WO2005114849A1

WO2005114849A1 - Encrypted data transmission method, data transmission system and data reception system using digital holography

Info

Publication number: WO2005114849A1
Application number: PCT/JP2004/007412
Authority: WO
Inventors: Nobukatsu Takai
Original assignee: Hokkaido Technology Licensing Office Co., Ltd.
Priority date: 2004-05-24
Filing date: 2004-05-24
Publication date: 2005-12-01

Abstract

In an encrypted data transmission technology using digital holography, information of each pixel of image data of one picture is expressed by 8-bit data, and the 8-bit data is disassembled into data of four upper order bits and that of four lower order bits. Each of the data of four upper and four lower order bits is made into four-upper-order-bit data, to which dummy data of (1000)2 is added in the four lower order bit positions, thereby creating an 8-bit data group for transmission. The thus created 8-bit data groups are divided into data groups for one picture, and a digital hologram is created for the data groups of one picture for transmission, whereby the original data can be reassembled without occurrence of errors at the receiver end. In addition, this digital hologram itself is used as encrypted data.

Description

Specification

TECHNICAL FIELD The present invention relates to an encrypted data transmission method using digital holography, a data transmission system, and a data reception system.

The present invention provides a digital hologram creation method, a digital hologram creation device, a digital hologram restoration device, a data transmission method using digital holography, a data transmission system using digital holography, and encrypted data using digital holography. The present invention relates to a transmission method and a digital hologram data receiving system. Background art

A target object is irradiated with coherent light, and a reference wave is added to the light wave (object wave) from the target object to record the interference intensity. A hologram is created, and the recorded light wave is reproduced (restored) in perfect form. . If the object is a diffuse object that scatters light randomly, the light wave will undergo a random phase change there, and the hologram will record a completely random, usually fine speckle fringe. Then, the target information can be reproduced regardless of the random phase. That is, such an optical hologram can be considered as a recording medium for target information in a random form.

The same processing as holography developed in the field of optics can be realized by digital computation using a computer. This is digital holography. Although the target of this digital holography is often an image, it can be essentially any two-dimensional array data. It can be taken inside the computer This is because the array of numerical values does not change regardless of the data handled. In other words, if the object can be represented as two-dimensional array data such as an image, the process of recording and reproducing information in optical holography can be executed by a digital computer. Specifically, two-dimensional array data is treated as image data, and random-phase modulation is performed on the data using random numbers, followed by Fourier transform. You can get it. — The resulting digital hologram is a two-dimensional random signal with a statistically uniform intensity distribution. Nevertheless, the digital hologram can always reproduce the image information in perfect form. Therefore, if the spread hologram is used as a substitute for the original image information, the hologram signal itself is a completely random signal, so the original image information is concealed as it is, and the digital hologram itself is encrypted by one. Can be used for technology.

—On the other hand, diffusion holograms have the property of being a recording medium with a certain degree of redundancy because information is uniformly distributed and recorded over the entire hologram surface. That is, it is possible to embed additional information in a part of the hologram. Therefore, if this characteristic is used, it can be applied to digital watermarking technology.

Thus, the diffusion digital hologram has the potential to be used on both sides as information encryption technology or digital watermarking technology. That is, when digital content is converted into a hologram and distributed, even if the content is intercepted during transmission, the content information is random hologram data, so that information can be transmitted with high security. To achieve this, converting digital content into a hologram form means treating it as a two-dimensional array of data similar to image data. In other words, the content information is converted into a hologram in the form of image data and transmitted. By the way, in order to use a diffuse Fourier transform hologram created by applying random phase modulation to image information as an alternative to image information, the data reproduced from it must exactly match that of the original information. . However, when a digital hologram is created as a general-purpose 8-bit image, there is an unavoidable problem that a reproduction error due to bit loss occurs. The reproduction error includes a reproduction data error and a mouthgram defect. The error in the reproduced data is a numerical difference between the reproduced image data and the original image data for each pixel. Also, a hologram defect is an error that newly occurs in the reconstructed image due to the operation of replacing a part of the hologram with other data, assuming that digital watermark information is embedded in the part of the hologram. is there. Disclosure of the invention

The present invention has been made in view of such conventional technical problems, and it is an object of the present invention to provide an encryption technology applying digital holography that can completely reproduce the original data while eliminating the influence of a reproduction error. With the goal.

A first feature of the present invention is that information of each pixel of image data of one screen is represented by 8-bit data, and each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits of data. and, the upper 4 bits, each lower 4-bit data and the upper 4-bit data, to create each of the lower four bits (1 0 0 0) 8-bit data group by adding ₂ Damide data, the 8 A digital hologram creation method for dividing a bit data group into data groups for one screen and creating a digital hologram for each data group for one screen.

In the above digital hologram creation method, the data group in a predetermined area is replaced with respect to the digital hologram, and the encrypted digital hologram is Can be created.

In the digital hologram creation method described above, 8-bit data of a character code is assigned as 8-bit data of each pixel of image data, and a character document file can be converted into a digital hologram.

Also, in the above digital hologram creation method, two-pixel 16-bit data adjacent to image data can be divided by: 1- to 6-bit data of 2 pi .. The file can be digitally hologramized. A second feature of the present invention is that an image processing unit that expresses information of each pixel of image data of one screen by 8-bit data, and decomposes each of the 8-bit data into upper 4 bits and lower 4 bits data The upper 4 bits and lower 4 bits of data as upper 4 bits of data, and add (100 0) ₂ dummy data to each lower 4 bits to generate 8 bits of data. An 8-bit data group creation unit that creates groups; and a digital holography processing unit that divides the 8-bit data group into data groups for one screen and creates a digital hologram for each data group for one screen. Digital hologram making equipment.

