WO2018101881A1

WO2018101881A1 - Synthetic-image device with interlock features

Info

Publication number: WO2018101881A1
Application number: PCT/SE2017/051200
Authority: WO
Inventors: Daniel Parrat; Axel Lundvall; Nandi NOBELL
Original assignee: Rolling Optics Ab
Priority date: 2016-12-02
Filing date: 2017-12-01
Publication date: 2018-06-07
Also published as: GB201907487D0; DE112017005555T5; GB2571222B; GB2571222A; CH714544B1

Abstract

A synthetic-image device (1) comprises an image layer and a focusing element array. Composite image objects of the image layer are a merging of at least a first and a second set of image objects. The first set of image objects are arranged for giving rise to a guiding synthetic image (41). The guiding synthetic image, when being moved to be viewed in a direction, presents a first part image and a second part image moving towards a predetermined relative geometrical relation with respect to each other. The second set of image objects is arranged for giving rise to an effect synthetic image (42) within a limited effect field of view. The limited effect field-of-view is selected as including viewing directions only in angular vicinity of any of the direction, or excluding viewing directions only in angular vicinity of any of the direction.

Description

SYNTHETIC-IMAGE DEVICE WITH INTERLOCK FEATURES

TECHNICAL FIELD

The present invention relates in general to optical devices and manufacturing processes therefore, and in particular to synthetic-image devices and manufacturing methods therefore.

BACKGROUND

Synthetic-image devices are today often used for creating eye-catching visual effects for many different purposes. Examples of use are e.g. as security markings, tamper indications or simply as aesthetic images. Usually, 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 discovered and used and often different optical effects are combined to give a certain requested visual appearance.

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 element may be different kinds of lenses, apertures or reflectors. An 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 enlarged 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. viewing angles, are changed. A typical realization of the synthetic-image device is a thin polymer foil.

The actual perception of the synthetic image is performed by the user's eyes and brain. The ability of the human brain to create an understandable totality from fragmented part images can be used for creating "surprising effect". Such eye-catching effects are popular to be utilized for security and/ or authentication purposes.

If the focusing elements and the image objects are perfectly aligned, the intended "centre" synthetic image is seen by viewing the synthetic-image device in a direction perpendicular to the plane of the focusing elements. However, the alignment of focusing elements and the image objects is not very easy to accomplish, at least in mass-production lines, since present alignment techniques are expensive to implement.

If the focusing elements and the image objects instead are offset, the intended "centre" synthetic image may instead be seen at another direction, non- perpendicular to the plane of the focusing elements. A "surprising effect" is often provided in the intended "centre" synthetic image since this direction is believed to be easy to find. However, if a misalignment is present, the "surprising effect" may be difficult to find, since the viewer does not know in what viewing angle relative to the surface of the synthetic-image device to search for the "surprising effect". Authentication or security checks may therefore be difficult to perform in a safe manner.

Examples of synthetic image devices presenting different kinds of co-existing part synthetic images are disclosed in the published international patent application WO 2015/034551 A.

SUMMARY

A general object with the herein presented technology is to improve the ability to find particular viewing angles of synthetic images.

The above object is achieved by methods and devices according to the independent claims. Preferred embodiments are defined in dependent claims. In general words, in a first aspect, a synthetic-image device comprises an image layer and a focusing element array. The image layer is arranged in a vicinity of a focal distance of focusing elements of the focusing element array. Composite image objects of the image layer are a merging of at least a first set of image objects and a second set of image objects. The first set of image objects are arranged for giving rise to at least a, first, guiding synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through the focusing element array. The guiding synthetic image, when being moved to be viewed in a direction out of a set of discrete directions, presents a first part image and a second part image moving towards a predetermined relative geometrical relation with respect to each other. The second set of image objects are arranged for giving rise to at least a second, effect synthetic image, within a limited effect field of view of the effect synthetic image, when being placed in a vicinity of a focal distance of focusing elements and viewed through the focusing element array. The limited effect field-of-view of the effect synthetic image is selected as including viewing directions only in an angular vicinity of any of the directions of the set of discrete directions, or excluding viewing directions only in an angular vicinity of any of the directions of the set of discrete directions.

In a second aspect, a method for producing a synthetic-image device comprises creating of a numerical representation of a first set of image objects being arranged in image cells for giving rise to at least a, first, guiding synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through a focusing element array. The guiding synthetic image presents a first part image and a second part image, changing a relative geometrical relation to each other upon changing a view direction. A predetermined relative geometrical relation between the first part image and the second part image corresponds to image objects positioned at a first position in each image cell. An effect view-limiting area is defined, comprising the first position and a margin. A numerical representation of a second set of image object is created, which is arranged for giving rise to at least a, second, effect synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through the focusing element array. The numerical representation of the second set of image objects is modified within or outside the effect view-limiting area to give rise to an abrupt change of appearance of the effect synthetic image. The numerical representation of the first set of image objects and the numerical representation of the second set of image objects are merged into a numerical representation of composite image objects. An image layer is formed according to the numerical representation of composite image objects. A focusing element array is form, whereby the image layer being arranged in a vicinity of a focal distance (of focusing elements of the focusing element array.

In a third aspect, a method for authentication of an object having a synthetic - image device provided at a surface of the object, comprises observing of a, first, guiding synthetic image of the synthetic-image device in a viewing direction. The guiding synthetic image has a first part image and a second part image.

The synthetic-image device is moved to change the viewing direction to cause the first part image and the second part image to move towards a predetermined relative geometrical relation with respect to each other. An abrupt change in appearance of a second, effect synthetic image is observed when moving towards the predetermined relative geometrical relation, as sign of authenticity.

One advantage with the proposed technology is that surprising effects in the synthetic images of synthetic-image devices easily can be found without any demands of displacement alignment of the image layer and the focusing element array. Other advantages will be appreciated when reading the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which: FIGS. 1A-C are schematic drawings of synthetic-image devices utilizing different focusing elements;

FIG 2 is a schematic drawing illustrating viewing from different angles;

FIGS. 3A-B illustrate the formation of a synthetic image for two different viewing angles;

FIGS 4A-C illustrate the ideas of forming an example of an integral synthetic-image device;

FIG. 5 illustrate another example of an integral synthetic-image device;

FIG. 6 illustrates an example of how a three-dimensional image can be created;

FIG. 7 is an example of image objects of an integral synthetic-image device;

FIG. 8A illustrates an embodiment of a synthetic-image device having a guiding synthetic image;

FIG. 8B illustrates the embodiment of Fig. 8A when being tilted;

FIG. 8C illustrates a relation between a viewer and a guiding synthetic image;

FIG. 8D illustrates the embodiment of Fig. 8A when being tilted and when having an effect synthetic image;

FIG. 8E illustrates an effect limited field-of-view;

FIGS. 9A-C illustrate other embodiments of a synthetic-image device having a guiding synthetic image;

FIG. 10 illustrates different viewing direction giving a predetermined geometrical relation within the guiding synthetic image;

FIG. 1 1 illustrates another embodiment of a synthetic-image device having a guiding synthetic image;

FIGS. 12A-B illustrate another embodiment of a synthetic-image device having a guiding synthetic image in perspective view and from top;

FIGS. 13A-B illustrate yet another embodiment of a synthetic-image device having a guiding synthetic image in perspective view and from top;

FIG. 14A-B illustrate embodiment of a synthetic-image device having a three-layer guiding synthetic image; FIG. 15A-B illustrate embodiments of a synthetic-image device having a three-dimensional guiding synthetic image;

FIGS. 16A-B illustrate other embodiments of a synthetic-image device having a guiding synthetic image;

FIGS. 17A-H illustrate embodiments of a synthetic-image device having an effect synthetic image;

FIG. 18 illustrate an embodiment of a synthetic-image device having a two-stage guiding synthetic image and an effect synthetic image;

FIG. 19 is a flow diagram of steps of an embodiment of an authentication method;

FIGS. 20A-C illustrate embodiments of cells in a synthetic-image device having a guiding synthetic image;

FIGS. 21A-J illustrate embodiments of a cell in a synthetic-image device;

FIGS. 22A-C illustrate embodiments of cells in a synthetic-image device; FIGS. 23A-B illustrate a relation between a cell position and an associated focusing element;

FIG. 24 is a flow diagram of steps of an embodiment of a manufacturing method;

FIGS. 25A-B illustrate relations between cells and associated focusing elements;

FIG. 26 schematically illustrate an embodiment of a synthetic-image device having cells with a plurality of channels;

FIGS. 27A-B schematically illustrate an embodiment of a synthetic- image device having cells with a plurality of channels;

FIGS. 27C-d schematically illustrate another embodiment of a synthetic-image device having cells with a plurality of channels;

FIG. 28 schematically illustrates another embodiment of a synthetic- image device having cells with a plurality of channels;

FIGS. 29A-B schematically illustrate embodiments of synthetic-image devices presenting morphing synthetic images;

FIG. 30 schematically illustrates an embodiment of a synthetic-image device presenting a combined morphing synthetic image; and FIGS. 31A-C schematically illustrate another embodiment of a synthetic-image device presenting a combined synthetic image.

DETAILED DESCRIPTION

Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

For a better understanding of the proposed technology, it may be useful to begin with a brief overview of synthetic-image devices.

Fig. 1A schematically illustrates one example of a synthetic-image device 1. The synthetic-image device 1 comprises a focusing element array 20 of focusing elements 22. In this example, the focusing element is a lens 24. In a typical case, where the synthetic image is intended to be essentially the same in different surface directions, the lens 24 is typically a spherical lens. In applications, where a difference between image properties in different surface directions, lenticular lenses may be used.

