METHOD FOR PRODUCING A SAFETY HOLOGRAM AND SAFETY HOLOGRAM

Description

[0001] The invention relates to a method and a device for producing security holograms, such as those used as a security element in valuable or security documents.

[0002] Valuable and / or security items possess security features to verify their authenticity and integrity. A security feature is any characteristic suitable for verifying the authenticity of the item bearing that security feature. A security element is any physical unit that exhibits such a security feature. In particular, security documents such as passports, driver's licenses, visas, etc., or valuable documents such as bank cards, checks, tokens, etc., are security elements, as are semi-finished products such as hologram films for insertion into security documents, etc.

[0003] Checking a security feature is called verification. A group of security features is designed for optical verification. A subset of security features utilizes the properties of holograms.

[0004] For example, passports and identity cards issued by the Federal Republic of Germany use volumetric reflection holograms that store a passport photo and personal data, such as names and the ID number, which are also printed on the document. Under appropriate illumination with reconstruction light of a suitable wavelength and viewed from a specific angle during verification, the personal data is perceptible. These holograms are produced using a contact printing process. A master hologram, which might be a reflection hologram from a ground glass screen, is individually exposed into the volumetric reflection hologram later used on the security document via a spatial light modulator during contact printing. EP 0 896 260 A2 describes the production of such a hologram master.It is also mentioned that when copying the master hologram, exposure can be carried out from different aspect angles in order to achieve a stereo effect.

[0005] US2017 / 090421 A1 describes an image recording device comprising a laser beam source that emits a laser beam, a division unit that splits the laser beam emitted by the laser beam source into two laser beams, a display device that shows images over a display area divided into segments, a display controller that controls the display of the display device so that images are displayed on the segments of the display area to form a holographic stereogram and that one of the laser beams is modulated by the images displayed on the display device to become object beams, an optical system that maps the object beams onto a hologram recording medium so that the object beams are superimposed, and an irradiation unit that irradiates the hologram recording medium alongside the object beams with the other laser beam split by the division unit as a reference beam.

[0006] It is also known that holography makes it possible to directly project holograms of real three-dimensional objects onto film, allowing for a three-dimensional view of the object during reconstruction. If a user changes their viewing position, they see a different view of the three-dimensional object during reconstruction. However, producing such three-dimensional holograms is very complex and therefore only of limited use as a security element. In particular, it is difficult to produce individual holograms that provide a three-dimensional impression during reconstruction and offer different views of the object from different angles when viewed.

[0007] The invention is therefore based on the technical problem of creating an improved method for manufacturing holographic security elements and improved security elements that enable such three-dimensional detectability in the reconstruction of a security hologram.

[0008] The invention is solved by a method with the features of claim 1 and a security hologram with the features of claim 7. Advantageous embodiments of the invention are set forth in the dependent claims.

