WO2007064006A1

WO2007064006A1 - Image information producing apparatus and image information producing method

Info

Publication number: WO2007064006A1
Application number: PCT/JP2006/324138
Authority: WO
Inventors: Kenichi Tanaka; Hideaki Ishizuki
Original assignee: Kenichi Tanaka; Hideaki Ishizuki
Priority date: 2005-11-29
Filing date: 2006-11-28
Publication date: 2007-06-07
Also published as: JP2007150799A

Abstract

There are included a means (11) for preparing a secret image; a means (12) for performing a complex conversion of the secret image; a means (13) for synthesizing the complex-converted secret image into a pseudo-computer hologram; a means (14) for selecting a dither matrix for the pseudo-computer hologram; a means (15) for preparing a cover image into which the secret image will be embedded; a means (16) for subjecting the cover image and pseudo-computer hologram to a dither process; a means (17) for generating an embedded image; a means (18) for performing a complex conversion of the embedded image; and a means (19) for reproducing the secret image from the embedded image. Thus, the complex conversions allow the secret information to be reproduced without using any optical means.

Description

Specification

Image information creating apparatus and image information creating method

Technical field

The present invention relates to an image information creation apparatus and method for protecting image information. In particular, the present invention relates to an image information creating apparatus and an image information creating method configured to protect image information (secret images) as a pseudo computer hologram by performing complex transformation on the image information to be protected. Background art

In recent years, with the development of information networks such as the Internet, digital information such as multimedia contents has increased. Since these digital information is easy to copy, distribute, and browse, there is a problem that copyright-ignoring acts such as unauthorized copying and unauthorized distribution are easily performed. In order to avoid this situation, several methods for protecting digital information have been proposed.

An example of digital information protection is information encryption. Information encryption is a method of protecting copyrights by distributing information to the information distributor so that no one other than a known user can understand it. However, the information encryption technology has the problem of obstructing the transmission of information over a wide area and sacrificing the multimedia content advantage of the free distribution of information. Therefore, “digital watermarking” technology has been developed as a means to achieve both free information distribution and copyright protection.

Digital watermarking is a technology that embeds content secretly in a piece of content so that the content user who is not subject to information transmission cannot perceive the copyright information of the producer. Unintended users cannot perceive the information embedded in the content, so they can be copied and distributed in the same way as normal content, but the copyright information is hidden there. For this reason, in the case of fraud, the producer can take out copyright information and claim his rights. In this way, digital watermarking is considered to be effective as a technology that enables free distribution of multimedia content and copyright protection at the same time. It has been.

This development of digital watermark technology plays a major role in protecting the copyright of image information. Known methods for embedding a digital watermark include a method using pixel replacement, a method of embedding in the frequency domain, a method using u-X bullet transform, and a method using statistics. A method of embedding a computer program in a grayscale image is also being studied.

By the way, in general, in a grayscale image, one pixel is expressed by an 8-bit gradation value. Therefore, there are many methods for embedding a secret image since the gradation value is highly redundant and the modification in the lower bits has little visual impact. However, a pseudo halftone image represents one pixel with a small number of bits, and is extremely redundant, making it difficult to embed a secret image. In particular, it is very difficult to embed a secret image in an image obtained by quantizing a grayscale image into two values by pseudo halftone processing.

On the electronic media, the secret image embedded in the low-order bits of the grayscale image can be extracted by digital image processing. However, in the case of a hard copy by a printer or the like, only the embedded information of the low-order bits is used. The method of taking out cannot be used. Several methods have been proposed to embed a secret image even in such a binary image subjected to pseudo halftone processing. For example, there are a method using error diffusion and a method using dither method.

In addition, techniques for embedding and extracting digital information using orthogonal transform processing have been proposed. For example, Japanese Laid-Open Patent Publication No. 2 00 2 _ 9 4 7 8 0 describes that digital information is embedded and extracted by decentralized cosign transformation (D C T).