The synthetic-image device 1 further comprises an image layer 10 comprising image objects 12. The image objects 12 are objects that are optically distinguishable from parts 14 of the image layer 10 that are not covered by image objects 12. The image objects 12 may e.g. be constituted by printed product micro features 1 1 and/ or embossed microstructures. The image layer 10 is arranged in a vicinity of a focal distance d of the focusing elements 22 of the focusing element array 20. This means that a parallel beam 6 of light impinging on a focusing element 22 will be refracted 5 and focused at one point or small area 4 at the image layer 10. Likewise, light emanating from one point at the image layer 10 will give rise to a parallel beam 6 of light when passing the focusing elements 22. A point at an image object 12 will therefore appear to fill the entire surface of the focusing element 22 when viewed from a distance in the direction of the produced parallel beam 6 by a viewer, schematically illustrated by the eye of the viewer 2. The material 9 between the image layer 10 and the focusing element array 20 is at least partly transparent and is typically constituted by a thin polymer foil.

The distance d does not have to be exactly equal to the focusing distance of the focusing elements 22. First, there is always a certain degree of aberrations, which anyway broadens the area from which the optical information in a parallel beam 6 is collected. This appears more at shallower angles and in order to have a more even general resolution level, a distance in a vicinity, but not exactly equal to the focal distance may be beneficially selected. Furthermore, since the focusing element surface has a certain two- dimensional extension, also this surface could be used to produce fine objects of the total synthetic image. In such cases, fine objects of a small area on the image layer 10 may be beneficial to enlarge to cover the surface of the focusing element, which means that also in such a case, the actual selected distance d is selected to be in a vicinity, but not exactly equal to the focal distance. Such circumstances are well known in the art of synthetic images.

By arranging the image objects 12 of the image layer 10 in a suitable manner, the part images produced at each individual focusing element 22 surface will collectively be perceived by a viewer 2 as a synthetic image. Different images may be displayed for the viewer when the synthetic-image device 1 is viewed in different directions, which opens up for creating different kinds of optical effects, as will be described further below.

Fig. IB schematically illustrates another example of a synthetic-image device 1. In this embodiment, the focusing elements 22 are constituted by concave mirrors 26. The image layer 10 is here situated on the front surface with reference to the viewer 2 and the focusing element array 20 is situated behind the image layer 10. The rays 5 of light travelling from the image objects to the viewer 2 pass the material 9 of the synthetic-image device twice.

Fig. 1C schematically illustrates yet another example of a synthetic-image device 1. In this embodiment, the focusing elements are pinholes 28, restricting the light coming from the image layer 10 and passing through to the viewer 2. In this embodiment, the synthetic image is built by the narrow light beams passing the pinholes 28, and are typically only providing "light" or "dark". Since the pinholes 28 doesn't have any enlarging effect, most of the viewed surface does not contribute to the synthetic image.

Fig. 2 illustrates schematically the selection of different part areas 4 of the image layer 10. The image layer 10 comprises image objects 12. When the synthetic-image device 1 is viewed in a perpendicular direction with reference to the main surface of the synthetic-image device 1 , as illustrated in the left part of the drawings, the area 4 that is enlarged by the focusing element 22 is situated at the centre line, illustrated in the figure by a dotted line, of the focusing element 22. If an image object 12 is present at that position, an enlarged version is presented at the surface of the synthetic-image device 1. However, as in the case of Fig. 2, no image object is present, and there will be no enlarged image at the surface of the synthetic-image device 1.

When viewing the synthetic-image device 1 at another angle, as e.g. illustrated in the right part of the figure, the area 4 on which the focusing element 22 focuses is shifted at the side. In the illustrated situation, the area 4 overlaps with at least a part of an image object 12 and an enlarged version can be seen at the surface of the synthetic-image device 1. In this way, the images presented at the surface of the synthetic-image device 1 may change for different viewing angles, which can be used for achieving different kinds of optical effects of the synthetic images.

One type of synthetic image is a so-called moire image. The moire effect is well known since many years and is based on the cooperation of two slightly mismatching arrays. Fig. 3A schematically illustrates in the upper part an example of a part of an image layer 10. The image layer 10 comprises a repetitive pattern 15 of image objects 12. In this example, the image objects 12 are selected to be the letter "K". Focusing elements 22 associated with the illustrated part of the image layer 10 are illustrated by dotted circles, to indicate the relative lateral position. Both the repetitive pattern 15 of image objects 12 and the focusing element array 20 have a hexagonal symmetry. However, the distance between two neighbouring image objects 12 is slightly shorter than the distance between two neighbouring focusing elements 22 in the same direction.

An area 4 is also marked, which corresponds to the focusing area of each focusing element 22. In the illustrated case, the area 4 corresponds to a view direction straight from the front. The parts of the image objects 12 that are present within each of the areas 4 will thereby be presented in an enlarged version over the surface of the corresponding focusing element 22, here denoted as a projected image 25. In the lower part of Fig. 3A, the corresponding focusing element array 20 is illustrated including the projected images 25 of the image objects 12 of the areas 4. The dotted lines from one of the areas 4 in the upper part to one of the focusing elements 22 in the lower part illustrates the association. The different projected images at the focusing elements 22 together forms a synthetic image 100. In this case, the synthetic image 100 is a part of a large "K". If these structures are small enough, the human eye will typically fill in the empty areas between the focusing elements 22 and the viewer will perceive a full "K". The reason for the K to be produced is the existence of the slight period mismatch between the repetitive pattern 15 of image objects 12 and the focusing element array 20. In this example, using the mismatch between a repetitive image pattern 15 and an array of focusing elements 22, the synthetic image is called a moire image 105.

Fig. 3B schematically illustrates the same synthetic-image device 1 as in Fig. 3A, but when viewed in another direction. This corresponds to a slight tilting of the synthetic-image device 1 to the left. The areas 4 which corresponds to the focusing areas of the focusing elements 22 in this direction are thereby moved somewhat to the left. This results in that another part of the image objects 12 are projected to the focusing elements 22, as seen in the lower part of the Fig. 3B. The result of the tilting is that the synthetic image 100, i.e. the large "K" moves to the right. The viewer will interpret such a motion as a result of a position of the large "K" at a certain imaginary depth below the surface of the synthetic-image device 1. In other words, a depth feeling is achieved. Both the magnification and the experienced depth depends on the relation between the focusing element array 20 and the repetitive pattern 15 of image objects 12. It has in prior art been shown that the obtained magnification M is determined as:

M (1)

F - F'

P

where F =—,

p, where P₀ is the period of the repetitive pattern 15 of image objects 12 and P_t is the period of the focusing element array 20. For P₀ < P the magnification is positive, for P₀ > P the magnification becomes negative, i.e. the synthetic image 100 becomes inverted compared to the image objects 12.

The apparent image depth d_t of the moire image can also be determined as:

where d is the thickness of the synthetic-image device and R_/ is the radius of the curvature of the spherical microlenses. One can here notice that for P₀ < Pi , the apparent depth is typically positive, while for P₀ > P the apparent depth becomes negative, i.e. the moire image 105 seems to float above the surface of the synthetic-image device 1.

It should be noted that the differences in periods illustrated in Figs 3A and 3B are relatively large, which gives a relatively low magnification and a relatively small apparent depth. This is made for purposes of illustration. In typical moire synthetic-image devices, the relative period differences may typically be much less. Period differences of less than 1% and even less than 0. 1 % are not uncommon.

The moire images have, however, certain limitations. First of all, they can only result in repetitive images. Furthermore, the size of the image objects 12 is limited to the size of the focusing elements. In Fig. 4A, an image object 13 is schematically illustrated. If this image object is repeated with almost the same period as for the focusing elements 22 of Fig. 4B, the repeated patterns of image objects 13 will overlap. The moire image from such a structure will be almost impossible for the human brain to resolve, since parts of the image objects associated with a neighbouring focusing element 22 will interfere.

A solution is presented in Fig. 4C. Here a cell 16 of the image layer 10 is exclusively associated with each focusing element 22. Within each cell 16, only parts of an image object 17 belonging to one copy of the image object is preserved and the other interfering image objects are removed. The different image objects 17 will now not be identically repeated over the image layer 10 but instead the image objects 17 are successively changing in shape. By using these cut-out parts or fractions as the image object 17, a synthetic image will also be produced. A synthetic image based on non-identical fractioned image objects 17 within cells 16 associated with the focusing elements 22 is in this disclosure referred to as an integral synthetic image.

As long as the focusing area of the associated focusing element is kept within the cell 16 a synthetic image similar to a moire image will be produced.

However, when the focusing area of the associated focusing element enters into a neighbouring cell 16, the synthetic image will suddenly disappear and will instead appear at another position; a flip in the synthetic image occurs. Such flipping effects may be somewhat extenuated by introducing an image object-free zone between each cell at the image layer. Fig. 5 illustrates schematically such a design. Here, each cell 16 occupies an area that is smaller than the area of an associated focusing element. The result will be that the integral synthetic image will disappear when the area of focus of the associated focusing element reaches the edge of the cell. However, a further change in viewing angle has to be provided before a "new" integral synthetic image appears. The relation with the disappearing image will then not be equally apparent. This restriction of the angles in which a synthetic image may be seen is often referred to as a restricted field-of-view.

The ideas of having cells with different image objects can be driven further. The moire synthetic images can be given an apparent depth, but is in principle restricted to one depth only. A true three-dimensional appearance is difficult to achieve. However, when considering integral synthetic images, the freedom of changing the image objects from one cell to another can also be used e.g. to provide a more realistic three-dimensionality of the produced images.