In the above digital hologram creation apparatus, the image processing unit may assign 8-bit data of a character code as 8-bit data of each pixel of the image data.

In the digital hologram creating apparatus, the image processing unit may assign 16-bit data of a 2-byte character code as 16-bit data of two pixels adjacent to the image data.

According to the digital hologram creation method and creation apparatus of the present invention, if the image data is image data, 8-bit data is assigned to each pixel, and an 8-bit 1-bit character code is assigned. For document data, each character is assigned as an 8-bit character code for each pixel.For document data with 16-bit 2-byte character code, each character is assigned as a 16-bit character code for two adjacent pixels. Create image data for one screen. Then, each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits of data, and the decomposed upper 4 bits and lower 4 bits of data are each set as upper 4 bits, and each of the lower 4 bits is processed. (1. 0 0—0> ₂ ) ^ Add one piece of data to create an 8-bit transmission data group. Divide the 8-bit data group into data groups for each screen pixel. A digital hologram is created for each data group for one screen pixel.

For the digital hologram data created in this way, the original image or document content is restored on a screen-by-screen basis by the reverse procedure on the restoration device side. In this restoration, the original image and original document information can be restored without errors. A third feature of the present invention is that an 8-bit data decomposing unit that decomposes digital hologram data into an original 8-bit data group, and that data of lower 4 bits is provided for each of the decomposed 8-bit data. A dummy data deletion processing unit to be deleted, and a data group of the upper 4 bits from which the data of the lower 4 bits have been deleted is divided into original upper 4 bits and lower 4 bits of data, and an 8-bit data group of the original image An 8-bit data restoration processing unit for restoring image data, an image restoration processing unit that assigns the restored 8-bit data group to each pixel, and sets image data for each screen, and an image display unit that displays the image data To a digital hologram restoration device equipped with. ■

In the above digital hologram restoration apparatus, the image restoration processing unit can restore an 8-bit 1-byte character code with one 8-bit data. In the above-described digital hologram restoration apparatus, the image restoration processing unit can restore a 16-bit 2-byte character code with two adjacent 8-bit data.

In the digital hologram restoration device of the present invention, the digital hologram data created by the digital hologram creation device is decomposed into an original 8-bit data group, and each of the decomposed 8-bit data is divided into lower 4 bits. Dummy data is deleted, the upper 4-bit data group from which the lower 4-bit data has been deleted is divided into the original upper 4-bit and lower 4-bit data, and the 8-bit data group of the original image is restored from these. I do. Then, the 8-bit data group of the restored original image is assigned to each pixel and displayed as an original image for each screen. In the digital hologram created by the digital hologram creation device, dummy data is added to the lower 4 bits that are likely to cause an error during transmission, and the original data is all data of the upper 4 bits. The original hologram data can be restored without errors by deleting the dummy data and restoring the original data, especially when the document data is converted to digital hologram data. The original document data can be restored without errors.

A fourth feature of the present invention is that information of each pixel of image data of one screen is represented by 8-bit data, and each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits of data. The upper 4 bits and lower 4 bits of data are each set to upper 4 bits, and (10000) ₂ dummy data is added to each lower 4 bits to create an 8-bit transmission data group. A digital hologram that divides an 8-bit data group into data groups for one screen, creates a digital hologram for each of the one-screen data groups, and transmits the digital hologram There is a data transmission method using luffy.

In the above data transmission method using digital holography, a digital hologram to be transmitted can be transmitted after a data group in a predetermined area is replaced.

In the data transmission method using digital holography, a public key cryptosystem can be used for encryption.

In the data transmission method using digital holography, 8-bit data of a character code can be assigned as 8-bit data of each pixel of image data.

In the data transmission method using digital holography, 16-bit data of a 2-byte character code can be allocated as 16-bit data of two pixels adjacent to image data.

A fifth feature of the present invention is that an image processing unit that expresses information of each pixel of image data of one screen by 8-bit data, and decomposes each of the 8-bit data into upper 4 bits and lower 4 bits data 4-bit decomposition processing unit, and the upper 4 bits and lower 4 bits of data are converted to upper 4 bits,

A transmission data creation unit that creates a transmission 8-bit data group by adding (10000) ₂ dummy data to 4 bits, and divides the transmission 8-bit data group into a data group for each screen A transmission system using digital holography, comprising: a digital holography processing unit that creates a digital hologram for each data group for one screen; and a transmission unit that transmits the digital hologram.

In the above-mentioned transmission system using digital holography, the data group of a predetermined area is replaced with respect to the digital hologram. And an encryption processing unit for transmitting the data.

In the above transmission system using digital holography, the encryption processing unit may perform encryption processing using a public key in a public key cryptosystem.

In the above transmission system using digital holography, the image processing unit may assign .8-bit data of a character code as 8-bit data of each pixel of the image data.

In the transmission system using digital holography, the image processing unit may assign 16-bit data of a 2-byte character code as 16-bit data of two pixels adjacent to the image data.

In the data transmission method and transmission system using digital holography of the present invention, 8-bit data is assigned to each pixel in the case of image data, and each character is assigned to each pixel in the case of 8-bit 1-byte character code document data. If the document data is 16-bit 2-byte character code, each character is allocated as a 16-bit character code for two adjacent pixels, and the image data for one screen unit is assigned. create. Then, each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits of data, and the decomposed upper 4 bits and lower 4 bits of data are each converted into upper 4 bits, and each of the lower 4 bits is converted into lower 4 bits. (10000) Adds ₂ dummy data to create an 8-bit transmission data group, divides the 8-bit data group into data groups for each screen pixel, and A digital hologram is created for each data group corresponding to the number of surface pixels, and the digital hologram is transmitted.