However, according to the method disclosed in Japanese Patent Laid-Open No. 2 0 00 2-9 4 7 80 described above, since DCT is a calculation method that uses only real values, the magnitude of the wave in the converted wavefront It is impossible to avoid the nature of an image in which the height distribution is concentrated only in the low frequency region. If the DCT is applied without dividing the block as it is, only the outline is emphasized and the image information cannot be restored accurately. For this reason, it is necessary to divide the block to perform DCT. In addition, secret images are limited to two-dimensional images. This will be explained with reference to the characteristic diagram of FIG. The horizontal axis in Fig. 2 is the space circumference Wave number, vertical axis is amplitude. As shown in Fig. 22, the wavefront converted to the low frequency region is concentrated. For this reason, the conventional orthogonal transform processing that handles real numbers has the problem that the spectral amplitude distribution cannot be made uniform, and the image quality cannot be improved.

In view of such problems, the object of the present invention is to generate not only two-dimensional but also three-dimensional secret images into a pseudo computer hologram by complex transformation, and embed the pseudo computer hologram into a dummy image (cover image). Another object of the present invention is to provide an image information creating apparatus and an image information creating method capable of protecting image information (secret image) and improving image quality by reproducing a secret image from the embedded image.

Disclosure of invention

(1). In order to solve the above-described problem, an image information creating apparatus according to the present invention includes means for creating a cover image in which a secret image is embedded, means for creating a secret image to be protected, Means for performing a first complex transformation process; means for synthesizing a pseudo computer hologram with the secret image subjected to the complex transformation process; and embedding the synthesized pseudo computer hologram in the cover image to create an embedded image. Means for performing a second complex transformation process on the embedded image, and means for reproducing the secret image.

(2) Further, the image information creating apparatus of the present invention is characterized in that the first and second complex transformation processes are complex Fourier transformation or complex Hadamard transformation.

(3) In addition, the image information creation device of the present invention is characterized in that a random phase is added to image information in the first and second complex transformation processes.

(4) In addition, the image information creation device of the present invention is characterized in that black and white binarization processing is performed on complex image information in the first and second complex conversion processing.

(5) Further, in the image information creating apparatus of the present invention, the black and white binarization processing is any of a one-man hologram, a Lee hologram, a binary phase hologram, and an error diffusion hologram. Features.

(6) Further, in the image information creating apparatus of the present invention, the process of creating the embedded image is performed by combining the cover image with the synthesized computer using a systematic dither. A hologram is embedded.

(7). The image information creation device of the present invention comprises means for creating a cover image for embedding a secret image, means for creating a secret image to be protected, means for subjecting the secret image to complex transformation processing, Means for synthesizing a pseudo computer hologram to the secret image subjected to the complex transformation process; means for embedding the synthesized pseudo computer hologram in the cover image to create an embedded image; an X-ray lithography apparatus; an electron beam A lithography apparatus, an electron beam drawing apparatus, a focused ion beam drawing apparatus, and other semiconductor process apparatuses similar to these, and a control apparatus are provided, and these apparatuses are controlled by the control apparatus and embedded in an IC substrate. An image is formed.

(8). The image information creation method of the present invention includes a step of creating a cover image in which a secret image is embedded, a step of creating a secret image to be protected, and a first complex conversion process on the secret image. A step of synthesizing a pseudo-computer hologram to the secret image subjected to the complex transformation process, a step of embedding the synthesized pseudo-computer hologram in the cover image, and creating an embedded image; And a step of performing the complex transformation process of 2 and a step of reproducing the secret image.

(9) Further, in the image information creation method of the present invention, the first and second complex transformation processes are two-dimensional complex transformation processes by complex Fourier transformation or complex Hadamard transformation. To do.

Further, the image information creation method of the present invention includes adding a random phase to the image information to make the spatial frequency amplitude constant during the first and second complex transformation processes. Features.

Further, the image information creation method of the present invention performs black and white binarization processing on at least 4 × 4 pixel complex image information during the first and second complex conversion processing. It is characterized by that.

