JP4669330B2 - Two-dimensional reproduction equalizer and two-dimensional reproduction equalization method - Google Patents

Description

  The present invention relates to a two-dimensional reproduction equalizer and a two-dimensional reproduction equalization method for equalizing two-dimensional image data obtained by reproducing a hologram to original data recorded as the hologram.

  In recent years, research and development of a hologram recording / reproducing technique for recording and reproducing data on a recording medium using interference fringes (holograms) has been advanced. According to this technology, data of 200 Gbytes or more is recorded on a recording medium of the same size as a current CD (Compact Disc) or DVD (Digital Versatile Disk), and at a rotational speed of the recording medium equivalent to 1 × speed of the CD. Even in such a case, it is possible to realize a data transfer rate of 160 Mbit / second or more, and this hologram recording / reproducing technique is attracting much attention.

Here, with reference to FIG. 16, the outline | summary is demonstrated about the recording and reproduction | regeneration of the data by the conventional hologram. FIG. 16 is a schematic diagram showing an outline of a hologram recording / reproducing system, where (a) shows a recording system, (b) shows a recording medium on which interference fringes are recorded, and (c) shows a reproducing system.
As shown in FIG. 16A, when data is recorded on a hologram recording medium (recording medium D), a spatial light modulator (SLM) such as a transmissive liquid crystal panel is irradiated with laser light. This laser beam (object beam) is irradiated with the laser beam as a reference beam from another angle, and the recording medium D is placed where the interference fringes are generated. Thereby, the interference fringes (hologram) generated by the interference between the object beam and the reference beam are recorded on the recording medium D. FIG. 16B shows the recording medium D on which the interference fringes (holograms) are recorded.

  Further, as shown in FIG. 16C, when data is reproduced from the interference fringes (hologram) recorded on the recording medium D, the reference medium (laser light) is irradiated to the recording medium D at the same angle as at the time of recording. To do. Then, reproduction light is generated in the same direction as the object light at the time of recording. Since the reproduced object light stores the information (data) at the time of recording as it is, it is converted into an electric signal by the two-dimensional image sensor IS, and the original data is reproduced.

In the recording system and the reproducing system described with reference to FIGS. 16A and 16C, the pixels of the spatial light modulator S and the two-dimensional image sensor IS can be accurately matched (pixel matching). desirable. However, in reality, due to various factors such as mechanical attachment accuracy, it is not possible to completely match each pixel, and even if it is adjusted accurately, an error of about 0.2 pixels generally occurs. It is.
Therefore, conventionally, as a method of equalizing data, a method of removing intersymbol interference by using a partial response method or the like by a linear equalization (amplitude compensation) circuit on the assumption that pixel matching is performed. (See Non-Patent Document 1) and in order to reduce the influence of pixel matching errors, 1-bit data is converted into a large number of pixels (for example, 3 × 3 pixels [Non-Patent Document 2], 8 × 4 pixels [Non-Patent Document 1]. 3] etc.) and the like.

That is, in the conventional reproduction system, in the method of removing intersymbol interference by a linear equalization (amplitude compensation) circuit, the amplitude between the two-dimensional image sensor IS and the detector DE as shown in FIG. By providing the two-dimensional reproduction amplitude equalizer 1G including the compensation means 10, the amplitude change due to the pixel matching error or the like of the two-dimensional image data converted into the electric signal by the two-dimensional image sensor IS is compensated.
In the conventional reproduction system, in the method of detecting 1-bit data by a plurality of pixels, an equalizer is provided between the two-dimensional image sensor IS and the detector DE as shown in FIG. The two-dimensional image data output from the two-dimensional image sensor IS is used as a detection target as it is.
HJCoufal et al., `` Holographic Data Storage '', Springer Series in Optical Sciences pp309-317 Hideyoshi Horomi et al., “Holographic Media Near Takeoff Realizing 200 GB in 2006”, Nikkei Electronics, pp 105-114, 2005.1.17. M. Ezura et al., `` Holographic Memories Using 2-Dimensional Phase-Code Multiplexing Method '', Japanese Journal of Applied Physics, Vol.43, No.7B, 2004, pp.4954-4958

  However, in the method of removing intersymbol interference using the linear equalization (amplitude compensation) circuit described above, since the amplitude is compensated, it is possible to reduce the influence of the amplitude fluctuation caused by the intersymbol interference. It does not remove the error accurately. For this reason, this method has a problem that the equalization characteristic is not sufficient and the error rate does not reach a practical level.

Further, the above-described method of detecting 1-bit data by a plurality of pixels needs to express 1-bit data by a large number of pixels such as 3 × 3 pixels.
However, the relationship between the pixel of the spatial light modulator S and the pixel of the two-dimensional image sensor IS described in FIG. 16 is equivalent to the sampling of the data of the pixel of the spatial light modulator S by the two-dimensional image sensor IS. Therefore, it suffices to satisfy the sampling theorem both in the horizontal direction and in the vertical direction. Theoretically, if 2 × 2 pixels of the two-dimensional image sensor IS are associated with 1-bit data in both the horizontal direction and the vertical direction. It will be good.

There are two ways to realize this, as shown in FIG. One of them is a method as shown in FIG. 18A, in which the 1-bit data B ₁ of the spatial light modulator S is doubled by the objective lens L, and 2 × 2 of the two-dimensional image sensor IS. By making it correspond to a pixel (detection pixel P), 1-bit data can be represented by 2 × 2 pixels.
The other is a method as shown in FIG. 18B, in which the spatial relationship between the spatial light modulator S and the two-dimensional image sensor IS is 1: 1, and 2 × 2 pixels of the spatial light modulator S are By making it correspond to 1-bit data B ₂ , 1-bit data can be expressed by 2 × 2 pixels.

  Thus, in theory, 1-bit data may correspond to 2 × 2 pixels of the two-dimensional image sensor IS in both the horizontal direction and the vertical direction. Bit data must be expressed by a large number of pixels such as 3 × 3 pixels, which is an obstacle to increasing the recording density of data on a recording medium.

  The present invention has been made in view of the above problems, and a two-dimensional reproduction equalizer and a two-dimensional reproduction device that can correct a pixel matching error and increase a data recording density on a recording medium. An object is to provide a reproduction equalization method.

