JP3854220B2 - Method for producing hologram recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a hologram recording mediumHow to createIn particular, a hologram recording medium suitable for use as a security hologram seal for proving that it is an authentic articleHow to createAbout.
[0002]
[Prior art]
Hologram stickers are used as means for preventing counterfeiting of credit cards, bankbooks, cash vouchers, and the like. In addition, hologram stickers are also used for products such as videotapes and luxury watches to prevent pirated copies from circulating. In addition, hologram stickers are also used for purposes such as decoration and sales promotion. Such a hologram seal often uses a two-dimensional pattern as a motif instead of a three-dimensional stereoscopic image.
[0003]
In order to create such a hologram sticker, an optical hologram photographing method in which interference fringes are formed using a laser beam is usually used. That is, prepare a manuscript with a two-dimensional pattern motif, irradiate this manuscript with one of the two branched laser beams, and cause the reflected beam to interfere with the other branched laser beam. Interference fringes are recorded on the photosensitive material. Once the hologram master is prepared in this way, the hologram seal can be mass-produced by a pressing method using this master.
[0004]
[Problems to be solved by the invention]
However, the conventional optical hologram photographing method described above has a problem that a clear hologram image cannot be obtained. That is, since the optically formed interference fringes are sensitive to vibration, it is necessary to perform hologram imaging in an environment in which vibration is completely eliminated. However, it is difficult to completely eliminate vibrations even if shooting is performed using a vibration isolator with a high degree of accuracy. For this reason, a so-called “blur” occurs in the recorded image of interference fringes, and the contrast is bright. A hologram image cannot be obtained. In addition, fluctuations occur in the oscillation wavelength of the laser light to be used, so that cloudy glass noise is unavoidable. As described above, since there is a problem that optical hologram photographing has poor reproducibility, it is difficult to create several identical originals.
[0005]
A novel hologram recording medium for solving such a problem, and a production method and production apparatus thereof,JP-A-6-337622Is disclosed. According to this novel technique, in order to express a predetermined motif, a method is adopted in which the motif is composed of a plurality of pixels and a diffraction grating pattern is applied to each pixel position. According to this method, a clear hologram image can be obtained on the recording medium, and the reproducibility can be improved. However, this method cannot effectively express a motif with gradation.
[0006]
  Accordingly, the present invention provides a hologram recording medium capable of obtaining a clear and reproducible hologram image for a motif having a gradation.How to createThe purpose is to provide.
[0007]
[Means for Solving the Problems]
  (1) The first aspect of the present invention is:In a method of creating a hologram recording medium in which a predetermined motif having gradation is expressed by a diffraction grating,
A pattern definition stage for defining a plurality of pixel patterns in which a linear grid line having a predetermined line width is arranged in a predetermined closed region at a predetermined arrangement angle and a predetermined pitch;
Motif preparation stage for preparing motif pixel information that represents a predetermined motif with gradation by defining a plurality of pixels each having a predetermined density value at a predetermined position on a plane;
A pattern arrangement step of associating the pixel pattern with each pixel based on each density value in the motif pixel information and arranging a corresponding pixel pattern at each pixel position;
And do
The plurality of pixel patterns defined in the pattern definition step have the same line width and pitch of grid lines between the pixel patterns, but the grid line arrangement angle is different between the pixel patterns,
In the pattern arrangement step, a specific pixel pattern is associated with each pixel so that the shade information of the motif is expressed by the difference in the arrangement angle of the lattice lines of the plurality of pixel patterns.
[0008]
  (2) The second aspect of the present invention is:In the method for producing a hologram recording medium according to the first aspect described above,
In the pattern definition stage, a set of pixel patterns having lattice line arrangement angles that are approximate to each other is defined as one group, and a pixel pattern composed of a plurality of groups is defined.
In the motif preparation stage, prepare multiple different motif pixel information,
In the pattern placement stage, one motif is constituted by a set of pixel patterns belonging to one group, and a plurality of motifs are expressed in an overlapping manner on the same plane.