(1 2) Further, in the image information creation method of the present invention, the black and white binarization processing is any of a one-man hologram, a Lee hologram, a binary phase hologram, and an error diffusion hologram. Features.

(1 3). Further, the image information creation method of the present invention creates the embedded image. The processing includes performing a procedure for selecting a systematic dither in the cover image, and a step of embedding the synthesized pseudo computer generated hologram using the selected systematic dither.

(1 4). The image information creation method of the present invention includes a step of creating a cover image in which a secret image is embedded, a step of creating a secret image to be protected, and a first complex transformation process on the secret image. A step of synthesizing a pseudo-computer hologram to the secret image subjected to the complex transformation process, a step of embedding the synthesized pseudo-computer hologram into the cover image and creating an embedded image, Forming an embedded image on an IC substrate by controlling an X-ray lithography apparatus, an electron beam lithography apparatus, an electron beam lithography apparatus, a focused ion beam lithography apparatus, and other similar semiconductor process apparatuses by the apparatus, and It is characterized by Brief Description of Drawings

FIG. 1 is a schematic block diagram showing an embodiment of the present invention.

FIG. 2 is a partial block diagram of FIG.

FIG. 3 is a flowchart showing the image information security processing procedure of the present invention.

FIG. 4 is an explanatory view showing an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a L o hma n n (Roman) type cell.

Figure 6 is an explanatory diagram showing (a) a Lohmann n roman CJ gram and (b) a regenerated image.

FIG. 7 is an explanatory diagram showing a Lee (Lee) type cell.

Fig. 8 is an explanatory diagram showing (a) L e e type computer generated hologram and (b) reconstructed image.

FIG. 9 is an explanatory diagram showing (a) a binary phase type computer generated hologram and (b) a reproduced image.

FIG. 10 is an explanatory diagram showing the concept of the error diffusion method.

Figure 11 is an explanatory diagram showing (a) an error diffusion type computer generated hologram and (b) a reconstructed image. Fig. 12 is an explanatory diagram showing images with specific values of the three types of dither matrices and pseudo gray levels.

Fig. 13 is an explanatory diagram showing the determination of the dither matrix using a computer generated hologram. Figure 14 is a schematic diagram of the organized dither method.

Fig. 15 is an explanatory diagram showing combinations of dither matrices.

FIG. 16 is an explanatory diagram showing combinations of dither matrices.

FIG. 17 is an explanatory view showing an example of a hologram reproducing optical system.

Fig. 18 is an explanatory diagram showing resistance against external attacks.

Fig. 19 is an explanatory diagram showing resistance to external attacks.

FIG. 20 is an explanatory diagram showing an example of secret image reproduction when attacked.

FIG. 21 is an explanatory view showing an embodiment of the present invention.

Fig. 22 is a characteristic diagram showing the conventional complex amplitude.

Figure 23 shows the characteristics when a random phase is added.

FIG. 24 is an explanatory diagram showing X-ray lithography. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of an image information creation device and an image information creation method of the present invention will be described with reference to the drawings. In the following, the present invention will be described as a specific example in which various arithmetic processes are executed by a general PC (Persona 1 Computer). Next, the basic principle of the present invention will be described. In general, computer generated holograms perform light diffraction calculations, quantize the complex values obtained, and display them in a binary format. By the way, when using computer generated holograms from the viewpoint of information security, it is only possible to reproduce from numerical simulation, and optical reproduction is not necessary. In this way, considering reproduction by only numerical simulation, the confidentiality of confidential information can be improved by considering virtual wavefront calculation other than Fourier transform. For this reason, the basic principle of the present invention is to perform wavefront calculation of a pseudo computer generated hologram (a computer generated hologram not using optical processing is hereinafter referred to as a pseudo computer generated hologram) by a complex calculation method other than Fourier transform. The numerical calculation conditions required for the pseudo computer generated hologram will be explained. As a digital watermark, the numerical calculation method in the pseudo computer generated hologram according to the present invention is different from the conventional DCT, Wavelet transform, etc. in that it uses complex values. This makes it possible to use 3D images as secret images. That is, the conversion using complex numbers is a condition in the wavefront calculation of the pseudo computer hogram in the present invention. Specifically, for example, complex Fourier transform or complex Hadamard transform is used for wavefront calculation of pseudo computer hologram. In addition, since complex numbers are used, a random phase can be added to the secret image to flatten the spectral amplitude intensity distribution after conversion, so that block division as seen in DCT is not necessary. For this reason, not only does the procedure of division calculation become unnecessary, but the secret information spreads over the entire conversion surface, so it has the advantage of being robust against partial information deletion attacks. The reason for using the complex transformation is that, when considering Fraunhofer-Far diffraction or Fresnel diffraction in the light diffraction calculation, an approximate calculation can be performed by the complex Fourier transform near the focal axis. Next, the complex Hadamard transform will be described as an example of the complex transform of the present invention.