  The present invention was devised to achieve the above object. First, the two-dimensional reproduction equalizer according to claim 1 is such that the original data is modulated by the spatial light modulator and further mixed with the reference light. The generated interference fringes (holograms) are recorded on the recording medium, the reference fringes are irradiated onto the interference fringes on the recording medium, the hologram is reproduced, and is projected onto the two-dimensional image sensor to thereby generate an electric signal. This is a two-dimensional reproduction equalizer that equalizes the two-dimensional data converted into the original data recorded as the hologram, and includes a pixel shift amount storage means and a phase compensation means.

  In such a configuration, the two-dimensional reproduction equalizer stores, in the pixel deviation amount storage means, a pixel deviation amount indicating the magnitude of the horizontal or vertical deviation between the pixel of the spatial light modulator and the pixel of the two-dimensional image sensor. Is stored in advance. This pixel shift amount is a specific amount in the hologram reproduction system, that is, a certain amount in reproducing the hologram. Therefore, here, the pixel shift amount is measured and stored in advance.

  In the two-dimensional reproduction equalizer, the phase compensation unit compensates the phase in the horizontal direction or the vertical direction in the two-dimensional image data based on the pixel shift amount stored in the pixel shift amount storage unit. The pixel shift is a phase shift in the horizontal or vertical signal waveform in the two-dimensional image data. Therefore, the phase compensation means reproduces the two-dimensional image data (original data) compensated for the phase by changing the phase corresponding to the pixel shift amount with respect to the two-dimensional image data.

  In the two-dimensional reproduction equalizer according to claim 2, interference fringes (holograms) generated when original data is modulated by a spatial light modulator and mixed with reference light are recorded on a recording medium, The reference light is irradiated to the interference fringes on the recording medium, the hologram is reproduced, and the two-dimensional data converted into the electric signal by being projected onto the two-dimensional image sensor is converted into the original data recorded as the hologram. A two-dimensional reproduction equalizer for equalization is configured to include a pixel shift amount storage unit, a first phase compensation unit, and a second phase compensation unit.

In such a configuration, the two-dimensional reproduction equalizer stores, in the pixel shift amount storage means, each pixel indicating the size of the horizontal and vertical shift between the pixel of the spatial light modulator and the pixel of the two-dimensional image sensor. The amount of deviation is stored in advance.
In the two-dimensional reproduction equalizer, the first phase compensation unit compensates the horizontal phase in the two-dimensional image data based on the horizontal pixel shift amount stored in the pixel shift amount storage unit. In the two-dimensional reproduction equalizer, the second phase compensation unit compensates the vertical phase in the two-dimensional image data based on the vertical pixel shift amount stored in the pixel shift amount storage unit.
As a result, even if the pixels are shifted in both the horizontal direction and the vertical direction, the two-dimensional reproduction equalizer changes the phase corresponding to the pixel shift amount in each direction, thereby changing the phase. The compensated two-dimensional image data (original data) can be reproduced.

  Further, the two-dimensional reproduction equalizer according to claim 3 is the two-dimensional reproduction equalizer according to claim 1 or 2, wherein the phase compensation means includes a phase compensation amount calculation means and a Fourier transform means. And an adding means and an inverse Fourier transform means.

In such a configuration, the two-dimensional reproduction equalizer calculates the phase compensation amount for compensating the phase from the pixel shift amount by the phase compensation amount calculation means in the phase compensation means. For example, when 1-bit data is expressed by 2 pixels, in order to advance the phase by one sample data by the phase operation, when the total number of data is “n”, the phase amount is “n / 4” samples. The phase compensation amount may be calculated so as to be π / 2 ″.
The two-dimensional reproduction equalizer performs Fourier transform on the one-dimensional data divided from the two-dimensional image data by Fourier transform means (for example, Fast Fourier Transform (FFT)). Thereby, the amplitude data and the phase data are separated from the one-dimensional data divided from the two-dimensional image data.

Then, the two-dimensional reproduction equalizer adds the phase compensation amount calculated by the phase compensation amount calculating means to the phase data separated by the Fourier transform means by the adding means.
Further, the two-dimensional reproduction equalizer performs inverse Fourier transform on the phase data added with the phase compensation amount by the adder and the amplitude data separated by the Fourier transform by the inverse Fourier transform. As a result, two-dimensional image data whose phase is corrected by the amount of phase compensation is generated.

  A two-dimensional reproduction equalizer according to claim 4 is the two-dimensional reproduction equalizer according to any one of claims 1 to 3, wherein an amplitude compensation amount storage means, an amplitude compensation means, It was set as the structure provided with.

  In such a configuration, the two-dimensional reproduction equalizer stores in advance an amplitude compensation amount that has frequency characteristics for suppressing the amplitude of a band equal to or higher than the clock frequency in the two-dimensional image data in the amplitude compensation amount storage unit. Note that the band above the clock frequency is the harmonic component of the data itself and the harmonic distortion and noise components in the recording / playback system. By suppressing the amplitude of the band, the harmonic distortion and the frequency direction are uniformly distributed. It will also suppress the noise that is doing. Thus, in order to suppress the amplitude of a certain frequency band, for example, a raised cosine characteristic used as a roll-off filter can be used. That is, the amplitude compensation amount storage means stores an amplitude compensation amount that is data obtained by quantifying frequency characteristics such as cosine descending characteristics.

Then, the two-dimensional reproduction equalizer compensates the amplitude in the two-dimensional image data by the amplitude compensation means by the amplitude compensation means.
The two-dimensional reproduction equalizer may be provided with an amplitude compensation unit in front of the phase compensation unit and compensate the phase after compensating the amplitude of the input two-dimensional image data. An amplitude compensation means may be provided in the subsequent stage, and the amplitude may be compensated after the phase compensation.

  Furthermore, the two-dimensional reproduction equalizer according to claim 5 is the two-dimensional reproduction equalizer according to claim 4, wherein the amplitude compensation means includes a Fourier transform means, a multiplication means, an inverse Fourier transform means, It was set as the structure provided with.