[0009]
  (3)According to a third aspect of the present invention, in the method for producing a hologram recording medium according to the first or second aspect described above,
The motif pixel information in which characters are expressed as a motif is prepared.
[0010]
The present inventionJP-A-6-337622This is a technical idea for applying the novel method disclosed in the above to a motif having a gradation. SaidGazetteA feature of the hologram recording medium disclosed in is that the hologram pattern is recorded by arranging the pixels on which the diffraction grating is formed in a plane. The inventor of the present application paid attention to a phenomenon in which the brightness of a pixel changes depending on the grating line arrangement angle of the diffraction grating when the pixel on which such a diffraction grating is formed is visually observed. In other words, it has been found that a motif having a gradation can be expressed by replacing the density value of a pixel with an arrangement angle of a grid line. So, if you prepare multiple types of pixel patterns with different brightness due to the difference in grid line arrangement angle, and replace each pixel constituting the motif with a pixel pattern with brightness corresponding to its density value, A hologram recording medium in which a motif with gradation is expressed can be realized.
[0011]
Normally, the above processing is performed by a computer. At this time, when confirming whether a correct motif expression is made on the display screen, only a predetermined pixel pattern is selectively selected according to the arrangement angle of the grid lines. If displayed, the operator can check the pattern by a method with a higher degree of freedom.
[0012]
In general, the term “hologram” is used as a word indicating an image obtained by interference fringes. In this sense, an image created on the recording medium of the present invention is “hologram”. Instead, it should be called “pseudo hologram” or “diffraction grating pattern”. However, since the recording medium used as a seal for preventing counterfeiting is generally called a “hologram seal”, the “diffraction grating pattern” formed on the recording medium is also referred to as “ We will use the term “hologram”.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on embodiments shown in the drawings. As mentioned above, the present inventionJP-A-6-337622This is a technical idea for applying the novel method disclosed in the above to a motif having a gradation. Therefore, for convenience of explanation, first,GazetteAn example of a motif having no gradation disclosed in the above will be described.
[0014]
<<< §1. Examples of motifs without gradation >>>
The feature of the hologram recording medium according to the present invention is that a motif composed of a set of a plurality of pixels is expressed as a hologram on the medium. Here, a method of expressing a relatively simple motif (showing the English letter “A”) having no gradation on the hologram recording medium as shown in FIG. Note that the method for producing a hologram recording medium according to the present invention is premised on the use of a computer, and each process described below is executed using a computer.
[0015]
First, motif pixel information as shown in FIG. 1B is prepared as image data corresponding to the motif shown in FIG. In the example shown here, pixels are arranged in 7 rows and 7 columns, and each pixel has a pixel value of “0” or “1”, which is information indicating a so-called binary image. Such information is general image data called so-called “raster image data”, and can be created by a normal drawing device. Alternatively, such motif pixel information may be prepared by capturing a design image drawn on a paper surface with a scanner device.
[0016]
Subsequently, as shown in FIG. 2, a pixel pattern is defined in which lattice lines having a predetermined line width d are arranged in a predetermined closed region V at a predetermined pitch p and a predetermined angle θ. Here, the closed region V is a region constituting one pixel, and actually becomes a very small element. In other words, the size corresponds to each pixel in the 7 × 7 array shown in FIGS. 1 (a) and 1 (b). In this embodiment, as the closed region V, a rectangle having a size of 50 μm × 45 μm in length × width is used. Further, the line width d and the pitch p of the lattice lines L arranged in the closed region V also have minute dimensions in accordance with the wavelength of light. In this embodiment, the line width d = 0.6 μm. , Pitch p = 1.2 μm. In short, the grating lines L need to be arranged with a line width d and a pitch p that function as a diffraction grating. The arrangement angle θ of the lattice line L is an angle set with respect to a predetermined reference axis. In this specification, an XY coordinate system having the X axis and the Y axis in the directions shown in the figure is defined, and the arrangement angle θ of the lattice line L is expressed with the X axis as a reference axis. Such a pixel pattern is also prepared as pattern data on the computer. Note that the pattern data of the pixel pattern may be prepared as “raster image data” (in this case, each pixel constituting the motif is expressed by a smaller pixel). Alternatively, it may be prepared as “vector image data” in which the contour line of the grid line L is defined by designating the coordinate values of the four vertices of the quadrangle constituting the grid line L. The latter is preferable to reduce the amount of data.