[0009] The invention is based on the idea of ​​creating monoscopic images, i.e., images that themselves contain no depth information, from different directions and holographically exposing the various monoscopic images onto a recording material under different exposure directions. The exposure is carried out such that the exposure directions all lie in one plane and, at least in pairs, include a standard convergence angle for human viewing. This means that during reconstruction, individual monoscopic reconstructed images are reconstructed in reconstruction directions that correspond to the exposure directions but are oriented in opposite directions. The reconstruction directions corresponding to the exposure directions are chosen such that...that a human observer, under at least one viewing geometry, perceives one of the two reconstructed images with one eye and the other with the other eye, so that the human brain reconstructs a three-dimensional object from this. The standard convergence angle can be calculated from a standard distance, which corresponds to a target distance from which the hologram should be viewed during reconstruction, and a standard interpupillary distance, which can be determined based on an empirically established mean value for adults and is, for example, in the range between 5.2 cm and 7.8 cm, averaging 6.5 cm for men and 6.2 cm for women. In case of doubt, a value of 6 cm is used as the standard interpupillary distance.A distance of 5 cm is assumed. The target viewing distance for the reconstruction, and thus the standard distance, can be defined for a security hologram and is generally in the range of 30 cm to 50 cm. In particular, a method for producing a security hologram is created, which comprises the following steps: providing several, at least three, monoscopic images of a three-dimensional object from different detection directions, wherein each of the several images is assigned to exactly one of the different detection directions; providing holographic recording material; generating coherent laser radiation and splitting the laser radiation into a reference component and at least one object component, and guiding the reference component and the at least one object component.such that the reference component and the at least one object component illuminate the recording material from opposite sides and interfere within the recording material, the multiple images being projected onto the recording material from different exposure directions by means of the at least one object component, each of the multiple images being assigned to exactly one of the different exposure directions, the exposure directions all lying in one plane and at least pairwise enclosing a standard convergence angle for human viewing. In this way, a security hologram is obtained, which is designed as a multiplex volume reflection hologram in a hologram layer, into which several, at least three, monoscopic images of the same three-dimensional object are exposed, depicting the object from different detection directions.When reference light is shone onto the hologram layer, the multiple images are reconstructed from different reconstruction directions relative to the hologram layer. Each of the multiple images is precisely and uniquely assigned to one of the different reconstruction directions, all of which lie in a single plane and, at least in pairs, include a standard convergence angle for human viewing. This creates a security element in the form of a security hologram, which reproduces the depicted object three-dimensionally for human perception from different directions. A high degree of spatial depth can be achieved from significantly different viewing directions and / or very different perspectives of the three-dimensional object. Furthermore, because the exposure occurs directly into the recording material,The process also allows for the exposure of various three-dimensional objects in large series. This makes it possible to create a multitude of security holograms in the form of multiplex volume reflection holograms, each of which is individually distinct from the other security holograms in the batch.

[0010] When reference light is applied from one direction, at least two images are always reconstructed, whose reconstruction directions include the standard convergence angle for a human observer.

[0011] Overall, the viewing angle of an object can be significantly expanded compared to a simple volume hologram, which is recorded as a 3D volume hologram. The monoscopic images, which capture an object from different directions, can be produced easily. This makes the manufacturing process suitable for mass production.

[0012] According to the invention, the angle between two viewing directions is greater than the angle between the viewing directions of the corresponding stereoscopic views. A change in the viewing position or a tilting of the security hologram by an angle causes the object in the captured stereoscopic views to rotate by a larger angle.

[0013] According to the invention, small changes in the exposure direction correspond to larger changes in the detection direction. This makes it possible, for example, to associate a change in the detection direction of 180° with a change in the exposure direction of 45°. This means that smaller changes in the viewing direction of the security hologram correspond to larger changes in the detection directions of the object, thus enabling, for example, a 360° view around the three-dimensional object within an angle range of + / - 45° relative to the perpendicular of the security hologram. This opens up new possibilities for storing information about a three-dimensional object in the security hologram. Nevertheless, the human observer always perceives the three-dimensional object as a three-dimensional object with depth perception.

[0014] In unclaimed embodiments, the exposure directions correspond to the detection directions of the monoscopic images. This means that the angles of the detection directions in a plane enclose angles with each other that are identical to the angles of the exposure directions that these enclose in a plane. A movement of the human viewer relative to the generated security hologram results in the perception of the object, when the viewing direction changes, corresponding to the change in perception that would occur with a corresponding change in the viewing direction, as would be the case with a real object.

[0015] At least when the detection directions correspond to the exposure directions, in an unclaimed embodiment it is possible to select the detection directions such that for each detection direction there exists a further detection direction that together encompass the standard convergence angle of the eyes of a human observer. This results in, for example, a tilting of the security hologram or movement of the observer about an axis perpendicular to the plane in which the different exposure directions lie, with an image being perceived once with the left eye together with another image perceived with the right eye, and once with the right eye together with yet another image, whereby in each case a three-dimensional image is constructed in the brain by the human observer.