In Fig. 6, cells 16 of an image layer 10 are illustrated. Four different areas 4 for each cell 16, corresponding to focusing areas of associated focusing elements when viewed in four different directions are illustrated. Image objects of the centre area 4 in each cell corresponds to a viewing angle as achieved if the synthetic-image device is viewed in a perpendicular manner. Such image objects may then be designed such that they give rise to an integral synthetic image HOB as illustrated in the lower centre part of Fig. 6 showing a top surface of a box. Image objects of the uppermost area 4 in each cell corresponds to a viewing angle as achieved if the synthetic-image device is tilted away from the viewer. Such image objects may then be designed such that they give rise to an integral synthetic image 11 OA as illustrated in the lower left part of Fig. 6, showing the top surface and a front surface of a box. Image objects of the leftmost area 4 in each cell corresponds to a viewing angle as achieved if the synthetic-image device is tilted to the left with reference to the viewer. Such image objects may then be designed such that they give rise to an integral synthetic image HOC as illustrated in the lower right part of Fig. 6, showing the top surface and a side surface of a box. Image objects of the area 4 in the lower right part in each cell corresponds to a viewing angle as achieved if the synthetic-image device is tilted towards and to the right with reference to the viewer. Such image objects may then be designed such that they give rise to an integral synthetic image 1 10D as illustrated at the very bottom of Fig. 6, showing the top surface, a side surface and a back surface of a box. Together, these integral synthetic images 110A-D and further integral synthetic images emanating from other areas of the cells give an impression of a rotating box in a three-dimensional fashion.

In a similar fashion, by modifying the image content in each cell separately, different kinds of optical phenomena can be achieved. By adapting each part of the cell according to the requested image appearance in a corresponding viewing direction, the integral synthetic image can be caused to have almost any appearances. The so achieved image properties can be simulations of "real" optical properties, e.g. a true three-dimensional image, but the image properties may also show optical effects which are not present in "real" systems.

An example of a part of an image layer 10 of an integral synthetic-image device giving rise to an image of the figure "5" is illustrated in Fig. 7.

One effect that is possible to achieve by both moire synthetic images and integral synthetic images is that two or more synthetic images can be imaged at the same time. These synthetic images may have different apparent depth or height. When tiling such an optical device, the synthetic images moves relative each according to the ordinary parallax effect. The same is valid if one integral synthetic image has components at different depths or heights.

According to the technology presented here, such parallax effect can be utilized in order to define certain distinct viewing directions. If the integral synthetic image has an easily identified appearance when viewed in a particular direction, that particular direction is well defined by means of the integral synthetic image itself. This also means that a search for that easily identified appearance of the integral synthetic image also becomes a search for that particular viewing direction. An example, schematically illustrated in Figs. 8A-B, may perhaps facilitate the understanding. In this particular example, a synthetic-image device 1 presents a guiding synthetic image 41 that is composed by a first part image 46, in this embodiment being an array of circles 71 , provided at an apparent depth below the surface of the synthetic -image device 1 and by a second part image 47, in this embodiment being an array of crosses 72, provided at an apparent height above the surface of the synthetic-image device 1. In the viewing direction illustrated in Fig. 8A, the crosses 72 appear to be situated at the right side relative a respective circle 71.

In order to try to bring the cross 72 into the middle of the circle 71 , it is natural for a person to tilt the synthetic-image device 1 to the left. This is according to natural three-dimensional parallax rules since the crosses 72 appear to be situated at a higher elevation than the circles 71. In such a tilted viewing direction, the synthetic-image device 1 provides a guiding synthetic image 41 as illustrated in Fig. 8B. Such a manoeuvre is easily performed by any person, since the relative motion of the different parts of the guiding synthetic image 41 behaves in a traditional three-dimensional way.

As schematically illustrated in Fig. 8C, the viewing angle at which the circles 71 and the crosses 72 are aligned define a particular direction d with respect to the surface of the synthetic-image device 1.

By now combining such an integral synthetic image with another synthetic image having a narrow limited field-of-view centred around that particular direction, a surprising effect can be achieved. Alternatively, the other synthetic image may have a limited field-of-view excluding a small angle interval around that particular direction.

In other words, an apparent three-dimensional synthetic image can be used for guiding a viewer to a specific viewing angle. At this viewing angle, something "surprising" will happen with the three-dimensional synthetic image or an additional synthetic image. Since the relative alignment of image objects belonging to different synthetic images is easy, the "surprising effect" can be more or less perfectly aligned with the shape of the guiding three- dimensional synthetic image.

An example of a synthetic -image device 1 having such surprising effect is illustrated in Fig. 8D. This synthetic-image device 1 presents the same synthetic image as in Fig. 8A when viewed in that viewing direction. However, when the synthetic-image device 1 is tilted to give the same viewing direction d as was illustrated in Fig. 8B and 8C, an effect synthetic image 42 of Fig. 8D appears, showing the words "AUTHENTIC PRODUCT" over a large portion of the synthetic-image device 1. This particular effect is achieved by imposing a limited guiding field-of-view on the guiding synthetic image as was seen in Fig. 8A, which limited guiding field-of-view excludes viewing directions in a vicinity of the "aligned cross-circle" direction. The boundaries of such a limited guiding field-of-view 51 is illustrated in Fig. 8E. This means that the crosses and circles disappear at or close to this direction d. At the same time, an additional effect synthetic image 42 giving the text is provided. Also this effect synthetic image 42 has a limited effect field-of-view 52, which instead is limited to a small angle interval around the "aligned cross-circle" direction d (Fig. 8E). This means that the text "AUTHENTIC PRODUCT" only appears very close to that direction d. The circles 71 and crosses 72 define an object that is very easy to tilt into a specific angle, and these circles 71 and crosses 72 thus serve as a guide for the viewer as to where to find the "surprising effect". When the particular direction is reached, or just before, the circles 71 and crosses 72 suddenly disappear and instead the authenticity text appears.

In devices according to the technology presented here, at least two sets of image objects are provided, each giving rise to a particular synthetic image. Synthetic image devices, as such, are as discussed above, well known in prior art. Also a combination of two or more synthetic images within one synthetic image device is, as such, known from earlier. However, the ideas presented here are based on the further fact that despite that the two sets of image objects give rise to independent synthetic images, there is a particular relation between the two sets in terms of field-of-view. The two sets of image objects are in other words connected to each other in the field-of-view space. The first set, here denoted as a guiding synthetic image, has a well-defined direction of view in which the guiding synthetic image presents a natural "aligned" synthetic image. At this very same direction of view, defined based on the properties of the guiding synthetic image, the synthetic image based on the second set of image objects, here denoted as an effect synthetic image, provides a surprising effect, such as appearing, disappearing or presenting an abrupt non-logical change in appearance. There is thus a very particular relation in field-of view angles between the two sets of image objects, which sets in other aspects could be totally independent.

In a general case, and in other words, a synthetic-image device comprises an image layer and a focusing element array. The image layer is arranged in a vicinity of a focal distance of focusing elements of the focusing element array. Composite image objects of the image layer are a merging of at least a first set of image objects and a second set of image objects. The first set of image objects is arranged for giving rise to at least a, first, guiding synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through said focusing element array. The guiding synthetic image, when being moved to be viewed in a direction out of a set of discrete directions, presents a first part image and a second part image moving towards a predetermined relative geometrical relation with respect to each other. The second set of image objects is arranged for giving rise to at least a second, effect synthetic image, within a limited effect field of view of the effect synthetic image, when being placed in a vicinity of a focal distance of focusing elements and viewed through the focusing element array. The limited effect field-of-view of the effect synthetic image is either including viewing directions only in an angular vicinity of any of the directions of the set of discrete directions, or excluding viewing directions only in an angular vicinity of any of the directions of the set of discrete directions. Preferably, the first part image and the second part image are provided at different apparent depth or height. The guiding synthetic image is thus used to find a particular direction of view, in which something surprising will occur. The guiding synthetic image can be designed in very different ways. However, one common feature is that the guiding synthetic image comprises part images which behaves in a way that makes the viewer intuitively aware of how to tilt the synthetic -image device.

If the part images e.g. are provided at different height/ depth, a viewer may, from the normal way of a three-dimensional object behaves, expect the part images to move relative each other in certain directions when the guiding synthetic image is tilted.

The simplest example is a guiding synthetic image comprising two repetitive two-dimensional patterns provided at different apparent height/ depth, as indicated in Fig. 8A & C. However, the finding of the searched viewing direction may not be restricted to aligned centers. Fig. 9A illustrates another embodiment, where circles 71 in an upper layer 48 form the first part image 46. The circles 71 are supposed to be aligned with bridging objects 73 in a lower layer 49, forming the second part image 47, as illustrated at the top of the figure.

Fig. 9B illustrates another embodiment, where the letters "O" 74 and "K" 75 are provided at different apparent height/ depth as an upper layer 48 with a first part image 46 and a lower layer 49 with a second part image 47, respectively. The requested viewing direction is obtained when the phrase

"OK" is formed, as illustrated at the top of the figure.

The guiding synthetic image 41 of the embodiments of Fig. 9A-B are easily provided as combination of two moire-type of synthetic images, but may also be achieved by an integral synthetic image as well.

Fig. 9C illustrates yet another embodiment, where an "eclipse" sequence is utilized. A filled circle 77 is provided as a second part image 47 at certain apparent height/ depth. Another, unfilled, circular area 76 is provided as a first part image 46 at another apparent height/ depth above the apparent height/depth of the filled circles 77. When the two part images 46, 47 partly coincide, as is illustrated in the upper part of the figure, the unfilled circular area 76 will mask parts of the filled circle 77 and the requested viewing direction is found when a total "eclipse" is reached, i.e. when the filled circles 77 overlap completely with the unfilled circular area 76.

Anyone skilled in the art realizes that the variations of the design of the guiding synthetic image 41 are endless.

In the examples presented above, the part images of the guiding synthetic image have been repetitive patterns, and also with a same period. In other words, in one embodiment, the guiding synthetic image comprises two pattern layers at different apparent height and/ or depth. The predetermined relative geometrical relation to each other corresponds to a predetermined overlap relation.