(a) One-dimensional complex Hadamard transform

The conversion from complex numbers to complex numbers shown above is possible using the conversion that uses the complex-adamal conversion. The basic matrix in the complex Hadamard transform is expressed by equation (1). Where j is the imaginary unit

H = 1 j

j 1 (1) When this matrix is expanded to a 4 x 4 matrix, equation (2) is obtained.

Taking this as an example, the complex Hadamard transform of the one-dimensional signal sequence f (X) is converted to F (u), and (3) is obtained.

F (u) = Hf (x)

(3)

(b) Two-dimensional complex Hadamard transform When performing a complex Hadamard transform from a two-dimensional signal matrix () and converting to (",, first focus on the components in the X and u directions (however, /,) and (", Calculate the equation (4).

(", L) = Hf (x, \)

F (u, 2) = Hf (x, 2)

-… (Four)

F (u, n) = Hf (x, n)

Then, paying attention to the y direction and the v direction, calculate (5). In this way, a two-dimensional complex Hadamard transform is calculated. (L, v) = H / (l, v)

F (2, v) = H / (2, y)

. . . . (Five)

F (n, v) = Hf (n, y) By the way, in the present invention, the wavefront recorded in the pseudo computer generated hologram is a complex value. Thus, in the present invention, the reason why the numerical value used for the pseudo computer generated hologram is a complex value and not a real value will be described. As explained in Fig. 22, when real values are used, the wave size distribution is concentrated only in the low frequency region in the converted wavefront.

In the present invention, random phase addition is performed in order to avoid the property of an image in which the wave size distribution as described above is concentrated only in the low frequency region. Here, when capturing the secret image of the pseudo computer gram in the two-dimensional array, the density of the secret image is f (X, y), and the complex amplitude f '(x, y) with the random phase added In between

(6) There is a relationship of the formula. Here, (z,) is a random random number with respect to the coordinates X, y and is a random number in the range of 0 to 27 7Γ.

/ '(Zu, = / (zu, y) exp (y (jc, y)) (o) The reason for this random phase addition is as follows: Temporarily perform complex Fourier transform without adding random phase The magnitude of the complex amplitude on the Fourier transform plane (Hadamard transform plane) is concentrated in the low-frequency region of the Fourier transform plane (Hadamard transform plane). In Fig. 23, the horizontal axis represents the spatial frequency and the vertical axis represents the vibration. It is the size of the width. As shown in Fig. 23, a random phase is added to make the complex amplitude distribution on the Fourier transform plane (Hadamard transform plane) constant. For this reason, the image quality can be improved.

FIG. 1 is a schematic block diagram showing an example of image information creation in the embodiment of the present invention. 1 1 Prepares (creates) a secret image to be protected. For example, the image read by the scanner is stored in the PC storage means. 1 2 is a means for performing a complex transformation process (1) on the secret image, and it is calculated by CPU and the like. 13 is a step that synthesizes a secret image that has been subjected to complex transformation processing into a pseudo-computer hologram. 1 4 is a means of selecting a dither matrix for a pseudo-computer hologram, which is processed with CPU. Dither matrices include Bayer type dither matrix, halftone type dither matrix, magic group type dither matrix, etc., as explained in Fig. 12.