[0017]
Next, based on each pixel value in the motif pixel information as shown in FIG. 1B, the pixel pattern as shown in FIG. 2 is associated with a predetermined pixel, and the corresponding pixel pattern is arranged at each pixel position. Perform the process. Specifically, in the motif pixel information shown in FIG. 1B, the pixel pattern shown in FIG. 2 is associated with each pixel having a pixel value “1”. A pixel pattern is not associated with a pixel having a pixel value “0”. Pixel patterns are arranged at the pixel positions thus associated with each other. In other words, if the arrangement shown in FIG. 1 (b) is compared to a wall, a tile as shown in FIG. 2 is applied to each area labeled “1” in the wall. . As a result, an image pattern as shown in FIG. 3 is obtained. This image pattern is a pattern finally recorded on the hologram recording medium. Although the motif shown in FIG. 1A is expressed as it is, each pixel is formed of a diffraction grating, and a visual effect as a hologram can be obtained.
[0018]
However, the process of pasting the pixel pattern as shown in FIG. 2 as a “tile” is performed as an allocation process in the computer. In this process, for example, when the coordinate origin O is taken at the lower right position of the image corresponding to the entire motif, the offset amounts a and b based on the pixel position to be pasted are obtained by calculation, and the pixel pattern pasting process is performed. Just do it. As a result of such arithmetic processing, pattern data showing a pattern as shown in FIG. 3 is obtained. If this is physically output on a film or the like, a desired hologram recording medium can be created. In this embodiment, as will be described later, pattern data generated by a computer is given to an electron beam drawing apparatus, and a pattern as shown in FIG. 3 is drawn on the original by using an electron beam. The method is designed to mass produce hologram stickers.
[0019]
The above is an example of a motif having no gradation,JP-A-6-337622Discloses a method for applying this technique to a motif having a gradation. For example, a plurality of pixel patterns as shown in FIG. 4 are used. Here, the area indicated by the solid line is the entire occupied area V as a pixel, and the area indicated by the broken line is the closed area W in which the grid lines are to be placed in the entire occupied area V. The five pixel patterns shown in FIG. 4 are those in which the area ratio of the closed region W to the total occupied region V is 100%, 50%, 30%, 10%, and 5%, respectively, and the pixel values have different density values. It can be said. By using different pixel patterns having different density values according to the density value of each pixel constituting the original motif, it is possible to express a motif having a gradation.
[0020]
However, in such a gradation image expression method, a region where the diffraction grating is not formed (region outside the closed region W) is not used effectively, and there is a problem that the entire image becomes dark. In order to solve such a problem, the present invention presents another method for performing gradation expression.
[0021]
<<< §2. Method for expressing a motif with gradation according to the present invention >>>
Next, the basic principle of the present invention will be described. Now, as shown in FIG. 5A, a diffraction grating plate K is prepared in which a large number of grating lines are arranged in the horizontal direction of the figure. Each grid line is arranged with, for example, a line width d = about 0.6 μm and a pitch p = about 1.2 μm. Here, such a diffraction grating plate K is held vertically while being held in hand, and observed from the horizontal direction (corresponding to observing the diffraction grating plate K drawn in the figure from above vertically on the paper surface). ). That is, the line of sight is observed from a direction perpendicular to the diffraction grating plate K. In this state, the diffraction grating plate K is rotated about the line of sight as the rotation axis. FIGS. 5B to 5E show states when the state shown in FIG. 5A is 0 ° and rotated by 30 °, 45 °, 60 °, and 90 °, respectively. From the viewpoint of the observer, this rotation changes the arrangement angle of the grid lines from 0 ° to 90 °. When such observation is performed, in a normal lighting environment (outdoors or indoors where normal lighting is performed), the state of the arrangement angle of 0 ° as shown in FIG. The state of the 90 ° arrangement angle as shown in FIG. Therefore, when the diffraction grating plate K is held in the state as shown in FIG. 5 (a), and gradually rotated clockwise, the state shown in FIG. 5 (e) is obtained. Is observed so that the front surface of the diffraction grating plate K gradually becomes darker.