The digital hologram data transmitted in this way is received by the receiving side, and the original image or document contents are restored in units of one screen by the procedure reverse to that of the transmitting side. Is done. In this restoration, the original image and original document information can be restored without errors. A sixth feature of the present invention is that information of each pixel of image data of one screen is represented by 8-bit data, and each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits of data. The upper 4 bits and the lower 4 bits are each set to the upper 4 bits, and (100 0) ₂ dummy data is added to the lower 4 bits to create an 8-bit transmission data group. Digital holography that divides the 8-bit data group into data groups for one screen, creates a digital hologram for each data group for one screen, and transmits the digital hologram itself as encrypted data In the method of transmitting encrypted data. In the method of transmitting encrypted data using digital holography of the present invention, the digital hologram itself of an image or document data created in a manner that is unlikely to cause an error during transmission is transmitted as encrypted data, and is received. Only a receiving system equipped with a hologram restoration device can accurately restore the original image or document data. A seventh feature of the present invention is that a receiving unit that receives digital hologram data, a transmission 8-bit data decomposing unit that decomposes the digital hologram data into an original transmission 8-bit data group, A dummy data deletion processing unit that deletes data of lower 4 bits for each of the 8-bit data for transmission, and a data group of upper 4 bits from which the data of lower 4 bits are deleted is converted into an original data group. An 8-bit data restoration processing unit that divides the data into upper 4 bits and lower 4 bits and restores the original 8-bit data group, and assigns the restored 8-bit data group to each pixel, and image data for each screen A digital hologram receiving system comprising: an image restoration processing unit to be described below; and an image display unit for displaying the image data.

In the above digital hologram receiving system, the encrypted and transmitted It can be provided with a decoding processing section for decoding digital hologram data to be received.

In the digital hologram receiving system described above, the image restoration processing unit can restore a 16-bit 2-byte character code using two adjacent 8-bit data.

In the digital hologram receiving system of the present invention, the digital hologram data sent by the digital hologram transmission system is received, and the received digital hologram data is decomposed into the original transmission 8-bit data group. For each of the decomposed transmission 8-bit data, the lower 4 bits of dummy data are deleted, and the upper 4 bits of the data group from which the lower 4 bits of data are deleted are replaced with the original upper 4 bits and lower 4 bits. The data is divided into bit data, and the 8-bit data group of the original image is restored from these data. The 8-bit data group of the restored original image is assigned to each pixel and displayed as image data for one screen.

Digital hologram data is sent from the transmission system, and dummy data is added to the lower 4 bits of data that are likely to cause errors during transmission, and all original data is transmitted as upper 4 bits of data. By deleting the dummy data on the system side and then restoring the original transmission data, the original hologram data can be restored without error.In particular, the document data is converted to digital hologram data and transmitted. In such a case, the original document data can be restored without errors such as garbled characters. Brief Description of Drawings

Figure 1 is an illustration of general digital holography.

Figure 2A shows the original image used for general digital holography. Figure 2B shows an image of a digital hologram by general digital holography.

Fig. 2C shows a reproduced image of a digital hologram by general digital holography.

Figure 3 shows a graph that represents the value of the standard deviation σ _{Δ の} of the image difference between the original image and the reproduced image obtained in the experiment as a function of the amount obtained by normalizing the random deviation of the standard deviation σ _ρ by 2π. rough.

Figure 4 is a graph of the reconstructed image error as a function of the number of hologram defects. FIG. 5 is an explanatory diagram showing the effect of the number of hologram defects η on a bit plane of reproduced image data.

Fig. 6Α is an explanatory diagram comparing the values of six consecutive pixel values of the original data and a part of the reproduced data in decimal notation when the hologram data was reproduced without any change.

FIG. 6B is an explanatory diagram comparing binary values of six consecutive pixel values of the original data and a part of the reproduced data when the hologram data is reproduced without any change.

FIG. 7 is an explanatory diagram of a digital hologram creation procedure and a reproduction procedure thereof in a transmission method using digital holography according to one embodiment of the present invention. FIG. 8 is a block diagram showing a functional configuration of a transmission system used in the transmission method according to the above embodiment.

FIG. 9 is a block diagram showing a functional configuration of a receiving system for hologram data transmitted by the transmitting system according to the embodiment.

FIG. 10 is a flowchart of hologram data transmission processing by the transmission system. Fig. 11 is a flowchart of the character reproduction process from hologram data by the receiving system.

FIG. 12 is a pattern diagram of a hologram transmitted in the above embodiment.

FIG. 13 is an explanatory diagram of an encryption method for the hologram.

Figure 14A shows a hologram pattern of a text document embedded in the original image. Figure 1.4B is a pattern diagram of a hologram reproduced from the hologram of the text document.

Figure 14C is a pattern diagram of the hologram reproduced from the encrypted hologram of the text document.

FIG. 15 is a block diagram showing a functional configuration of a digital hologram creation device according to a second embodiment of the present invention.

FIG. 16 is a block diagram showing a functional configuration of a digital hologram restoration device according to a second embodiment of the present invention.

FIG. 17 is a flowchart of digital hologram data creation processing by the digital hologram creation device.

FIG. 18 is a flowchart of a process of restoring an original image from a digital hologram by the digital hologram restoring device. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the diffusion type Fourier transform digital hologram will be described. As is well known, optical holography is an optical technique that completely preserves both the amplitude and phase of an object and reconstructs a three-dimensional object as it is. At this time, all information on the amplitude and phase of the object is stored as a hologram on a recording medium such as a photographic plate. The This record is an intensity record of the interference pattern of the diffracted light wave (object wave) from the object and the reference light wave (reference wave). An interference pattern results.

