JP2009176349A - Reproducing device, reproducing method, recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discriminate all values multi-value-recorded in the intensity direction even when a dynamic range of an image sensor becomes narrower than a dynamic range of reproduction light. <P>SOLUTION: At least either of power of irradiation light or light receiving sensitivity of an image sensor is controlled so that a dynamic range of reproduction light of a part of value is successively within a dynamic range of the image sensor out of multi-values recorded in a recording medium. Then, out of values of a pixel unit received under respective control states, a value within the dynamic range of the image sensor is selected. Thereby, all values being multi-value-recorded can be discriminated even when a dynamic range of an image sensor becomes narrower than a dynamic range of reproduction light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reproducing apparatus and a reproducing method for performing reproduction on a recording medium on which multilevel recording has been performed so that the reproduction light intensity is varied in multiple stages in units of pixels, and in particular, an image for receiving the reproduction light. The present invention proposes a suitable technique when the dynamic range of the sensor is narrower than the dynamic range of the reproduction light received. The present invention also relates to the recording medium.

2. Description of the Related Art Conventionally, optical discs such as CD (Compact Disc), DVD (Digital Versatile Disc), and BD (Blu-ray Disc: registered trademark) are known as optical recording media on which signals are reproduced by light irradiation. .
In these optical discs, data recording is performed with or without pits or marks. That is, data recording is performed using binary values of “0” and “1”.

Further, as an optical recording medium, there is also known an optical recording medium that records a value such that the intensity of reproduction light is different for each predetermined pixel, such as a hologram memory.
In the hologram memory, data reproduction is performed based on a result of receiving reproduction light by an image sensor such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. That is, in the hologram memory, a plurality of pixels that can be read out by receiving light once by the image sensor form one recording unit (one hologram page), and data is recorded in the hologram page unit.

In addition, about the related prior art, the following patent documents can be mentioned.
JP 2007-25417 A

Here, in a system for recording and reproducing a conventional optical disc such as a CD or a DVD, for example, in order to increase the recording density, the size of recorded pits and marks is further miniaturized and a large amount of information is spatially obtained. Will be stuffed.
On the other hand, in a system for recording / reproducing with respect to a hologram memory, an image sensor is used to receive reproduction light, so that the intensity difference of reproduction light can be detected with more detailed resolution. Using this point, in the recording / reproducing system in this case, it is also possible to increase the recording density by performing multi-level recording so that the light intensity of the reproducing light is different in three or more stages. The That is, more information is packed in the intensity direction of the reproduction light.

  Thus, when multi-value recording is performed in the intensity direction of the reproduction light, a wider dynamic range of the image sensor is preferable. In other words, as the number of values assigned to the intensity direction of the reproduction light increases, the dynamic range of the reproduction light tends to be expanded. In response, the dynamic range on the image sensor side is increased. It is necessary to secure.

  On the other hand, the pixel size of the image sensor has been miniaturized along with the recent progress of the fine processing technology. As the pixel size is further miniaturized, the overall size of the image sensor can be reduced, and the mounting area of the image sensor can be reduced.

However, when the pixel size is further miniaturized, the dynamic range of the image sensor tends to decrease accordingly.
According to this, it can be understood that there is a trade-off between reducing the size of the image sensor and increasing the recording density by multi-value recording in the intensity direction.
That is, when reducing the size of the image sensor, the dynamic range on the reproduction light (recording signal) side is limited accordingly, and the number of values that can be allocated in multi-level recording is also limited. That is, it hinders the increase in recording density.
Conversely, when the number of values to be allocated in multi-value recording is increased to increase the recording density, the dynamic range on the image sensor side must be secured as the recording signal dynamic range increases, so the pixel size Subject to restrictions. That is, this prevents the size reduction of the image sensor.

In view of the above problems, the present invention aims to achieve both reduction in size by miniaturization of pixels of an image sensor and high recording density by multi-value recording in the intensity direction. To do.
Therefore, in the present invention, the reproducing apparatus is configured as follows.
That is, the reproducing apparatus of the present invention is a reproducing apparatus that performs reproduction on a recording medium on which multilevel recording has been performed so that the reproduction light intensity is varied in multiple stages in units of pixels, and is recorded on the recording medium. Light emitting means for emitting irradiation light for reading values, and an image sensor for receiving reproduction light obtained from the recording medium in units of pixels according to the irradiation light.
Further, the relative relationship between the dynamic range of the reproduction light from the recording medium and the dynamic range of the image sensor is controlled by at least one of power control of light emitted by the light emitting means and light receiving sensitivity control of the image sensor. A range shift means for changing is provided.
Further, a control means is provided for controlling the range shift means so that the dynamic range of the reproduction light of some values among the multi-values recorded on the recording medium sequentially falls within the dynamic range of the image sensor.
Further, the image processing apparatus includes a selection unit that selects a value that falls within a dynamic range of the image sensor from light reception signal values for each pixel obtained by the image sensor under each control state by the control unit.
In addition, data reproducing means for reproducing data based on values obtained as a result of the selection by the selecting means is provided.