In such a configuration, the two-dimensional reproduction equalizer performs Fourier transform on the one-dimensional data divided from the two-dimensional image data by Fourier transform means (for example, fast Fourier transform [FFT]) in the amplitude compensation means. Thereby, the amplitude data and the phase data are separated from the one-dimensional data divided from the two-dimensional image data.
The two-dimensional reproduction equalizer multiplies the amplitude data separated by the Fourier transform unit and the amplitude compensation amount by the multiplying unit.

  Further, the two-dimensional reproduction equalizer performs inverse Fourier transform on the amplitude data multiplied by the amplitude compensation amount by the multiplication unit and the phase data separated by the Fourier transform unit by the inverse Fourier transform unit. As a result, two-dimensional image data whose amplitude is corrected by the amplitude compensation amount is generated.

  Further, the two-dimensional reproduction equalizer described in claim 6 is the two-dimensional reproduction equalizer described in any one of claims 1 to 5 and includes a route calculation unit.

In such a configuration, the two-dimensional reproduction equalizer performs a root (square root) operation on the two-dimensional image data by the route calculation means. This is because the transfer function in the hologram recording / reproducing system is x ² with respect to the input signal x, and due to the transfer function, a slight difference in the input signal becomes a large signal difference, which affects the pixel shift. Because it gives. Therefore, the root calculation, which is the inverse calculation of the transfer function, is performed to suppress the expansion of the influence of pixel shift due to the transfer function.
Incidentally, in the two-dimensional reproduction equalizer, the order of the route calculation and phase compensation, the deviation order pixel transfer function of the hologram recording and reproducing system, the route calculation because it is the order of the x ^2, vice versa, the pixel Deviation compensation (phase compensation) is performed. Amplitude compensation is intended to suppress harmonic distortion and noise that are not related to the transfer function, so the order may be anywhere.

  Furthermore, in the two-dimensional reproduction equalization method according to claim 7, interference fringes (holograms) generated when the original data is modulated by the spatial light modulator and further mixed with the reference light are recorded on the recording medium, The reference light is irradiated to the interference fringes on the recording medium, the hologram is reproduced, and the two-dimensional data converted into the electric signal by being projected onto the two-dimensional image sensor is converted into the original data recorded as the hologram. A two-dimensional reproduction equalization method for equalization, comprising a phase compensation step.

According to this two-dimensional reproduction equalization method, in the phase compensation step, the displacement of at least one of the horizontal direction and the vertical direction between the pixel of the spatial light modulator used at the time of hologram recording and the pixel of the two-dimensional image sensor is reduced. The phase in the two-dimensional image data is compensated based on the pixel shift amount stored in advance in the storage means indicating the size. When the amount of pixel shift in the vertical direction is small, phase compensation only in the horizontal direction may be performed. When the amount of pixel shift in the horizontal direction is small, phase compensation only in the vertical direction may be performed.

  In the two-dimensional reproduction equalization method according to claim 8, interference fringes (holograms) generated when the original data is modulated by the spatial light modulator and mixed with the reference light are recorded on the recording medium, The reference light is irradiated to the interference fringes on the recording medium, the hologram is reproduced, and the two-dimensional data converted into the electric signal by being projected onto the two-dimensional image sensor is converted into the original data recorded as the hologram. A two-dimensional reproduction equalization method for equalization, comprising a route calculation step and a phase compensation step.

According to this two-dimensional reproduction equalization method, a route calculation which is an inverse operation of a transfer function in a hologram recording / reproduction system is performed on two-dimensional image data in a route calculation step.
In the two-dimensional reproduction equalization method, the horizontal direction between the spatial light modulator pixel and the two-dimensional image sensor pixel used in hologram recording is obtained with respect to the two-dimensional image data route-calculated in the phase compensation step. Alternatively, the phase in the two-dimensional image data is compensated based on the pixel shift amount stored in advance in the storage means, which indicates the magnitude of the shift in at least one of the vertical directions. Accordingly, pixel shift can be corrected in the two-dimensional image data.

  Furthermore, the two-dimensional reproduction equalization method according to claim 9 is the two-dimensional reproduction equalization method according to claim 8, further comprising an amplitude compensation step.

  According to this two-dimensional reproduction equalization method, in the amplitude compensation step, for the two-dimensional image data whose phase has been compensated in the phase compensation step, the frequency for suppressing the amplitude of the band equal to or higher than the clock frequency in the two-dimensional image data Based on the characteristic amplitude compensation amount, the amplitude of the two-dimensional image data is compensated.

  According to the first or seventh aspect of the invention, the two-dimensional image data, which is reproduced from the hologram and converted into the electric signal, is equalized to the original data recorded as the hologram, and the pixel matching error is corrected. can do. In addition, according to the present invention, the number of pixels used in the two-dimensional image sensor per bit of data can be set low to the theoretical limit under conditions that satisfy the sampling theorem in information theory. Thereby, the recording density of data in the recording medium can be increased.

According to the second aspect of the present invention, it is possible to equalize the two-dimensional image data to the original data recorded as a hologram even if the pixel shift is both in the horizontal direction and the vertical direction.
According to the third aspect of the present invention, phase compensation can be performed at high speed by using FFT as Fourier transform.

According to the invention described in claim 4 or claim 9, it becomes possible to perform amplitude compensation for two-dimensional image data in addition to phase compensation. As a result, harmonic components can be suppressed, noise can be reduced, and harmonic distortion caused by the recording / reproducing system can be suppressed.
According to the fifth aspect of the present invention, amplitude compensation can be performed at high speed by using FFT as Fourier transform.

  According to the invention described in claim 6 or claim 8, the pixel shift compensation error due to the transfer function can be reduced by performing the inverse operation of the transfer function in the hologram recording / reproducing system. Thereby, the two-dimensional image data can be equalized with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the two-dimensional reproduction equalizer performs hologram equalization when 2 × 2 pixels of the spatial light modulator S correspond to 1-bit data, as shown in FIG. 18B. The explanation will be given as an implementation.

[Configuration of two-dimensional reproduction equalizer]
First, the configuration of a two-dimensional reproduction equalizer according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a two-dimensional reproduction equalizer according to the first embodiment of the present invention.