[0016] Preferably, the pairwise reconstructed monoscopic images comprise monoscopic images for three different stereo views of the object from different perspectives. Each perspective includes two acquisition directions, representing the views of the right and left eyes of a human observer. The monoscopic images can thus be captured, for example, using a camera.

[0017] Alternatively, the different monoscopic images of a three-dimensional object for the various acquisition directions can also be calculated. Regardless of whether the monoscopic image was captured with a camera or calculated, the corresponding direction from which the three-dimensional object is shown in the image is referred to here as the acquisition direction.

[0018] In a preferred embodiment, for at least one of the exposure directions, there are two further exposure directions, each encompassing a standard convergence angle for human viewing. In such an embodiment, where each exposure direction is assigned exactly one image and a corresponding reconstruction direction, the reconstructed image associated with the at least one reconstruction direction (exposure direction) is, for example, first perceived by the viewer's left eye. The right eye then perceives a reconstructed image associated with one of the two further reconstruction directions (exposure directions). From these jointly perceived images, a three-dimensional image of the three-dimensional object is generated in the viewer's mind.The viewing direction relative to the security hologram is then changed, so that the reconstructed image associated with at least one of the reconstruction directions (exposure direction) is now perceived by the viewer's right eye. The left eye then perceives the reconstructed image associated with the other of the two remaining reconstruction directions (exposure directions). Again, the viewer uses the jointly perceived images to create a three-dimensional image of the three-dimensional object, but from a different viewing angle.

[0019] This allows for a continuous transition when viewing the object. One method involves successively recording the images, including the object portion, under the different exposure directions onto the recording material. A particularly preferred and faster embodiment involves dividing the object portion into as many parts as there are monoscopic images exposed into the security hologram under the different exposure directions, with the exposure of the monoscopic images occurring simultaneously. In the alternative method, the monoscopic images are exposed into the recording material at staggered intervals.

[0020] In one embodiment, the reference light component is identical for all object components and thus for all images exposed into the hologram under the different exposure directions, i.e., it is emitted from the same direction.

[0021] In the reconstruction of the resulting multiplex volume reflection hologram, the reconstruction light is shone from a direction diametrically opposite to the direction of the reference light used in the exposure. All monoscopically reconstructed images are reconstructed. If the viewer moves in the plane of the reconstruction directions, they can perceive the different stereoscopic views of the three-dimensional object from the different viewing directions.

[0022] In another embodiment, for each exposure direction, a reference component is illuminated such that its projection into the plane spanned by the exposure directions is diametrically opposite to that exposure direction, or forms an angle with the exposure direction equal to half the standard convergence angle. This means that for each exposure direction, the projection of the reference light, or the projection of a component of the reference light, into the plane of the exposure directions is diametrically opposite, or opposite to the viewing direction to which the exposure direction / reconstruction direction and its associated image or reconstructed image belong.

[0023] When the reference light is shone onto the volume reflection hologram from one direction during reconstruction, at least two of the stored images are reconstructed, allowing a human observer to create a stereoscopic image of the three-dimensional object. If the volume reflection hologram, or more precisely the recording material in which the volume reflection hologram is stored, is then rotated about an axis perpendicular to the plane of the reconstruction directions and preferably passing through the volume reflection hologram, other stored images are reconstructed, enabling the human observer to create another stereoscopic image of the three-dimensional object without having to change their position.

[0024] Since, in the reconstruction of a volume hologram, viewing and illumination of the reconstruction light in the case of a volume reflection hologram occur from the same side of the volume reflection hologram or the recording material in which the volume reflection hologram is stored, it is preferred that the reference light, or each reference light component, has a non-zero elevation angle relative to the plane spanned by the illumination directions. When projecting / imaging an image onto the hologram, the direction that coincides with a central ray of the projection / image is considered the illumination direction. The elevation angle is preferably greater than 25°, preferably in the range of 35° to 65°, and most preferably in the range of 45° ± 5°.

[0025] The plane of the exposure directions is preferably oriented perpendicular to the plane of the recording material.