15 is a means for preparing (creating) a cover image for embedding a secret image. For example, an image read by a scanner is stored in a PC storage means. 1 6 is a means of dithering the cover image and the pseudo computer generated hologram. 1 7 is a means for generating an embedded image, 1 8 is a means for performing a complex transformation process (2) on the embedded image, and 19 is a means for reproducing a secret image from the embedded image. Each of these methods will be implemented by the CPU as appropriate.

FIG. 2 is a schematic block diagram showing details of the complex transformation process (1) in FIG. 1, and the complex transformation process (1) is executed by CPU as described above. In FIG. 2, 2 1 is a means for adding a random phase to a complex wavefront, and 2 2 is a means for performing a two-dimensional complex transformation on a complex wavefront to which a random phase is added. For example, complex Fourier transform or complex Hadamard transform I do. 2 3 is a means for black and white binarization of complex information. The means for binarizing complex information into black and white is means for executing the Roman method, the Lee method, the error diffusion method, etc., as will be described later. The complex transformation process (2) is the same as the complex transformation process (1).

FIG. 3 is a flowchart showing the processing procedure of the present invention. In FIG. 3, the process is started (step S 1), and a cover image in which a secret image is embedded is prepared (step S 2). The cover image can be any image that can be read by a PC. An image in such a format may be used. The secret image can be read in any way, such as downloading by a PC, scanning by a scanner, or reading from a storage medium. Next, a secret image to be protected is prepared (step S 3). At this time, the secret image may be an image in any format as long as it is an image that can be read by a PC as in the case of the cover image. The secret image can be read in any way, such as downloading with a PC, scanning with a scanner, or reading from a storage medium.

Next, a complex transformation process is performed on the secret image (step S4). The complex transformation process includes complex Fourier transformation, complex Hadamard transformation, etc., which will be described in detail later. Next, the secret image that has undergone the complex transformation process is synthesized into a pseudo computer hologram (step S 5). The process of synthesizing the pseudo computer program in step S5 will also be described later. Next, the synthesized pseudo computer generated hologram is embedded in a cover image (step S 6) to generate an embedded image (step S 7). As a result, an image in which the secret image is protected is generated. Complex conversion processing is performed on the embedded image (step S8), and the secret image is reproduced from the embedded image (step S9). As a result, the secret image can be taken out and verified. In this way, the process of embedding and reproducing the secret image is completed (step S 10).

FIG. 4 is an explanatory diagram showing specific examples of the cover image (a) and the secret image (b) of the present invention. We will explain how to create a simple pseudo computer gram for an example using a cover image and a secret image using the letter “A”. In the generation of input image (a), an input image is created and an amplitude distribution according to the density information is given. At this time, a random phase is added as described above in order to equalize the amplitude of the wavefront to be the hologram.

In the secret image generation (b), the wavefront is calculated. Conventionally, when calculating the wavefront, diffraction calculation using Fourier transform was performed. However, in the embodiment of the present invention, in order to prevent a secret image from being seen through by the optical system, a complex Hadamard is used. The pseudo wavefront is generated using orthogonal transformation that transforms complex numbers to complex numbers such as transformation.

In the completion of the secret image (c), the wavefront is quantized. The quantization method includes There are various methods, such as Lohraann's method, Lee's method, and error diffusion method, which can be determined appropriately according to the purpose of use and the size of the input object. A computer photogram (pseudo secret image) is created by displaying the quantized numerical value in black and white. The wavefront quantization method will be described later.

Computer hologram reconstruction ( _e ) is performed by calculating the pseudo computer program embedded in (d) using the orthogonal transform of the complex transform used to generate the secret image and displaying the amplitude. By such processing, the confidential information “A” can be extracted from the confidential image. In Fig. 4, (i) ~

The processing in (e) basically corresponds to the flowchart in Fig. 3, and detailed explanation is omitted.