As shown in FIG. 1, a two-dimensional reproduction equalizer 1 equalizes two-dimensional image data obtained by reproducing a hologram into original data recorded as a hologram. That is, the two-dimensional reproduction equalizer 1 is provided between the two-dimensional image sensor IS and the detector DE, and equalizes two-dimensional image data in which a hologram is converted into an electric signal by the two-dimensional image sensor IS. The equalized data (original data) is output to the detector DE.
Here, the two-dimensional reproduction equalizer 1 includes a transfer function correction unit 2, a horizontal phase compensation unit 3, a vertical direction phase amplitude compensation unit 4, and a storage unit 5.

  The transfer function correcting means 2 corrects the two-dimensional image data by performing the inverse operation of the transfer function in the hologram reproduction system on the input two-dimensional image data. Arithmetic means 20 is provided.

The root (square root) calculation means 20 performs a root calculation on the value of each pixel of the two-dimensional image data in either the horizontal direction or the vertical direction.
The hologram reproduction system has a transfer function of x ² with respect to the input signal x in order for the two-dimensional image sensor IS to detect the power of light. Therefore, here, a root operation that is an inverse operation of the transfer function is performed on the two-dimensional image data. As a result, the nonlinearity generated by the transfer function can be compensated, so that the next phase compensation can be performed accurately.
The two-dimensional image data subjected to the route calculation by the route calculation unit 20 is output to the horizontal direction phase compensation unit 3.

  The horizontal direction compensation unit 3 performs horizontal phase compensation on the two-dimensional image data based on a pre-measured (horizontal) pixel shift amount stored in the storage unit 5. Here, the phase compensation means 30 is provided.

The phase compensation means 30 compensates the phase of a one-dimensional line data string obtained by dividing two-dimensional image data in the horizontal direction. Here, the phase compensation unit 30 performs phase compensation for the pixel shift amount on the two-dimensional image data corrected by the transfer function correction unit 2.
This pixel shift amount can be compensated by using the time mobility of Fourier transform. Here, the time mobility of Fourier transform refers to a property that satisfies the following formula (1).

Note that f (t) is a function of time t, and F (ω) is a Fourier transform of f (t) where ω is an angular frequency. In addition, t ₀ indicates a shift amount of time. That is, the shift amount t ₀ of this time is measured in advance as a pixel shift amount, and the phase compensation amount θ = ωt ₀ is added to the phase of the Fourier transform F (ω) to perform the inverse Fourier transform, thereby obtaining the pixel shift amount. Compensation can be performed.
That is, by measuring the amount of time shift (pixel shift amount) in advance and storing it in the storage unit 5, the phase compensation unit 30 can perform phase compensation based on the pixel shift amount.
The two-dimensional image data whose phase in the horizontal direction is compensated by the phase compensation unit 30 is output to the vertical phase amplitude compensation unit 4.

Here, with reference to FIG. 2 and FIG. 3, a method for measuring the amount of pixel shift performed in advance will be described. FIG. 2 is a diagram illustrating a lighting pattern of the spatial light modulator. FIG. 3 is a graph showing the relationship between the amount of pixel shift and secondary distortion for one pixel.
First, in the hologram reproduction system (for example, the reproduction system in FIG. 16C), the pixels of the spatial light modulator S and the pixels of the two-dimensional image sensor IS are made to correspond one-to-one in advance, and the vertical and horizontal In both cases, the optical axis is adjusted so that the shift amount is within 0.5 pixels.
In the hologram reproduction system, the pixel shift amount is measured in this adjusted state.

  Here, the spatial light modulator is turned on in a checkered lighting pattern as shown in FIG. The lighting pattern at this time is a checkered pattern in which 1 × 1 bit of data is 3 × 3 pixels at locations where data is ON (white) and 3 × 3 pixels at locations where data is OFF (black). The lighting pattern may be a condition that satisfies the sampling theorem, and may be 2 × 2 pixels or more.

Next, one line in the horizontal direction (which becomes a rectangular wave) is taken out from the two-dimensional image data converted into an electrical signal in the two-dimensional image sensor, and Fourier transform (FFT) is performed. Here, if there is a pixel shift, second-order distortion occurs at a frequency twice as high as the fundamental frequency. FIG. 3 shows the ratio of the second order distortion with respect to the pixel shift amount for one pixel and the fundamental wave amplitude of the rectangular wave by simulation. In actual measurement, since a plurality of pixels are continuous, the pixel shift amount with respect to the continuous pixels is measured. Therefore, for example, when 3 pixels are associated with 1-bit data, the pixel shift amount shown in FIG.
The pixel shift amount measured in this way is used as a phase compensation amount for compensating the phase.
The phase compensation amount used in the phase compensation means 30B (FIG. 1) described later is the ratio of the secondary distortion to the fundamental wave amplitude generated when one line is extracted from the two-dimensional image data in the vertical direction and Fourier transform is performed. It is determined by

Next, an example of the internal configuration of the phase compensation means 30 will be described with reference to FIG. FIG. 4 is a block diagram showing the internal configuration of the phase compensation means.
Here, the phase compensation unit 30 includes a Fourier transform unit 31, a phase compensation amount calculation unit 32, an addition unit 33, and an inverse Fourier transform unit 34.

The Fourier transform unit 31 performs a Fourier transform (fast Fourier transform: FFT) on one line of the horizontal one-dimensional data string output from the two-dimensional image sensor, and an absolute value | F (ω) of the Fourier transform F (ω) ) | Is generated as amplitude data (amplitude spectrum) and declination Arg {F (ω)} of Fourier transform F (ω) is generated as phase data (phase spectrum) and output.
The amplitude data generated by the Fourier transform unit 31 is output to the inverse Fourier transform unit 34, and the phase data is output to the addition unit 33.

The phase compensation amount calculation means 32 calculates a phase compensation amount from a pixel shift amount measured in advance.
For example, when 1 bit of data is expressed by 2 pixels, in order to advance the phase by one sample data by the phase operation, when the total number of data is “n”, the phase amount is “π” with “n / 4” samples. The phase compensation amount may be calculated so as to be / 2 ".
Therefore, the phase compensation amount calculation means 32 assumes that the pixel shift amount per pixel is a (assuming −0.5 ≦ a ≦ 0.5), and the “k (0 ≦ k ≦ n)” th data. The phase compensation amount θ is calculated by the following equation (2).

