JP4866866B2 - Information recording and playback method - Google Patents

Description

  The present invention relates to an information recording / reproducing method for a large-capacity and high-density information recording medium that records information as two-dimensional image data, such as hologram recording for recording using hologram technology.

  In recent years, development of a hologram recording / reproducing system that records and reproduces information using hologram technology has been promoted (see, for example, Non-Patent Document 1). The principle of information recording / reproducing in this hologram recording / reproducing system is as follows.

  A recording medium on which information is recorded (hereinafter sometimes simply referred to as a recording medium) is a photosensitive medium such as a photopolymer whose refractive index changes by causing a chemical change or a physical change in response to irradiated light. It has a recording layer made of a hologram recording material made of a curable material.

  For recording on this recording medium, first, laser light emitted from a laser light source is subjected to SLM (Spatial Light Modulator) such as a liquid crystal element, that is, object light including recording information modulated by a spatial light modulator, and a reference The light is generated, and these two lights (hereinafter also referred to as “recording light” as appropriate) are irradiated onto the recording medium under predetermined conditions. As a result, interference fringes are generated in the recording layer of the recording medium due to the interference between the object light and the reference light, and the refractive index of the photosensitive hologram recording material is changed in accordance with the interference fringes, so that A kind of diffraction grating is formed.

  On the other hand, the reproduction of the recorded information recorded on the recording medium as described above is performed by irradiating the recording layer of the recording medium with reference light under a predetermined condition. When the reference light is radiated, in the recording medium, the reference light is diffracted by the diffraction grating formed in the recording layer, and the diffracted light in a state where the object light at the time of recording is reproduced (hereinafter referred to as “reproduction light” as appropriate). Are also described). Therefore, the modulated recording information can be reproduced by detecting the diffracted light with a light receiving element such as an imaging element.

  Here, in the case of hologram recording, recording information is generally converted into a two-dimensional dot pattern, and this is recorded on a recording medium as an image. Information of several thousand to several tens of thousands of bits in one recording Can be recorded. Various modulation schemes have been proposed for modulating recording information into a two-dimensional dot pattern (see Patent Documents 1 to 4). An example of the flow of data actually displayed on the spatial light modulator (SLM, etc.) is shown in FIG.

  First, data to be recorded is stored in a buffer until it reaches a certain capacity (step S10). Thereafter, a certain amount of data to be recorded on the recording medium at one time is extracted from the buffer, and information such as address information and error correction code (ECC) is added to these data (steps S20 and S30). . The entire data to be recorded on the recording medium to which the address information is added is called page data. Subsequently, each byte data constituting the page data is subjected to pattern conversion (step S40), and further, a position detection mark is added (step S50), and converted to a constant two-dimensional dot pattern (step S60). As shown in FIG. 2, this two-dimensional dot pattern has a plurality of regions divided in two dimensions, and each region corresponds to 1/0 (or on / off) digital information. Is done. Here, the minimum unit of the area is called a pixel.

  As a method for converting the byte data into the two-dimensional dot pattern, various conversion methods can be used as appropriate. Here, a 3/16 modulation method will be described as an example. In this modulation system, for example, as shown in FIG. 2, a cell having a set of 16 pixels of 4 × 4 is basically set, and only three pixels in one cell are “1” of digital information. It corresponds to. A dot pattern corresponding to numerical data from 0 to 255 is set in advance by the combination of the positions of the three pixels, and each byte data is converted into a dot pattern using this conversion table.

  An aggregate of dot patterns obtained by converting all the byte data of page data is called a data page. A data page is an embodiment of page data as a collection of dot patterns, and 1/0 (or on / off) digital information is made to correspond to the brightness of light (intensity of brightness), so that SLM and DMD ( It can be embodied as an image pattern by a spatial light modulator such as a digital micromirror device. In general, a pixel with high luminance representing 1 or on is called a bright spot, and a pixel with low luminance representing 0 or off is called a dark spot.

An example of a detailed configuration of the data page will be described with reference to FIG.
The data page (FIG. 3A) is divided into small areas called subframes (FIG. 3B). In this example, a position detection mark is located at the center of each subframe (FIG. 3B). It is recorded. Further, each subframe (FIG. 3B) is divided into cells (FIG. 3C). That is, there exists a cell (FIG. 3C) corresponding to each byte data, and a certain set of cells (FIG. 3C) hits a subframe (FIG. 3B). A certain set of numbers in FIG. 3B corresponds to the data page (FIG. 3A). When the 3/16 modulation method is used, one cell corresponds to an information amount of 8 bits, that is, 1 byte, and thus the information amount of one data page is 32 cells × 64 subframes, which is 2048 bytes. Such a data page is embodied as an image pattern by an SLM or the like, and is recorded as an image pattern on a recording medium.

  Next, FIG. 4 shows an example of the data flow during reproduction. The image pattern contained in the reproduction light guided onto the image sensor is generally read as luminance information of each pixel by a CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) image sensor and converted to image data. (Step s10). Subsequently, the position of the position detection mark is detected from the image data (step s20). Since the position of the position detection mark and the image pattern are fixed in all data pages, it can be easily determined from the obtained image data.

  Next, based on the detected position detection mark, image distortion of the reproduced image data is corrected (step s30). Specifically, the original XY coordinates of the position detection mark and the XY coordinates of the position detection mark of the reproduced image data are compared, and the entire image data is affine transformed to correct distortion and the like.

  Since the obtained image data corresponds to the data page at the time of recording, based on the corrected image data, the data is cut into each subframe (step s40), and this subframe is further divided into each cell. (Step s50). In the dot pattern decomposed into each cell, the top three pixels are determined to be 1 (on) in descending order of luminance, and 0 (off) otherwise. Thereafter, the dot pattern is compared with the conversion table (FIG. 2) described above (step s60), and if the pattern exists, it is converted into byte data (step s70). On the other hand, if there is no corresponding dot pattern, it is determined as an error, and the position information of the cell is transmitted to the error correction circuit and recorded (step s80).

  After the conversion of the dot pattern of all the cells into byte data is completed, the error correction is performed on the correctable error based on other normally restored information through the error correction circuit (step s90). . Thereafter, address information and the like are demodulated from the data processed by the error correction circuit (step s100), and all recorded data is demodulated (step s110).