This also means that there are other possibilities to combine the part images. Returning to Figs. 8A and B as an example, the crosses 72 can be brought to coincide with at least a plurality of the circles 71, thereby defining other viewing directions. The "effect" is then to be performed in any of these directions. This is illustrated in Fig. 10. Here two circles 71 are illustrated, and two directions d that connects a center of a circle with the cross 72 are possible. These directions d thus together form a set D of discrete directions where alignment is achieved.

In a further embodiment, an upper pattern layer of the two pattern layers has an apparent height that in size is in a vicinity of an apparent depth of a lower pattern layer of the two patterns layers. This means that when tilting the synthetic-image device, the upper pattern layer appears to move a distance in one direction and the lower pattern layer appears to move a same distance in an opposite direction. The apparent height distance between the patterns thus becomes relatively large without having to use extremely high magnifications, which in turn means that the angular distance between two neighbouring directions of the set of discrete directions at which aligning occurs easily may be designed to be reasonably small. In order to move from one discrete direction where overlap exists to a neighbouring one, each pattern layer only has to move half the period distance.

In a further embodiment, the upper pattern layer and the lower pattern layer have a same periodicity. In such an embodiment, the coinciding of the patterns will occur at the same direction over the entire surface of the synthetic-image device, which typically simplifies the design. A simple embodiment is illustrated in Fig. 1 1. In this embodiment, the upper layer 48 comprising the first image part 46 is provided at an apparent height +h above a synthetic- image device surface 50. The lower layer 49 comprising the second image part 47 is provided at an apparent height -h, i.e. a depth of h, below the synthetic- image device surface 50.

In another embodiment, the upper pattern layer and the lower pattern layer have different periodicities, as illustrated in Figs 12A-B. In this embodiment, the upper layer 48 comprising the first image part 46 is provided at an apparent height hi above a synthetic-image device surface 50. The lower layer 49 comprising the second image part 47 is provided at an apparent height h2, above the synthetic-image device surface 50. Furthermore, the periodicity is different for the different layers. As can be seen in Fig. 12B, one instance of the repetitive item of the first image part 46 can be brought in alignment 59 with one instance of the repetitive item of the second image part 47 at a time. Any appearance or disappearance of an effect synthetic image can then take place in a part P of total image area A, as will be discussed more in detail below.

In yet another embodiment, as illustrated in Figs. 13A-B, a first image part 46 in an upper layer 48 can cooperate with a printed second image part 57 at or in the synthetic-image device, e.g. in the image layer 10. This printed second image part 57 thus appears at a height above the synthetic-image device that is essentially equal to zero.

Also more than two image parts can be used for the aligning purposes of the present disclosure. Fig. 14A illustrates one embodiment, where three layers are used. In a first part image 46 of a first layer, large circles are presented. In a second part image 47 of a second layer, smaller circles are presented, three of which fit into one of the larger circles. In a third part image 43 of a third layer, even smaller circles are presented, three of which fit within the circles of the second part image 47. The part images are provided at different heights and in certain well-determined directions, the smaller circles will fit into each other, as illustrated in Fig. 14B. As anyone skilled in the art realizes, any other types of images and any number of layers can be utilized for the alignment or guiding purpose.

However, also non-repetitive guiding synthetic images are of course also possible to use. Such guiding synthetic images can by advantage be integral synthetic images.

As an example, the first and second part images 46, 47 may be parts of a common three-dimensional guiding synthetic image 41, as illustrated by an embodiment in Fig. 15A. The guiding synthetic image in this embodiment is in the shape of a frustum of a pyramid 78. In the left part of the figure, the pyramid 78 is seen somewhat from the side. A viewer can easily tilt the synthetic image device in order to achieve a perfect top view instead, as illustrated in the right part of the figure. The second part image 47 is here constituted by the bottom edge of the frustum of a pyramid 78 and the first part image 46 is constituted by the top edge of the frustum of a pyramid 78. When these two part images 46, 47 are centered with respect to each other a "top view" is achieved.

Fig. 15B illustrates a similar embodiment, where a post 79 is used as guiding synthetic image 41. In the left part of the figure, the post 79 is viewed somewhat from the side, while in the right part of the figure, the post is viewed straight on the top of the post 79. The first part image 46 is constituted by the top edge of the post 79 and the second part image 47 is here constituted by the bottom edge of post 79.

The guiding synthetic image may also involve different kinds of animation effects. In Fig. 16A, the synthetic-image device 1 presents a guiding synthetic image 41 comprising a sphere 82 and a circle 81. When tilting the synthetic- image device 1 in order to place the sphere 82 into the circle 81 , the guiding synthetic image 41 changes in that the circle 81 is reduced in size. It therefore seems as if the sphere 82 pushes on the circle 81 in order to make it shrink. When the circle 81 eventually disappears, the requested viewing direction is reached, and a "surprising effect", as will be discussed more further below, may occur.

In Fig. 16B, another embodiment using an animated guiding synthetic image 41 is shown. The guiding synthetic image 41 is here a pattern of circles, including a first circle 83 and a second circle 84. When tilting the synthetic- image device 1 towards the "right" direction, the circles 83, 84 expand until they touch each other. Then, the requested viewing direction is found. A "surprising effect", in this particular embodiment the appearance of the text "SECURE", occurs.

In many applications, it is of benefit for the clarity of the synthetic image to remove at least some parts of the guiding synthetic image when the requested viewing direction is reached, or on the way towards this direction. To that end, in certain embodiments, at least part of the guiding synthetic image has a limited guiding field-of-view. This guiding field-of-view preferably excludes the directions in which the effect synthetic image exists or does not exist. The first part image and/ or the second part image will then disappear when the surprising effect occurs. To that end, the guiding synthetic image, when being viewed in the particular direction, would have presented the first part image and the second part image in the predetermined relative geometrical relation with respect to each other if the limited guiding field-of-view would have been disregarded.

In one embodiment, the guiding field-of-view is valid only for a part of the guiding synthetic image.

In one embodiment, the part of the guiding synthetic image for which the guiding field-of-view is valid comprises the first part image or the second part image.

In some applications, as will be discussed further below, it is not necessary for the guiding synthetic image to disappear over the entire synthetic-image device. This may e.g. be the case when the effect synthetic image only appears at a limited part of the device area. In such embodiment, it is then of use to let the guiding field-of-view be valid only for a part of a total image area of the synthetic -image device.

The guiding field of view is in certain embodiments a two-dimensional field-of- view.

In other embodiments, the guiding field-of-view is a one-dimensional field-of- view.

So far, most of the description above focuses on the behaviour or design of the guiding synthetic image. Here below, the effect synthetic image will be the main target. In general, it is possible to combine essentially any type of guiding synthetic image approach with essentially any type of effect synthetic image approach.

The surprising effect created by the effect synthetic image is mainly caused by restricting the field-of-view of the effect synthetic image. In this respect, there are three main groups of effect synthetic images. One group comprises effect synthetic images with a field-of-view restricted to a small angle range around the direction selected by the guiding synthetic image. Another group comprises effect synthetic images with a field-of-view restricted to all angles except a small angle range around the direction selected by the guiding synthetic image. Finally, the last group comprises effect synthetic images composed of effect synthetic images of the other two groups, thereby providing a switch from one image to another upon entering the small angle range around the direction selected by the guiding synthetic image.

In certain embodiments, it is of interest that the total image area of the synthetic-image device presents the effect synthetic image. However, in other embodiments, it may instead by preferred to present the effect synthetic image only in selected parts of said total image area (A) of said synthetic-image device. The effect synthetic image may also be designed to cooperate with the guiding synthetic image to form a combined synthetic image within the effect field-of- view. Further examples are presented below.

One possibility of interaction with the guiding synthetic image is to replace one of the part images of the guiding synthetic image with the effect synthetic image within the effect field-of-view.

Fig. 17A illustrates one embodiment of a synthetic-image device 1. In this embodiment, the cross-and-circle guiding synthetic image (c.f. Fig. 8A&D) is used for defining the requested viewing direction. However, as discussed above any kind of guiding synthetic image approach can be utilized. In the left part of the figure, representing a view outside of the requested viewing direction, only the guiding synthetic image 41 is seen. When the requested viewing direction is reached, which is illustrated in the right part of the figure, the guiding synthetic image 41 disappears completely and is replaced by the effect synthetic image 42, in this embodiment presenting the words "SAFE". Here, the entire guiding synthetic image 41 has a limited guiding field-of-view which excludes the angles in vicinity of the requested viewing direction. The effect synthetic image 42 has an effect field-of-view which instead only includes the angles in vicinity of the requested viewing direction.

In Fig. 17B another embodiment of a synthetic-image device 1 is illustrated. The situation outside of the requested viewing direction, is similar as in Fig. 17A, only showing the guiding synthetic image 41. When the requested viewing direction is reached, which is illustrated in the right part of the figure, a part of the guiding synthetic image 41, the crosses, disappears and are replaced by the effect synthetic image 42, in this embodiment presenting the words "OK" inside the circles of the guiding synthetic image 41. Here, one part image of the guiding synthetic image 41 has a limited guiding field-of-view which excludes the angles in vicinity of the requested viewing direction. The other part image, the circles, do not have any limited field-of-view. Also here, the effect synthetic image 42 has an effect field-of-view which only includes the angles in vicinity of the requested viewing direction.

In Fig. 17C another embodiment of a synthetic-image device 1 is illustrated. The guiding synthetic image 41 here comprises a pattern of circles and a pattern of filled squares, constituting two part images. When the requested viewing direction is reached, when the squared totally covers the circles, which is illustrated in the right part of the figure, an overlapping part of the filled squares and the circles of the guiding synthetic image 41 disappear and are replaced by the effect synthetic image 42, in this embodiment presenting the words "OK" inside the circles of the guiding synthetic image 41. Here, a part of one of the part images of the guiding synthetic image 41 has a limited guiding field-of-view which excludes the angles in vicinity of the requested viewing direction. The other part image, the circles, do not have any limited field-of-view. Also here, the effect synthetic image 42 has an effect field-of-view which only includes the angles in vicinity of the requested viewing direction.