  The adding unit 33 adds the phase data output from the Fourier transform unit 31 and the phase compensation amount output from the phase compensation amount calculating unit 32. The addition means 33 corrects the pixel shift amount in the phase data. The phase data to which the pixel shift amount is added by the adding unit 33 is output to the inverse Fourier transform unit 34.

The inverse Fourier transform unit 34 performs inverse Fourier transform (inverse fast Fourier transform: inverse FFT) on the amplitude data and the phase data. Here, the inverse Fourier transform unit 34 performs inverse Fourier transform on the amplitude data output from the Fourier transform unit 31 and the phase data output from the addition unit 33.
In the data output from the inverse Fourier transform unit 34, one line data of the two-dimensional image data input to the phase compensation unit 30 is shifted by the pixel shift amount a in the horizontal direction, and the phase in the horizontal direction is compensated. It becomes data. The two-dimensional image data in which the pixel shift amount is compensated by the inverse Fourier transform unit 34 is output to the vertical direction phase amplitude compensation unit 4 (FIG. 1).
Returning to FIG. 1, the overall configuration of the two-dimensional reproduction equalizer 1 will be described.

  The vertical phase amplitude compensation means 4 is measured in advance (vertical) stored in the storage means 5 for the two-dimensional image data in which the horizontal phase compensation means 3 compensates for the phase shift in the horizontal direction. Direction) Compensates for the phase and amplitude in the vertical direction based on the pixel shift amount and the preset amplitude compensation amount. Here, the phase compensation means 30B and the amplitude compensation means 40 are provided. .

The phase compensation means 30B compensates the phase of the one-dimensional line data string in the vertical direction of the two-dimensional image data. The phase compensation unit 30 compensates the phase of the horizontal pixel shift amount of the two-dimensional image data, whereas the phase compensation unit 30B includes the vertical pixel shift amount of the two-dimensional image data. Compensates for phase. That is, the phase compensation unit 30B can have the same configuration as the phase compensation unit 30 by changing the scanning direction. For example, the phase compensation unit 30B can have the same configuration as the phase compensation unit 30 described in FIG.
The two-dimensional image data whose vertical phase is compensated by the phase compensation unit 30B is output to the amplitude compensation unit 40.

The amplitude compensation means 40 compensates the amplitude of the one-dimensional line data string in the horizontal direction or the vertical direction of the two-dimensional image data. Here, the amplitude compensation is performed on the two-dimensional image data in which the phase in the vertical direction is compensated by the phase compensation unit 30B. The amplitude compensation in the amplitude compensation means 40 is to suppress harmonic distortion in the hologram recording / reproducing system, computation errors in the route computation means 20, noise, and the like.
For example, if random data is encoded with an NRZ (Non Return to Zero) code and the clock frequency is f (Hz), the signal spectrum in the frequency range of “0” to “2f” has a waveform as shown in FIG. It becomes. That is, the range of frequencies “0” to “f” is a signal component, and the range of frequencies “f” to “2f” is a harmonic component (harmonic distortion) of the signal itself.

The amplitude compensation means 40 suppresses the amplitude in the range of frequencies “f” to “2f” in the spectrum of the random signal in FIG. The suppression of the amplitude can be performed by utilizing a raised cosine characteristic used as a roll-off filter.
That is, by storing the amplitude compensation amount based on the cosine descending characteristic in the storage unit 5, the amplitude compensation unit 40 can perform amplitude compensation based on the amplitude compensation amount.

Here, an internal configuration example of the amplitude compensation means 40 will be described with reference to FIG. FIG. 6 is a block diagram showing the internal configuration of the amplitude compensation means.
Here, the amplitude compensation unit 40 includes a Fourier transform unit 31, an inverse Fourier transform unit 34, and a multiplication unit 41.
The Fourier transform unit 31 and the inverse Fourier transform unit 34 are the same as those described in the configuration of the phase compensation unit 30 described with reference to FIG.

  The multiplying unit 41 multiplies the amplitude data output from the Fourier transform unit 31 and the amplitude compensation amount read from the storage unit 5 (FIG. 1). The multiplication means 41 compensates the amplitude in the amplitude data. The amplitude data whose amplitude has been compensated by the multiplication means is output to the inverse Fourier transform means 34.

  Here, with reference to FIG. 7, the amplitude equalization characteristic for obtaining the amplitude compensation amount input to the multiplication means 41 will be described. FIG. 7 is a graph showing an example of the amplitude equalization characteristic, where (a) shows a cosine descending characteristic and (b) shows another characteristic example. In each graph, the horizontal axis represents frequency and the vertical axis represents amplitude.

Here, since it is assumed that 1 bit of data is sampled by 2 pixels, the maximum frequency of data is f _0/4 , and the maximum frequency of the sample sequence for 2 pixels is f _0/2 .
Therefore, as shown in FIG. 7 (a), between ₀ ≦ f ≦ f 0/4 does not change the amplitude characteristics, to gradually attenuate the amplitude between _{f 0/4 <f <f} 0/2 By using the raised cosine characteristic, it is possible to suppress the amplitude in the frequency range “f” to “2f” shown in FIG. The characteristic between _{f 0/2 ≦ f ≦ f} 0 is the nature of the Fourier transform, which is folded between _{0 ≦ f ≦ f 0/2} .
The cosine descent characteristic of FIG. 7A is expressed by the following equation (3).

  Further, the amplitude equalization characteristic may be the characteristic shown in FIG. When the characteristics in FIG. 7B are expressed by mathematical formulas, the following formula (4) is obtained.

Here, the multiplication means 41 (FIG. 6) multiplies the amplitude data by a preset amplitude compensation amount. This amplitude compensation amount is obtained by using the above-described equations (3) and (4). Can be calculated.
Therefore, the amplitude compensation means 40 (FIG. 6) replaces the amplitude compensation amount read from the storage means 5 (FIG. 1) as the multiplication value in the multiplication means 41 (FIG. 6), instead of using the equation (3) described above. Compensation value calculation means (not shown) for calculating the equation (4) may be provided, and the calculation result may be used as a multiplication value in the multiplication means 41 (FIG. 6).
Returning to FIG. 1, the overall configuration of the two-dimensional reproduction equalizer 1 will be described.