[0022]
If this principle is applied to the hologram recording medium described above, a motif having a gradation can be expressed. For example, five types of pixel patterns P1 to P5 as shown in FIG. 6 are prepared. Here, each of the pixel patterns P1 to P5 is a diffraction grating pattern in which grid lines having the same line width are arranged at the same pitch, but the arrangement angle of the grid lines is different from 0 ° to 90 °. Therefore, according to the above-described principle, when each of these pixel patterns P1 to P5 is held vertically in a normal illumination environment and observed from the horizontal direction, the pixel pattern P1 looks brightest and the pixels It becomes darker as the patterns P2 to P4 become darker, and the pixel pattern P5 looks darkest. Therefore, if these pixel patterns are associated with each other according to the density value of each pixel, a motif having a gradation can be expressed. For example, for pixels to which the density value C = 0% (brightest) to 100% (darkest) is given, the pixel patterns P1 to P1 are based on the density value range as shown in the bottom row of FIG. Any one of P5 may be associated. That is, a pixel pattern P1 is associated with a pixel having a density value of 0% ≦ C <20%, a pixel pattern P2 is associated with a pixel having a density value of 20% ≦ C <40%, and 40% A pixel pattern P3 is associated with a pixel having a density value of ≦ C <60%, a pixel pattern P4 is associated with a pixel having a density value of 60% ≦ C <80%, and 80% ≦ C ≦ 100. A pixel pattern P5 is associated with a pixel having a density value of%.
[0023]
Next, an example in which the present invention is applied to a specific motif will be shown. The motif in FIG. 1 (a) described above is a picture showing the English letter “A”, but is a binary image having no gradation, and each pixel is “0” as shown in FIG. 1 (b). "Or" 1 "only. On the other hand, consider a motif in which each pixel has a density value C of 0% to 100%. The image showing the density value of each pixel in FIG. 7 (a) is a picture showing the English letter “A”, similar to the motif in FIG. The portion is a pixel having a density value C = 5%, and the pattern portion is composed of any pixel having a density value C = 95%, 90%, 70%, 35%, or 30%. When the pixels having these density values are associated with the five pixel patterns P1 to P5 by the method shown in FIG. 6, the correspondence shown in FIG. 7B is obtained. Therefore, if each pixel pattern is arranged at each pixel position based on this correspondence, the pattern “A” having a gradation can be expressed by a diffraction grating.
[0024]
In the above-described embodiment, the grid line arrangement angle of the pixel pattern is distributed over a wide range of 0 ° to 90 °. However, in practice, it is not necessary to distribute in such a wide range. Specifically, by changing the grid line arrangement angle from 0 ° to 45 °, the grid line arrangement angle can be changed from a bright state (0 °) to a considerably dark state (45 °). Even if it is changed from 45 ° to 90 °, the brightness does not change so much. Therefore, in practice, it is sufficient to associate the range of the lattice line arrangement angle of 0 ° to 45 ° or the range of 0 ° to 30 ° with the range of the density value of 0% to 100%.
[0025]
By the way, according to the principle described with reference to FIG. 5, a pixel pattern having horizontal grid lines looks bright and a pixel pattern having vertical grid lines looks dark in a normal illumination environment. For this reason, when the hologram recording medium itself expressing the gradation image by the above-described method is rotated 90 ° and observed, the light / dark relationship is reversed. Let's illustrate this with a concrete example. FIG. 8A shows a gradation image having a density value as shown in FIG. 7A by arranging pixel patterns using the correspondence shown in FIG. 7B. Suppose that such a recording medium M is obtained. When the recording medium M is observed while being held in a vertical state as shown in FIG. 8 (a), a light and dark state as planned can be obtained. That is, in FIG. 7A, a pixel with a density value of 5% (the grid line is horizontal) is the brightest (white) pixel, and a pixel with a density value of 95% (the grid line is vertical) is the darkest ( Black) pixels. However, when this recording medium M is observed in the horizontal state as shown in FIG. 8B, the bright and dark state is reversed, and a negative image is observed when the original image is a positive image. Become. That is, a pixel with a density value of 5% (the grid line is now vertical) is the darkest (black) pixel, and a pixel with a density value of 95% (the grid line is now horizontal) is the brightest (white) pixel. It becomes.