Supervised by Tsutomu Shimura “Holographic Memory System and Materials” CM Publishing Japanese Patent Laid-Open No. 9-197947 JP 2000-123133 A JP 2006-179079 A JP 2006-251675 A

  As described above, when information recorded on a recording medium is reproduced, it is common to demodulate the reproduced dot pattern into byte data by comparing it with a conversion table. Here, when the recording density on the recording medium is increased by increasing the multiplicity or the like, the recording condition tends to deteriorate due to the stricter recording conditions. That is, due to a phenomenon such as a decrease in the brightness of a bright spot existing at a position that should be detected as a bright spot or an increase in the brightness of a dark spot existing at a position that should be detected as a dark spot. A dot pattern that does not exist is detected, and as a result, the number of cells that are determined to be errors increases.

  As the number of cells determined to be errors increases, the data that cannot be corrected by the error correction circuit also increases, and the reliability of the recording / reproducing system decreases. Therefore, it is desired from the viewpoint of improving the reliability of the recording / reproducing system to reduce the number of errors that occur when the dot pattern and the conversion table are compared.

  In view of the above problems, the present invention provides an information recording / reproducing method with few errors in an information recording medium that records and reproduces recording information such as a hologram into a dot pattern that is two-dimensional image information.

A first gist of the present invention is an information recording / reproducing method in an information recording medium for recording and modulating recording information into a dot pattern which is two-dimensional image information, and a predetermined number k (k is 1 or more) in the dot pattern. (Integer integer) and a combination of bright spot positions corresponding to numerical data to modulate the recorded information into a dot pattern. When demodulating the recorded dot pattern to the recorded information, an error occurs. In the case of the occurrence of the error, the pixels are ranked in descending order of brightness, the kth pixel is regarded as a dark spot, the k + 1th pixel is regarded as a bright spot, the correspondence with the numerical data is determined, and the recording information is demodulated. The present invention resides in an information recording / reproducing method characterized in that:

According to a second aspect of the present invention, there is provided an information recording / reproducing method in an information recording medium for recording and modulating recording information into a dot pattern that is two-dimensional image information. When a demodulated dot pattern is demodulated from a reproduced dot pattern in a method of modulating recording information into a dot pattern by arranging bright spots of an integer of 1 or more and making the combination of the positions of the bright spots correspond to numerical data If an error occurs, the pixels are ranked in descending order of brightness, the k + 1st pixel is regarded as a bright spot, and the pixels having the 1st brightness from the kth to the first brightness are regarded as dark spots in descending order of brightness. An information recording / reproducing method characterized by determining correspondence with numerical data and demodulating recorded information using a combination of bright spots when no error occurs at first. (Claim 2).

  According to the present invention, even if an error occurs when demodulating the recorded information from the reproduced dot pattern, the obtained bright spot and dark spot information is corrected and the recorded information is demodulated. Therefore, an information recording / reproducing method with few errors during information reproduction can be achieved.

  The information recording / reproducing method of the present invention is used for an information recording medium that records and modulates recording information into a dot pattern that is two-dimensional image information. A typical example of such an information recording medium is a hologram recording medium. In the description of the constituent requirements described below, a recording / reproducing method in a hologram recording / reproducing system is taken as an example. This is an embodiment of the present invention. It is an example (representative example) and is not limited to this example.

(1) Hologram recording / reproducing system There are two types of hologram recording / reproducing systems that have been proposed depending on the configuration of the optical system. One is a coaxial method in which object light and reference light are irradiated coaxially, or a method called a collinear method, and the other is a method called an off-axial method or a two-beam interference method. Hereinafter, the coaxial method will be described with reference to FIG. 5, and the off-axial method will be described with reference to FIG.

(Coaxial method)
An example of a recording method on the recording medium 101 by the coaxial method will be described with reference to FIG. The coherent light emitted from the laser light source (laser diode) 1 is spread to a required size through the collimator lens 2, reflected by the mirror 3, and guided to, for example, a DMD 4 which is a kind of SLM of a spatial light modulator. It is burned. On the DMD 4, for example, as shown in a DMD display pattern 102 in FIG. 5A, an annular band 103 is displayed on the outer periphery, and a two-dimensional dot pattern (recording information) is displayed on the central portion 104. The incident light can be spatially modulated. That is, in the light reflected from the DMD 4, the light corresponding to the annular band 103 corresponds to the reference light 5, and the light corresponding to the central portion 104 corresponds to the object light 6 including recording information.

  Subsequently, the reference light 5 and the object light 6 are coaxially incident on the objective lens 7 to be condensed and irradiated onto the recording medium 101. In the recording layer of the recording medium 101, the reference light 5 and the object light 6 interfere with each other, and light intensity due to interference fringes is generated. As described above, in the recording layer, the optical characteristics such as the refractive index of the photosensitive hologram recording material change corresponding to the intensity of the light, that is, the distribution of the light intensity, and form a kind of diffraction grating. Is recorded. In the case of recording another recording information (hereinafter sometimes referred to as data) on the recording medium 101, in the coaxial method, the incident positions of the reference light 5 and the object light 6 are determined by moving the recording medium 101. change.

  In the case of the coaxial system, for example, a laser light source 1 having a wavelength of 400 nm to 700 nm can be used, but among them, a laser light source 1 having a wavelength of 532 nm or 405 nm is generally used.

  On the other hand, when reproducing recorded information on the recording medium 101, as shown in FIG. 5B, for example, as in recording, the coherent light emitted from the laser light source 1 has a necessary size through the collimator lens 2. Is reflected by the mirror 3 and guided to the DMD 4. On the DMD 4, for example, as shown in the DMD display pattern 105 in FIG. 5B, only the annular band 106 is displayed on the outer periphery, so that the reflected light from the DMD 4 can be only the reference light 5. . The reference light 5 is condensed by the objective lens 7 and irradiated to a position where information to be reproduced by the recording medium 101 is recorded. The irradiated reference light 5 is diffracted by the diffraction grating recorded on the recording medium 101, and the reproduction light 8 in which the object light 6 at the time of recording is reproduced is reflected. The reproduction light 8 reflected from the recording medium 101 passes through the objective lens 7 and is further guided to the image sensor (image sensor) 10 by the dichroic beam splitter 9. As shown in the image sensor detection image 107, the image detected by the image sensor 10 becomes a pattern 108 including the two-dimensional dot pattern of the DMD display pattern 102 shown in FIG. 5A described above, and this pattern 108 is analyzed. The recorded information is demodulated. Here, as the image pickup element 10, a CCD (Charge Coupled Device), a CMOS (Complementary Metal-Oxide Semiconductor) image sensor, or the like can be generally used.