Here, the vertical phase amplitude compensation means 4 is composed of the phase compensation means 30B and the amplitude compensation means 40, but the Fourier transform means 31 and the inverse Fourier transform means 34 (see FIGS. 4 and 6) are used in common. Therefore, the configuration shown in FIG. 8 may be used.
That is, the vertical phase amplitude compensation unit 4 includes a Fourier transform unit 31, a phase compensation amount calculation unit 32, an addition unit 33, an inverse Fourier transform unit 34, and a multiplication unit 41, and outputs from the Fourier transform unit 31. The phase of the phase data is compensated by the phase compensation amount, and the amplitude of the amplitude data output from the Fourier transform means 31 is compensated by the amplitude compensation amount.

In this case, the Fourier transform unit 31, the phase compensation amount calculation unit 32, the addition unit 33, and the inverse Fourier transform unit 34 shown in FIG. 8 correspond to the phase compensation unit 30B in FIG. Further, the Fourier transform unit 31, the inverse Fourier transform unit 34, and the multiplication unit 41 shown in FIG. 8 correspond to the amplitude compensation unit 40 of FIG.
Thereby, the configuration can be simplified as compared with the configuration in which the phase compensation unit 30B (FIG. 4) and the amplitude compensation unit 40 (FIG. 6) are separated.

  The storage means (pixel deviation amount storage means, amplitude compensation amount storage means) 5 stores a pixel deviation amount measured in advance and a preset amplitude compensation amount, and is a storage device such as a general semiconductor memory. .

Although the configuration of the two-dimensional reproduction equalizer 1 has been described above, the present invention is not limited to this configuration. For example, here, the horizontal phase compensation unit 3 and the vertical direction phase amplitude compensation unit 4 perform the horizontal phase compensation and the vertical phase and amplitude compensation, respectively. Can be realized even if the compensation direction is changed.
That is, the two-dimensional reproduction equalizer 1 performs horizontal phase compensation means 3, vertical phase compensation means that performs vertical phase compensation, and vertical direction amplitude compensation means 4 that performs horizontal phase and amplitude compensation. You may comprise as a horizontal direction phase amplitude compensation means. Further, the order may be changed.

As described above, the two-dimensional reproduction equalizer 1 (FIG. 1) reduces the influence of the transfer function of the recording / reproduction system in the two-dimensional image data by the transfer function correction unit 2, and the horizontal direction compensation unit 3 The phase is compensated for the amount of pixel deviation of 0.5 pixels or less in the horizontal direction, and the vertical phase amplitude compensation means 4 compensates the phase for the amount of pixel deviation of 0.5 pixels or less in the vertical direction, and the amplitude Can be compensated for.
As a result, the two-dimensional reproduction equalizer 1 can associate 2 × 2 pixels of the two-dimensional image sensor with one bit of data in both the horizontal direction and the vertical direction, and increase the recording density of data on the recording medium. Can do.

[Operation of two-dimensional reproduction equalizer]
Next, the operation of the two-dimensional reproduction equalizer will be described with reference to FIG. 9 (refer to FIG. 1, FIG. 4, and FIG. 6 as appropriate for the configuration). FIG. 9 is a flowchart showing the operation of the two-dimensional reproduction equalizer according to the first embodiment of the present invention.
First, as advance preparation for operating the two-dimensional reproduction equalizer 1, the pixel shift amount described in FIGS. 2 and 3 and the amplitude compensation amount for compensating the amplitude described in FIG. 7 are measured (step). S0). Note that the pixel shift amount and the amplitude compensation amount are stored in the storage unit 5 in advance.

(Route calculation step)
In the two-dimensional reproduction equalizer 1, the route calculation unit 20 of the transfer function correction unit 2 performs a route calculation for each line in either the horizontal direction or the vertical direction of the input two-dimensional image data ( Step S1).

(Phase compensation step; horizontal direction)
Then, the two-dimensional reproduction equalizer 1 converts the two-dimensional image data route-calculated in step S1 by the Fourier transform unit 31 in the phase compensation unit 30 (see FIG. 4) of the horizontal phase compensation unit 3 in the horizontal direction. For each line, phase data and amplitude data are generated (step S2).

  Further, the two-dimensional reproduction equalizer 1 calculates the phase compensation amount from the pixel shift amount by the phase compensation amount calculation unit 32, and adds the phase compensation amount and the phase data generated in step S2 by the addition unit 33. As a result, phase data compensated for the phase is generated (step S3). Then, the two-dimensional reproduction equalizer 1 generates two-dimensional image data by performing inverse Fourier transform on the amplitude data generated in step S2 and the phase data generated in step S3 by the inverse Fourier transform unit 34. (Step S4).

(Phase compensation step; vertical direction)
Subsequently, in the two-dimensional reproduction equalizer 1, the phase compensation unit 30 </ b> B (see FIG. 4) of the vertical phase amplitude compensation unit 4 vertically converts the two-dimensional image data generated in step S <b> 4 by the Fourier transform unit 31. For each line in the direction, Fourier transform is performed to generate phase data and amplitude data (step S5).

  Further, the two-dimensional reproduction equalizer 1 calculates the phase compensation amount from the pixel shift amount by the phase compensation amount calculation unit 32, and adds the phase compensation amount and the phase data generated in step S5 by the addition unit 33. As a result, phase data compensated for the phase is generated (step S6). Then, the two-dimensional reproduction equalizer 1 generates two-dimensional image data by performing inverse Fourier transform on the amplitude data generated in step S5 and the phase data generated in step S6 by the inverse Fourier transform unit 34. (Step S7).

(Amplitude compensation step)
The two-dimensional reproduction equalizer 1 converts the two-dimensional image data generated in step S7 by the Fourier transform unit 31 in the vertical direction in the amplitude compensation unit 40 (see FIG. 6) of the vertical phase amplitude compensation unit 4. For each line, phase data and amplitude data are generated (step S8).