[0026] Preferably, the standard convergence angle is designed for a target viewing distance between 30 cm and 50 cm for a standard interpupillary distance of 6.5 cm.

[0027] The security hologram, designed as a multiplex volume reflection hologram, can be created by storing each of the multiple images in a dedicated area, preferably a strip-shaped area, of the recording material. This allows the optimal diffraction efficiency of the holographic recording material to be utilized for each image, resulting in high-contrast images. If the areas are too narrow or too small, this can impair the viewing perception of the stereoscopic images.

[0028] Much more difficult to reproduce are embodiments in which the multiple images are exposed to the same area of ​​the recording material. The available diffraction efficiency must be "divided" among the multiple images. Overall, the stereoscopic images have slightly lower contrast. However, the negative viewing sensations caused by streaks or small flat areas, which can occur in the previously described embodiment, do not arise. Overall, the stereoscopic images appear somewhat less visible. Furthermore, the exposure of all the multiple images preferably occurs simultaneously, which significantly speeds up the manufacturing process. Overexposures due to temporal fluctuations in the intensity of the exposure light are minimized. However, staggered exposures are also possible.

[0029] Some embodiments provide for the holographic recording material to be divided into different planar areas, particularly strips. At least two of the multiple images are stored in each planar area, for example, strips. This allows a greater number of monoscopic images to be stored with the same number of areas, for example, strips, into which the recording material is divided. The number of multiple images can thus be increased while maintaining the same number of planar areas. Alternatively, the planar areas can be made larger while maintaining the same number of multiple images. This reduces the negative viewing sensations caused by small planar areas or strips.Furthermore, if, for example, at least two of the multiple images are always exposed simultaneously in a flat area, such as strips, it can be ensured that both partial images are optimally exposed for the subsequent perception of the stereoscopic image. Exposure intensity fluctuations between the two monoscopic images that comprise a stereoscopic image cannot occur in this case.

[0030] The invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 a schematic representation for capturing monoscopic images of an object; Fig. 2 a schematic representation to explain the exposure of various monoscopic images into a hologram; Fig. 3 another schematic representation to explain the exposure of monoscopic images into a hologram; Fig. 4 a schematic representation of the reconstruction of a hologram; and Fig. 5 another schematic representation of the reconstruction of a hologram.

[0031] In Fig. 1 The diagram schematically illustrates how five different monoscopic images 12-1 to 12-6 of an object are acquired. The object 5 forms the center of a circle 25 with radius R. If a human observer views the object 5 while standing on the circle 25, for example, under a viewing direction 11-1, then the right eye 31-1 and the left eye 31-2 perceive the object under slightly different viewing directions 10-1 and 10-2, respectively. The viewing directions include a so-called convergence angle α. Based on the monoscopic images acquired by the eyes 31-1 and 31-2, the human brain is able to construct the object 5 three-dimensionally, including its depth. If one acquires images at the positions where the eyes are located, i.e., under viewing direction 10-1 and viewing direction 10-2, using a viewing device not shown, e.g., a camera, the image is then reconstructed.If a camera projects a monoscopic image 12-1 or 12-2, it is possible to perceive the object in three dimensions if the right eye sees image 12-1 and the left eye sees image 12-2. This effect is also known as stereoscopy.

[0032] To store the three-dimensional object 5 using monoscopic images 12-x for different viewing directions 11-x, two monoscopic images, here 12-1 to 12-6, are captured for each of the different viewing directions 11-x, here 11-1, 11-2, 11-3. These images are each assigned in pairs to viewing directions that include a convergence angle α of a human observer 30°. The number of captured monoscopic images is chosen here only as an example.If the viewing directions are chosen such that an angle γ between adjacent viewing directions corresponds to twice the convergence angle α, then, in an unclaimed embodiment, a stereoscopic view for a viewing direction 11-4 can be generated using the image 10-2, which is captured for the left eye in relation to viewing direction 11-1, together with the image 10-3, which is captured for the right eye in viewing direction 11-2, by now using the monoscopic image 12-2 for the right eye and the monoscopic image 12-3 for the left eye. With a clever choice of viewing directions, most monoscopic images can thus be used to generate stereoscopic views for two viewing directions.However, it is ensured that the detection directions 10-1 to 10-6 each enclose the convergence angle α for a human observer on the circle 25 in pairs, and thus the captured monoscopic images 12-1 to 12-6 assigned to these detection directions 12-1 to 12-6 can each be used in pairs to generate a stereoscopic view.