  In FIG. 5, the DMD is used as the spatial light modulation element. However, other types of spatial light modulation elements such as a liquid crystal type or a type using a magneto-optical effect may be used. In FIG. 5B, reflected light from the recording medium is used as reproduction light, but transmitted light can also be used as reproduction light. As such a coaxial hologram recording / reproducing system, a commercially available system can be used as appropriate. In the present invention, SHOT-1000 manufactured by Pulstec Corporation is used as an evaluation machine for the coaxial hologram recording / reproducing system in the examination of the following examples.

(Off-axial method)
On the other hand, in the recording in the off-axial system shown in FIG. 6, after the coherent light emitted from the laser light source (laser diode) 1 passes through the collimator lens 2, the beam splitter 9 uses the light 6 ′ for object light. And reference light 5. The object light 6 ′ passes through a transmissive spatial light modulator (SLM) 11. For example, as shown in the SLM display pattern 109 in FIG. 6A, the SLM 11 displays the recording information 104 converted into a two-dimensional dot pattern, so that incident light can be spatially modulated. it can. That is, the light that has passed through the SLM 11 becomes the object light 6 including the recording information. This object light 6 is condensed through the objective lens 7 and enters the recording medium 101 as a spherical wave.

  On the other hand, the reference light 5 passes through a series of galvanometer mirrors 12 and enters the recording medium 101 so as to overlap the object light 6 at an angle θ with the object light 6. Thereafter, as in the case of the coaxial method described above, information is recorded on the recording medium 101 by the object light 6 and the reference light 5 interfering in the recording layer.

  In the off-axial method, when further data is recorded on the recording medium 101, the galvano mirror 12 is driven to change the angle θ between the reference light 5 and the object light 6, or the recording medium 101 It becomes possible to record new data by the method of moving.

  When reproducing the recorded information on the recording medium 101, as shown in FIG. 6B, the coherent light emitted from the laser light source 1 is spread to a necessary size through the collimator lens 2, and the recording medium 101 The galvano mirror 12 is driven to irradiate the reference light 5 at a position where information to be reproduced is recorded so that the incident angle to the recording medium 101 is the same angle θ as that at the time of recording. The reference light 5 irradiated to the recording medium 101 is diffracted by the diffraction grating recorded on the recording medium 101 to become reproduction light 8 in which the object light 6 at the time of recording is reproduced. The reproduction light 8 passes through the recording medium 101, passes through the objective lens 7, and is guided to the image sensor (image sensor) 10. As shown in the image sensor detection image 110, the image detected by the image sensor 10 becomes a pattern 111 corresponding to the SLM display pattern 109 in FIG. 6A described above, and this pattern 111 is analyzed to demodulate the recorded information. Is done.

  In FIG. 6, a transmissive SLM has been described. However, a reflective SLM such as a DMD may be used. In FIG. 6, the light transmitted through the recording medium 101 is used as the reproduction light, but the reflected light can be used as the reproduction light 8.

  In addition to the above two methods, apart from the laser beam used for recording / reproduction, for example, in order to obtain address information, focus signal, tracking signal, etc. necessary for recording / reproduction, a wavelength different from the recording / reproduction laser wavelength is used. Laser light can be used as servo light. The servo light generally uses a laser wavelength different from that of the object light and the reference light, and a laser wavelength of 600 nm or more is preferably used. The wavelength is preferably 900 nm or less, more preferably 700 nm or less.

  Hereinafter, the present invention will be described using the coaxial method, and the coaxial method is also used in the embodiments. Needless to say, the present invention is also applicable to the off-axial method.

(2) Hologram recording / reproducing method In the hologram recording / reproducing system, as described above, first, recording information is modulated into a two-dimensional dot pattern, and this is recorded on a recording medium as image information. At the time of reproduction, the dot pattern as reproduced image information is demodulated into recording information, and the recording information is reproduced.

The modulation method that can be used in the present invention is a method in which recording information is modulated into a two-dimensional dot pattern, and this is recorded as image information on a recording medium, so long as the effects and objects of the present invention are not impaired. There is no particular limitation, for example, a fixed number k (k is an integer of 1 or more, k <m) is arranged in a dot pattern consisting of m pixels, and the combination of the positions of the bright points corresponds to numerical data. By doing so, a method of modulating recording information into a dot pattern can be used. As such a modulation method, for example, a 3/16 modulation method as shown in FIG. 2 can be cited. Hereinafter, the 3/16 modulation method will be described as an example, but the same applies to other modulation methods. .
In the 3/16 modulation method, 8-bit data is represented as the positions of three bright spots in 16 dots (m = 16, k = 3), and other bright spots exist above, below, left and right of the bright spots. It is prescribed not to.

  Here, when the present inventor analyzed a dot pattern in which an error occurred when recording / reproducing in a hologram recording / reproducing system using a 3/16 modulation method, a certain tendency was observed in the error occurrence state. Was found. This tendency is the same in other modulation schemes.

  Specifically, for example, as shown in FIG. 7, when two luminescent spots exist with a distance of one pixel, or when they are diagonally adjacent, pixels between these luminescent spots, or these luminescent spots. The brightness of the pixel that touches the two sides increases, and the pixel that should originally be a dark spot is mistakenly determined as a bright spot, so it has been found that errors tend to occur frequently (hereinafter, erroneously determined as bright spots) The point (pixel) is also called a false bright spot.)

  As described above, the phenomenon in which the brightness of high-brightness pixels or the brightness of adjacent pixels increases is caused by the fact that the recording resolution of the hologram recording material in the recording layer is less than the resolution of the light interference fringes, or the dynamic range of the hologram recording material It is presumed that this is due to the fact that the high frequency components of the interference fringes generated in the recording layer are not accurately recorded on the recording medium due to the lowness.

  In the information recording / reproducing method of the present invention, the dot pattern recognized in error is corrected to the original dot pattern. In the present invention, since the recorded information is demodulated at the time of comparison between the dot pattern and the conversion table, the number of errors sent to the error correction circuit can be suppressed, and a highly reliable recording / reproducing system can be obtained. . The information recording / reproducing method of the present invention has two embodiments. Hereinafter, each embodiment will be described.