In the present invention, among the multivalues recorded on the recording medium, the dynamic range of the reproduction light of some values is sequentially kept within the dynamic range of the image sensor, so that the light power or the light receiving sensitivity of the image sensor is adjusted. At least one of them is controlled. Then, the values that fall within the dynamic range of the image sensor are selected from the pixel unit values received under each control state.
In this way, even when the dynamic range of the image sensor becomes narrower than the dynamic range of the reproduction light due to the size reduction of the image sensor and the high recording density by multi-value recording, all the multi-value recorded values are Can be identified.

As described above, according to the present invention, even when the dynamic range of the image sensor becomes narrower than the dynamic range of the reproduction light due to the reduction in the size of the image sensor and the increase in the recording density by multi-value recording, All recorded values can be identified.
As a result, it is possible to achieve both a reduction in the size of the image sensor and an increase in recording density by increasing the value allocated in the intensity direction of the reproduction light.

Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an embodiment) will be described.
FIG. 1 is a block diagram showing an internal configuration of a playback apparatus 1 as an embodiment of the present invention.
The reproducing apparatus 1 is configured to perform reproduction on a recording medium HM in the figure, on which a value of three or more values is recorded due to a difference in reproduction light intensity (that is, multi-value recording is performed). The

Here, prior to the description of the internal configuration of the playback apparatus 1, first, an example of the recording medium HM will be described with reference to FIGS.
FIG. 2 shows a cross-sectional structure diagram of the recording medium HM.
In this case, the recording medium HM is a transmissive recording medium, and includes a substrate 100 having a concavo-convex cross-sectional shape as shown in the figure and a cover layer 101 laminated on the substrate 100.

  In the recording medium HM, the uneven cross-sectional pattern formed on the substrate 100 reflects the recording data. Specifically, such a concavo-convex cross-sectional shape is formed such that the depth is different at a plurality of gradations such as 16 gradations or more. By forming patterns having different depths as described above, patterns having different optical path lengths with respect to incident light are formed, and patterns based on such optical path length differences form diffraction gratings, that is, holograms.

In the recording medium HM of this example, multi-value recording in the intensity direction of the reproduction light is performed by forming an image pattern using such a hologram.
FIG. 3 shows an example of the recording format of the recording medium HM.
First, in the recording format in this case, a recording unit as a hologram page as shown in FIG. 3A is defined. This hologram page defines a pixel range that can be received at a time by an image sensor 6 (described later) provided in the reproducing apparatus 1. Specifically, for example, when the image sensor 6 has an effective pixel range of vertical n pixels × horizontal m pixels, at least the number of pixels in the vertical direction is n or less and the number of pixels in the horizontal direction is m or less. The set range.

  In one hologram page defined in this way, a 1-bit value is assigned to the position of each pixel. In this case, for each pixel, any one of eight values “0” to “7” is assigned as a 1-bit value. That is, multi-value recording of three or more values is thereby performed.

Here, the original data string to be recorded (for example, a predetermined data string such as music content or video content) is based on binary values of “0” and “1”. In the actual manufacturing process of the recording medium HM, such a binary data string to be recorded is converted into a multi-value data string, and each value of the multi-value data string obtained by the conversion is converted. For example, the hologram page is assigned to each pixel in order from the top row to the bottom row.
At this time, each value to be recorded is recorded so as to be expressed by a difference in intensity of the reproduction light. That is, when a hologram page is actually recorded, the intensity of the reproduction light is varied in multiple steps for each pixel.

  Then, on the recording medium HM in this case, a plurality of pieces of image information as hologram pages as described above are formed as shown in FIG. 3B. That is, the reproduction apparatus 1 performs data reproduction by sequentially reading out the reproduction light from each hologram page formed on the recording medium HM in this manner by the image sensor 6.

As can be understood from the above description, the recording medium HM used in the present example is a hologram image formed by forming a concavo-convex cross-sectional shape on the substrate 100 in such a manner that the intensity of the reproduction light is varied in multiple steps for each predetermined pixel. May be recorded.
Specifically, when such a recording medium HM is manufactured, the binary data string to be recorded is converted into a multi-value data string as described above, and the multi-value data obtained by the conversion is converted. Each value of the column is assigned as a gradation value in units of pixels to obtain image data as each hologram page to be formed on the recording medium HM. Then, overall image data is obtained when the image data as each hologram page is arranged on the recording medium HM at a predetermined interval, and the hologram corresponding to the image data thus obtained is actually on the recording medium HM. The concavo-convex cross-sectional shape pattern of the substrate 100 to be formed is determined by, for example, designing a CGH (Computer Generated Hologram) by an iterative Fourier method.