In Fig. 17D another embodiment of a synthetic-image device 1 is illustrated. The guiding synthetic image 41 is similar to Fig. 17A outside the requested viewing direction. When the requested viewing direction is reached, which is illustrated in the right part of the figure, the effect synthetic image appears, but only in a part P of the total image area A, replacing the guiding synthetic image 41. The guiding synthetic image 41 is however still present outside the part P of the total image area A. Here, the guiding synthetic image 41 has a limited guiding field-of-view which excludes the angles in vicinity of the requested viewing direction, but only within area P. Also, the effect synthetic image 42 has, within the area P, an effect field-of-view which only includes the angles in vicinity of the requested viewing direction.

It should be noticed that the effect synthetic image can be of any kind. Texts are often self-explaining, but other types of images, e.g. three-dimensional synthetic images could be used. In the end of the present disclosure, many different kinds of synthetic images are presented, which may constitute the effect synthetic image and/ or the guiding synthetic image.

In one embodiment, a change in colour may be used as "surprising effect". If one has a guiding synthetic image in one colour, which is used for finding the requested viewing direction, an effect synthetic image in another colour with an effect field-of-view which only includes the angles in vicinity of the requested viewing direction will cause an eye-catching effect. The effect synthetic image may be identical to the guiding synthetic image, except for the colour, or may be another image.

In Fig. 17E another embodiment of a synthetic-image device 1 is illustrated. The guiding synthetic image 41 is similar as in Fig. 17D outside the requested viewing direction. In this embodiment, the effect synthetic image 42, in this particular embodiment a pattern of rectangles, is present outside the requested viewing direction, as illustrated in the left part of the figure. However, when the requested viewing direction is reached, which is illustrated in the right part of the figure, the effect synthetic image disappears. In this embodiment, the effect synthetic image 42 has an effect field-of-view which excludes the angles in vicinity of the requested viewing direction. In Fig. 17F another embodiment of a synthetic-image device 1 is illustrated. The guiding synthetic image 41 is similar as in Fig. 17D outside the requested viewing direction. In this embodiment, the effect synthetic image 42, in this particular embodiment a text "ALIGN CROSS AND CIRCLE", is present outside the requested viewing direction, as illustrated in the left part of the figure. However, when the requested viewing direction is reached, which is illustrated in the right part of the figure, the guiding synthetic image 41 disappears. Furthermore, the effect synthetic image 42 presents a flip from the text "ALIGN CROSS AND CIRCLE" to a thumb-up sketch. In this embodiment, the entire guiding synthetic image 41 has a limited guiding field-of-view which excludes the angles in vicinity of the requested viewing direction. The effect synthetic image 42 is composed by two parts, one corresponding to the thumb-up figure having an effect field-of-view which only includes the angles in vicinity of the requested viewing direction, and one corresponding to the text having an effect field-of-view which excludes the angles in vicinity of the requested viewing direction.

In Fig. 17G another embodiment of a synthetic-image device 1 is illustrated. The guiding synthetic image 41 is similar as before, where crosses 72 in an upper layer 48 are supposed to be aligned to circles 71 in a lower layer 49, as illustrated in the upper part of the figure. However, when the requested viewing direction is reached, which is illustrated in the lower part of the figure, the upper layer 48 of the guiding synthetic image 41 disappears. Instead, the effect synthetic image 42 appears at an effect layer 44 having an apparent position below the circles 71. The result for the view is thus that when the cross is placed aligned to the circles, the crosses "fall through" the circles and end up in another deeper layer. A depth change is thus used as the "surprising effect". In this embodiment, the upper layer 48 of the guiding synthetic image 41 has a limited guiding field-of-view which excludes the angles in vicinity of the requested viewing direction. The effect synthetic image 42, which also is a pattern of crosses, has an effect field-of-view which only includes the angles in vicinity of the requested viewing direction. In Fig. 17H another embodiment of a synthetic-image device 1 is illustrated. The guiding synthetic image 41 comprises a small filled square in an upper layer and a large unfilled square in a lower layer outside the requested viewing direction. When the requested viewing direction is reached, which is illustrated in the right part of the figure, the guiding synthetic image 41 is combined with the effect synthetic image 42 to present a three-dimensional image of a frustum of a pyramid. An abrupt change from two separate layers of two-dimensional figures to a full 3D image serves as the "surprising effect". In this embodiment, the guiding synthetic image 41 has no limited guiding field-of-view, but is always present. The effect synthetic image 42 has an effect field-of-view which only includes the angles in vicinity of the requested viewing direction.

The guiding and/ or the surprising effects can also take place in two or more steps. In Fig. 18, one embodiment is illustrated where a circle-and-cross guiding synthetic image 41 is visible outside the requested viewing direction.

When the synthetic-image device 1 is tilted so that the crosses comes closer to the circle centre, a new part of the guiding synthetic image 41 turns up, in this embodiment a smaller circle. This smaller circle assists in the fine tuning of the tilting. When the requested viewing direction is reached, the crosses disappear, and instead an effect synthetic image 42 appear, in this embodiment a pattern of stars.

In an alternative view, the small circles may be interpreted as a first part of an effect synthetic image. When the more precise viewing direction is reached, the effect synthetic image is developed into a star.

As anyone skilled in the art understands, the variations concerning the "surprising effect" can be designed using any effects of synthetic images known in prior-art. These effects can be provided only by a separate effect synthetic image or by a combination between the effect synthetic image and changes in the guiding synthetic image. By use of a combination of a guiding synthetic image and an effect synthetic image, the use of a synthetic-image device e.g. as an authentication sign is easy, regardless of the relative alignment of the focusing elements and the image objects.

In Fig. 19, a flow diagram of steps of an embodiment of an authentication method is illustrated. The method for authentication of an object having a synthetic -image device provided at a surface of the object starts in step 200. In step 210, a, first, guiding synthetic image of the synthetic-image device is observed in a viewing direction. The guiding synthetic image has a first part image and a second part image. In step 220, the synthetic-image device is moved to change the viewing direction. This changing viewing direction causes the first part image and the second part image to move towards a predetermined relative geometrical relation with respect to each other. In step 230, an abrupt change in appearance of a second, effect synthetic image is observed when moving towards the predetermined relative geometrical relation, as sign of authenticity. The procedure ends in step 299.

The different embodiments of synthetic-image devices presented above can be manufactured by many different methods, which in a general form is known in prior art. Here below, a method for producing a synthetic-image device is presented, which method is particularly well suited for synthetic-image devices of the kind discussed here above. In an integral synthetic image approach, as mentioned earlier, non-identical fractioned image objects are provided within cells associated with a respective focusing element.

In Fig. 20A, a number of cells C from different parts of an embodiment of a synthetic-image device are illustrated. The cells comprise a first set of image objects giving rise to a first guiding synthetic image when placed in the right position in front of an array of focusing elements. A first type of image objects 17A gives rise to an image of crosses, while a second type of image objects 17B gives rise to an image of pluses. As anyone skilled in the art understands, image objects for all different designs of guiding synthetic images presented here above and variations of these are possible to use.

The image of the crosses has an apparent height above the synthetic-image device and the periodicity of the image objects 17A of the crosses is slightly larger than the periodicity of the cells C. Similarly, the image of the pluses has an apparent depth below the synthetic- image device and the periodicity of the image objects 17B of the pluses is slightly smaller than the periodicity of the cells C. The positions of the image objects 17A, 17B within the cells C will therefore vary between different cells, as can be seen in the figure. In the second cell from the left in the figure, the image objects 17A, 17B overlap. This occurs at a certain first position 60. This means that the synthetic-image device when being viewed in a direction that makes the focusing element above the cell to select the first position 60, and an image of an overlapping cross and plus will be seen. In the situation at the right part of the figure, a similar situation occurs. However, here the first position 60 is situated close to a cell border. In the present embodiment, totally four such first positions 60 can be found. When a viewing direction is selected that corresponds to any of these first positions 60, an overlapping cross/plus image is seen. Note that there are in the present embodiment more such first positions within each cell, connected to overlapping situations in cell above and below the illustrated cells, c.f. Fig. 20B.

In Fig. 20B, guiding view-limiting areas 62 enclosing one first position 60 each are illustrated. As can be seen in the cell, second from the left, parts of the image objects 17A, 17B that should have been present within the guiding view- limiting area 62, are removed. This corresponds to that the image disappears when being viewed in the direction corresponding to the first position 60.

In Fig. 20C, effect view- limiting areas 63 enclosing one first position 60 each are illustrated. In this embodiment, the effect view- limiting areas 63 are the same as the guiding view-limiting areas 62. Image objects 17C belonging to an effect synthetic image are provided within the effect view-limiting areas 63. In the present embodiment, the image objects 17C belongs to an effect synthetic image in the form of a letter "A". The parts of the image objects falling outside the effect view-limiting areas 63 are "removed" in reality, but for explanatory reasons indicated by a broken line notation in the figure. This corresponds to that the image of "A" suddenly appears when being viewed in one of the directions corresponding to the first position 60.

The full effect of the synthetic-image device having the cells of Fig. 20C is then that the cross and plus patterns are visible at most viewing directions in different relation to each other. When the viewing direction comes into the vicinity of the requested one, the pluses and crosses disappear and instead the letter "A" turns up.