[0033] The monoscopic images 12-x, which are assigned to the detection directions 10-x, can also be generated in other ways, for example, by calculating them for the three-dimensional object 5 using a computer. Although in such a case the images are not "detected" but calculated, the assigned direction from which the three-dimensional object 5 is represented is referred to as the detection direction. In the following, the act of detecting a monoscopic image will always include the act of calculating the monoscopic image.

[0034] In Fig. 2 A schematic representation shows a device with which the various monoscopic images 12-1 to 12-6 can be used to form a multiplex volume reflection hologram. The device 100 comprises a light source 110 for generating coherent light 120. In a beam splitter 130, the coherent light 120 is split into an object component 140 and a reference component 150. The object component 140 and the reference component 150 are directed from opposite directions onto a holographic recording material 200, which is arranged in a holder 205. Both the reference component 150 and the object component 140 pass through the holographic recording material 200 and interfere, thereby generating a volume reflection hologram for each of the different exposure directions 210-x based on the interference patterns.The different exposure directions 210-x all lie in the same plane 220, which in the illustrated embodiment is oriented perpendicular to the plane of the flat holographic recording material. The exposure directions 210-1, 210-2; 210-3, 210-4; 210-5, 210-6, in pairs, enclose a standard convergence angle α, so that a human observer of the hologram, when reconstructing it from a suitably chosen viewing distance, can perceive stereoscopic images of the object depicted in the monoscopic images 12-1 to 12-6 for different viewing directions 211-x.

[0035] In an unclaimed embodiment, the position of the exposure directions 210-1 to 210-6 in the plane 220 is chosen analogously to the position of the detection directions 10-1 to 10-6 when detecting the monoscopic images 12-1 to 12-6.

[0036] At the in Fig. 2 In the illustrated embodiment, the reference light 250 is illuminated at an elevation angle θ relative to the plane 220, which is defined by the exposure directions 210-x, but identically for all exposure directions, onto the holographic recording material 200. A projection 250' of the reference light onto the plane 220, defined by the exposure directions 210-x, forms an azimuth angle φ with the plane of the recording material 200. The azimuth angle φ is preferably 90°, and the elevation angle θ is, for example, 45°. The plane 220 defined by the exposure directions 210-x is preferably oriented perpendicular to the plane of the recording material.

[0037] The object component 140 of the coherent light 120 is used to project the individual monoscopic images 12-1 to 12-6 onto the recording material 200. For this purpose, a projection device 280 or, as shown here, several projection devices 280-x are provided. These each comprise an illumination optic 281-x, a holder 282-x in which the monoscopic image 12-x is held, and a projection optic 283-x. If the monoscopic images 12-x are digitally captured, a digital spatial light modulator 285-x, for example an LCD screen, can be provided instead of the holder 282-x with the monoscopic image 12-x.A digital spatial light modulator 285-x can also be present together with the holder 282-x and the figure 12-x to individualize the projection of the figure 12-x, in order to be able to produce a large number of different multiplex volume reflection holograms as security elements 202 with the same figures 12-x.

[0038] In the illustrated embodiment, the object component 140 of the coherent light 120 is divided into as many components 140-1 to 140-6 as there are monoscopic images simultaneously exposed into the holographic recording material under the different exposure directions 210-1 to 210-6. Alternatively, it is possible to expose the different monoscopic images 12-1 to 12-6 under the different exposure directions 210-1 to 210-6 sequentially into the recording material 200.