[0026]
Such negative / positive reversal also occurs when the angle formed between the line of sight and the recording medium M is changed. For example, all of the discussions so far have been discussions on a case where the line of sight E is observed from a direction perpendicular to the surface of the recording medium M as shown in FIG. As shown in FIG. 9B, when the recording medium M is tilted with respect to the line of sight E, negative / positive reversal occurs. FIG. 9B shows the inclination in the vertical direction (the direction in which the upper side of the recording medium M is separated from the observer and the lower side is closer to the observer, or the opposite direction). It also occurs in a direction tilt (a direction in which the right side of the recording medium M is separated from the observer and the left side is closer to the observer, or the reverse direction). Alternatively, negative / positive inversion may occur depending on the lighting environment. Moreover, this phenomenon does not always appear as negative / positive reversal, and when observed in a halfway direction or angle, an image in which the density relationship is complicated and disturbed with respect to the original motif appears. In short, when the gradation image is expressed on the recording medium M according to the present invention, the original gradation image may not be correctly observed depending on the holding state of the recording medium M by the observer, the observation angle, and the illumination environment.
[0027]
However, this is not a problem in practice. For example, assume that the recording medium M is formed on a credit card to prevent forgery. This is because the observer usually holds the credit card in the correct orientation on the front as shown in FIG. 9 (a) when confirming the description of the credit card. As long as the image is held and observed in this way, an image having the same gradation as the original motif can be observed. Further, even if the observer holds the credit card vertically and horizontally and observes it or inclines it, no practical problem arises. In this case, considering the original motif as a reference, the gradation information is not correctly reproduced, but such a hologram sticker originally reproduces the subject faithfully like a photograph. Since it is not intended, there is no problem in practical use. Rather, this is a preferable phenomenon from the viewpoint of giving a fantastic image because the density of each part changes in various ways by changing the observation angle and direction.
[0028]
<<< §3. Method for producing hologram recording medium according to the present invention >>
Next, the procedure of the method for producing a hologram recording medium according to the present invention will be described based on the flowchart of FIG. This procedure is composed of six stages of steps S1 to S6. Among these steps, steps S1 to S4 are executed by the computer and its peripheral devices, step S5 is executed by the electron beam drawing apparatus, and step S6 is executed. Executed by the printing press.
[0029]
The pattern definition stage of step S1 is a stage of defining a plurality of pixel patterns in which grid lines having a predetermined line width are arranged in a predetermined closed region at a predetermined pitch. Here, the defined pixel patterns have different grid line arrangement angles, for example, patterns P1 to P5 in FIG. The number of pixel patterns to be defined is determined by how many levels the density value is divided. In the example of FIG. 6, the density values of 0% to 100% are divided into five levels and five types of pixel patterns P1 to P5 are defined. However, if finer division is made, What is necessary is just to define many kinds of pixel patterns by making the step of the arrangement angle finer.
[0030]
The motif preparation stage of step S2 is a stage for preparing motif pixel information. Here, the motif pixel information is information in which a plurality of pixels each having a predetermined density value are defined at predetermined positions on a plane in order to express a predetermined motif having gradation. For example, information as shown in FIG. 7A is motif pixel information. There are various methods for preparing such motif pixel information. For example, if a photo original or an illustration original drawn by a designer is read as image data having gradation by a scanner device, it can be used as motif pixel information. Alternatively, the motif pixel information can be prepared by operating graphic application software on a computer and drawing such a gradation image.