(First embodiment)
In the first embodiment, in an information recording medium that records and modulates recording information into a dot pattern that is two-dimensional image information, a certain number k (k is an integer of 1 or more) bright spots are included in the dot pattern. This is a method that modulates the recording information into a dot pattern by arranging and combining the position of the bright spot with the numerical data.If an error occurs when demodulating the recorded information from the reproduced dot pattern, the luminance The pixels are ranked in descending order, the kth pixel is regarded as a dark spot, the k + 1th pixel is regarded as a bright spot, the correspondence with numerical data is determined, and the recorded information is demodulated. .

  Hereinafter, a two-dimensional dot pattern is created by a 3/16 modulation method, and a result obtained when recording / reproduction is performed on a recording medium by using SHOT-1000 manufactured by Pulstec Corporation is used to focus on one cell. Will be described in detail.

  FIG. 8A shows a dot pattern used for recording. Here, the dot pattern corresponds to the numerical value 6. FIG. This dot pattern is a dot pattern in which luminescent spots are present at intervals of one pixel and errors are likely to occur.

  FIG. 8B illustrates the luminance value at each pixel when the area in which FIG. 8A is recorded is reproduced. Looking at each luminance value, the luminance value of the pixel between the bright spots, which should be the dark spot, is 79, which exceeds the luminance 60 of the upper right pixel, which should be the bright spot. Here, in the 3/16 modulation method, since the number of bright spots in one cell is determined to be 3, the upper 3 pixels of the luminance value are determined to be 1 (on), and the others are determined to be 0 (off). . Therefore, the reproduced dot pattern is regarded as the pattern of FIG. 8C, and a dot pattern different from the recorded dot pattern (FIG. 8A) is detected. Further, in the 3/16 modulation method, since it is specified that adjacent pixels do not become bright spots at the same time, there is no numerical data corresponding to this dot pattern, and this cell is detected as an error.

  Here, in the conventional method, when this cell is determined to be in error, the position information of this cell is sent to the error correction circuit. Thereafter, the error correction circuit may correct this error based on other normally restored information. However, as the number of cells determined to be errors in the data page increases, data that cannot be corrected by the error correction circuit increases, and the reliability of the recording / reproducing system decreases.

  Therefore, in this embodiment, the record information is demodulated before the cell position information is sent to the error correction circuit. A specific mode will be described with reference to FIG.

  If the dot pattern at the time of recording is a pattern as shown in FIG. 9A, and luminance information as shown in FIG. 9B is obtained, the dot pattern shown in FIG. It is determined that it is an error. Therefore, in the present embodiment, of the luminance information shown in FIG. 9B, the pixel having the luminance value k, which is the third highest luminance value in this case, is regarded as the dark spot. Furthermore, the pixel of the k + 1th, that is, the fourth luminance value 60 is regarded as a bright spot. Accordingly, the dot pattern is regarded as shown in FIG. 9E, and matches the dot pattern FIG. 9A during recording. Accordingly, the corresponding numerical data is correctly demodulated, and the occurrence of errors can be suppressed.

(Second Embodiment)
According to a second embodiment, in an information recording medium that records and modulates recording information into a dot pattern that is two-dimensional image information, a certain number k (k is an integer of 1 or more) bright spots are included in the dot pattern. When an error occurs when demodulating recorded information from a reproduced dot pattern when using a method that modulates the recorded information into a dot pattern by arranging and matching the combination of bright spot positions to numerical data The pixels are ranked in descending order of brightness, the k + 1st pixel is regarded as a bright spot, and the pixels having the 1st brightness from the kth to the first brightness are regarded as dark spots in order from the lowest brightness to correspond to numerical data. The recording information is demodulated by using the combination of bright spots in the case where a determination is made and no error first occurs.

  Even when the recording information is demodulated in the first embodiment, if there is no dot pattern corresponding to the obtained pattern, the second embodiment demodulates the numerical data. Is preferably performed.

  This embodiment will be described with reference to the flowchart of FIG. First, the luminance is read from the image element (step ss10), and each position detection mark is detected (step ss20). Thereafter, each subframe is cut out (step ss30), and further cut out for each cell (step ss40). Subsequently, the pixels in each cell are assigned in order of increasing luminance (step ss50), assumed as bright spots in order of increasing luminance (step ss60), and the reproduction pattern is compared with a predetermined data pattern (step ss70). At this time, if the reproduction pattern exists, the numerical data corresponding to the data pattern is converted into bytes (step ss80).

  On the other hand, if it is determined that the reproduction pattern is an error, the pixel with the highest brightness of k + 1 is regarded as a bright spot (step ss90). Here, for convenience, it is assumed that the variable i = k (step ss100), and the i-th (here, k-th) pixel having the highest brightness is assumed to be a dark spot (step ss110) to determine whether a corresponding data pattern exists. (Step ss120). If there is a corresponding data pattern, the numerical data corresponding to the data pattern is treated as demodulated data and converted into bytes (step ss80). If the corresponding data does not exist, that is, it is an error, it is determined whether the variable i is 1 (step ss130). Otherwise, the variable i = i-1 is set (step ss140). .

  Subsequently, the i-th, that is, the k-th highest point (k-1) is assumed to be a dark point (step ss110), and it is determined whether corresponding data exists (step ss120). If an error further occurs, the same procedure is repeated with the variable i = i−1. That is, the same procedure is repeated until no error occurs until the pixel having the highest luminance in order of k-2 and k-3 (steps 110, 120, and 130). When this procedure is repeated, the numerical data corresponding to the combination of bright spots when no error has occurred first is adopted as demodulated data of the dot pattern and converted into bytes (step ss80). If the error is not resolved even after the first highest luminance pixel, the dot pattern data is treated as an error, and the cell position information is transmitted to the error correction circuit. It is recorded (step ss150).

  After the conversion of dot patterns of all cells into byte data is completed, error correction is performed on the above-described correctable error based on other normally restored information (step ss160). Thereafter, address information and the like are demodulated from the data processed by the error correction circuit (step s170), and all recorded data is demodulated (step s180).

(3) Recording medium FIG. 11 shows an example of a layer structure of a recording medium used in the hologram recording / reproducing method described above. FIG. 11 is a partial schematic cross-sectional view schematically.