For the calculation of pseudo computer generated holograms, calculation based on diffraction calculation has been performed faithfully. In the embodiment of the present invention, when performing transmission of a secret image or the like, it is possible to realize a complex Fourier transform used for a calculation in accordance with a diffraction calculation by a complex orthogonal transform such as a complex adamar transform. .

Next, with regard to the above-described method for black and white binarization of image information, (1) a method for synthesizing into a Löhmann (Roman) type hologram, (2) a method for synthesizing into a Lee (Lee) type hologram 3) A method for synthesizing into a binary phase hologram, and (4) A method for synthesizing into an error diffusion hologram. These processes correspond to the process of synthesizing a pseudo-computer hologram (step S5) in the flowchart of Fig. 3. The black and white binarization of image information requires a minimum of 4 x 4 pixels.

(1) L o hma n n (Roman) type hologram

FIG. 5 shows a L o hma nn (Roman) type cell. The L o hm ann (π-man) type hologram is divided into cells with a side Δ around the sample point (m, n) on the computer hologram plane. As shown in Fig. 5, each cell S m η opens a rectangular small window according to the amplitude and phase to be expressed. The window width c is an arbitrary value, and its height Vmn is proportional to the amplitude. The shift Pmn between the center of the window and the center of the cell corresponds to the phase. The values of Vmn and Pmn can be determined by the following equation (7). =

Figure 6 shows the Lohma nn (Roman) type pseudo computer hologram when the width Δ ι of each cell is 4 dots and Vmn and Pmn are quantized to 4 values. The image in Fig. 6 (a) shows the Lohmann pseudo computer hologram completed in step S7, and the image in Fig. 6 (b) is the reconstructed image (secret image) regenerated in step S9. Indicates.

(2) L e e type hologram

FIG. 7 is a diagram showing a Lee-type cell. The Lee hologram divides the complex amplitude distribution of a hologram into a real part and an imaginary part, and gives up the position of the aperture depending on whether they are positive or negative. As shown in Fig. 7, positive real part, positive imaginary part, negative real part, and negative imaginary part are assigned from the left end of the cell. The size of the opening is proportional to each component. If the size of the opening is Om n and the value of the real or imaginary part is Bmn, equation (8)

It becomes. Here, Fig. 8 shows the Le e (Lie) -type pseudo-computer hologram and the reconstructed image when the width Δ of each cell is 4 卞. The image in Fig. 8 (a) shows the Lee-type pseudo computer hologram completed in step S7, and the image in Fig. 8 (b) is the reconstructed image (secret image) reconstructed in step S9. )

(3) Binary phase hologram

The phase type photogram is a gradation display of only the phase, assuming that the amplitude is 1. This is commonly called a kinoform. For the sake of simplicity, we will use a computer generated hologram that is phase-quantized to two values. Binary phase hologram H mn is expressed by equation (9)

It can be expressed. The image in Fig. 9 (a) shows the binary phase-type pseudo-computer hologram completed in step S7, and the image in Fig. 9 (b) shows the reconstructed image (secret image) regenerated in step S9. )

(4) Error diffusion hologram

FIG. 10 is an explanatory diagram showing the concept of the error diffusion method. For error diffusion holograms, the error diffusion method is applied when quantizing a 2'-value phase hologram into a binary one hologram. Em n is the error between the binarized value Hmn and the actual value Dmn. Multiply that value by the diffusion coefficients a, b, c, d so that the sum is 1, and the surrounding four Dm + 1, n, Dm + 1, n + l, Dm, n + l, Dm—1, n + Add to each one. Recall that Dm + 1, n, Dm + 1, n + 1, Dm.n + 1, Dm— 1. n + 1. The same operation is repeated in the order of raster scanning. If expressed as an equation, it becomes as follows. Figure 10 (a) shows the input data, Figure 10 (b) shows the error data, and Figure 10 (c) shows the output data.