After the concave / convex cross-sectional pattern to be formed on the substrate 100 is obtained in this way, the master is manufactured by forming the concave / convex cross-sectional pattern on the silicon substrate by lithography such as electron beam drawing.
And after producing a metal mold from the master, the substrate 100 is produced by resin injection molding using this metal mold. By laminating the above-described cover layer 101 on the substrate 100, the recording medium HM according to the present embodiment in which multi-value data is recorded according to the format shown in FIG. 3 is manufactured.

Returning to FIG.
In FIG. 1, the recording medium HM is held at a predetermined position in the reproducing apparatus 1 so as to be movable in a two-dimensional direction by a slide mechanism 7 in the drawing. That is, in this case, the hologram pages formed as shown in FIG. 3B are held so as to be slidable in the direction of the laser light irradiation surface so that the hologram pages can be read.
For the slide control of the recording medium HM, the control unit 10 described later instructs the slide control unit 8 about the slide amount in the two-dimensional direction, and the slide control unit 8 obtains the slide drive state corresponding to the slide amount. This is realized by controlling the slide mechanism 7.

  The reproducing apparatus 1 includes a laser diode (LD) 2, a collimator lens 3, and an objective as an optical system for performing reproduction by irradiating the recording medium HM held slidably in this way. A lens 4, a condenser lens 5, and an image sensor 6 are provided.

In this optical system, the laser diode 2 is driven to emit light by a laser drive unit 9 in the figure, and the laser light emitted from the laser diode 2 is converted into parallel light by a collimator lens 3. The light is condensed by the objective lens 4 and irradiated onto the substrate 100 through the cover layer 101 in the recording medium HM. At this time, the optical system is adjusted so that the focal point (focusing point) is on the substrate 100 in the recording medium HM. Further, the laser spot diameter is adjusted to a size that enables reading of one hologram page recorded on the recording medium HM.
A focus control means for adjusting the focal point may be provided.

The laser beam irradiated in this way enters the condenser lens 5 through the substrate 100. Then, after being made parallel light through the condenser lens 5, it is irradiated onto the image sensor 6.
The image sensor 6 is composed of, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. The image sensor 6 receives the reproduction light in pixel units (pixel units) and converts it into an electrical signal corresponding to the received light amount. By performing this conversion, a received light signal representing the received light amount for each pixel is obtained.

At this time, the laser light emitted through the substrate 100 as described above becomes reproduction light reflecting a hologram image formed in accordance with the uneven cross-sectional shape pattern on the substrate 100. Specifically, an image in which the light intensity is modulated in a multi-value in a predetermined pixel unit as a hologram page as shown in FIG. 3A is output.
On the image sensor 6, an image as such a hologram page is formed. In this case, a pair of each pixel on the image sensor 6 (hereinafter also referred to as a light receiving pixel) and each pixel on the hologram page (hereinafter referred to as a recording pixel) formed on the image sensor 6 as described above. The optical system is adjusted so as to correspond to 1. Specifically, the optical system is adjusted so that one light receiving pixel receives a reproduced image of one recording pixel. Thereby, as the light reception signal by the image sensor 6, the light reception signal value of each pixel reflects the value of each pixel of the recorded hologram page.

  A light reception signal (hereinafter also referred to as a read signal) obtained by the image sensor 6 is a reproduction signal processing system (selection unit 11, memory 12, intensity value restoration unit in the figure) that executes reproduction signal processing according to the present embodiment. 13 and the data reproduction unit 14), the configuration and operation of the reproduction signal processing system as the present example will be described later.

The control unit 10 is configured by a microcomputer including, for example, a CPU (Central Processing Unit), a ROM (Reed Only Memory), a RAM (Random Access Memory), and the like, and for example, arithmetic processing based on an operation program stored in the ROM or the like By executing the control process, the entire playback apparatus 1 is controlled.
For example, the control of the reading position on the recording medium HM is executed by instructing the slide amount to the slide control unit 8 described above.
Further, particularly in the present embodiment, the present embodiment is implemented by issuing a laser emission power switching instruction in the laser driving section 9 and an operation switching instruction in the selecting section 11 described later by a read mode instruction signal RM-cnt in the figure. Control is performed so that the reproduction operation in the form of is performed.

[Playback operation as an embodiment]
Here, as described above, along with the recent progress of microfabrication technology, the pixel size of the image sensor 6 has been reduced, and the sensor size has been reduced.
On the other hand, when the sensor size is further reduced, the dynamic range of the sensor is also reduced as the pixel size is reduced.