  FIG. 11A shows a recording medium 101 mainly used in the coaxial system, and the reference light 5 for reproduction incident on the recording medium 101 is reflected in the recording medium 101, and the incident surface of the reference light 5 It is emitted from the same surface as reproduction light 8 (hereinafter referred to as a reflection type). On the other hand, FIG. 11B shows a recording medium 101 mainly used in an off-axial system, and the reference light 5 for reproduction incident on the recording medium 101 is transmitted through the recording medium 101 and incident on the reference light 5. It is emitted as reproduction light 8 from the surface opposite to the surface (hereinafter referred to as transmission type). The present invention can be applied to any type of recording medium 101. Hereinafter, the layer structure of each type of recording medium will be described.

(A) Reflection type recording medium As a configuration of the reflection type recording medium 101 shown in FIG. 11A, for example, an AR (Anti-Reflect) coating layer 31 from the surface on which the reference light 5 is incident. The first substrate 32, the recording layer 33, the wavelength selection film 34, the spacer layer 35, the reflection layer 36, and the second substrate 37 may be stacked in this order. In addition, unless the objective and effect of this invention are impaired, it is not limited to the said structure, The structure without any layer may be sufficient, and the formation order may differ as needed. In addition to the above layers, necessary layers may be appropriately formed.

For convenience of explanation, in the recording medium, the side on which the AR coating layer 31 on which the laser light is incident is the upper side, and the side on which the second substrate 37 is present is the lower side. Let each surface be the upper surface and the lower surface of each layer.
Details of each layer will be described below.

(A) AR Coat Layer The AR coat layer 31 is provided so that incident laser light is not reflected on the upper surface of the first substrate 32. Accordingly, the recording medium 101 is provided on the surface on the incident side of laser light (for example, the reference light 5). If the recording light is reflected on the surface of the recording medium 101, the intensity of the laser light incident on the recording layer 33 is reduced, and the recording sensitivity is lowered. Further, when the reference light 5 is incident on the recording medium 101 at the time of reproduction, if there is light reflected on the surface of the first substrate 32, the light reflected from the surface is superimposed on the reproduction light 8, which causes noise. It becomes. In order to suppress these influences, it is preferable that the AR coating layer 31 has a reflectance of 10% or less, preferably 1% or less at the wavelength used.

  In general, the AR coat layer 31 can be formed by alternately laminating a high refractive index dielectric material and a low refractive index dielectric material. The number of layers is usually 2 or more, and usually 20 or less, preferably 10 or less. The film thickness per layer of the high refractive index dielectric material is usually 10 nm or more. The thickness is usually 200 nm or less, preferably 100 nm or less. On the other hand, the film thickness per layer of the low refractive index dielectric material is usually 10 nm or more, preferably 100 nm or more. Moreover, it is normally set to 200 nm or less. The film thickness of the entire AR coating layer 31 is usually 100 nm or more, preferably 300 nm or more. Moreover, it is 1000 nm or less normally, Preferably it is 500 nm or less.

  The film thickness and the layer configuration of each layer can be obtained, for example, by multilayer simulation. A number of configurations having a predetermined reflectance characteristic are obtained by multilayer simulation. Among these, it is preferable to adopt a layer configuration in which the reflectance variation is the smallest for each film thickness variation and refractive index variation. .

Examples of the high refractive index dielectric material include Bi ₂ O ₃ , CeO ₂ , CeF ₃ , HfO ₂ , SiO, Ta ₂ O ₅ , TiO ₂ , Y ₂ O ₃ , ZnSe, ZnS, ZrO _{2 and the} like. These can be used alone or in combination of two or more in any ratio and combination. Of these, SiO, Ta ₂ O ₅ , TiO ₂ , Y ₂ O ₃ , ZnSe, ZnS, and ZrO ₂ are more preferable.

On the other hand, examples of the low refractive index dielectric material include Al ₂ O ₃ , CaF ₂ , MgF ₂ , MgO, SiO ₂ , Si ₂ O _{3, and the} like. Can be used in any ratio and combination.

  Examples of the film formation method of the high refractive index dielectric material and the low refractive index dielectric material include a vacuum deposition method, a sputtering method, a chemical vapor deposition method (CVD method), and the like. Only one of these may be used, or any combination thereof may be used. Among these, the vacuum evaporation method and the sputtering method are preferable, and the sputtering method is more preferable.

(B) First Substrate The function of the first substrate 32 is mainly physical protection of the recording medium 101. Further, by using the first substrate 32, the distance between the recording layer 33 and the surface of the recording medium 101 can be secured. If there is a distance between the recording layer 33 and the surface of the recording medium 101, the beam spot on the surface of the recording medium 101 can be expanded to a size of several mm. Therefore, even when dust of about several hundred μm exists on the surface, the intensity of the light condensed on the recording layer 33 does not change greatly, and stable recording / reproduction is possible.

  As the material of the first substrate 32, various materials can be used as long as they are basically transparent at the wavelengths of recording light, reproducing light, and servo light. For example, acrylic resin, methacrylic resin, polycarbonate resin, polyolefin resin (especially amorphous polyolefin), polyester resin, polystyrene resin, epoxy resin, and the like; glass, and the like, Two or more kinds can be used in any ratio and combination. A substrate having a structure in which a resin layer made of a radiation curable resin such as a photocurable resin is provided on glass can also be used. Among these, from the viewpoint of high productivity, cost, moisture absorption resistance, etc., the polycarbonate resin used in the injection molding method is preferable, and from the viewpoint of chemical resistance and moisture absorption resistance, amorphous polyolefin is preferable. Furthermore, glass is preferable from the viewpoint of high-speed response.

  The film thickness of the first substrate 32 is usually 100 μm or more, more preferably 500 μm or more. Moreover, it is usually 1000 μm or less, more preferably 700 μm or less. As a result, the distance between the surface of the recording medium 101 and the recording layer 33 can be set within a suitable range.

(C) Recording layer The recording layer 33 may be formed of, for example, a photosensitive hologram recording material. As described above, it is preferable that the optical characteristics such as the refractive index of the hologram recording material change according to the interference pattern of the recording light. As the hologram recording material, photopolymers made of various resins are usually used. As the resin for forming the recording layer 33, for example, a photo-curing or thermosetting resin, specifically, a polymer that is polymerized by a radical reaction of an ethylenically unsaturated double bond-containing compound such as acrylic or methacrylic, , A photocurable monomer such as an epoxy-based one that undergoes a cation reaction with light, a material containing a binder resin that can be photocured or heat-cured as necessary, poly (p-hydroxystyrene), and hexamethoxymethyl A combination of melamine and the like is conceivable, but it is appropriately selected according to the recording method.