When providing a manufacturing method, a similar approach is indicated in the Figs. 20A-C can be utilized. Image objects of a guiding synthetic image can be represented by a numerical representation. Similarly, image objects of an effect synthetic image can also be represented by a numerical representation. By then defining an effect view-limiting area enclosing the position in a cell where the part images of the guiding synthetic image reaches the requested geometrical relationship, the numerical representation of the image objects of the effect synthetic image can be modified to be seen either inside or outside the effect view-limiting area. This modified representation of the image objects of the effect synthetic image can then be merged with the image objects of the guiding synthetic image, possibly also modified within or without a guiding view-limiting area. This numerical representation of composite image objects can then by methods, known as such, be used for forming an image layer.

Fig. 21A illustrates one cell C of a synthetic-image device. In this embodiment, the guiding view-limiting area 62 coincides with the effect view-limiting area 63. The result is that the changes in the guiding synthetic image and the effect synthetic image occur at the same viewing directions. Fig. 2 IB illustrates one cell C of another synthetic-image device. In this embodiment, there is no guiding view-limiting area, and the guiding synthetic image is therefore possible to perceive in all viewing directions. However, the effect view-limiting area 63 still controls the appearance of the effect synthetic image.

Fig. 21C illustrates one cell C of another synthetic-image device. In this embodiment, there is one guiding view-limiting area 62 and one effect view- limiting area 63. In this embodiment, the guiding view-limiting area 62 encloses the effect view- limiting area 63. The result is that when the viewing direction comes closer to the requested one, the guiding synthetic image or at least part thereof will first disappear and when the viewing direction is further changed towards the requested viewing direction, the effect synthetic image will appear. In an alternative, the effect view-limiting area 63 encloses the guiding view- limiting area 62, which will result in that the effect synthetic image first will appear together with the guiding synthetic image, but when the viewing direction comes closer to the target, the guiding synthetic image or at least part thereof disappears.

Fig. 2 ID illustrates one cell C of another synthetic-image device. In this embodiment, the effect view-limiting area 63 encloses the first position 60, but in an asymmetric manner. This means that the appearance / disappearance of the effect synthetic image is different depending on the direction in which the viewing angle is changed.

In the previous embodiments, the effect view-limiting area (63) and the guiding view-limiting area (62) has been limited in two dimensions. Fig. 2 IE illustrates one cell C of another synthetic-image device. In this embodiment, the effect view-limiting area 63 and the guiding view-limiting area 62 instead are limited in one dimension. This means that encloses the first position 60, but in an asymmetric manner. The appearance/ disappearance of the effect synthetic image and the disappearance of at least a part of the guiding synthetic image is here only dependent on the viewing angle component in the vertical direction (as defined in the figure). In different alternatives, one of the effect view-limiting area 63 and the guiding view-limiting area 62 can be limited in two dimensions while the other is limited in one dimension. In many of the embodiments presented above, the effect view-limiting area 63 and the guiding view-limiting area 62 have a same symmetry as the cell C. However, this is not absolutely necessary. In Fig. 20C, circular effect view- limiting areas 63 and guiding view-limiting areas 62 are illustrated within a hexagonal cell C. In Fig. 2 IE, a rectangular effect view-limiting area 63 is illustrated within a hexagonal cell C, as another example of differing symmetries.

In Fig. 21G, one cell C of another synthetic-image device is illustrated. In this embodiment, there are two guiding view-limiting areas 62A,B. Outside the first guiding view- limiting area 62A, a full guiding synthetic image is seen. When the viewing direction corresponds to a point between the first guiding view- limiting area 62A and the second guiding view-limiting area 62B, a first change in the guiding synthetic image is seen. When the viewing direction corresponds to the first position 60, the effect synthetic image has appeared together with a second change of the guiding synthetic image. This embodiment can for instance be used for creating the situation described in Fig. 18.

This approach can be further developed into the use of animation features in the guiding synthetic image, c.f. e.g. Figs. 16A-B. In Fig. 21H, the guiding synthetic image is associated with five guiding view-limiting areas 62A-E, giving a gradual change of the guiding synthetic image when approaching the requested viewing direction.

In the above presented embodiments, hexagonal cells have been used as examples. This might be a natural choice in many cases, in particular if close- packed focusing element arrays are used. However, depending on the application, all kinds of cell geometries may be used. As non-limiting examples, Fig. 211 illustrates a rhombic cell C and Fig. 21J illustrates a rectangular cell C, which can be used together with all different approaches presented above.

In an embodiment, where the ratio between the periodicity of image objects of one part image of the guiding synthetic image and the cell periodicity is equal to the ratio between the cell periodicity and the periodicity of image objects of another part image of the guiding synthetic image, the part images appear at a height and depth, respectively that are separated from the plane of the synthetic-image device with a same distance, as e.g. in the Fig. 11. In other words, a ratio of a periodicity of a first subset of a first set of image objects and a focusing array periodicity of the synthetic-image device is equal to a ratio of the focusing array periodicity and a periodicity of a second subset of the first set of image objects. When the synthetic-image device is tilted, the different part images appear to move in opposite directions, and will overlap again when the point on which the focusing elements target has moved half a cell period. This results in that there are four first positions 60 in each cell and therefore also four effect view-limiting areas in each cell, as illustrated in Fig. 22A.

However, in an approach similar to the one illustrated in Figs 13A-B, it is necessary for the depicted point in the cell to move an entire cell period before a next coinciding guiding synthetic image can be achieved. In such a system, only one first position 60 is present in every cell C, as illustrated in Fig. 22B.

Moreover, in an approach similar to the one illustrated in Figs 12A-B, the coinciding of the part images of the guiding synthetic image occurs at different viewing directions for different parts of the synthetic-image device. As illustrated in Fig. 22C, the effect view-limiting areas 63 may therefore also be positioned in different areas, depending on where on the synthetic-image device 1 the cell is situated. This shifting in position within the cell may be provided in a gradual manner over the surface or in steps, giving part constant effect view-limiting area 63 positions in different parts of the entire area of the synthetic-image device 1. The present approach, having a guiding synthetic image and an effect synthetic image makes the aligning of focusing elements and cells less sensitive. In Fig. 23A, a situation where a cell C is perfectly aligned with a focusing element 24 is illustrated from the top in the upper part of the figure, and in a side cross-sectional view in the lower part of the figure. The first position 60 is in this example designed to be positioned in the centre of the cell C. The effect synthetic image will in such a situation be seen when the synthetic-image device is viewed in a perpendicular direction with reference to the main surface.

However, if the alignment is not perfect, such as illustrated by Fig. 23B, the usability will not be considerably deteriorated. Even if the cell C and focusing element are displaced, there is a well-defined direction in which the first position 60 in the cell can be viewed through the focusing element 24. Since the guiding synthetic image tells the viewer how to reach to this viewing direction, the switch of the effect synthetic image will easily be found, regardless of any misalignment.

In Fig. 24, a flow diagram is shown, illustrating steps of an embodiment of a method for producing a synthetic-image device. The process starts in step 300. In step 310, a numerical representation of a first set of image objects is created. The image objects are arranged in image cells for giving rise to at least a, first, guiding synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through a focusing element array. The guiding synthetic image presents a first part image and a second part image, changing a relative geometrical relation to each other upon changing a view direction. A predetermined relative geometrical relation between the first part image and the second part image corresponds to image objects positioned at a first position in each image cell. In step 320, an effect view-limiting area is defined. The effect view-limiting area comprises the first position and a margin. In step 320, a numerical representation of a second set of image objects is created. The second set of image objects is arranged for giving rise to at least a, second, effect synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through the focusing element array. In step 340, the numerical representation of the second set of image objects is modified within or outside the effect view- limiting area to give rise to an abrupt change of appearance of the effect synthetic image. In step 350, the numerical representation of the first set of image objects and the numerical representation of the second set of image object are merged into a numerical representation of composite image objects. In step 360 an image layer is formed according to the numerical representation of composite image objects. In step 370, a focusing element array is formed. The image layer is arranged in a vicinity of a focal distance of focusing elements of the focusing element array.

In one embodiment, the first part image and the second part image are presented at different apparent depth or height.

In one embodiment, the method comprises the further step 321, in which a guiding view-limiting area, comprising the first position and a margin is defined. In step 341, the numerical representation of the first set of image objects is modified within the guiding view-limiting area before the step 350 of merging.

In a further embodiment, the step 341 of modifying the numerical representation of the first set of image objects comprises modifying the numerical representation to correspond to a removal of parts of the first set of image objects.

In a further embodiment, the removal of parts of the first set of image objects comprises removal of at least one of the first part image and the second part image. In one embodiment, the modifying 341 of the numerical representation of the first set of image objects is performed for cells within only a part of a total image area of the synthetic-image device.

In one embodiment, the modifying 340 of the numerical representation of the second set of image objects is performed for cells within only a part of the total image area of the synthetic-image device.

In one embodiment, the composite image objects within the effect view-limiting area gives rise to a combined three-dimensional synthetic image.

In one embodiment, the first set of image objects comprises two subsets of image objects, each corresponding to a pattern layer. The pattern layers have differing periodicity, wherein the predetermined relative geometrical relation corresponds to a predetermined overlap relation.

The production method thus gives a synthetic-image device having an image layer, formed according to a numerical representation of composite image objects, and a focusing element array. The image layer is arranged in a vicinity of a focal distance of focusing elements of the focusing element array.

The numerical representation of the composite image objects is a merging of a numerical representation of a first set of image objects and a numerical representation of a second set of image object. The first set of image objects are arranged in image cells for giving rise to at least a, first, guiding synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through a focusing element array. The guiding synthetic image presents a first part image and a second part image, changing a relative geometrical relation to each other upon changing a view direction. A predetermined relative geometrical relation between the first part image and said second part image corresponds to image objects positioned at a first position in each said image cell. An effect view-limiting area comprises the first position and a margin. The second set of image objects is arranged for giving rise to at least a, second, effect synthetic image when being placed in a vicinity of a focal distance of focusing elements and viewed through said focusing element array. The numerical representation of the second set of image objects is modified within or outside the effect view-limiting area to give rise to an abrupt change of appearance of the effect synthetic image before the merging is performed.