Here, digital holography, in which this optical process is performed in a computer, will be described first. Figure 1 shows the procedure for creating a digital hologram for two-dimensional array data. Below, this — two-dimensional array data g. (x, y) is called image data. However, this is not limited to image data, but may be an array of numerical data or text data. However, g is used in both cases as image data. (X, y) is non-negative numerical data.

The procedure for creating a digital hologram is as follows. After modulating (x, y) with a random phase ψ (x, y), two-dimensional Fourier transform is performed using fast Fourier transform (FFT).

Next, if the intensity is detected by adding the obliquely illuminated reference wave plane wave signal to the result, a diffuse Fourier transform hologram of two-dimensional array data is obtained. That is, g (, y) = g ₀ (, y) exp [ΐφ (χ, y)] h)

Fourier transform of

Θ {ξ, η) = || g (, y) exp [ΐ (χ, y) I exp dxdy (2)

And the reference signal

Add. Here, a and b are constants that give the slope of the reference wave signal. When the intensity is detected as a hologram,

+ G (ξ, η) Κ {ξ, η) + β (ξ, rf) R * (ξ, η) (4). Here, * represents a complex conjugate.

Next, the computer processing finally removes terms that are not related to the reconstructed image. By post-processing, the last two terms in equation (4) Η {ξ, η) = G (ξ, η) 式, η) + β (ξ, η) (ξ, η) (5) is obtained. This is the expression of the digital hologram. Since it consists of G (, 77) related to the random phase φ (X, y), it is a diffuse Fourier transform hologram. Therefore, if the distribution of φ (x, y) is large to some extent, it can usually be obtained as a statistically uniform intensity distribution.

The reconstructed image g _R (x, y) from the digital hologram can be obtained by multiplying the reconstructed wave signal.In a simple case, simply using a plane wave of amplitude 1, the reconstructed image is obtained by the inverse Fourier transform of equation (5). Yes, g _R ix, y) = g ₀ '(x-, yb) exp

+ go-(x + a),-(y + (6)

Is obtained as Although the result of this equation (6) is for random phase φ, when the one item and the two items on the right side are completely spatially separated, the absolute value of each item is obtained by

\ g _R (x, = go * (—, — b) + g. [one 0c + a),-(y + b), ')

It becomes. Here, two-dimensional array data g. We used that (X, y) is non-negative data. From these results, the reconstructed image is composed of two images that are symmetrical about the origin at the coordinate points (a, b) and (-a, -b) on the (x, y) coordinate plane, and are hologram-created. It is clear that it does not depend on the random phase φ (X, _y ) used at that time. And these two images correspond to the real and virtual images of the reconstructed image from the optical hologram, respectively.

FIG. 2 is an example of a digital hologram of image data obtained by such an arithmetic processing and a reproduced image from the digital hologram. Figure 2A shows the original image, Figure 2B shows the digital hologram, and Figure 2C shows the reproduced image.

Next, error evaluation of a reproduced image will be described. The reproduced image in FIG. 2C visually looks like the original image shown in FIG. 2A is correctly reproduced. Certainly, when a digital hologram is created, if an arithmetic precision of 64 bits (double precision) is used, an original image having a negligible error can be reproduced with high accuracy as in the equation. However, this is not always the case if we take into account realistic factors. In other words, considering that the hologram is used as an encrypted medium of the original image data, it must be treated as 8-bit data, like general-purpose image data, and the quantization error becomes a problem.

The error of the reproduced image strongly depends on the random phase applied to the original image data. Here, the random phase is actually given by a Gaussian random number. However, if the standard deviation σ _ρ of the random phase is changed, the error of the reproduced image greatly changes. However, as will be described later, this dependency results in "the larger the random phase amount _{ρ, the} smaller the error". In general, in a phenomenon involving fluctuation, a large fluctuation often causes a large error in the result, whereas in digital holography, the error is small.

The cause of the error is that the horror Due to quantization errors in the data. Performing 8-bit quantization on a digital hologram means converting the hologram intensity value of each pixel into an integer value in 256 steps from 0 to 255, and the hologram data in this dynamic range Depends on value distribution. The fact that the random phase amount is related to this distribution governs the error of the reproduced image.

This can be easily understood by considering the extreme case of σ _ρ = 0. That is, no random phase modulation is applied. At this time, what is recorded as a hologram is the interference pattern between the Fourier spectrum of the original image data and the reference wave signal. Normally, in the case of the image data in Fig. 2 (2), the distribution of the Fourier vector is concentrated in the low frequency region. Then, when the interference pattern of this and the reference signal is quantized with 8 bits, the strong part in the low frequency region is quantized with good accuracy, but the components in the high frequency region are virtually ignored by the quantization. (Removed). As a result, the reproduced image is significantly degraded, resulting in a large error. On the other hand, when the random phase amount is large to some extent and hologram intensity consisting of a statistically uniform intensity distribution in the spectral region is recorded, quantization processing is performed with the same degree of accuracy for all frequency components. Therefore, a reproduced image with a small error can be obtained.

'This is supported by the following experimental results. First, the digital hologram created by the 64-bit precision (double precision) operation is converted into 8-bit data, and the difference (error) between the original image and the reproduced image (one of the reproduced images) is calculated. Numerically examined. That is, the original image. riginal and reconstructed image

丄 reconstructed ^,

^J reconstructed original Standard deviation over all pixel values of one screen of-. = ^) ( ⁸ )

The error of the reproduced image was evaluated using, and the condition of the random phase amount that minimized the error was examined. At this time, we also considered a method for accurately reproducing the original image data. At the same time, the effect of a defect on the hologram on the reconstructed image was numerically investigated. This hologram defect was provided with the intention of clarifying the permissible amount of embedding an encryption key in a hologram when using information of image data as an encryption medium. Here, each of the two image data to be evaluated is 8-bit data.