  Examples of the method for forming the recording layer 33 include various commonly used thin film forming methods such as a doctor blade method, a casting method, and a spin coating method. In addition to the above, for example, a method of injecting a hologram recording material between the first substrate 32 mechanically held and the second substrate 37 manufactured up to the wavelength selection film 34, or the first substrate 32 And a second substrate 37 formed up to the wavelength selection film 34, a material is applied, a spacer is inserted between the two substrates, and a method of pressing is used.

Examples of the method for curing the film after formation include thermal curing and ultraviolet curing. Since these curing methods vary depending on the type of hologram recording material, it is preferable to employ a curing method suitable for the hologram recording material.
Further, an appropriate buffer layer or the like may be provided at both interfaces of the recording layer 33 in order to prevent turbidity with a substance in contact with the surface.

  The film thickness of the recording layer 33 is usually 100 μm or more, more preferably 600 μm or more. Also, it can be usually 2000 μm or less, more preferably 1500 μm or less.

(D) Reflective layer The reflective layer 36 is usually formed to reflect servo light and return the focus signal and tracking signal necessary for controlling the medium to the pickup optical system. For this reason, the reflective layer 36 is required to have a certain reflectance with respect to the servo light. The reflective layer 36 is formed above a second substrate 37 (to be described later) on which address signals or the like are normally recorded as irregularities, and the interface shape on the upper surface of the reflective layer 36 has an irregular shape on the upper surface of the second substrate 37. Is reflected. The servo light is normally adjusted so as to be focused on the upper surface of the reflective layer 36, and the servo light is reflected by the reflective layer 36 to obtain reflected light corresponding to the uneven signal on the second substrate 37. Address information, focus signal, tracking signal, etc. can be obtained.

  The reflective layer 36 desirably has high reflectivity and high durability. The reflectance of the reflective layer 36 with respect to the servo light is usually 50% or more, preferably 80% or more, and more preferably 90% or more.

  The thickness of the reflective layer 36 is preferably 50 nm or more, and preferably 300 nm or less. Examples of the material of the reflective layer 36 include materials having a sufficiently high reflectance at the wavelength of the servo light. For example, metals such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, and Pd are used. It can be used alone or as an alloy. Among these, Au, Al, and Ag have high reflectivity and are suitable as a material for the reflective layer. In addition to these metals as main components, other materials may be added. Here, the “main component” means that whose content is 50% by weight or more. Examples of materials other than the main component include Mg, Se, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, Cu, Zn, Cd, Ga, In, Si, Mention may be made of metals and semi-metals such as Ge, Te, Pb, Po, Sn, Bi, Ta, Ti, Pt, Pd, Nd. Among these, those containing Ag as a main component are particularly preferable from the viewpoints of low cost and high reflectivity.

  For example, an alloy containing not less than 0.1 atomic% and not more than 5 atomic% of one or more atoms selected from Au, Pd, Pt, Cu, and Nd in Ag has high reflectivity, high durability, high sensitivity, and Low cost and preferable. Specific examples include an Ag / Pd / Cu alloy, an Ag / Cu / Au alloy, an Ag / Cu / Au / Nd alloy, and an Ag / Cu / Nd alloy. It is also possible to form a multilayer film by alternately stacking a low refractive index thin film and a high refractive index thin film made of a material other than metal, and use this as the reflective layer 36.

  Examples of the method for forming the reflective layer 36 include sputtering, ion plating, chemical vapor deposition, and vacuum vapor deposition. Further, in order to reduce the influence of the recording light and the reference light at the time of reproduction, it is possible to apply a dye or the like that absorbs the laser wavelength of the recording light or the reference light at the time of reproduction on the reflective layer 36.

(E) Spacer layer The spacer layer 35 is usually formed between the reflective layer 36 and the wavelength selection film 34. When recording a hologram image by the coaxial method, since the recording light is collected by the objective lens, the recording light forms a conical light beam in the recording layer. Therefore, the density of the luminous flux of the recording light, that is, the light intensity, increases as it approaches the apex (closer to the focal point) in this cone.

  On the other hand, the recordable light intensity range (dynamic range) of the hologram recording material is naturally limited, and it is difficult to accurately record light intensity exceeding this range. For this reason, when the focal point of the recording light is present in the recording layer 33, there is a high possibility that a light intensity higher than the dynamic range of the recording medium is present near the focal point, and recording that accurately reflects the light intensity distribution of the recording light. There is a tendency not to be able to. Therefore, as a countermeasure against this phenomenon, it is effective to adjust the focus of the recording light so as to be located outside the recording layer 33.

  On the other hand, in consideration of reproduction compatibility in various recording / reproducing apparatuses (hereinafter sometimes referred to as drives), the positional relationship between the focal points of the recording light and the servo light is important. If the relationship is different, compatibility may be lost. When optical adjustment is considered, the easiest adjustment as the positional relationship between the two is to make the focal depths of the recording light and the servo light the same.

  However, as described above, since the servo light is adjusted so as to be focused on the upper surface of the reflective layer 36, for example, when the recording layer 33 and the reflective layer 36 are in contact with each other as shown in FIG. If the focal depths of the light 42 and the recording light 41 are the same, the vicinity of the focal point of the recording light 41 exists in the recording layer 36, and the problem of the dynamic range is likely to occur.

  Therefore, for example, as shown in FIG. 12B, a spacer layer 35 having an appropriate transmittance and thickness with respect to both the servo light 42 and the recording light 41 is provided between the recording layer 33 and the reflective layer 36. Thus, the focal points of the recording light and the servo light can be taken out of the recording layer 35, and the adjustment of the optical system can be facilitated.

  Here, if the dynamic range of the recording layer 33 is sufficient, the spacer layer 35 may not be provided. Also, the spacer layer 35 can be omitted when the adjustment of the optical system can be compensated and the focus of the servo light 42 and the recording light 41 can be shifted.

The material of the spacer layer 35 is not particularly limited as long as it has a certain degree of transparency to the servo light. The transmittance is usually 50% or more, preferably 80% or more, more preferably 90% or more. Examples of the material of the organic substance include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, and an ultraviolet curable resin. Examples of the inorganic substance include silicon oxide, silicon nitride, magnesium fluoride (MgF ₂ ), tin oxide (SnO ₂ ), and the like.