[0039] In Fig. 4 The reconstruction of the security hologram 201, which results from the developed recording material 200, is shown. Reconstruction light 350 is shone in a direction opposite to the direction in which the reference light 150 used for recording struck the recording material. The hologram now reconstructs the images 12-1 to 12-6 stored in the hologram as reconstructed images 12'-1 to 12'-6 under the various reconstruction directions 310-1 to 310-6, wherein each pair of reconstruction directions 310-1, 310-2; 310-3, 310-4; 310-5, 310-6 encloses a standard convergence angle α, which corresponds to a standard convergence angle for viewing from a target distance L to the hologram.If a viewer moves their head along a circular segment 325, the user can perceive the object 5' stored in images 12'-1 to 12'-6 stereoscopically from different viewing directions 311-1, 311-2, 311-3. If the exposure directions for the captured monoscopic images 12'-1 to 12'-6 are cleverly chosen, then, in addition to the three viewing directions 311-1 to 311-3, there are also further viewing directions 311-4, 311-5 that enable stereoscopic perception with the reconstructed images 12'-2, 12'-3 or 12'-4 and 12'-5.

[0040] In Fig. 3 An alternative method for producing a security hologram 201, which is a multiplex volume reflection hologram, is shown. Identical technical features are indicated in the figures with the same reference numerals and are not described again in detail. This embodiment differs in that the reference component for the exposure of the individual images 12-1 to 12-6 is also illuminated in such a way that a projection into the plane 220 of the corresponding reference component 150-x is diametrically opposed to the corresponding exposure direction.

[0041] In one embodiment, the reference component of the coherent light 120 is divided into components 150-1 to 150-6, and the exposure of all monoscopic images 12-1 to 12-6 is carried out simultaneously. However, in this embodiment, it is preferred that the individual images 12-1 to 12-6 are exposed sequentially such that, during the exposure of the monoscopic image 12-1 from the exposure direction 210-1, the reference component 150-1 is illuminated as a reference light. For the exposure of the monoscopic image 12-2 from the exposure direction 210-2, the reference light is illuminated from the direction 250-2, the projection 250'-2 of which is diametrically opposite to the exposure direction 210-2.

[0042] Alternatively, it is possible to design the illumination of the reference component 1150-1 of the light along a direction 1250-1 such that its projection 1250'-1 into the plane of the exposure directions 10-x diametrically opposite to the later viewing direction 311-1 (cf. Fig. 5 ) or opposite the viewing direction 11-1, from which the exposed monoscopic images 12-2, 12-1 can be perceived as stereoscopically during reconstruction.

[0043] For a direction 1250-1 of the reference light component 1150-1, two monoscopic images, the monoscopic image 12-1 from the exposure direction 10-1 and the monoscopic image 12-2 from the exposure direction 10-2, can then be exposed into the recording material simultaneously or with a time delay. These exposure directions establish a standard convergence angle α for a human observer. In this case, the projection 1250'-1 of the reference light component 1150-1 is chosen to be diametrically opposed to the viewing direction 311-1 under which the two reconstructed monoscopic images 12'-1 and 12'-2 are perceptible as a stereoscopic image by a human observer 30 during the reconstruction and verification of the security element 202 (cf. Fig. 5 ).

[0044] The further images, here 12-3 to 12-6, can be exposed into the recording material 200 using the same projection devices 280-1, 280-2, by exchanging the corresponding images, by rotating the recording material about an axis 260, which is oriented perpendicular to the exposure directions 210-1, 210-2, for example in an unclaimed variant by an angle γ which corresponds to the angle between the viewing directions 11-x when capturing the monoscopic images.