As mentioned earlier, animation techniques can by advantage be used in connection with the guiding synthetic image and/ or the effect synthetic image. Here below, different animation aspects are discussed, which may be used in connection with the guiding synthetic image and/ or the effect synthetic image. However, it is also possible to use these animation aspects in other types of applications as well, not connected to any cooperation between guiding and effect synthetic images.

When using different kinds of integral image techniques, there is no limitation to repeated patterns or to two-dimensional images. Furthermore, it is also possible to change the appearance of the synthetic image for different viewing directions. This opens up for presenting different kinds of animations or morphing effects. A limitation of prior art integral image techniques is that the animations and morphing effects are limited to one single cell. When the viewing direction changes, the point in the cell from which the visual information is collected also changes. When that point reaches the cell border and continues into a neighboring cell, the typical result is a sudden "flip" of the synthetic image into the synthetic image of the neighboring cell.

There are, however, arrangements that will at least partly remove such unwanted flips.

Cells, used for defining integral synthetic image, have typically a same period as the array of focusing elements with which they are supposed to interact. However, the shape and relative positioning may differ. Fig. 25A illustrates schematically one embodiment of the relation between an array of focusing elements 24 and an array of cells C for image object. In this embodiment, the focusing elements 24 are spherical lenses. The cells C have instead been given a rectangular shape. The image objects being present within the cell C is associated with one of the focusing elements 24 and are supposed to be mainly viewed through that focusing element. However, if there is a significant misalignment or if the synthetic-image device is viewed in a relatively shallow angle, the image objects may also be viewed through a neighboring focusing element. The switch of the viewed point between two neighboring cells often results in a sudden "flip" of the synthetic image.

In Fig. 25B, another embodiment of the relation between an array of focusing elements 24 and an array of cells C for image object is illustrated. In this embodiment, the cells are rectangular and an aspect ratio of the cells C is higher than in previous embodiment, with a longer extension in the lateral direction, as illustrated. This results in that the cells comprises points that physically may be situated below a neighboring focusing element instead of the associated one. Similarly, there are points physically situated below the associated focusing element that instead belongs to a neighboring cell. In such an approach, the "flips" of the synthetic image occur less frequent in viewing angle if the synthetic-image device is tilted sideways than if the synthetic- image device is tilted up-and-down.

Fig. 25C illustrates an embodiment of the relation between an array of focusing elements 24 and an array of cells C for image object, where the cells have a regular hexagonal shape. In this embodiment, however, there is a misalignment between the focusing element array and the cells C. This means that the image objects being situated in the middle of the cell will be seen by a viewer in a non-perpendicular angle with respect to the main surface of the synthetic-image device.

In Fig. 26, a number of cells C of an embodiment of a synthetic image device is illustrated. The area of the cell is in this embodiment divided into five channels 80A-80E. Within each channel, image objects corresponding to a certain integral synthetic image are provided. In other words, a channel is a part of a cell that comprises image objects used for creating a same synthetic image. The integral synthetic images associated with the different channels 80A-80E differ. The differences can be large, and in such cases, sudden abrupt changes of the viewed synthetic image are perceived by a viewer if the synthetic -image device is tilted. The differences may alternatively be small, at least relative to the neighboring channels. This opens up for synthetic images that are morphing upon tilting the synthetic-image device, or other kinds of animation effects.

In Fig. 26, three examples of synthetic images created by image objects of the different channels are illustrated. The image objects within channel 80A gives rise to a pattern of star-like objects 81A. The image objects within channel 80C gives rise to a pattern of squares 8 IB. The image objects within channel

80E gives rise to a pattern of circles 81C. When tilting the synthetic -image device, a gradual change from the star-like objects 81A to the circles 81C will be perceived by a viewer. Furthermore, when the point from which the focusing element collects its information crosses the cell border and enters into a neighboring cell, the same image objects are present also there, which means that there will be no "flip" in the synthetic image.

It might be difficult to design image objects that give such "seamless" synthetic images in all direction, since there are many relationships within the image that has to be fulfilled. However, since the natural way of tilting a synthetic- image device is either sideward or up-ad-down, and not in any intermediate directions, it is often sufficient to arrange for a continuous synthetic image behavior in only one direction. In Fig. 27 A, a few cells C of another embodiment are schematically illustrated.

In this embodiment, the cell is divided into parallel stripe- shaped channels 80A-80I. Each channel 80A-80I comprises image objects that in cooperation with image objects of other cells, when viewed through an array of focusing element, gives rise to a synthetic image. The synthetic image associated with one channel differs from the synthetic image associated with a neighboring channel in the same cell C. The associated synthetic images of the present embodiment are schematically illustrated in a row below the cells.

Assume that the synthetic-image device 1 with the cells are viewed in a direction where the focusing elements select a point 84 in each cell C from where image information is collected. Together, the image objects at these points 84 give rise to a synthetic image showing a square 82A. This is illustrated in the lower left part of Fig. 27B. If the synthetic-image device 1 is tilted sideward to the right, the point from which the focusing element collects information moves to the right, as illustrated by the arrow 83A in Fig. 27A. The resulting synthetic image at the synthetic-image device 1 shows a square with a rounded-off end 82B. This is illustrated in the lower middle part of Fig. 27B. A further tilt of the synthetic-image device 1 moves the point according to arrow 83B in Fig. 27A and a circle 82C appears as the synthetic image. This is illustrated in the lower right part of Fig. 27B. During the sideward tilting the synthetic image presents a gradual change or a morphing of the image. Even if the sideward tilting brings the point 84 outside the intended cell and into a neighboring cell at the side, the smooth morphing will still be present.

However, if the synthetic-image device 1, from the situation when a square 82A is shown, will be tilted upwards, the point 84 will also move upwards according to arrow 83C and will therefore enter into a neighboring cell above the original cell. This causes a sudden "flip" of the square 82A into a circle 82C, as illustrated in the upper left part of Fig. 27B.

As anyone skilled in the art understands, the synthetic-image device 1 can be rotated in any direction, e.g. so that the morphing direction corresponds to an up-and-down tilting, while the flip direction is to the side.

Figs. 27C and 27D illustrate another similar embodiment, where the synthetic images are three-dimensional bodies. A cube 82D turns via a partly rounded- off cube 82 E into a sphere 82 F in a morphing manner when the synthetic- image device 1 is tilted sideward. However, a sudden flip from the cube 82D to the sphere 82F occurs when tilting the synthetic-image device 1 upwards.

When using three-dimensional synthetic images, it is a particular advantage to have the morphing direction as a sideward tilting. Since the three- dimensional perception is caused by the distance between the eyes of the viewer, a gradual change of the synthetic image in the same direction, i.e. the direction between the eyes, makes it easier to perceive a realistic three- dimensional impression even during a morphing process.

As one example, a synthetic -image device has an image layer, having image objects provided in a plurality of cells, and a focusing element array, having a plurality of focusing elements. Each cell is associated with a respective focusing element. The image layer is arranged in a vicinity of a focal distance of the focusing elements.

Each cell is divided into a plurality of stripe- shaped channels. The image objects of each channel are, together with image objects of the corresponding channel of other cells, when viewed through the focusing element array, forming a synthetic image. The synthetic image associated with one channel differs from the synthetic image associated with a neighboring channel in the same cell C. Preferably, the stripe-shaped channels are straight and parallel.

Preferably, the synthetic image associated with the channel closest to one end of the cell, in a direction across the stripe-shaped channels, is the same or at least almost the same as the synthetic image associated with the channel closest to the opposite end of the cell. This gives a flip-free transition over the cell border.

The possible variations of objects are endless. Fig. 28 schematically illustrate a series of arrows, which are associated with stripe-like channels, in analogy with the earlier figures. In one viewing direction an arrow directed to the right 82G is seen. By tilting the synthetic-image device 1 sideward, the arrow "rotates" e.g. to the position pointing upwards 82H, and also all the way to the left directed arrow 821. A tilt in the vertical direction instead gives a flip directly into the left directed arrow 821.

There are many possibilities for using morphing to achieve an eye-catching effect. In Fig. 29A, a series of synthetic images of a synthetic -image device 1 is illustrated. Typically, the different images are reached by tilting the synthetic -image device 1 in a direction across the stripe-like channels as discussed before. In a first direction, no synthetic image at all can be seen. By tilting the synthetic-image device 1 slightly, a pattern of dots appear. By a further tilting, the dots develop into small stars, which upon further tilting grows until the tips meet. A pattern of lines, creating triangles in two directions is thereby created.

In an alternative embodiment, the images in Fig. 29A may have items at different apparent heights /depths. For instance, every second star could be provided at another height than the others. This will then result in a relative displacement upon tilting between the different heights.

Yet another similar embodiment is illustrated in Fig. 29B. Here, two sets of synthetic images are provided, which are morphing in opposite ways. When one set starts from an empty pattern, via dots and stars into a line pattern, the other set instead starts from the line pattern, via stars and dots into an empty pattern.

Fig. 30 illustrates an embodiment of an animation, where a combination of two cooperating patterns is utilized. A pattern of circles 85 first appear. The circles are expanding and morphing into windows 86. Through the windows 86, a patterns of letters "A" 87 is seen at an apparent depth below the surface. The windows 86 expand further and eventually, the pattern of "A" 87 covers the entire image. This scenario is also achieved by using different channel within the cells. Preferably, stripe-shaped channels are used. Within each channel, image objects contribute in building up the combination of images. To that end, image objects being associated with the pattern of "A" are removed anywhere outside the image objects being associated with the window. It should be noted here that the image that appears in the windows can in different embodiments be of any kind; two-dimensional or three-dimensional, moire type or integral synthetic image. The shape of the "opening windows" may of course also be different in alternative embodiments.