  Further, the two-dimensional reproduction equalizer 1 multiplies the amplitude compensation amount prepared in step S0 and the amplitude data generated in step S8 by the multiplying unit 41, thereby generating amplitude data in which the amplitude is compensated ( Step S9). Then, the two-dimensional reproduction equalizer 1 generates two-dimensional image data by performing an inverse Fourier transform on the phase data generated in step S8 and the amplitude data generated in step S9 by the inverse Fourier transform unit 34. (Step S10).

  Through the above operation, the two-dimensional reproduction equalizer 1 reduces the influence of secondary distortion and noise in the two-dimensional image data, and compensates for a pixel shift amount of 0.5 pixels or less in the horizontal direction and the vertical direction. Can do.

[Evaluation of two-dimensional regenerative equalizer]
Here, the evaluation of the two-dimensional reproduction equalizer according to the present invention will be described with reference to FIG. 10 (refer to FIG. 1 as appropriate). 10A and 10B are graphs showing experimental results, where FIG. 10A shows the output waveform of the two-dimensional image sensor, and FIG. 10B shows the output waveform of the two-dimensional reproduction equalizer.
Here, the experiment is performed using a repetitive waveform (11001100 waveform) in which two pixels are continuous.

At this time, as shown in FIG. 10A, the output waveform from the two-dimensional image sensor IS is not a vertically symmetrical waveform, and in the upper part, two pixels cannot be distinguished.
On the other hand, as shown in FIG. 10B, it can be seen that the waveform output from the two-dimensional reproduction equalizer 1 is continuously output by two pixels. In the figure, “□” indicates a pixel value.

Thus, by using the two-dimensional reproduction equalizer of the present invention, it is possible to make 1-bit data correspond to two pixels of the two-dimensional image sensor in both the horizontal direction and the vertical direction.
As a result, conventionally, 1-bit data is detected by a large number of pixels (for example, 3 × 3 = 9 pixels, 4 × 4 = 16 pixels), and 2 × 2 = 4 pixels can be detected. Possible. Therefore, the recording density on the recording medium can be increased in inverse proportion to the number of pixels per bit data.

[Other configurations of two-dimensional reproduction equalizer]
The present invention can be realized as another configuration by omitting the configuration of the two-dimensional reproduction equalizer 1 described with reference to FIG. In addition, about each structure already demonstrated, the same code | symbol is attached | subjected and description is abbreviate | omitted.
For example, when the amount of pixel shift in the horizontal direction is small (for example, 0.05 pixel or less), it is not necessary to compensate for the phase in the horizontal direction. In this case, as shown in FIG. 11, the two-dimensional reproduction equalizer 1B according to the second embodiment in which the horizontal phase compensation means 3 is omitted from the two-dimensional reproduction equalizer 1 of FIG. Is possible.

Further, for example, in a hologram recording / reproducing system (see FIG. 16), when the S / N ratio (Signal to Noise Ratio) is high (for example, 30 dB [pp / rms] or more) and the noise is small, Even if it has a transfer function of x ² with respect to the input signal x, it is not necessary to compensate the amplitude characteristic. In this case, as shown in FIG. 12, the two-dimensional reproduction equalizer 1C of the third embodiment in which the transfer function correcting means 2 is omitted from the two-dimensional reproduction equalizer 1 of FIG. Is possible.

  For example, when the S / N ratio is high and the second harmonic distortion of the recording / reproducing system is small (in the signal spectrum, the low-frequency amplitude and the amplitude near twice the maximum frequency of the signal are opened by about 30 dB or more. ), There is no need to perform route calculation and no need for amplitude compensation. In this case, as shown in FIG. 13, the transfer function correction means 2 is omitted from the two-dimensional reproduction equalizer 1 of FIG. 1, and the vertical phase phase is obtained by omitting the amplitude compensation means 40 from the vertical phase amplitude compensation means 4. The compensation means 6 can be configured as a two-dimensional reproduction equalizer 1D according to the fourth embodiment.

  For example, when the S / N ratio is high and the amount of pixel shift in the horizontal direction is small, there is no need for route calculation or phase compensation in the horizontal direction. In this case, as shown in FIG. 14, the two-dimensional reproduction which is the fifth embodiment in which the transfer function correction means 2 and the horizontal phase compensation means 3 are omitted from the two-dimensional reproduction equalizer 1 of FIG. It can be configured as an equalizer 1E.

Further, for example, when the S / N ratio is high, the harmonic distortion is small, and the amount of pixel shift in the vertical direction is small, as shown in FIG. 15, the transfer function correcting means is obtained from the two-dimensional reproduction equalizer 1 of FIG. 2 and the vertical phase amplitude compensation means 4 can be configured as a two-dimensional reproduction equalizer 1F according to a sixth embodiment.
Each of the two-dimensional reproduction equalizers shown in FIGS. 11 to 15 has the same configuration even when the horizontal direction and the vertical direction, which are compensation directions, are changed because the target image data is two-dimensional. .
As described above, the present invention can be variously modified based on the phase compensation means for compensating at least one of the horizontal direction and the vertical direction for two-dimensional image data. A simplified configuration can be obtained depending on the amount of deviation.