FIG. 3 shows the value of the standard deviation σ _{Δ の} of the image difference between the original image and the reproduced image obtained in the experiment as a function of the amount obtained by normalizing the standard deviation σ _ρ of the random phase by _2π . Here, the random phase is given using Gaussian random numbers, and σ _ρ is its standard deviation. Marker における in FIG. 3 indicates a case where there is no hologram defect, and markers □, + and ◊ indicate cases where the number of hologram defects η is 20, 100, and 512, respectively. Here, the hologram defect number η is the number of pixels when a part of the hologram is replaced with another value, assuming that additional information is written. The following two things can be read from the results shown in FIG.

First, when the random phase amount σ _ρ is small, the error of the reconstructed image is very large. In the region where σ _ρ > π, it depends on the number of defects η, but the value is almost constant. The phenomenon that the error is large when the amount of random phase is small, and the error decreases rapidly as the amount increases is seemingly strange behavior, but this is thought to be due to the quantization error of the hologram as described above. Can be In other words, digital holography with 8-bit quantization can reduce this error In order to obtain a high quality reconstructed image, a hologram having a steady intensity distribution as shown in Fig. 2 is a necessary condition. Therefore, it is necessary to satisfy the condition of σ _ρ > π for the amount of random phase.

The second thing seen in Fig. 3 is the dependence of the reproduced image error on the number η of defects in the hologram. Here, the number of defects is defined as a defect by replacing the il pixel value in the middle of the hologram and the η pixel values in the part. -.

The error of the reconstructed image shows a substantially constant value for each number of defects η in the region of the error of the reconstructed image as a function of the number of hologram defects shown in Fig. 4. Is clearly observed to increase. Fig. 4 shows the results of a detailed examination of this tendency using the average error obtained by averaging the errors of the reproduced images obtained in the region where the random phase amount is σ _ρ > π. In Fig. 4, the average error when all η consecutive pixels of the hologram are replaced with zero is shown as a function of the number of defects η.

From Fig. 4, it can be seen that the reproduced image error monotonically increases with the number of defects η, but the important point is the magnitude of the error. First, when there are no defects, the average error shown in FIG. 4 is 0.5924, which is less than 1. That is, even if the value of the standard deviation is taken into account, even if the error of the reproduced image is largely estimated, it occurs in the 0-bit plane of the reproduced image data (8-bit data). When the number of defects η was 50, the average error was 0.9951. Since this is an error of about 1 or 2 in a decimal number, the value of the 0 to 1 bit plane fluctuates with high probability.

Figure 5 shows the effect of the number of hologram defects η (the number of pixels in which the negative part was replaced with another value) on the bit plane of the reproduced image data. The average error obtained when the number of defects η is 300 is 2.035, and in this case, FIG. As shown in (2), error fluctuation also appears on the 2-bit plane.

Next, a description will be given of a method of performing complete reproduction by bit operation without being affected by the above-mentioned error fluctuation. Figures 6A and 6B compare the values of six consecutive pixel values of the original data and a part of the reproduced data in decimal and binary numbers when the hologram data was reproduced without any changes. Things. The numbers are compared in both decimal and binary numbers, and the reproduced data with errors is shaded. As can be seen, the reproduced data has an error in the range of 1 to 2 in the decimal notation shown in FIG. 6A. As described above, when the hologram data is not replaced, the error is extremely small.

However, in the binary notation shown in Fig. 6B, even if such a small error causes carry-up or carry-down, the values of all bit planes are affected. For example, if the original data is 63 (decimal) and the reproduced data is 65 (decimal), as in the second case from the bottom of Fig. 6B, the error is 2 (decimal). 63 = (01 1 1 1 1 1) ₂ plus error 2 = (1 0) ₂ to give 65 = (1000001) ₂ , and the carry of the lower bits affects the upper bits.

This error is an unavoidable problem with a diffusion hologram of 8-bit data created using random phase modulation on the original data. Therefore, in order to reproduce the original data in a perfect form by using this method, it is necessary to devise a method that takes account of the above-mentioned error characteristics. The present invention solves this.

Hereinafter, as one embodiment of the present invention, a method of completely reproducing original data consisting of 8 bits will be described. Figure 7 shows this method, and the procedure is as follows.

First, as shown in step (1), the 8-bit data of one pixel of the original data is It is broken down into two bits: the upper 4 bits and the lower 4 bits.

In the following procedure (2), an 8-bit data group is created in which each of the decomposed two data is set to the upper 4 bits, and the lower 4 bits are all set to (10000). Then, these arrangements are determined, and a diffusion-type digital hologram is created using the arrangement as the original data.

At the time of reproduction, as shown in step (3), a reproduction data group is obtained as a reproduced image of the hologram in step (2), and only the upper 4 bits are taken out. The lower 4 bits (XXXX in Fig. 7) are discarded.

In the following step (4), an 8-bit data group is reconstructed from the two sets of 4-bit data groups extracted in step (3) according to the data arrangement determined in step (2).

By performing the above operation, the upper 4 bits and lower 4 bits of the original data are omitted as upper bits in the processing process, so that the effect of the reproduction error appearing in the lower bits can be avoided. At this time, it is important to perform the bit operation of setting the lower 4 bits of all the data in step (2) to (10000) ₂ . By doing so, even if a large error of +7 occurs in base 10, the part is only (1 1 1 1) ₂ and the carry to the upper 4 bits does not occur. Conversely, when a large error of 18 occurs, it becomes (0 0 0 0) ₂ , so that there is no influence of the borrow to the upper 4 bits. In other words, by setting the lower 4 bits to (10000) ₂ , an error in the range of 18 to 17 in base 10 can be absorbed by this part. As a result, the values of the upper 4 bits are reproduced in perfect form without being affected by errors, and the original data can be reproduced in perfect form by reconstructing the two sets of reproduced data.

