Patent Application
20070188836
The present invention relates generally to a hologram that has authenticating information recorded in it, and more particularly to a hologram wherein there is recorded authenticating information that is difficult to view in normal viewing states.
So far there have been known counterfeit-proof means for recording authenticating information by printing of as fine patterns as cannot be copied with copiers. However, such counterfeit-proof means are on the way out because recent performance improvements in copiers enable even fine patterns to be copied.
More recently, techniques for forming fine patterns by means of diffraction gratings have been figured out (see patent publication 1), and are now still available as counterfeit-proof means because it is possible to record authenticating information of as fine size as cannot perceive its shape visually.
In any case, the authenticating information is recorded directly on a given recording surface. Therefore, one can immediately see through what information is recorded by observation under a loupe or microscope. Further, if what information is recorded can be seen through, it is then easy to forge that information, because easier access is now given to cheaper devices for recording fine diffraction gratings.
To avoid direct formation of the shape of authenticating information on a recording surface, on the other hand, it has also been attempted to record authenticating information by holography (see patent Publication 2). Holography requires a real-size object, but it is difficult to fabricate an object of visually hard-to-perceive size. For this reason, this patent publication 2 shows an example of the method for implementing lens reductions simultaneously with holography using a negative plane image as a subject.
This holographic method for fabricating a hologram that reconstructs a fine 3D image, however, is practically not preferred because of some restrictions on the size, position, alignment precision, etc. of the object to be used.
On the other hand, a computer-generated hologram (CGH) is fabricated using a computer, for which only the storage as digital data of the shape and location of an object is needed, lightens many such restrictions on the object, and so is desired for the fabrication of minute 3D image-reconstructing holograms.
In this connection, the inventor has already come up with a hologram having authenticating information recorded in it, which comprises a shielding block of visually easy-to-perceive size and a minute object forming the authenticating information which is located behind said shielding block, wherein said minute object is hidden by said shielding block in a given viewing direction such that said minute object cannot be viewed from said given viewing direction and can be viewed from a viewing direction different from said given viewing direction (see Patent Publication 3). According to the invention set forth in Patent Publication 3, there can be provided a hologram that ensures high concealability for the authenticating information and is much less vulnerable to illegal copying, because even if the hologram is irradiated with proper illumination light, the presence of the recorded authenticating information is much less noticeable (because that authenticating information is of as fine size as cannot be perceptible to the naked eye), and because even upon observation under a loupe or the like, the presence of the authenticating information is much less noticeable from the front direction that is a normal viewing direction.
With the hologram set forth in patent publication 3, wherein the minute object that is the authenticating information is located behind the shielding block of visually easy-to-perceive size, however, it is found to be not necessarily easy for an authenticator to look into and check up the authenticating information, because upon viewing the authenticating information comes out of behind the shielding block.
In view of such problems with the prior art as explained above, an object of the present invention is to provide a hologram having authenticating information recorded therein in such a way that it is substantially difficult to view in a normal viewing state and it is easy for an authenticator to check up the authenticating information through a color difference, and so having improved counterfeit-proofness.
According to the present invention, this object is achieved by the provision of a 3D image-reconstruction hologram having authenticating information recorded therein, characterized in that:
a minute object that is the authenticating information is located behind a shielding block of visually easy-to-perceive size, so that the authenticating information is hidden by the shielding block in a given viewing direction and so is not exposed to view, but can be viewed from a direction different from said given direction, and said authenticating information and said shielding block are recorded in such a way as to be viewable in mutually different colors.
Preferably, the minute object is of visually difficult-to-resolve size, and is viewable through a magnifying viewing means.
Preferably, the given direction is a front direction with respect to said hologram.
Preferably, the hologram is recorded in a computer-generated hologram form.
Preferably, the minute object has a maximum size of 300 μm or less.
The shielding block may comprise a pattern constructed of a diffraction grating recorded in a hologram surface.
The minute object may be in a character form.
The minute object may have an angle of radiation of object light, at which the minute object is fully visible on one side of the shielding block.
The distance between the minute object and the shielding block may be determined such that the minute object is fully visible on one side of the shielding block in a direction different from the given direction.
The minute object may be invisible on one side that is opposite to the other side on which the minute object is fully visible.
Preferably, the angle range in which the minute object is partly or wholly visible is equal to or narrower than the angle, range in which the minute object is hidden by the shielding block, more preferably ½ of that angle range.
In another embodiment of the present invention, another minute object may be recorded therein such that said another minute object is viewable on one side that is opposite to the other side on which the minute object is fully visible.
Preferably, the minute object is reconstructed within 1 mm from the surface of the hologram.
The holograms of the present invention may be applied onto a card or a document.
The present invention also includes an authenticating information check system, wherein an illumination optical system and a viewing position are provided such that the minute object in the hologram having authenticating information recorded therein is viewable.