[0045] The reconstruction of this security element 202, designed as a security hologram 201, which results after the development and fixing of the recording material, is in Fig. 5 schematically represented. The developed recording material is a hologram layer 200. The reconstruction light is shone onto the security hologram 201 from a predetermined reconstruction light direction 1350, the projection 1350' of which into the plane 200 of the reconstruction directions 310-x is also shown, and viewed from a viewing direction, for example 311-2, so that the reconstruction direction 310-3, 310-4 provides a stereoscopic view of the object 5 similar to the view from the viewing direction 11-2 (cf. Fig. 1 ) for the human observer, who perceives the reconstructed image 12-3 with the right eye and the reconstructed image 12-4 with the left eye. If the security hologram is now tilted around an axis 360°, which lies in the plane of the security hologram 201 and is oriented perpendicular to the plane in which the reconstruction directions 310-x lie, then, when tilted to the left, the reconstructed monoscopic images 12'-1 and 12'-2 are reconstructed in the right and left eyes, respectively, so that a stereoscopic view similar to that obtained with the viewing direction 11-1 (cf. Fig. 1 ) results in a stereoscopic view for the human observer. Tilting to the right leads to a view similar to the viewing direction 11-3, resulting in a stereoscopic view of the reconstructed images 12-5', 12-6'.

[0046] In the embodiments described here, monoscopic images for three, or optionally five, viewing directions of the reconstructed hologram are described. It is understood that significantly more different viewing directions, under which a stereoscopic perception of the object is possible for the viewer, can be copied into the hologram. Likewise, it is possible to select the exposure angles so that they do not directly correspond to the detection directions. This makes it possible, for example, to capture or calculate a complete 360° view of object 5 using monoscopic images and to expose all views into the hologram in such a way that, when transitioning from one viewing direction to the next, an "object rotation" in space is perceived, which is independent of the actual change in the viewing position.The image changes depending on the viewing direction. This makes it possible to achieve three-dimensional effects that differ significantly from those of pure 3D holograms projected with parallax into a volume reflection hologram. Such security holograms cannot be replicated using volume reflection holograms recorded with parallax.

[0047] In the described embodiments, the individual images can each be exposed into different two-dimensional areas, in particular strips of equal width, or can be exposed into the same area of ​​the recording material in a two-dimensional overlap. It is also possible that several of the images are stored in different two-dimensional areas, preferably strips, and that different strips contain different images. Each of the multiple images is preferably exposed into only one two-dimensional area.

[0048] One embodiment provides that two of the multiple images are or will be exposed in each of the strips.

[0049] Other embodiments provide that more than two of the multiple images, for example three, are exposed and stored in each of the areas, preferably each of the strips, of the recording material. In some of the resulting stereoscopic images, both monoscopic images are stored in the same planar area, e.g., strips; in other stereoscopic images, the monoscopic images are stored in different, preferably adjacent, planar areas, preferably strips.

[0050] Preferably, images that together form a stereoscopic image are exposed into adjacent areas, preferably adjacent strips, if they are not stored in the same volume area or planar area of ​​the recording material. Reference symbol list

[0051] 5, Object 5' Stereoscopically perceived object 10-x Detection direction x 11-x Viewing direction x 12-x Monoscopic image x 12-x' Reconstructed monoscopic image x 20 Plane 25 Detection circle 30 Human observer 31 Right eye 32 Left eye α Convergence angle R Radius γ Angle between two viewing directions 100 Device 110 Light source 120 Coherent light 130 Beam splitter 140, 140-x Object component 150, 150-x Reference component 200 Recording material / hologram layer 201 Security hologram 202 Security element 205 Mount 210-x Exposure direction 211-x Viewing direction 220 Plane of exposure directions 250, 250-xReference component direction / Direction of the reference light 250', 250'-xProjection of the reference component direction into the plane 220 θElevation angle φAzimuth angle 260Axis 280,280-x Projection device x 281-x Illumination optics 282-x Mount 283-x Imaging optics x / Projection optics 285-x Spatial light modulator 310-x Reconstruction direction 311-x Viewing direction 325 Circular segment 350 Reconstruction light 360 Axis 1150-x Reference light component x 1250-x Reference light direction x 1250'-x Projection of the reference light direction x into the plane 220 1350 Reconstruction light direction 1350' Projection of the reconstruction light direction into the plane of the reconstruction directions,