Next, character data is hologram-encrypted and transmitted using the above principle, The process of restoring the same will be described. If a text document can be converted into a digital hologram and then restored without a 1-bit error, the digital hologram can be used as an encryption medium for digital content. Here, we explain a method of encrypting a text document (character data) in the form of a hologram and then accurately restoring the document information. At this time, character data is treated as an image, and it is encrypted as a digital hologram. Since all characters, whether Japanese or Western, are coded, if there is an error even in a single bit in the restoration result, garbled characters occur and accurate document information cannot be obtained. The following shows the case of a Japanese document.

8 shows a data transmission system using holography, and FIG. 9 shows a functional configuration of the data reception system. FIGS. 10 and 11 show flowcharts of data transmission processing and data reception processing using holography. The data transmission system 100 shown in Fig. 8 divides each 16-bit 2-byte character code included in a Japanese document into upper 8 bits and lower 8 bits, and generates an 8-bit data string. Pre-processing unit 11 1, upper and lower 4-bit division processing unit 12 that divides each 8-bit data into upper 4 bits and lower 4 bits, and sets each 4-bit data into upper 4 bits and lower 4 bits Lower dummy data addition processing unit 13 that adds dummy data (10000) ₂ to bits 13 Transmission data creation unit 1 that rearranges the 8-bit data string to which the dummy data is added and creates transmission data 4. Create a hologram from the transmitted data. The hologram creation unit 15 by the arithmetic processing shown in FIG. 1, replace predetermined areas with each other from the created hologram, and perform predetermined encryption using a public key obtained in advance. Hologram encryption processing unit 1 6 for executing processing, and the encrypted data from the transmit processor 1 7 transmits through the network. The document decryption system 200 shown in FIG. 9 is a data receiving unit 21 that receives encrypted data via a network, decrypts the received encrypted data using a secret key, and restores the original hologram. Decoding processing unit 22, Hologram decomposing unit 23 that extracts 8-bit data for each pixel from the restored hologram, Upper and lower 4-bit division processing unit that decomposes each of these 8-bit data into upper and lower 4 bits 2 Lower 4-bit discard processing unit 2.5 that discards lower 4 bits of dummy data of 4 and 8 bit data 2.5, upper 4 bits of remaining upper 4 bit data string, lower 4 bits of 8 bit data 8-bit data reconstructing unit 26, which restores to columns, and 16-bit 2-byte document data playback processing unit 27, which combines 16-bit 2-byte Japanese character codes by combining two 8-bit data It has been.

Next, the document transmission processing by the data transmission system 100 using holography having the above configuration and the reception processing by the data reception system 200 will be described with reference to the flowcharts of FIGS. 10 and 11. In the data transmission system 100, in the case of a Japanese document, one character of a Japanese sentence is coded with 16 bits and 2 bytes, so the preprocessing unit 11 decomposes one character into two 8 bits. To create a digital hologram, encrypt it, and transmit it. Note that this preprocessing is not required for European characters in which one character can be handled by 8 bits.

In the following description, the encrypted transmission and reception decryption processing of a Japanese document composed of 363 characters will be described. First, the 16-bit character code of the Japanese document is divided into two 8-bit codes (step S 1), and then, according to the procedure shown in FIG. (Step S 3).

Then, these upper 4 bits and lower 4 bits are respectively set as upper 4 bits. Then, (10000) ₂ dummy data is added to the lower 4 bits of each to create 8-bit data (step S5).

Next, the created 8-bit data group is arranged in a predetermined order to create an 8-bit data string for transmission, and a hologram is created for this. For example, extract the image matrix data of 12 rows x 128 columns including the blank-white part of the last row. Therefore, for Japanese characters, the image data is four times the size of the number of characters (step S7). Subsequently, an original image (256 x 256) is created by incorporating the imaged character data, and a digital hologram is created by the above-described method (step S9). FIG. 12 illustrates the created digital hologram. This hologram is created by applying random phase modulation with a standard deviation of 2π to the entire surface of the original image based on Gaussian random numbers. Therefore, the fine structure of the hologram differs depending on the random number used.

A digital hologram as shown in FIG. 12 is subjected to encryption processing using a public key as a signal key previously obtained from the receiving side, and a predetermined address data receiving system 200 (Steps S11, S13). For this encryption, a method of exchanging predetermined areas Rl and R2 of the digital hologram as shown in Fig. 13 can be adopted, but a general public key cryptosystem generally used for ordinary transmission data is used. A public key based on a scheme can also be used.

Next, the decoding process by the receiving system 200 and the restoration process of the original document information from the digital hologram will be described with reference to the flowchart of FIG. If the encrypted data is received from the transmitting system 100 (step S21), decryption processing is performed using the secret 鐽 of the receiving system 200 to restore the original digital hologram data (step S21). S2 3). Then, the original transmission 8-bit data group is restored from the digital hologram, and the upper 4 bits are left from each 8-bit data, and the lower 4 bits dummy data are discarded (step S25, step S25). S27).

Next, the remaining upper 4-bit data group is divided into the original upper 4-bit and lower 4-bit data group by the reverse procedure of the transmitting side, and the original 8-bit data group is restored. (Step S29). Furthermore, the original Japanese document is restored by restoring 16-bit 2-byte data using the restored 8-bit data and arranging the 16-bit 2-byte data sequence in the original order. And output (steps S31, S33).