  As a method for forming the spacer layer 35, a coating method such as a spin coating method or a casting method, a method such as a sputtering method or a chemical vapor deposition method is used, and the spin coating method is particularly preferable. The spacer layer 35 can be formed by, for example, a method of bonding a film or sheet-like layer with an adhesive.

(F) Wavelength selection film The wavelength selection film 34 is provided between the recording layer 33 and the spacer layer 35 in order to selectively transmit and reflect the servo light and the reference light 5 for recording and reproduction. . That is, it is preferable to have a function of transmitting the servo light and partially reflecting the reference light 5 for recording and reproduction. The reason why such a function is preferable is as follows.

  As described above, the address information of the recording medium is recorded by providing irregularities on the upper surface of the second substrate 37, and the reflection layer 36 reflecting the irregularities of the second substrate 37 is irradiated with servo light to reflect the reflection. By detecting light, it is possible to obtain a focus signal, a tracking signal, and the like.

Therefore, it is preferable that only the servo light reaches the reflective layer 36. When the reference light 5 for recording and reproduction reaches the reflective layer 36, there is only a possibility that the servo light is superimposed as noise. However, the reflected light due to the unevenness of the reflective layer is also superimposed on the reproduction light, which may cause noise of the reproduction light.
Therefore, it is preferable that the wavelength selection film 34 has a characteristic of transmitting the servo light as much as possible and reflecting the reference light 5 for recording and reproduction.

As a characteristic of the wavelength selection film 34, the transmittance is usually 80% or more, and more preferably 90% or more, with respect to the laser wavelength of the servo light. On the other hand, with respect to the laser wavelength of the reference light 5 for recording and reproduction, the reflectance is usually preferably 60% or more, and more preferably 80% or more.
By giving the above characteristics, noise components can be reduced, and good recording and reproduction can be performed.

  In general, the wavelength selection film 34 can be produced by alternately laminating a high refractive index dielectric material and a low refractive index dielectric material, similarly to the AR coating layer 31. The number of layers is usually 2 or more, and usually 20 or less, more preferably 10 or less.

  The film thickness per layer of the high refractive index dielectric material is usually 10 nm or more, and is usually 200 nm or less, preferably 100 nm or less. The film thickness per layer of the low refractive index dielectric material is usually 10 nm or more, preferably 100 nm or more. Moreover, it is 200 nm or less normally. The film thickness of the entire wavelength selection film 34 is usually 100 nm or more, preferably 300 nm or more. Moreover, it is 1000 nm or less normally, Preferably it is 500 nm or less.

  The film thickness and the layer configuration of each layer are obtained, for example, by multilayer simulation. Multi-layer simulations require many configurations with predetermined reflectance characteristics. Among these, the layer configuration has the smallest predetermined reflectance (transmittance) variation for each film thickness variation and refractive index variation. Is preferably adopted.

Examples of the high refractive index dielectric material include Bi ₂ O ₃ , CeO ₂ , CeF ₃ , HfO ₂ , SiO, Ta ₂ O ₅ , TiO ₂ , Y ₂ O ₃ , ZnSe, ZnS, and ZrO _2. These may be used alone or in combination of two or more in any ratio and combination. Of these, SiO, Ta ₂ O ₅ , TiO ₂ , Y ₂ O ₃ , ZnSe, ZnS, and ZrO ₂ are more preferable.

On the other hand, examples of the low refractive index dielectric material include Al ₂ O ₃ , CaF ₂ , MgF ₂ , MgO, SiO ₂ , Si ₂ O _{3, and the} like. Any ratio and combination can be used.

  Examples of the method for forming each dielectric material include a vacuum deposition method, a sputtering method, a chemical vapor deposition method (CVD method), and the like, and these may be combined as necessary. Among these, the vacuum evaporation method and the sputtering method are preferable, and the sputtering method is more preferable.

(G) Second substrate The second substrate 37 is disposed at a position farthest from the laser beam incident side in the recording medium. Various materials can be used as the material of the second substrate 37. Examples thereof include acrylic resins, methacrylic resins, polycarbonate resins, polyolefin resins (particularly amorphous polyolefins), polyester resins, polystyrene resins, epoxy resins, and the like; glass and the like. For example, a substrate having a structure in which a resin layer made of a radiation curable resin such as a photocurable resin is provided on glass can be used. Among these, from the viewpoint of high productivity, cost, moisture absorption resistance, etc., the polycarbonate resin used in the injection molding method is preferable, and from the viewpoint of chemical resistance and moisture absorption resistance, amorphous polyolefin is preferable. Furthermore, glass is preferable from the viewpoint of high-speed response.

  The upper surface of the second substrate 37 is usually formed with irregularities, and guide grooves and pits are formed. Address information etc. can be recorded by the shape of these guide grooves and pits, and the address information etc. can be read and focused by irradiating the reflective layer reflecting these shapes with servo light and detecting the reflected light. Signals, tracking signals, etc. can be obtained. Examples of the shape of the guide groove include a concentric shape and a spiral shape with respect to the center of the recording medium 101. When the spiral guide groove is formed, the groove pitch is preferably 0.2 μm or more and usually 1.2 μm or less.

  As a method for forming such irregularities, for example, when a resin substrate is injection-molded, a stamper having an irregular pattern complementary to a desired irregular pattern is used as a part of a mold, and the irregular pattern is formed on the substrate surface. The method of forming by transferring is mentioned.

(B) Transmission Type Recording Medium Next, the transmission type recording medium shown in FIG. 11B will be described. As a configuration of the transmission type recording medium, for example, the AR coating layer 31, the first substrate 32, the wavelength selection film 34, the recording layer 33, the spacer layer 35, and the second substrate 37 are arranged from the surface on which the reference light is incident. The layers may be laminated in this order. In addition, unless the objective and effect of this invention are impaired, it is not limited to the said structure, The structure without any layer may be sufficient, and the formation order may differ as needed. In addition to the above layers, necessary layers may be appropriately formed.

  For convenience of explanation, in the recording medium, the side on which the AR coating layer 31 on which the laser light is incident is the upper side, and the side on which the second substrate 37 is present is the lower side. Let each surface be the upper surface and the lower surface of each layer.

The address information in the transmission type recording medium is recorded by providing irregularities on the incident side surface or the emission side surface of the reference light and recording light of the first substrate 32. When unevenness is provided on the incident side, the AR coating layer 31 can also serve as a wavelength selection film.
On the other hand, when unevenness is provided on the emission side, the wavelength selection film 34 is used on the lower surface of the first substrate 32.