[0031]
The pattern placement stage of step S3 is a stage in which individual pixel patterns are associated with each pixel based on each density value in the motif pixel information, and a corresponding pixel pattern is placed at each pixel position. For example, if the pixel patterns P1 to P5 are associated with the pixels shown in FIG. 7A according to the condition defined by the inequality shown in the bottom row of FIG. 6, the correspondence shown in FIG. A relationship is obtained. Subsequently, based on this correspondence, actual pixel patterns P1 to P5 are arranged at the respective pixel positions. The above process is executed as an allocation process inside the computer.
[0032]
The pattern inspection stage in step S4 is a stage in which it is inspected whether or not the pattern placement is correctly performed in the pattern placement stage in step S3. That is, a unique display mode on the display screen is determined for each of the plurality of pixel patterns defined in step S1, and the arranged individual pixel patterns are displayed on the display screen in a unique display mode. is there. As described above, since the actual pixel pattern is a fine pattern having a line width or pitch on the order of 1 μm, it cannot be displayed on the display screen as it is. Therefore, a unique display mode is determined for each pixel pattern so that the operator can visually grasp each pixel pattern on the display screen. This display mode may be any display mode as long as individual pixel patterns can be distinguished from each other. In this embodiment, the actual grid line width can be observed with the naked eye. The pitch of the lattice lines is expanded to such an extent that it can be observed with the naked eye by further thinning out and displaying each pixel pattern (the pixel patterns shown in FIGS. 5 and 6 are actually like this). And displayed in a mode that can be observed with the naked eye).
[0033]
However, this method makes it difficult to grasp the shape of the motif. For example, a pattern having a density value as shown in FIG. 7A can recognize a motif composed of English letters “A” because the bright and dark areas can be clearly distinguished on an actual hologram sticker. In the pattern inspection stage of step S4, when each pixel pattern shown in FIG. 6 is arranged in a mosaic pattern on the display screen, the English character motif “A” is grasped by the difference in the arrangement angle of the grid lines. It is difficult to do. Therefore, in this embodiment, a function is added to display only the pixel pattern in which the grid line arrangement angle is included in a predetermined range on the display screen at the pattern inspection stage. For example, in the case of the above-described example, if only the pixel pattern having a grid line arrangement angle of 30 ° or more is displayed, only the pixel patterns P2, P4, and P5 are displayed on the display screen as shown in FIG. Therefore, the shape of the motif can be easily grasped.
[0034]
Further, the display brightness of the pixel pattern on the display screen may be changed according to the arrangement angle of the grid lines. For example, in the case of the above-described example, if the luminance of a pixel pattern having a grid line arrangement angle of less than 30 ° is reduced, the display luminance of the pixel pattern P1 becomes dark, and the shape of the motif can be easily grasped. Can do. Alternatively, it is also possible to display the operations in which only the grid line arrangement angles within a predetermined range are displayed in a time-division manner. For example, in the case of the above-described example, it is possible to display only a pixel pattern having a grid line arrangement angle of 60 ° or more and then display only a pixel pattern of 30 ° to 60 °.
[0035]
Up to the above steps are executed by the computer, and finally image data consisting of a set of pixel patterns can be prepared. Therefore, in the subsequent step S5, an original is created based on this image data. In this embodiment, based on the obtained image data, a hologram original plate having a fine pixel pattern arrangement is created using an electron beam drawing apparatus. When the original plate can be created in this way, a hologram seal is manufactured in the next step S6. In this embodiment, the concave / convex pattern on the original plate is transferred to a roll-shaped film by using a printing method using the original plate to create a hologram seal.