It should be noted that stripe- shaped channels can be used together with any type of cell shapes. However, it is preferred if the stripe-shaped channels are positioned essentially parallel with one of the main cell border sections.

Fig. 31A illustrates a schematic illustration of a synthetic-image device 1 presenting a combination of a two-dimensional and three-dimensional synthetic image. A pattern of two-dimensional hexagons 88 covers the most of the surface. One of the hexagons, e.g. the one that at each occasion seems to be situated right in front of the viewer's eyes, is replaced or completed to form a hexagonal- shaped cup 89 having an apparent extension below the surface. The three-dimensional hexagonal- shaped cup 89 has a limited field of view that is determined by the associated hexagon 88. The top of the three- dimensional hexagonal- shaped cup 89 coincides with the two-dimensional hexagons 88, laterally as well as in apparent height/ depth.

If the synthetic-image device 1 is tilted, the cup will close, and another hexagon will instead open to reveal another cup, such as in Fig. 3 IB.

In a further embodiment, this can be further combined with yet another synthetic image, as illustrated in Fig. 31C. The synthetic image in shape of a hand 90 has an apparent height above the surface. By tilting the synthetic- image device 1 so that the hand 90 comes above a certain hexagon, the hexagon opens and reveals the cup below. At the same time, the hand disappears. The effect then looks as if the hand removes a lid above each hexagon. The hexagon pattern 88 and the hand 90 may be seen as a composed guiding synthetic image and the three-dimensional hexagonal-shaped cup 89 then constitutes an effect synthetic image.

The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims

1. A synthetic-image device (1), comprising

an image layer ( 10); and

a focusing element array (20);

said image layer ( 10) being arranged in a vicinity of a focal distance (f) of focusing elements (22) of said focusing element array (20);

wherein composite image objects (36) of said image layer ( 10) being a merging of at least a first set (31) of image objects ( 12) and a second set (32) of image objects ( 12);

said first set (31) of image objects ( 12) being arranged for giving rise to at least a, first, guiding synthetic image (41) when being placed in a vicinity of a focal distance (f) of focusing elements (22) and viewed through said focusing element array (20);

said guiding synthetic image (41), when being moved to be viewed in a direction (d) out of a set (D) of discrete directions, presenting a first part image (46) and a second part image (47) moving towards a predetermined relative geometrical relation with respect to each other;

said second set (32) of image objects ( 12) being arranged for giving rise to at least a second, effect synthetic image (42), within a limited effect field of view (52) of said effect synthetic image (42), when being placed in a vicinity of a focal distance (f) of focusing elements (22) and viewed through said focusing element array (20);

said limited effect field-of-view (52) of said effect synthetic image (42) being selected as one of:

including viewing directions only in an angular vicinity of any of said directions (d) of said set (D) of discrete directions; and

excluding viewing directions only in an angular vicinity of any of said directions (d) of said set (D) of discrete directions.

2. The synthetic-image device according to claim 1 , characterized in that said first part image (46) and said second part image (47) are presented at different apparent depth or height.

3. The synthetic-image device according to claim 1 or 2, characterized in that said guiding synthetic image (41), when being viewed in said direction (d), would have presented said first part image (46) and said second part image (47) in said predetermined relative geometrical relation with respect to each other if a limited guiding field-of-view (51) , if any, of at least part of said guiding synthetic image (41) would have been disregarded.

4. The synthetic-image device according to claim 3, characterized in that said guiding field-of-view (51) is valid only for a part of said guiding synthetic image (41).

5. The synthetic-image device according to claim 4, characterized in that said part of said guiding synthetic image (41) for which said guiding field-of- view (51) is valid comprises said first part image (46).

6. The synthetic-image device according to any of the claims 3 to 5, characterized in that said guiding field-of-view (51) is valid only for a part (PI) of a total image area (A) of said synthetic-image device (10).

7. The synthetic-image device according to any of the claims 1 to 6, characterized in that said effect synthetic image (42) is restricted to be seen only in selected parts of said total image area (A) of said sy thetic-image device (10).

8. The synthetic -image device according to any of the claims 1 to 7, characterized in that said guiding synthetic image (41) and said effect synthetic image (42) cooperates to form a combined synthetic image (45) within said effect field-of-view (52).

9. The synthetic-image device according to any of the claims 1 to 8, characterized in that said guiding synthetic image (41) comprises two pattern layers at different apparent height and/ or depth, wherein said predetermined relative geometrical relation to each other corresponds to a predetermined overlap relation.

10. The synthetic-image device according to claim 9, characterized in that an upper pattern layer of said two pattern layers has an apparent height that in size is in a vicinity of an apparent depth of a lower pattern layer of said two patterns layers.

1 1. The synthetic-image device according to claim 10, characterized in that said upper pattern layer and said lower pattern layer have a same periodicity.

12. The synthetic -image device according to claim 10, characterized in that said upper pattern layer and said lower pattern layer have different periodicities.

13. The synthetic-image device according to any of the claims 1 to 12, characterized in that said effect synthetic image (42) replaces said first part image (46) of said guiding synthetic image (41) within said effect field-of-view (52).

14. The synthetic-image device according to any of the claims 1 to 13, characterized in that said guiding field-of-view (51) is a two-dimensional field-of-view.

15. The synthetic-image device according to any of the claims 1 to 13, characterized in that said guiding field-of-view (51) is a one-dimensional field-of-view.

16. A method for producing a synthetic -image device, comprising the steps of:

- creating (310) a numerical representation of a first set of image objects (17A, 17B) being arranged in image cells (C) for giving rise to at least a, first, guiding synthetic image (41) when being placed in a vicinity of a focal distance (f) of focusing elements (22) and viewed through a focusing element array (20); said guiding synthetic image (41), presenting a first part image (46) and a second part image (47), changing a relative geometrical relation to each other upon changing a view direction;

wherein a predetermined relative geometrical relation between said first part image (46) and said second part image (47) corresponds to image objects ( 12) positioned at a first position (60) in each said image cell (C);

- defining (320) an effect view-limiting area (63) comprising said first position (60) and a margin;

- creating (330) a numerical representation of a second set of image objects (17C) being arranged for giving rise to at least a, second, effect synthetic image (42) when being placed in a vicinity of a focal distance (f) of focusing elements (22) and viewed through said focusing element array (20);

- modifying (340) said numerical representation of said second set of image objects ( 17C) within or outside said effect view-limiting area (63) to give rise to an abrupt change of appearance of said effect synthetic image (42);

- merging (350) said numerical representation of said first set of image objects (17A, 17B) and said numerical representation of said second set of image object (17C) into a numerical representation of composite image objects

(30);

- forming (360) an image layer (10) according to said numerical representation of composite image objects (30); and

- forming (370) a focusing element array (20);

said image layer (10) being arranged in a vicinity of a focal distance (f) of focusing elements (22) of said focusing element array (20).

17. The method according to claim 16, characterized in that said first part image (46) and said second part image (47) are presented at different apparent depth or height.

18. The method according to claim 16 or 17, characterized by the further step of: - defining (321) a guiding view-limiting area (62) comprising said first position (60) and a margin;

- modifying (341) said numerical representation of said first set of image objects (17A, 17B) within said guiding view-limiting area (62) before said step of merging (350).

19. The method according to claim 18, characterized in that said step of modifying (341) said numerical representation of said first set of image objects (17A, 17B) comprises modifying said numerical representation to correspond to a removal of parts of said first set of image objects (7A, 17B).

20. The method according to claim 19, characterized in that said removal of parts of said first set of image objects (7A, 17B) comprises removal of said first part image (46).

21. The method according to claim 19 or 20, characterized in that said removal of parts of said first set of image objects (7A, 17B) comprises removal of said second part image (47). 22. The method according to any of the claims 18 to 21, characterized in that said modifying (341) said numerical representation of said first set of image objects (7A, 17B) is performed for cells within only a part (P) of a total image area (A) of said synthetic-image device (10). 23. The method according to any of the claims 16 to 22, characterized in that said modifying (340) said numerical representation of said second set of image objects (17C) is performed for cells within only a part (P) of said total image area (A) of said synthetic-image device (10).

24. The method according to any of the claims 16 to 23, characterized in that said composite image objects (30) within said effect view-limiting area (63) gives rise to a combined three-dimensional synthetic image.

25. The method according to any of the claims 16 to 24, characterized in that said first set of image objects (17A, 17B) comprises two subsets of image objects, each corresponding to a pattern layer, said pattern layers having differing periodicity, wherein said predetermined relative geometrical relation corresponds to a predetermined overlap relation.

26. The method according to claim 25, characterized in that a ratio of a periodicity of said first subset and a focusing array periodicity of said synthetic-image device (10) is equal to a ration of said focusing array periodicity and a periodicity of said second subset.

27. The method according to any of the claims 16 to 26, characterized in that at least one of said effect view-limiting area (63) and said guiding view- limiting area (62) is limited in two dimensions.

28. The method according to any of the claims 16 to 26, characterized in that at least one of said effect view-limiting area (63) and said guiding view- limiting area (62) is limited in one dimension.

29. A method for authentication of an object having a synthetic-image device provided at a surface of said object, said method comprising

- observing a, first, guiding synthetic image (41) of said synthetic-image device in a viewing direction, said guiding synthetic image (41) having a first part image (46) and a second part image (47) at different apparent depth or height;

- moving said synthetic-image device to change said viewing direction to cause said first part image (46) and said second part image to move towards a predetermined relative geometrical relation with respect to each other;

- observing an abrupt change in appearance of a second, effect synthetic image (42) when moving towards said predetermined relative geometrical relation, as sign of authenticity.