It is a block diagram which shows the structure of the two-dimensional reproduction | regeneration equalizer based on 1st Embodiment in this invention. It is a figure which shows the lighting pattern of a spatial light modulator. It is a graph which shows the relationship between the pixel deviation | shift amount with respect to 1 pixel, and a secondary distortion. It is a block diagram which shows the internal structure of a phase compensation means. It is a graph which shows the spectrum of the random signal in two-dimensional image data. It is a block diagram which shows the internal structure of an amplitude compensation means. It is a graph which shows the example of an amplitude equalization characteristic, Comprising: (a) is a cosine fall characteristic, (b) shows the other characteristic example. It is a block diagram which shows the other structure of a perpendicular direction phase amplitude compensation means. It is a flowchart which shows operation | movement of the two-dimensional reproduction | regeneration equalizer based on 1st Embodiment in this invention. It is a graph which shows an experimental result, (a) is an output waveform of a two-dimensional image sensor, (b) is an output waveform of a two-dimensional reproduction | regeneration equalizer. It is a block diagram which shows the structure of the two-dimensional reproduction | regeneration equalizer based on 2nd Embodiment in this invention. It is a block diagram which shows the structure of the two-dimensional reproduction | regeneration equalizer based on 3rd Embodiment in this invention. It is a block diagram which shows the structure of the two-dimensional reproduction | regeneration equalizer based on 4th Embodiment in this invention. It is a block diagram which shows the structure of the two-dimensional reproduction | regeneration equalizer based on 5th Embodiment in this invention. It is a block diagram which shows the structure of the two-dimensional reproduction | regeneration equalizer based on 6th Embodiment in this invention. FIG. 2 is a schematic diagram showing an outline of a hologram recording / reproducing system, where (a) shows a recording system, (b) shows a recording medium on which interference fringes are recorded, and (c) shows a reproducing system. It is a block diagram which shows the structure of the conventional hologram reproduction system. It is a schematic diagram which shows the relationship between the pixel of a spatial light modulator and the pixel of a two-dimensional image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Two-dimensional reproduction | regeneration equalizer 2 Transfer function correction | amendment means 20 Route calculation means 3 Horizontal direction phase compensation means 30 Phase compensation means (1st phase compensation means)
30B Phase compensation means (second phase compensation means)
31 Fourier transform means 32 Phase compensation amount calculation means 33 Addition means 34 Inverse Fourier transform means 4 Vertical phase amplitude compensation means 40 Amplitude compensation means 41 Multiplication means 5 Storage means (pixel deviation amount storage means, amplitude compensation amount storage means)

Claims (9)

A two-dimensional reproduction equalizer for equalizing two-dimensional image data, which is reproduced as a hologram and converted into an electric signal by a two-dimensional image sensor, into original data recorded as the hologram,
A pixel shift amount storage means for preliminarily storing a pixel shift amount indicating the magnitude of the horizontal or vertical shift between the pixel of the spatial light modulator used at the time of hologram recording and the pixel of the two-dimensional image sensor;
Phase compensation means for compensating a horizontal or vertical phase in the two-dimensional image data based on the pixel deviation amount stored in the pixel deviation amount storage means;
A two-dimensional reproduction equalizer comprising: A two-dimensional reproduction equalizer that equalizes two-dimensional image data, which is reproduced as a hologram and converted into an electric signal by a two-dimensional image sensor, into original data recorded as the hologram,
Pixel shift amount storage means for preliminarily storing respective pixel shift amounts indicating magnitudes of horizontal and vertical shifts between the pixels of the spatial light modulator used at the time of hologram recording and the pixels of the two-dimensional image sensor;
First phase compensation means for compensating a horizontal phase in the two-dimensional image data based on a horizontal pixel deviation amount stored in the pixel deviation amount storage means;
Second phase compensation means for compensating a vertical phase in the two-dimensional image data based on a vertical pixel deviation amount stored in the pixel deviation amount storage means;
A two-dimensional reproduction equalizer characterized by comprising: The phase compensation means includes
A phase compensation amount calculating means for calculating a phase compensation amount for compensating the phase from the pixel shift amount;
Fourier transform means for separating the one-dimensional data when the two-dimensional image data is divided in the horizontal direction or the vertical direction into amplitude data and phase data;
Adding means for adding the phase compensation amount calculated by the phase compensation amount calculating means to the phase data separated by the Fourier transform means;
Inverse Fourier transform means for performing inverse Fourier transform on the phase data to which the phase compensation amount is added by the addition means and the amplitude data;
The two-dimensional reproduction equalizer according to claim 1, wherein the two-dimensional reproduction equalizer is provided. An amplitude compensation amount storage means for storing in advance an amplitude compensation amount serving as a frequency characteristic for suppressing an amplitude of a band of a clock frequency or higher in the two-dimensional image data;
Amplitude compensation means for compensating the amplitude of the two-dimensional image data based on the amplitude compensation amount stored in the amplitude compensation amount storage means;
The two-dimensional reproduction equalizer according to any one of claims 1 to 3, further comprising: The amplitude compensation means includes
Fourier transform means for separating the one-dimensional data when the two-dimensional image data is divided in the horizontal direction or the vertical direction into amplitude data and phase data;
Multiplication means for multiplying the amplitude data separated by the Fourier transform means and the amplitude compensation amount;
Inverse Fourier transform means for inverse Fourier transforming the amplitude data multiplied by the amplitude compensation amount by the multiplication means and the phase data;
The two-dimensional reproduction equalizer according to claim 4, comprising:   6. The two-dimensional reproduction equalizer according to claim 1, further comprising route calculation means for performing a route calculation on the two-dimensional image data. A two-dimensional reproduction equalization method for equalizing two-dimensional image data, which is reproduced as a hologram and converted into an electrical signal by a two-dimensional image sensor, into original data recorded as the hologram,
A pixel shift amount stored in advance in the storage means, which indicates the magnitude of the shift in at least one of the horizontal direction and the vertical direction between the pixel of the spatial light modulator used in hologram recording and the pixel of the two-dimensional image sensor. And a phase compensation step for compensating for the phase in the two-dimensional image data. A two-dimensional reproduction equalization method for equalizing two-dimensional image data, which is reproduced as a hologram and converted into an electrical signal by a two-dimensional image sensor, into original data recorded as the hologram,
A route calculation step for performing a route calculation on the two-dimensional image data;
With respect to the two-dimensional image data route-calculated in this route calculation step, at least one of the pixel of the spatial light modulator used at the time of hologram recording and the pixel of the two-dimensional image sensor in the horizontal direction or the vertical direction. A phase compensation step for compensating a phase in the two-dimensional image data based on a pixel shift amount stored in advance in a storage unit, indicating a magnitude of the shift;
A two-dimensional reproduction equalization method comprising:   The two-dimensional image data based on an amplitude compensation amount having a frequency characteristic for suppressing the amplitude of a band equal to or higher than a clock frequency in the two-dimensional image data with respect to the two-dimensional image data whose phase has been compensated in the phase compensation step. 9. The two-dimensional reproduction equalization method according to claim 8, further comprising an amplitude compensation step for compensating for the amplitude of the two-dimensional reproduction.

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