In the authenticating information check system of the present invention, the hologram and the illumination optical system are fixedly provided while the viewing position is relatively movable; the illumination optical system and the viewing position are fixedly provided while said hologram is relatively rotatable; the hologram and the viewing position are fixed provided while the illumination optical system is relatively movable; and the like.
Further, the present invention includes a card or a document onto which the hologram having authenticating information recorded therein is applied.
FIGS. 5(a), 5(b) and 5(c) are illustrative of exemplary authenticating information check systems according to the invention.
In the inventive hologram having authenticating information recorded therein, the minute object that is the authenticating information cannot be viewed in a given viewing direction but can be viewed only in a certain viewing direction different from that direction. For instance, the authenticating information or minute object is gradually visible from behind the shielding block.
The hologram having authenticating information recorded in it according to the present invention is now explained with reference to patent publication 3. Although the inventive hologram may be fabricated by ordinary holography as described later, it should preferably be fabricated by computer generation. Thus, a computer-generated hologram (CGH) is first explained.
How to fabricate CGHs is well known (from, for instance, non-patent publication 1). As an exemplary CGH, a binary hologram obtained by recording an intensity profile of interference fringes is explained. Reference is briefly made to the case wherein a reconstructed image having parallax in the horizontal direction only is observed while illuminated with white light coming from above. As shown in
In the computation of interference fringes, the “hidden surface removal” processing is implemented in such a way that when an object is viewed from a certain visual point, a portion of the object hidden by another object placed in front thereof is invisible. By this processing, information of the object that is overlapping is added to a retinal image, applying a 3D appearance thereto. For CGH recording, the hidden surface removal processing is carried out by the following steps.
For each of point light sources that form an object 1, an area (hatched in
To achieve the hologram of the invention, there is provided a minute object 11 used as authenticating information of visually difficult-to-resolve size, specifically, a character or the like of maximum size of 300 μm or less, as depicted in
The foregoing explanation is the same as in patent publication 3, and according to the present invention, the shielding block 12 and the minute object 11 are recorded in different colors. For instance, the hologram recording is implemented such that the shielding block 12 is reconstructed in red with diffracted light having a red wavelength, and the minute object 11 is reconstructed in blue with diffracted light having a blue wavelength. Although the “different colors” means different hues, and different color saturations, it is desired that the hue is different.
Recording the object in the same CGH 10 in such a way that the image of the object is reconstructed with a plurality of wavelengths may be implemented in the mode of patent publication 4 proposed by the inventor. Reference is now briefly made to that mode. As depicted in
Thus, to record the shielding block 12 and minute object 11 in different colors in the recording surface 20 of the CGH 10 such that they can be reconstructed at the same time, the recording surface 20 is divided into minute R, G and B areas. Then, the interference fringe data for the primary color R separation image are discretely recorded in the R areas; the interference fringe data for the primary color G separation image are discretely recorded in the G areas; and the interference fringe data for the primary color B separation image are discretely recorded in the B areas. When the reconstructed image has parallax in the horizontal direction only, it is preferable that each unit sub-area extends in the horizontal direction of each minute width, as shown in
The shielding block 12 used herein may be either an ordinary 2 or 3D object or an object comprising a diffraction grating pattern provided on the surface of the CGH 10 and known from, for instance, patent publications 1, 5 and 6. In this case, a pattern constructed of a diffraction grating that is the shielding block 12 is directly recorded in a corresponding area on the surface of the CGH 10 rather than recorded as a hologram.
Referring further to patent publication 3, the arrangement of
In this embodiment, too, the shielding block 12 and the minute object 11 are recorded in different colors, for instance, such that the shielding block 12 is reconstructed in red with diffracted light having a red wavelength, and the minute object 11 is reconstructed in blue with diffracted light having a blue wavelength.
In
In this embodiment, too, the shielding block 12 and the minute object 11 are recorded in different colors, for instance, such that the shielding block 12 is reconstructed in red with diffracted light having a red wavelength, and the minute object 11 is reconstructed in blue with diffracted light having a blue wavelength.
Referring back to
Here the case where the right-hand angle of radiation, γ2, of object light is smaller than the angle β2 so that, on the right side, the minute object 11 is fully hidden by the shielding block 12 and so is invisible is defined by γ2=β2, and the case wherein the left-hand angle of radiation, γ3, of object light is smaller than the angle β3 so that, on the left side, the minute object 11 is fully hidden by the shielding block 12 and so is invisible is defined by γ3=β3. Then, the aforesaid relations may be written as
|γ2−β2|+|γ3−β3|≦½×(|β2|+|β3|)
Referring then to
In this embodiment, the shielding block 12, the minute object 11 and the minute object 11′ are recorded in mutually different colors, for instance, such that the shielding block 12 is reconstructed in red with diffracted light having a red wavelength; the minute object 11 is reconstructed in yellow by additive color mixing of diffracted light having red and green wavelengths; and the minute object 11′ is reconstructed in blue with diffracted light having a blue wavelength. On the recording surface 20 of
In the hologram of the present invention as explained above, the authenticating information (minute objects 11, 11′) that is as small as cannot visually be perceived is recorded therein. Accordingly, even when the hologram is irradiated with proper illumination light, the presence of that authenticating information is greatly unlikely to be noticeable. Furthermore, even when viewed on an enlarged scale under a loupe or the like, the presence of the authenticating information is little noticeable from an ordinary viewing direction, e.g., from the front. Thus, the concealability of the authenticating information is much more enhanced, considerably reducing the risk of forgery.