  Here, on the premise of such a situation, let us consider reproducing the recording medium HM on which multilevel recording is performed in the intensity direction as in this example. At this time, as the number of values to be allocated in the intensity direction increases, the dynamic range on the recording signal side (reproducing light side) tends to expand. At present, the dynamic range on the image sensor 6 side has some margin with respect to the dynamic range on the recording signal side. However, when the sensor dynamic range is reduced with the fine processing as described above, These relationships will be reversed. That is, it is predicted that the recording signal side dynamic range becomes wider than the image sensor 6 side dynamic range.

  When such a reversal phenomenon occurs, it is obvious that the recorded data cannot be properly reproduced if the reproduction is performed by the conventional method. That is, it is not possible to properly read out values outside the dynamic range of the image sensor 6, and as a result, data reproduction cannot be performed properly.

  In the present embodiment, even when such a reverse phenomenon occurs, the recorded data can be properly reproduced. As a result, both high recording density by multi-value recording and size reduction of the image sensor 6 can be achieved. The purpose is to ensure that

  Therefore, in the present embodiment, the power of the laser beam irradiated during reproduction is set so that the dynamic range of the reproduction light of some values among the multiple values recorded on the recording medium HM is sequentially within the dynamic range on the image sensor 6 side. Reading is carried out while changing so as to fit. That is, reading is performed by dividing the range into the dynamic range of the image sensor 6.

Here, the relationship between the dynamic range on the recording signal side and the dynamic range on the image sensor 6 side when the power of the irradiation light to the recording medium HM is changed will be described with reference to FIG.
In FIG. 4, the horizontal axis represents the irradiation light power to the recording medium HM, and the vertical axis represents the reproduction light intensity of each value recorded on the recording medium HM, showing the change characteristic of the reproduction light intensity with respect to the change of the irradiation light power. Yes. As an example, FIG. 4 illustrates a case where the values recorded on the recording medium HM are eight values “0” to “7”. The change characteristic of the reproduction light intensity of the recorded values “0” to “2” is indicated by a solid line, and the change characteristic of the reproduction light intensity of the values “3” to “7” is indicated by a broken line.

As is clear from this figure, the reproduction light intensity of each value recorded on the recording medium HM is proportional to the power of irradiation light during reproduction.
Here, in the drawing, the dynamic range of the image sensor 6 is indicated by a thick broken line. However, when each value recorded on the recording medium HM is reproduced, it is natural that the intensity of the reproduced light is within this range. Must be in place.
Therefore, in the present embodiment, as shown in the figure, among the eight values recorded from “0” to “7”, the three values “0” to “2” are the power Pw2 in the figure. Is read out, and the remaining five values “3” to “7” are read out by setting the power Pw1.

By controlling the irradiation light power as described above, the reproduction light dynamic range of each value to be read can be sequentially stored within the dynamic range of the image sensor 6 under each power setting. it can.
As described above, in the present embodiment, the power of the irradiation light is set such that the dynamic range of the reproduction light of some values among the multiple values recorded on the recording medium HM sequentially falls within the dynamic range on the image sensor 6 side. Is read out.

  By adopting such a reading division method, it is possible to appropriately detect a reproduction light intensity difference of a target value at the time of each reading. That is, the recorded value can be properly determined.

  However, as can be seen with reference to FIG. 4, at the time of each readout, the reproduction light intensity of the value that is not the target is out of the dynamic range of the image sensor 6, and the value of the pixel position is correctly determined. I can't. That is, at the time of each reading, it is necessary to select and acquire only the light reception signal value of the target value.

  Therefore, in the present embodiment, at the time of reading each of the powers Pw1 and Pw2, the level of the received light signal value of each pixel obtained by the image sensor 6 is detected, and the level is within the dynamic range of the image sensor 6. Only the light reception signal values of the pixels are selected and read out.

FIG. 5 is a diagram for specifically explaining such a sorting operation.
In this figure, the relationship between each pixel (light receiving pixel) of the image sensor 6 and a value received by each pixel is schematically shown. Here, for convenience of explanation, the number of pixels of the image sensor 6 is set to 4 × 4 = 16. However, as a matter of course, the number of pixels of the image sensor 6 should not be limited to this.

  First, FIG. 5A shows a state in which laser light is irradiated with power Pw1 as the first read operation. As shown in FIG. 4, under the setting of the power Pw1, the reproduction light intensity of “3” to “7” among the recorded values falls within the dynamic range of the image sensor 6. Therefore, at the time of the first reading, the pixels that have received the reproduction light of the values “3” to “7” are selected as shown in the figure.

  Here, under the setting of the power Pw1, the reproduction light intensity of values “0” to “2” that are not to be read out is on the lower limit side of the dynamic range of the image sensor 6. That is, as the received light signals for these values “0” to “2”, only a very small amplitude that is buried in the noise component can be obtained. Therefore, the selection at the time of the first reading is performed so as to exclude pixels in which the level of the received light signal is buried in noise.