Figure 14A shows the imaging pattern of the text document embedded in the original image, and Figures 14B and 14C show the images reproduced from the hologram. Figure 14B shows the hologram reproduced without any manipulation, and the character information can now be restored correctly. On the other hand, the pattern in Fig. 14C is a pattern in which the hologram is modified and character information cannot be restored.

The reproduced image in Fig. 14B is very similar to the original image in Fig. 14A, and the difference is visually indistinguishable, but has an error of about 1 or 2 bits as described above. . On the other hand, if the above-mentioned complete restoration method that avoids errors is applied, a restoration result that exactly matches the original text one by one can be obtained. Even if this digital hologram is reconstructed repeatedly by changing the value of the random phase used for its creation, if the standard deviation of the phase distribution is 2π, accurate results can be obtained. .

The fact that character data can be completely restored from a digital hologram means, of course, that all information of the character data is present in the hologram in a random state. Generally, holograms have the following characteristics: It is known that an image can be reproduced from a part of the image, but a high-precision reproduced image cannot be obtained beyond visual observation. Taking this into account, if a part of the hologram created is replaced with another part, the reproduced image can be changed to a random image while the entire digital hologram retains all digital content information. The reconstructed image in FIG. 14C is a reconstructed image obtained after such replacement of the hologram data. Character data cannot be reproduced from a reconstructed image such as Muronko. You only get a list of symbols that have no meaning. Therefore, if a receiver who does not have a decryption key transmits encrypted hologram data that cannot be accurately restored, even if the data is restored using digital holo-drama reconstructing means, this meaning is unknown. You will only be able to obtain a series of symbols and you will not be able to decipher the original document content.

In general, encryption technology is a technology that combines encryption and decryption. When a digital hologram is used as an encryption medium, it must be accompanied by a decryption key that only a specific person can recover. In other words, the system must be able to decrypt without knowing the decryption key. In the case of data exchange (replacement) on the hologram surface shown above, knowing the information of the exchange (parameters specifying the two areas to be exchanged) can return the hologram data to its original state. Wear. And then you can recover the encrypted data in perfect form. In other words, the encryption and decryption methods shown here are the simplest case, but they are used as one encryption technique with the exchange parameter as the encryption key. And this technology can be used for all digital contents, not limited to two-dimensional array data represented by images.

In the above embodiment, the digital hologram is further encrypted and transmitted, and the receiving side decrypts the digital hologram using the decryption key. A system and method for restoring document data that matches word by word has been described. However, the technology is not limited to this, and is widely used as a digital hologram data transmission technology that does not involve encryption processing in fields that require restoration technology that transmits image data and that does not allow 1-bit errors on the receiving side. It can be used.

-Next, a digital hologram creation device and a digital hologram restoration device according to a second embodiment of the present invention will be described. FIG. 15 shows the functional configuration of the digital hologram creation device 300, and FIG. 16 shows the functional configuration of the digital hologram restoration device 400.

The digital hologram creation device 300 has almost the same configuration as the digital hologram creation device 100 shown in FIG. 8, but includes a data storage unit 31 for saving the data created by the hologram creation unit 15. It has a feature in that. On the other hand, the digital hologram restoring device 400 has almost the same configuration as the digital hologram receiving device 200 shown in FIG. 9, but is created by the digital hologram creating device 300 and has some data storage medium. It is characterized by having a data storage section 21 'for reading and storing digital hologram data stored in the memory.

In the digital hologram creating apparatus of the present embodiment, digital hologram data is created by the procedure shown in the flowchart of FIG. 17 and stored in the data storage unit 31. This digital hologram creation procedure is almost the same as the processing procedure of the digital hologram transmitting apparatus 100 of the first embodiment shown in the flowchart of FIG. 10, except that the data storage processing is performed in step S11 '. The points are different. The digital hologram data created in this manner is stored on a recording medium such as a flexible disk or a magnetic storage disk, for example, as shown in FIG. The data can be copied to the data storage unit 2 1 ′ of the program restoring device 400. The restoration process of the original image from the digital hologram data by the digital hologram restoration device 400 is performed according to the procedure shown in the flowchart of FIG. This procedure is almost the same as the processing procedure of the digital hologram receiver 200 shown in FIG. 11, but the digital hologram data is read from the data storage unit 21 ′ in the first step S21 ′. Is passed to the decryption processing section 22. The procedure from step S23 is the same as that of the flowchart of FIG.

Thus, the digital hologram data created by the digital hologram creation device 300 of the second embodiment can be accurately restored by the digital hologram restoration device 400 by being restored by the digital hologram restoration device 400. As a data, a document file in a format in which 8-bit 1-byte character codes are assigned to each pixel, or a Japanese document file in a format in which 16-bit 2-byte character codes are assigned to every two adjacent pixels Can be used for encrypted recording and playback.

Claims

The scope of the claims

1.1 Express the information of each pixel of the image data of one screen with 8-bit data, decompose each of the 8-bit data into upper 4 bits and lower 4 bits,

The upper 4 bits and lower 4 bits of data are defined as upper 4 bits of data, and (100 0) ₂ dummy data is added to each lower 4 bits to create an 8-bit data group.

A method for creating a digital hologram, comprising: dividing the 8-bit data group into data groups for one screen, and creating a digital hologram for each data group for one screen.

2. The digital hologram creation method according to claim 1, wherein a data group in a predetermined area is exchanged with respect to the digital hologram.

3. The digital hologram creation method according to claim 1, wherein 8-bit data of a character code is allocated as 8-bit data of each pixel of the image data.