  In addition, the formation method, materials, and the like of the AR coating layer 31, the first substrate 32, the recording layer 33, and the second substrate 37 in the transmission type recording medium are the same as those in the case of the reflection type recording medium. be able to. The method for forming the unevenness provided on the first substrate 32 can be the same as the method for forming the unevenness on the second substrate 37 of the reflection type recording medium described above.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by a following example, unless it deviates from the summary.

Example 1
In this example, a polyester photopolymer was used as the hologram recording material. The photopolymer was a mixture of a matrix material A for supporting the structure of the hologram recording material and a monomer material A that causes a refractive index change by being polymerized by irradiation with light. The configuration of the recording medium of the present example was a structure according to FIG. However, the wavelength selection film 34 and the spacer layer 35 are omitted depending on the specifications of the SHOT-1000 used for the measurement.

  A hologram recording material for forming a recording layer 33 on the silver alloy reflective film 36 by preparing a second substrate 37 on which the silver alloy reflective film 36 is formed and a first substrate 32 on which the AR coat layer 31 is formed. And the second substrate 37 was pressed against the first substrate 32 to uniformly form the hologram recording material on the substrate. Thereafter, the hologram recording material was thermally cured by placing in a high-temperature bath at 60 ° C. to form the recording layer 33, and the recording medium A was produced.

As the hologram recording / reproducing system, SHOT-1000 manufactured by Pulstec was used, and the modulation method was a 3/16 modulation method. For recording / reproduction, one data page having 64 subframes shown in FIG. 3 was used. That is, the number of cells to be recorded was 2048.
When the above information was recorded and reproduced, and dot patterns were compared by a conventional method, 22 errors were detected in 2048 reproduction data demodulated over the entire data page.
On the other hand, when data was demodulated using the first embodiment of the recording information demodulation method of the present invention, the number of errors could be reduced to five. Further, the second embodiment of the recording information demodulating method according to the present invention is applied to the dot pattern that could not be demodulated in this data. In this case, however, the number of errors is not improved and the error is 5 The pieces remained.

(Examples 2 and 3)
In the second and third embodiments, the recording / reproducing system and the modulation method are the same as those in the first embodiment, and the amount of information to be recorded is 10 data pages, which is 10 times that in the first embodiment.
In Example 2, the same recording medium A as in Example 1 was used, and in Example 3, the recording medium B was used.
For the recording medium B, the monomer material of the recording medium A described above was changed and a polyester material (monomer material B) was used.

Normally, the monomer material B is disadvantageous in terms of sensitivity because the polymerization phenomenon is less than that of the monomer material A at the same light amount as that of the monomer material A. However, since the polymerization reaction occurs in a narrower range than the monomer material A, there is little noise during reproduction.
The same method as in Example 1 was performed, and for each recording medium, the number of errors after recording and reproduction in the conventional method and the number of errors after using the first embodiment of the recording information demodulation method in the present invention Table 1 shows the results of the comparison.
Table 2 shows a comparison between the case where only the demodulation method according to the first embodiment is performed and the case where the second embodiment is performed regarding errors remaining after the first embodiment. From Tables 1 and 2, the number of errors can be greatly reduced by using the first embodiment, and the number of errors can be further reduced by about 10% by using the second embodiment. Was obvious.

  In any of the above-described embodiments, it was clear that the number of errors was significantly reduced as compared with the conventional method. From this result, it can be seen that this reproducing method is effective regardless of the type of hologram recording material.

  The present invention can be applied to a large-capacity, high-density information recording medium that records information as two-dimensional image data, such as hologram recording that performs recording using the hologram technology of the present invention.

It is a flowchart which shows the flow of the data at the time of the recording in hologram recording. It is explanatory drawing explaining a 3/16 modulation system. It is explanatory drawing explaining the structure of a data page. It is a flowchart which shows the flow of the data at the time of reproduction | regeneration in hologram recording. It is a figure explaining the hologram recording / reproducing system of a coaxial system. It is a figure explaining the hologram recording / reproducing system of an off-axial system. It is explanatory drawing for demonstrating a false bright spot. It is explanatory drawing for demonstrating the occurrence condition of an error. It is explanatory drawing explaining the principle of the error reduction in the 1st embodiment of this invention. It is a flowchart explaining the flow of the error correction at the time of reproduction | regeneration in the 2nd embodiment of this invention. It is a schematic sectional drawing which represents typically the structure of a recording medium. It is explanatory drawing for demonstrating the spacer layer in a recording medium.

Explanation of symbols

1 Laser light source 2 Collimator lens 3 Mirror 4 DMD
5 Reference Light 6 Object Light 7 Objective Lens 8 Reproduction Light 9 Beam Splitter 10 Image Sensor 11 SLM
12 Galvano mirror 31 AR coating layer 32 First substrate 33 Recording layer 34 Wavelength selection film 35 Spacer layer 36 Reflective layer 37 Second substrate 101 Recording medium 102, 105 DMD display pattern 109 SLM display pattern

Claims (2)

In an information recording / reproducing method in an information recording medium for recording and modulating recording information into a dot pattern which is two-dimensional image information,
A method of modulating recording information into a dot pattern by arranging a certain number of bright spots (k is an integer equal to or greater than 1) in the dot pattern and making the combination of bright spot positions correspond to numerical data.
If an error occurs when demodulating recorded information from the reproduced dot pattern, the pixels are ranked in descending order of brightness, the kth pixel is regarded as a dark spot, and the k + 1st pixel is regarded as a bright spot. An information recording / reproducing method characterized by determining correspondence with numerical data and demodulating recorded information. In an information recording / reproducing method in an information recording medium for recording and modulating recording information into a dot pattern which is two-dimensional image information,
A method of modulating recording information into a dot pattern by arranging a certain number of bright spots (k is an integer equal to or greater than 1) in the dot pattern and making the combination of bright spot positions correspond to numerical data.
If an error occurs when demodulating recorded information from the reproduced dot pattern, the pixels are ranked in descending order of brightness, and the (k + 1) th pixel is regarded as a bright spot,
From the k-th pixel to the first luminance pixel, it is regarded as a dark spot in ascending order of luminance, the correspondence with the numerical data is judged, and the recorded information is used using the combination of bright spots when no error first occurs. An information recording / reproducing method comprising:

Images