  FIG. 5B shows a state in which laser light is irradiated with power Pw2 as the second read operation. Under the setting of the power Pw2, the reproduction light intensity of values “0” to “2” among the recorded values falls within the dynamic range of the image sensor 6. On the other hand, the values “3” to “7” that are not targeted are levels that exceed the upper limit of the dynamic range of the image sensor 6. Therefore, at the time of the second reading, the selection is performed so as to exclude pixels in which the level of the received light signal is stuck to the upper limit level.

  By performing such reading twice and selection at each reading, all recorded values can be read appropriately as shown in FIG. 5C. That is, even when the dynamic range on the recording signal side is wider than the dynamic range on the image sensor 6 side, all recorded values can be read out appropriately.

In FIG. 5, the values “0” to “7” recorded on the recording medium HM are shown on each pixel of the image sensor 6, but the two readings described above are performed. In this case, the level of the light reception signal of each pixel actually obtained by the image sensor 6 is naturally obtained at a level within the dynamic range of the image sensor 6.
For example, when “0” and “3” are taken as examples of target values at the first and second reading, the received light signal level of the image sensor 6 of these values is the same level. In such a case, the values “0” and “3” can no longer be distinguished from the difference in the received light signal level.
As described above, when the reading division method of this example is adopted, even if the value should be detected as exceeding the dynamic range of the image sensor 6, the light is received at a level within the dynamic range of the image sensor 6. As a result, even if bit determination is performed on the received light signal as it is, there is a possibility that the recorded value cannot be properly determined.

Therefore, in the present embodiment, for a value exceeding the dynamic range of the image sensor 6, the received light signal value is restored to a value corresponding to the original intensity. Specifically, a predetermined offset value is given to the light reception signal value of the pixel selected at the time of the first reading, thereby restoring the original intensity value corresponding to “3” to “7”. is there.
By doing so, it is possible to restore the light reception signal values for the values “3” to “7” that originally exceed the dynamic range of the image sensor 6 to values corresponding to the original intensity. That is, by performing such intensity restoration, it is possible to obtain a value that appropriately represents the intensity difference between “0” to “7” as the received light signal value, and as a result, the recorded “0” to “ 7 ”can be properly determined.

[Configuration for playback operation]
In the reproducing apparatus 1 of the present embodiment, as a configuration for realizing the reproducing operation described above, the selecting unit 11 and the memory 12 shown in FIG. An intensity value restoration unit 13 and a data reproduction unit 14 are provided.

First, the laser driving unit 9 switches the laser emission power by the laser diode 2 between the power Pw1 and the power Pw2 described above based on the read mode instruction signal RM-cnt from the control unit 10. That is, when the control unit 10 performs reading under the setting of the first power Pw1, the control unit 10 outputs, for example, a signal at L level as the reading mode instruction signal RM-cnt, and the second power Pw2 For example, a signal at H level is output as the read mode instruction signal RM-cnt.
The laser drive unit 9 sets the laser emission power to the power Pw1 in response to the read mode instruction signal RM-cnt based on the L level, and the laser emission power is set to power in response to the read mode instruction signal RM-cnt based on the H level. Set to Pw2.

A light receiving signal from the image sensor 6 and a reading mode instruction signal RM-cnt from the control unit 10 are input to the selection unit 11.
When the reading mode instruction signal RM-cnt is at the L level (when the power Pw1 is instructed), the selecting unit 11 excludes the light reception signal of each pixel obtained from the image sensor 6 that is buried in noise. The values of the received light signals of the other pixels are stored in the image memory 12 a in the memory 12.
Here, in the memory 12, as the image memory 12a, a storage area for storing a light reception signal value corresponding to each pixel of the image sensor 6 is secured. The selection unit 11 stores the light reception signal values of the pixels that are not excluded as described above in the image memory 12a in correspondence with the pixels. In other words, the pixels received within the dynamic range of the image sensor 6 and the light reception signal values thereof are thereby selected.
Further, when the read mode instruction signal RM-cnt is at the H level (when the power Pw2 is instructed), the selecting unit 11 sets the light receiving signal of each pixel obtained from the image sensor 6 to the upper limit level. And the received light signal values of the other pixels are stored in the image memory 12a. As a result, the pixels received within the dynamic range of the image sensor 6 and the received light signal values are selected.

  In addition to the storage of the received light signal value in the image memory 12a, the selection unit 11 performs the target under the setting of the power Pw1 as information used for the intensity restoration process by the intensity value restoration unit 13 described below. Information representing the pixel selected as having received the value is stored in the memory 12. Specifically, in the selection process executed when the readout mode instruction signal RM-cnt is at the L level, information on pixels other than the pixel for which the light reception signal is buried in noise (reconstruction target pixel information and Is stored in the memory 12.