Claims

1. Method for producing a security hologram (201) comprising the steps: providing multiple, at least three, monoscopic images (12-x) of a three-dimensional object (5) from different capture directions (10-x), each of the multiple images (12-x) being associated with exactly one of the different capture directions (10-x); providing a holographic recording material (200); generating coherent light (120) and splitting the coherent light (120) into at least one reference portion (150; 150-x) and at least one object portion (140; 140-x); and guiding the at least one reference portion (150; 150-x) and the at least one object portion (140; 140-x) so that the at least one object portion (140; 140-x) and the at least one reference portion (150; 150-x) pass through the recording material (200) from opposite sides and interfere inside the recording material (200), wherein, by means of the at least one object portion (140; 140-x) the multiple images (12-x) are projected under different exposure directions (210-x) with respect to the recording material (200), wherein each of the multiple images (12-x) is assigned exactly one of the different exposure directions (210-x), wherein the exposure directions (210-x) all lie in one plane and at least in pairs enclose a standard convergence angle (α) for human viewing from a standard distance and can be assigned to a viewing direction, so that for a human viewer with a standard eye distance, upon reconstruction a stereoscopic effect is perceptible from the viewing direction, characterized in that an angle (y) between two viewing directions (11-x), for each of which from two of the different capture directions (10-x) enclosing a standard convergence angle (α) a pair of monoscopic images (12-x) embodying a stereoscopic view is captured, is greater than an angle between the associated sighting directions (211-x), that correspond to the exposure directions (210-x) exposing the corresponding pairs of monoscopic images.

2. Method according to claim 1, characterized in that the monoscopic images (12-x) comprise the monoscopic images (12-x) for at least three different stereo views from different viewing directions (11-x) of the three-dimensional object (5).

3. Method according to one of claims 1 or 2, characterized in that for at least one of the exposure directions (210-x) two other exposure directions (210-x) exist, all of which together with the at least one exposure direction (210-x) enclose the standard convergence angle (α) for human viewing.

4. Method according to one of claims 1 to 3, characterized in that the at least one object portion (140-x) is divided into as many portions as monoscopic images (12-x) projected by means of the portions are exposed into the security hologram under the different exposure directions, and the exposure of the monoscopic images takes place simultaneously.

5. Method according to one of claims 1 to 3, characterized in that the monoscopic images (12-x) are exposed into the recording material time shifted or pairwise time shifted.

6. Method according to one of claims 1 to 5, characterized in that the standard convergence angle for a target viewing distance between 30 cm and 50 cm as the standard viewing distance is designed for a standard eye distance of 6,5 cm.

7. Security hologram 201, which is formed as a multiplex volume hologram in a hologram layer (200), into which multiple, at least three, monoscopic images (12-x) of the same three-dimensional object (5) are exposed, which depict the three-dimensional object (5) from different capture directions (10-x), and when reference light (350) is irradiated onto the hologram layer reconstruct the multiple reconstructed monoscopic images (12'-x) under different reconstruction directions (310-x) relative to the hologram layer (200), wherein to each of the multiple reconstructed monoscopic images (12'-x) precisely and uniquely one of the different reconstruction directions (310-x) is assigned, wherein the reconstruction directions (310-x) all lie in one plane and at least pairwise enclose a standard convergence angle (α) for human viewing, so that a stereoscopic effect is perceptible for a human viewer from one of different sighting directions, characterized in that an angle (y) between two viewing directions (11-x), for each of which from two of the different capture directions (10-x) enclosing a standard convergence angle (α) a pair of monoscopic images (12-x) embodying a stereoscopic image is captured, is greater than an angle between the associated sighting directions (211-x), under which the corresponding pairs of monoscopic images reconstruct, that correspond to the two viewing directions (11-x).

8. Security hologram according to claim 7, characterized in that the multiple monoscopic images (12-x) comprise the monoscopic images (12-x) for at least three different viewing directions (311-x) for generating stereoscopic views of the three-dimensional object (5).