focusing elements 22 is still valid.

[0110] Figure 14D An example is shown in which the image cells 16 are smaller than the maximum size. This means that, at certain viewing angles, the composite image animation provided by the image objects within the image cells 16 disappears. The area not covered by the image cells 16 can also be used to provide other composite images or composite image animations. In other words, there can be additional arrays of image cells for creating other composite images that are provided side by side on the image layer, as well as the image cells 16 that give the composite image animation discussed above.

[0111] In the above example, the digital image cell portions are stripes having a rectangular shape. However, this is not a necessity and digital image cell portions of various shapes and sizes can be utilized. Figure 15A Seven digital image cells 116 with hexagonal symmetry are shown, which are divided into digital image cell portions 118 as hexagonally closed stripes. Figure 15BA digital image unit 116 is shown, which is divided into digital image unit portions 118 of different sizes and shapes. It is also possible that one digital image unit 116 is divided into digital image unit portions 118 in a different way than another digital image unit 116 in the same digital image layer model. This opens up for adaptations, e.g. to treat different digital image units 116 differently depending on the complexity of the structures in a particular unit. The digital image unit portions 118 do not necessarily have straight edges, as e.g. shown in Figure 15C

[0112] The above-described embodiments should be understood as a few illustrative examples of the present application. Those of skill in the art will understand, upon consideration of the disclosure, that various modifications, combinations, and enhancements can be made to the described embodiments. For example, different parts of different embodiments can be combined to achieve yet other embodiments. Also, other modifications, combinations, and enhancements can be made in light of the above teachings. The scope of the application will thus be determined without departure from the spirit of the application, as recorded in the appended claims.​

Claims

1. A method for manufacturing a synthetic image device, the method comprising the following steps: - Provides (S10) a focused element array (20); - An image layer (10) is arranged (S20) near the focal length (d) of the focusing element (22) in the focusing element array (20) so that the composite image composed of the magnified portion of the image layer becomes perceptible to the viewer (2); The image layer (10) includes an array (7) of image units (16), wherein each image unit (16) is associated with a corresponding focusing element (22) in the focusing element array (20), and wherein the array (7) of image units (16) has the same symmetry and element spacing as the focusing element array (20). The arrangement (S20) step includes creating (S22) continuous image objects (19) within the image unit (16) such that the synthetic image to be viewed presents a smooth and continuous non-parallax change when the viewing direction (3) is changed, and all synthetic images have a contribution from one of the continuous image objects (19) from at least one of the image units (16); The creation (S22) of the continuous image object (19) is performed (S30) based on an array of digital image units (116) of the digital image layer model (101), wherein each digital image unit (116) includes a digital representation of the shape of the digital image unit (116) and a digital description of the digital image object (117) within the corresponding digital image unit (116); The creation (S22) of the continuous image object (19) includes the following steps: - Define the synthesized image animation requested in (S23); - Derive (S24) the array of digital image units (116) of the digital image layer model (101); The derivation (S24) of the creation (S22) of the continuous image object (19) further includes the following steps: - Divide each digital image unit (116) into multiple digital image unit parts (118) (S25); - Create (S22) digital image objects (117) for these digital unit parts (118), which generate a composite image corresponding to the digital image model when they are converted together with the digital image objects (117) of the corresponding digital unit parts of other digital image units (116) in the manner of viewing via the associated focusing element (22), thereby continuously changing their appearance for different viewing directions (3). - The digital image objects (117) of each digital unit portion (118) within each digital image unit (116) are fused (S26) into a digital continuous image object (119) of the digital image unit (116), whereby the digital continuous image object extends over the plurality of digital unit portions (118); Thus, the creation (S22) of the continuous image object (19) in the image layer (10) is performed according to the digital continuous image object (119) of the digital image unit (116).

2. The method according to claim 1, characterized in that, Each digital unit section (118) is associated with a corresponding viewing direction (3).

3. The method according to claim 1 or 2, characterized in that, The fusion (S26) step includes the following steps: - If two digital unit portions (118) have a common edge and a boundary of a corresponding digital image object (117) at the common edge, then the facing boundary portions of the corresponding digital image objects (117) at the common edge are removed, thereby merging the digital image objects (117); and - Smooth the boundaries of the merged digital image objects (117) at least in the interpolation zone near the common edge, thereby giving the digital continuous image objects (119) extending over multiple digital unit portions (118).

4. The method according to claim 1 or 2, characterized in that, The fusion (S26) step includes the following steps: - If two digital unit portions (118) overlap and have the boundary of a corresponding digital image object (117) at the edge of the overlap, then remove the boundary portion of the overlapping corresponding digital image object, thereby merging the digital image objects (117); and - Smooth the boundaries of the merged digital image objects (117) at least in the interpolation region near the overlap, thereby giving the digital continuous image objects (119) extending over multiple digital unit portions (118).

5. The method according to claim 1 or 2, characterized in that, The fusion (S26) step includes the following steps: - If two digital unit portions (118) have mutually facing separation edges and the boundaries of corresponding digital image objects (117) at the mutually facing separation edges, then the boundary portions of the corresponding digital image objects (117) at the mutually facing separation edges are removed and the corresponding digital image objects (117) at the mutually facing separation edges are joined, thereby merging the digital image objects (117); and - Smooth the boundaries of the merged digital image objects (117) at least in the interpolation zone near the separating edges that face each other, thereby giving the digital continuous image objects (119) that extend over multiple digital unit portions (118).

6. The method according to claim 1 or 2, characterized in that, The creation (S22) of a continuous image object (19) in each of the image units (16) includes creating a continuous image object (19) that repeats in at least a first direction, wherein the distance between adjacent focusing elements (22) in the first direction is an integer multiple of the repeating distance of the continuous image object (19) in the first direction.

7. The method according to claim 1 or 2, characterized in that, The creation (S22) of the continuous image object (19) in each of the image units (16) includes embossing the continuous image object (19) in the polymer layer on the polymer substrate on which the focusing element (22) is presented, or printing the continuous image object (19) on the polymer substrate.

8. The method according to claim 7, characterized in that, The creation (S22) of the continuous image object (19) in each of the image units (16) includes forming a tool for the embossing or printing, the tool having a recess formed according to the continuous image object (19) to be created.

9. The method according to claim 7, characterized in that, The printing includes controlling the print head to print the continuous image object to be created (19).

Images