The intensity value restoration unit 13 receives the light reception signal value for each pixel (that is, the image signal for one hologram page) that has been stored in the image memory 12a by the sorting process under the setting of each power Pw by the sorting unit 11. And a predetermined offset value is given to the value of the pixel indicated by the restoration target pixel information stored in the memory 12 in the image signal.
As can be understood from the above description, the offset value includes the original intensity difference between the values recorded on the recording medium HM (that is, the intensity difference between the values “0” to “7” in this case). Any value may be set as long as the relationship can be properly expressed.

  The data reproduction unit 14 inputs an image signal for one hologram page that has been subjected to the intensity restoration processing by the intensity value restoration unit 13, performs bit determination on the value of each pixel in the image signal, and outputs one hologram page Data is reproduced by detecting the value of each recording pixel and performing multi-value-> binary conversion. As a result, reproduction data using a binary data string of “0” and “1” is obtained.

Here, the present applicant conducted an experiment for verifying the effectiveness of the reproduction method as the embodiment described above.
In the experiment, the wavelength of the laser beam was 632.8 nm. Further, the concave-convex cross-sectional shape pattern formed on the recording medium HM is the same as that of the recording medium HM when the recording medium HM is irradiated with a plane wave with the wavelength of 632.8 nm as shown in FIG. It was set by designing 8 stages of CGH by the iterative Fourier method so that an information image whose intensity was randomly modulated to 8 values with a period of 3.5 nm was formed at a position 10 mm behind.
The master of the recording medium HM was manufactured by forming the uneven cross-sectional shape on the silicon substrate by lithography using electron beam drawing. A metal mold is produced by nickel plating on this master, and a resin (for example, polystyrene) heated to the vicinity of the glass transition point is pressed against the metal mold. After the resin is peeled off, a cover layer is formed on the resin. Thus, a recording medium HM was produced.
In the experiment, a HeNe laser having a wavelength of 632.8 nm and a single-mode transverse mode TEMOO was used. Although not shown in the figure, the laser beam was collimated after passing through a spatial filter, and irradiated to the recording medium HM at 45 °. The image sensor 6 in FIG. 6 is arranged so that its light receiving surface is located at a position of 10 nm behind the recording medium HM in the optical path.

Under the setting of the above conditions, an information image modulated at about 45 dB is formed on the image sensor 6. In this case, a CMOS sensor is used as the image sensor 6 and its dynamic range is effectively about 40 dB.
At this time, the laser beam power was separately irradiated at 10 μW and 50 μW, and the received light signal obtained under each power setting was subjected to bit determination using the reproduction signal processing system shown in FIG.
As a result, each value recorded on the recording medium HM was able to be read with a low error rate that could withstand practical use.

As described above, according to the present embodiment, a value whose intensity is modulated in a dynamic range wider than the dynamic range of the image sensor 6 can be properly reproduced.
In the specific example described above, the case where the power Pw of the laser beam is changed in two stages and the reading is divided twice is illustrated. However, the number of times of reading can be increased by changing the power Pw into three or more stages. Thus, it is possible to cope with an increase in the value assigned in the intensity direction (that is, higher recording density) and a further reduction in sensor size.
As described above, according to the present embodiment, it is possible to achieve both high recording density realized by multi-value recording by intensity difference of reproduction light and size reduction of the image sensor.

In the case of performing three or more reading divisions as described above, the selection of a target value is different from the selection method in the case of performing the two-stage reading division exemplified above.
That is, in the two-stage reading division, the target values in each reading are divided into “0” to “2” and “3” to “7”, so whether or not the level of the received light signal is buried in noise. Or whether it is attached to the upper limit side or not. However, when there are three or more stages, there are cases where both the reproduction light intensity is smaller and the reproduction light intensity is lower than the value to be read, and it is necessary to exclude both of them. Specifically, for example, when values to be recorded are “0” to “11”, and these are read and separated into “0” to “3”, “4” to “7”, and “8” to “11”, At the time of reading for intermediate values of “4” to “7”, the received light signals of “0” to “3” having a smaller reproduction light intensity and “8” to “11” having a larger reproduction light intensity are used. It is necessary to exclude both received light signals.
For this reason, when performing readout division in three or more stages, when performing readout for the intermediate portion value in which the reproduction light intensity does not include the weakest and strongest values, the light receiving signal is used in the sorting process. Excludes both those buried in noise and those stuck to the upper limit.

[Modification]
Here, the present invention should not be limited to the specific examples described so far.
For example, in the description so far, in changing the relative relationship between the dynamic range of the image sensor and the dynamic range of the reproduction light of each value recorded, the case where the power side of the irradiation light is changed is exemplified. Conversely, the same effect can be obtained by changing the light receiving sensitivity side of the image sensor.