For the purpose of authentication, the hologram of the present invention is observed on an enlarged scale under a loupe or the like while illuminated with proper white light. As, in this state, the hologram is observed from a direction other than the ordinary front direction, the authenticating information (minute objects 11, 11′) comes out in a color different from that of the shielding block 12. As the position of viewing is moved to the front position that is in the ordinary viewing direction, the authenticating information 11, 11′ is hidden by the shielding block 12 and so is not exposed to view. In this way, the hologram of the present invention is authenticated.
Further, if the hologram of the present invention is designed such that the minute object 11 does not develop from one side (the right side of
Furthermore, if the hologram of the present invention is designed such that the second minute object 11′ comes out on one side that is opposite to the other side on which the minute object 11 comes out from the shielding block 12 as shown in
Note here that the more away the minute object 11 is located from the surface of the CGH 10, the more the reconstructed image of the minute object 11 is blurred and so the more difficult the image is to view. Thus, it is desired that the minute objects 11, 11′ be spaced at most 1 mm away from the surface of the CGH 10.
The boundary of diffracted light for the reconstruction of the minute object 11 or the angle of radiation of object light has been described as being determined by the hidden surface removal processing for CGH fabrication. Even when a hologram is fabricated by two-beam interference, however, an equivalent hologram may be fabricated by using a mask or the like to limit the range of incidence on a hologram medium of object light from the minute object to be recorded. Thus, the present invention is applicable not only to CGHs but also to holograms fabricated by a conventional two-beam interference process.
In use, the hologram of the present invention having authenticating information recorded therein may be applied onto the articles desired to be counterfeit-proof such as cards or documents.
Whether or not a certain hologram has authenticating information recorded therein may be checked as follows. The hologram of the present invention is designed such that the authenticating information is viewable only from a specific direction predetermined depending on a specific direction of illumination with reconstructing light. Thus, with an authenticating information check system comprising an illumination optical system and a viewing optical system located in that direction, it is easy to test for genuineness of holograms, and cards, documents or the like onto which they are applied.
Some exemplary authenticating information check systems are now explained with reference to
In another check system of
In yet another check system of
As already mentioned, when the hologram of the present invention is recorded as a relief hologram, wavelength selectivity is not very high. Thus, when a common white light source, for instance, a fluorescent lamp is used as the light source for the authenticating information check system 101, it is difficult to tell the colors of the minute objects 11, 11′ from that of the shielding block 12. Therefore, it is required that a white light source approximate to a point light source be used as the light source for the authenticating information check system 101.
It is here noted that a hologram wherein, as contemplated herein, a minute object is located behind a shielding block, so that the minute object is hidden by the shielding block in a given viewing direction and so is not exposed to view, but can be viewed from a direction different from said given direction, and the minute object and the shielding block are recorded in such a way as to be viewable in mutually different colors, could be recorded in the form of a holographic stereogram. The holographic stereogram, for instance, includes a computer-generated holographic stereogram as proposed in Japanese Patent Application No. 2003-101736, a one-step holographic stereogram obtained by laser holography for each pixel as proposed in patent publication 7, and a holographic stereogram as proposed in patent publication 8, wherein a Fourier transform pattern is recorded for each pixel; however, the computer-generated holographic stereogram as proposed in Japanese Patent Application No. 2003-101736 is particularly preferred because of having high resolution and a lot more parallaxes.
While the hologram having authenticating information recorded therein according to the present invention has been described with reference to its principles and examples, it is understood that the present invention is never limited thereto and so may be modified in various forms.
In the hologram having authenticating information recorded therein according to the present invention, a minute object that is the authenticating information is located behind a shielding block of visually easy-to-perceive size, so that the authenticating information is hidden by the shielding block in a given viewing direction and so is not exposed to view, but can be viewed from a direction different from said given direction, and said authenticating information and said shielding block are recorded in such a way as to be viewable in mutually different colors; the presence of the authenticating information is little noticeable. Further, even when the hologram is viewed through a magnifying viewing means such as a loupe, the presence of the authenticating information is little noticeable from an ordinary viewing direction. The hologram of the present invention thus ensures that the concealability of the authenticating information is extremely enhanced, and so has much higher counterfeit-proofness. Furthermore, the authenticating information and the shielding block are viewable in mutually different colors, so that an authenticator can easily check the authenticating information.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-001807 | Jan 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/19831 | 12/28/2004 | WO | 7/6/2006 |