[0036]
<<< §4. Example expressing multiple motifs >>>
JP-A-6-337622Discloses a technique for expressing a plurality of motifs in an overlapping manner on the same plane. For example, motif A (English letter “A” shape) as shown in FIG. 12 (a) overlaps with motif B (English letter “B” shape) as shown in FIG. 12 (b). Each pixel is divided into four sub-pixels, and the upper left sub-pixel and lower right sub-pixel are assigned to motif A, and the lower left sub-pixel and upper right sub-pixel are assigned to motif B. The sub-pixels are assigned and each pixel is represented by a sub-pixel. Thus, the motif A is expressed by arranging the sub-pixel pattern (in this example, the grid line arrangement angle is 0 °) as shown in FIG. 13 (a), and the motif B is as shown in FIG. 13 (b). This is expressed by arranging subpixel patterns (in this example, the grid line arrangement angle is 90 °). Then, by overlapping these subpixel patterns, a hologram recording medium as shown in FIG. 14 is obtained.
[0037]
The present invention can also be applied to a case where a plurality of motifs are displayed in an overlapping manner. The motifs A and B shown in FIG. 12 are binary images having no gradation, but when these are gradation images, the following handling may be performed. That is, a plurality of pixel patterns having a lattice line arrangement angle approximate to each other are defined as one group, and pixel patterns belonging to different groups are associated with each motif. For example, for the motif A, a plurality of pixel patterns having a grid line arrangement angle near 0 ° is defined, and for the motif B, a plurality of pixel patterns having a grid line arrangement angle near 90 ° is defined. To do. More specifically, for the sub-pixel used for the motif A, a plurality of types of pixel patterns having a grid line arrangement angle within an angle range of −5 ° to + 5 ° are defined. A plurality of types of pixel patterns having grid line arrangement angles within a range of angles of 85 ° to 95 ° are defined. Since there is a large difference in viewing angle between a pixel pattern group having a grid line arrangement angle near 0 ° and a pixel pattern group having a grid line arrangement angle near 90 °, the hologram recording medium shown in FIG. When observed from a certain specific direction and angle, motif A is observed, and from another specific direction and angle, motif B is observed. Moreover, when the motif A is observed, there is a difference in the grid line arrangement angle within an angle range of −5 ° to + 5 ° depending on each sub-pixel, so that a density difference is observed between the individual sub-pixels. Become. Similarly, when the motif B is observed, there is a difference in the grid line arrangement angle within an angle range of 85 ° to 95 ° depending on each sub-pixel, so that a density difference is also observed between the individual sub-pixels. become. Thus, a plurality of motifs each having a gradation can be displayed in an overlapping manner.
[0038]
Note that, as described above, in the pattern inspection stage (step S4 in the flowchart of FIG. 10), a function is added to display only pixel patterns whose grid line arrangement angles are within a predetermined range on the display screen. This makes it easy to inspect a pattern in which a plurality of motifs as described above are displayed in an overlapping manner. That is, if only the pixel pattern having the grid line arrangement angle within the range of the angle −5 ° to + 5 ° is displayed, only the motif A as shown in FIG. If only the pixel pattern having the grid line arrangement angle in the range of ° to 95 ° is displayed, only the motif B as shown in FIG. 13B can be recognized.
[0039]
As mentioned above, although this invention was demonstrated based on the Example shown in figure, this invention is not limited only to these Examples, In addition, it can implement in a various aspect. For example, in the above-described embodiment, the grid line arrangement angle of the pixel pattern used for the motif A has a width of ± 5 ° around 0 °, and the grid line arrangement angle of the pixel pattern used for the motif B Although a width of ± 5 ° is given around 90 °, these center angles and widths can be freely set. However, in order to prevent the motif A and the motif B from interfering with each other, the center value of the grid line arrangement angle of the pixel pattern used for the motif A (0 ° in the above example) and the pixel pattern used for the motif B It is preferable that the central value (90 ° in the above example) of the grid line arrangement angle is at least 30 ° apart. Further, the boundary value on the motif B side of the grid line arrangement angle of the pixel pattern used for the motif A (+ 5 ° in the above case) and the boundary value on the motif A side of the grid line arrangement angle of the pixel pattern used for the motif B (described above) In the case of 85 °), it is preferable to separate at least 30 °. Actually, the pixel having the grid line arrangement angle of 0 ° is observed most brightly. Therefore, in order to make the motif A brighter, by giving a width of ± 5 ° around 5 °, It is preferable to define a pixel pattern group in which the grid line arrangement angle is distributed in the range of 0 ° to 10 °, and to express the motif A using this pixel pattern group.