FIG. 7 shows an internal configuration of the reproduction apparatus 20 as a modified example in which reading sensitivity is changed by changing the light receiving sensitivity in this way. In this figure, parts that are the same as those already described with reference to FIG.
In the reproducing apparatus 20, a gain adjusting unit 21 is added to the reproducing apparatus 1 shown in FIG. 1, and the read mode instruction signal RM-cnt from the control unit 10 is not the laser driving unit 9 but the gain adjusting unit. The point which is supplied with respect to the part 21 is different.

As shown in the figure, the gain adjusting unit 21 is provided so as to adjust the gain of the light reception signal of the image sensor 6, and the gain adjusting unit 21 responds to a read mode switching instruction by the read mode instruction signal RM-cnt. Then, the gain given to the light reception signal is switched.
In this case, each gain given to the light reception signal corresponding to each reading mode is such that the dynamic range of the reproduction light of some values among the multiple values recorded on the recording medium HM is sequentially within the dynamic range of the image sensor 6. What is necessary is just to set so that it may be settled. That is, in this case, for example, if “0” to “2” and “3” to “7” are separately read out of the eight values recorded on the recording medium HM, the read mode instruction signal RM-cnt is at the L level. The gain to be sometimes given may be set so that the dynamic range of the reproduction light of the values “3” to “7” falls within the dynamic range of the image sensor 6, and the read mode instruction signal RM-cnt is The gain to be given at the H level may be set so that the dynamic range of the reproduction light of the values “0” to “2” falls within the dynamic range of the image sensor 6.

  Further, the relative relationship between the dynamic range of the image sensor and the dynamic range of the reproduction light of each value to be recorded is, for example, the light irradiated on the recording medium by an optical element such as an ND filter or a liquid crystal panel inserted in the optical path. It can also be changed by controlling the intensity (power) of light (which may be light irradiated to the image sensor). Alternatively, it can be changed by controlling both the light intensity control and the light receiving sensitivity of the image sensor.

In the description so far, in order to appropriately perform bit determination of each recorded value, a method of restoring the intensity of the recorded value by giving an offset value to the received light signal is exemplified. There is no need to give an offset.
At this time, each value recorded on the recording medium HM includes information on the value of the light reception signal by the image sensor and the power (or the light reception signal) of the irradiation light set when the value of the light reception signal is obtained. It is uniquely determined by the combination with the value information of gain (light receiving sensitivity). Therefore, each recorded value may be determined from a combination of these pieces of information.
Specifically, in this case, the intensity value restoration unit 13 is omitted, and the data reproduction unit 14 is configured to read the light reception signal value from the memory 12. Each combination of the “light reception signal value” and the “irradiation light power (or gain) value” (in this case, information indicating a different read mode), Table information indicating the correspondence with each recorded value is stored. In this case, the selection unit 11 stores, in the memory 12, information indicating the different reading modes when the light reception signal value of the pixel is obtained for each pixel in which the light reception signal value is stored by the selection process.
In this case, the data reproducing unit 14 reads out an image signal for one hologram page from the image memory 12 a, and the value of each pixel in the image signal and the pixel value stored in the memory 12 by the selecting unit 11. Each recorded value is determined based on the read mode information and the table information.
Even in such a configuration, each recorded value can be properly determined.

As a modification, a configuration as shown in FIG.
When the reference signal is recorded at a predetermined position on the recording medium HM as shown in FIG. 9, the reproduction apparatus 25 as a modification is irradiated light power (or image) based on the received light level of the reference signal. The light receiving sensitivity of the sensor 6 is controlled to a target level.
Here, the case of controlling the irradiation light power will be described as an example, but it is needless to say that the light receiving sensitivity side of the image sensor 6 can be controlled.

In this case, for example, for each hologram page, a power reference signal for defining a reference level of the received light signal to be obtained under the setting of the power Pw1 and the power Pw2 is recorded on the recording medium HM. (Power Pw1 reference signal, power Pw2 reference signal in the figure).
The Pw1 reference signal is set so that the reproduction light intensity (that is, the light reception signal value) when the laser beam is irradiated with the power assumed in advance as the power Pw1 is a predetermined value (the first predetermined value). It becomes a recorded signal. Further, the Pw2 reference signal is such that the reproduction light intensity (that is, the received light signal value) when the laser light irradiation is performed with the power assumed in advance as the power Pw2 is a predetermined value (second predetermined value). Thus, the recorded signal is obtained.
That is, if the light reception signal value of the Pw1 reference signal is a predetermined first predetermined value, it can be determined that the power of the laser beam is Pw1, and similarly, the light reception signal value of the Pw2 reference signal is predetermined. If the obtained second predetermined value is reached, it can be determined that the power of the laser beam is Pw2.