4. The digital hologram creation method according to claim 1, wherein 16-bit data of a 2-byte character code is allocated as 2-pixel 16-bit data adjacent to the image data.

5.1 An image processing unit that expresses information of each pixel of image data of one screen with 8-bit data,

A bit data decomposition processing unit for decomposing each of the 8-bit data into upper 4 bits and lower 4 bits of data;

The upper 4 bits and lower 4 bits of data are converted to the upper 4 bits An 8-bit data group creation unit that creates 8-bit data groups by adding dummy data of (10000) ₂ to the lower 4 bits of each as data,

A digital holographic processing apparatus, comprising: a digital holographic processing unit that divides the 8-bit data group into data groups for one screen and generates a digital hologram for each data group for one screen.

6. The digital hologram creation device according to claim 5, wherein the image processing unit assigns 8-bit data of a character code as 8-bit data of each pixel of the image data.

7. The digital hologram creating apparatus according to claim 5, wherein the image processing unit assigns 16-bit data of a 2-byte character code as 16-bit data of adjacent two pixels of the image data.

8. An 8-bit data decomposing unit that decomposes digital hologram data into an original 8-bit data group,

A dummy data deletion processing unit that deletes data of lower 4 bits for each of the decomposed 8-bit data;

8-bit data restoration process for restoring the original 4-bit data group by dividing the upper 4-bit data group into the original upper 4-bit and lower 4-bit data Department and

An image restoration processing unit that assigns the 8-bit data group of the restored original image to each pixel and generates image data for each screen,

A digital hologram restoring device, comprising: an image display unit that displays the image data.

9. The digital hodala according to claim 8, wherein the image restoration processing unit restores an 8-bit 1-byte character code with one 8-bit data. System restoration device.

10. The image restoration processing unit is 16 bits with two adjacent 8-bit data.

9. The digital no-regram gram restoration device according to claim 8, wherein a two-byte character code is restored.

11.1 Each pixel information of image data of one screen is represented by 8-bit data, and each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits,

The upper 4 bits and lower 4 bits of data are set as upper 4 bits of data, and (10000) ₂ dummy data is added to each lower 4 bits to create an 8-bit transmission data group.

The digital holography is characterized in that the 8-bit data group is divided into data groups for one screen, a digital hologram is created for each data group for one screen, and the digital hologram is transmitted. The data transmission method to use.

12. The data transmission method using digital holography according to claim 11, wherein the digital hologram is transmitted after a data group in a predetermined area is exchanged.

13. The data transmission method using digital holography according to claim 12, wherein a public key cryptosystem is used for the encryption.

14. The data transmission method using digital holography according to any one of claims 11 to 13, wherein 8-bit data of a character code is assigned as 8-bit data of each pixel of the image data.

15. The method according to claim 11, wherein 16-bit data of 2-bit character code is allocated as 2-bit 16-bit data adjacent to the image data. 13. A data transmission method using digital holography according to any one of 3.

16.1 an image processing unit that expresses information of each pixel of image data of one screen with 8-bit data,

A 4-bit decomposition processing unit for decomposing each of the 8-bit data into upper 4 bits and lower 4 bits of data;

The upper 4 bits and lower 4 bits of data are set as upper 4 bits of data, and (10000) ₂ dummy data is added to each lower 4 bits to create an 8-bit data group for transmission. A transmission data creation unit;

A digital holography processing unit that divides the transmission 8-bit data group into data groups for one screen, and creates a digital hologram for each data group for one screen;

A transmission system using digital holography, comprising: a transmission unit that transmits the digital hologram.

17. The digital hologram further includes an encryption processing unit that transmits a data group of a predetermined area after exchanging the data group.

A transmission system using digital holography described in 6.

18. The transmission system using digital holography according to claim 17, wherein the encryption processing unit performs an encryption process using a public key in a public key cryptosystem.

19. The digital holography according to any one of claims 16 to 18, wherein the image processing unit allocates 8-bit data of a character code as 8-bit data of each pixel of the image data. Sending system.

20. The image processing unit is characterized in that 16-bit data of 2-bit character code is allocated as 2-pixel 16-bit data adjacent to image data. A transmission system using digital holography according to any one of claims 16 to 18.

2.1.1 Each pixel information of image data of one screen is represented by 8-bit data, and each of the 8-bit data is decomposed into upper 4 bits and lower 4 bits,

The upper 4 bits and lower 4 bits of data are defined as upper 4 bits of data, and (10000) ₂ dummy data is added to each lower 4 bits to create an 8-bit transmission data group. ,

Dividing the 8-bit data group into data groups for one screen, creating a digital hologram for each data group for one screen, and transmitting the digital hologram itself as encrypted data. A method of transmitting encrypted data using holography.

2 2. A receiver for receiving digital hologram data,

A transmission 8-bit data decomposing unit for decomposing the digital hologram data into an original transmission 8-bit data group,

A dummy data deletion processing unit that deletes the lower 4 bits of data for each of the transmitted 8-bit data that has been self-decomposed;

The original 4-bit data group from which the lower 4-bit data is deleted is divided into the original upper 4-bit and lower 4-bit data, and the original 8-bit data group of the original image is restored. A restoration processing unit;

An image restoration processing unit that assigns the 8-bit data group of the restored original image to each pixel and sets image data for each screen;

A digital hologram receiving system, comprising: an image display unit that displays the image data.

23. The digital holo-drum receiving system according to claim 22, further comprising a decoding processing unit for decoding digital hologram data transmitted after being encrypted. '

24. The digital hologram receiving system according to claim 22, wherein the image restoration processing unit restores a 16-bit 2-byte character code using two adjacent 8-bit data. .