[0040]
【The invention's effect】
As described above, according to the present invention, since the density value of the pixel is replaced with the arrangement angle of the lattice line, a clear and reproducible hologram image can be obtained even for a motif having a gradation.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a motif having no gradation and pixel information thereof.
FIG. 2 is a diagram showing an example of a pixel pattern used in a hologram recording medium according to the present invention.
FIG. 3 is a diagram showing a hologram recording medium created using the motif shown in FIG. 1 and the pixel pattern shown in FIG.
FIG. 4 is a diagram showing a pixel pattern used in one method for expressing a motif with gradation.
FIG. 5 is a diagram for explaining the relationship between the direction of observing a diffraction grating and the brightness as the basic principle of the present invention.
FIG. 6 is a diagram showing an example of a plurality of pixel patterns used for expressing different density values in the present invention.
FIG. 7 is a diagram showing a density value of each pixel constituting a motif having a gradation and a corresponding pixel pattern.
FIG. 8 is a diagram for explaining that a negative / positive inversion phenomenon occurs in the hologram recording medium according to the present invention depending on the viewing direction.
FIG. 9 is a diagram for explaining that a negative / positive reversal phenomenon occurs in the hologram recording medium according to the present invention depending on an observation angle.
FIG. 10 is a flowchart showing a procedure of a method for producing a hologram recording medium according to an embodiment of the present invention.
FIG. 11 is a diagram showing a display example in a case where a restriction by a grid line arrangement angle is added to a pixel pattern displayed on a display screen in step S4 (pattern inspection stage) of the flowchart shown in FIG.
FIG. 12 is a diagram showing two different motifs to be recorded redundantly on the hologram recording medium.
13 is a diagram illustrating a state in which a sub-pixel pattern is arranged in each motif illustrated in FIG.
14 is a diagram showing a hologram recording medium obtained by overlapping two subpixel pattern arrangements shown in FIG.
[Explanation of symbols]
A, B ... Motif
E ... Gaze
K ... Diffraction grating plate
L ... Lattice line
M ... Hologram recording medium
P1 to P5: Pixel pattern
V: Closed region where grid lines are placed
W: All occupied areas as pixels
d: Line width of the lattice line
p ... Pitch of lattice line
θ: Arrangement angle of grid lines

Claims (3)

A method of creating a hologram recording medium in which a predetermined motif having gradation is represented by a diffraction grating,
  A pattern definition stage for defining a plurality of pixel patterns in which a linear grid line having a predetermined line width is arranged in a predetermined closed region at a predetermined arrangement angle and a predetermined pitch;
  Motif preparation stage for preparing motif pixel information that represents a predetermined motif with gradation by defining a plurality of pixels each having a predetermined density value at a predetermined position on a plane;
  A pattern arrangement step of associating the pixel pattern with each pixel based on each density value in the motif pixel information and arranging a corresponding pixel pattern at each pixel position;
  Have
  The plurality of pixel patterns defined in the pattern definition step have the same line width and pitch of grid lines between the pixel patterns, but the grid line arrangement angle is different between the pixel patterns,
  A hologram recording medium characterized in that, in the pattern arranging step, a specific pixel pattern is associated with each pixel so that the shading information of the motif is expressed by a difference in arrangement angle of lattice lines of the plurality of pixel patterns. How to create The creation method according to claim 1,
  In the pattern definition stage, a set of pixel patterns having lattice line arrangement angles that are approximate to each other is defined as one group, and a pixel pattern composed of a plurality of groups is defined.
  In the motif preparation stage, prepare several different motif pixel information,
  Creation of a hologram recording medium characterized in that, in the pattern placement stage, one motif is constituted by a set of pixel patterns belonging to one group, and a plurality of motifs are expressed in duplicate on the same plane. Method. In the creation method according to claim 1 or 2,
  A method of creating a hologram recording medium, comprising preparing motif pixel information in which characters are expressed as a motif.

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