In this case, the control unit 26 in FIG. 8 instructs the laser drive unit 9 on the laser power based on the values as the Pw1 reference signal and the Pw2 reference signal stored in the image memory 12a.
Specifically, the control unit 26 in this case reads the light reception signal value of the pixel in which the Pw1 reference signal is recorded in the image memory 12a at the time of reading under the setting of the power Pw1, and is preset with the light reception signal value. A difference value from the first predetermined value is calculated, a laser power value is calculated with the difference value being zero, and the calculated laser power is instructed to the laser driving unit 9. At the time of reading under the setting of power Pw2, the light reception signal value of the pixel in which the Pw2 reference signal is recorded in the image memory 12a is read, and the difference value between the light reception signal value and the second predetermined value set in advance. Is calculated, a laser power value is calculated with the difference value being zero, and the calculated laser power is instructed to the laser drive unit 9.
By such laser power control, it is possible to make the laser power at the time of each reading constant at a predetermined power even with respect to, for example, a temperature change or a change with time.

In the above description, the case where the recording medium to be reproduced in the present invention is a so-called hologram memory has been exemplified. However, in the present invention, the reproduction light intensity is varied in multiple stages for each pixel. The present invention is widely applicable when reproducing a recording medium on which multilevel recording has been performed.
For example, the present invention can be suitably applied to a case where reproduction is performed on a barcode recording medium.

It is the block diagram which showed the internal structure of the reproducing | regenerating apparatus as embodiment of this invention. FIG. 3 is a diagram schematically showing a cross-sectional structure of a recording medium to be played back by the playback device of the embodiment. It is a figure for demonstrating the data recording format of a recording medium. It is the figure which showed the change characteristic of the reproduction light intensity with respect to the change of irradiation light power. It is a figure for demonstrating the reproduction | regeneration operation | movement as embodiment. It is a figure for demonstrating the reproducing | regenerating apparatus used for experiment. It is the block diagram which showed the internal structure of the reproducing | regenerating apparatus as a modification. It is the block diagram which showed the internal structure of the reproducing | regenerating apparatus as another modification. It is a figure for demonstrating the recording medium made into reproduction | regeneration object by the reproducing | regenerating apparatus shown in FIG.

Explanation of symbols

  1, 20, 25 Playback device, 2 Laser diode, 3 Collimator lens, 4 Objective lens, 5 Condensing lens, 6 Image sensor, 7 Slide mechanism, 8 Slide control unit, 9 Laser drive unit, 10, 26 Control unit, 11 Sorting unit, 12 memory, 12a image memory, 13 intensity value restoring unit, 14 data reproducing unit, 21 gain adjusting unit

Claims (5)

A playback device for playing back a recording medium on which multilevel recording has been performed so that the playback light intensity is varied in multiple stages in units of pixels,
A light emitting means for emitting irradiation light for reading the value recorded on the recording medium;
An image sensor that receives, in pixel units, reproduction light obtained from the recording medium in response to the irradiation light;
The relative relationship between the dynamic range of the reproduction light from the recording medium and the dynamic range of the image sensor is changed by at least one of power control of light emitted by the light emitting means and light receiving sensitivity control of the image sensor. Range shifting means;
Control means for controlling the range shift means so that the dynamic range of the reproduction light of some values among the multiple values recorded on the recording medium is successively within the dynamic range of the image sensor;
A selection means for selecting a value that falls within a dynamic range of the image sensor among light reception signal values for each pixel obtained by the image sensor under each control state by the control means;
Data reproduction means for reproducing data based on the value obtained as a result of the selection by the selection means;
A playback apparatus comprising: The data reproducing means is
Reproducing data based on each value selected by the selection means and information indicating the control state of the range shift means when those values are obtained,
The reproducing apparatus according to claim 1. In the recording medium, a reference signal value is recorded in a pixel at a predetermined position,
The control means includes
Based on the light reception signal value for the pixel in which the reference signal value is recorded, at least one of power control of the light or light reception sensitivity control of the image sensor is performed.
The reproducing apparatus according to claim 2, wherein: As a reproduction method for reproducing a recording medium on which multilevel recording has been performed so that the reproduction light intensity is varied in multiple stages in units of pixels, the reproduction light obtained according to the irradiation light with respect to the recording medium is pixelated by an image sensor. A reproduction method for performing reproduction based on the result of receiving light in units,
At least one of light power control and light reception sensitivity control of the image sensor so that the dynamic range of the reproduction light of some values among the multiple values recorded on the recording medium is sequentially within the dynamic range of the image sensor. A control procedure for controlling so that
A selection procedure for selecting a value that falls within the dynamic range of the image sensor from among the received light signal values for each pixel obtained by the image sensor under each control state according to the control procedure,
A data reproduction procedure for performing data reproduction based on the value obtained as a result of the sorting by the sorting procedure;
A playback method comprising:   A recording medium on which a hologram image associated with the formation of a concavo-convex pattern is recorded in such a manner that reproduction light intensity is varied in multiple stages for each pixel.

Images