'I

D = ― ~ cos 6 _mn

max Α _ιηη

E "mn =" -D mn

D _{m +] tn} = D _{m + ln} + aE _mn

n ₌ D + bE (10) n, " ₊₁ =", +

The image in Fig. 11 (a) shows the error diffusion type pseudo computer hologram completed in step S7, and the image in Fig. 11 (b) is the reconstructed image (secret image) reproduced in step S9. Indicates. In the case of the error diffusion type pseudo computer hologram, the shape of the binary pattern is random, and the secret image has the characteristic that its shape is not easily known. Therefore, error diffusion type pseudo calculation Machine holograms are superior in confidentiality compared to Lohmmann-type pseudo computer holograms and Lee-type pseudo computer holograms. Next, a method for embedding a secret image in pseudo halftone processing that is highly resistant to various modification operations will be described. In this method, the secret image is converted into a pseudo computer hologram, and the dither matrix of the systematic dither method is changed according to the shape, thereby embedding the hologram in the entire image. By this method, it is possible to embed information that is not affected by modification operations such as image rotation and cropping. Also, even if hard copy is made, watermark information can be extracted by optical holographic playback processing. The specific method is described below.

The principle of organized dithering is described below. The systematic dither method is a method of expressing a grayscale image in a pseudo manner by changing the threshold value for quantization to binary for each pixel. In the systematic dither method, a threshold matrix called an N x N dither matrix is superimposed on the input image, and the corresponding pixels are binarized using the dither matrix elements as thresholds. Since it is a two-tone representation of white and black, grayscale cannot be displayed in pixel units, but the entire image can be perceived as if grayscale is displayed due to visual integration effects. There are several types of dither matrices. In the following, we use three types of dither matrices: Bayer type (a), halftone type (b), and magic group type (c), as shown in Fig. 12.

Fig. 12 is an explanatory diagram showing specific values of the three types of dither matrices and an image with pseudo gray levels. Hereinafter, a method for embedding a hologram in the systematic dither method will be described. Here, a method for embedding holograms using the systematic dither method is shown.

(step 1 )

To use the systematic dither method, the cover image is quantized to 16 gray levels. (Here, 16 gray levels are used to use a 4 X 4 dither matrix.) The image is divided into 4 X 4 blocks.

(Step 2)

The secret image is converted into the form of a pseudo computer ho hogram according to the above-mentioned method of synthesizing the pseudo computer ho hogram. Here, the pseudo computer generated hologram is displayed in two gradations. Let's say. Any type of pseudo-computer hologram can be used, but considering the effect of embedding, a high-complexity error-diffusion type is suitable for the two-gradation phase type with conjugation. The size of the pseudo-computer hologram is set equal to the number of blocks when the cover image is divided by 4 x 4. For example, in the case of a cover image of 2 5 6 x 2 5 6 size, a hologram of 6 4 x 6 4 size is used. This is in order to correspond to each block of a 16-tone cover image obtained by dividing each pixel of the hologram by 4 × 4. In other words, the upper left pixel of the hologram corresponds to the upper left block of the input image.

(Step 3)

'Figure 1 2 (a) shows a B a y e r type dither matrix, Figure 1 2 (b) shows a halftone type dither matrix, and Figure 1 2 (c) shows an example of a magic formation type dither matrix. Here, two kinds of dither matrices are prepared. Any dither matrix may be used, but the combination of the matrices used will affect the image quality when the computer hologram of the secret image is embedded. Here, for convenience, it is assumed that two types of dither matrices D 1 and D O are used. FIG. 13 is an explanatory diagram of D 0 and D 1. In Fig.13, it is 1 (white) when the dither matrix threshold is exceeded, and 0 (black) when the dither matrix threshold is not exceeded.

(Step 4)

1 Take one block of the 6-tone cover image and check the brightness level of the corresponding hologram. If the corresponding hologram pixel is 1 (white), use the dither matrix D 1. If it is 0 (black), the dither matrix D 0 is used. Once the dither matrix to be used is determined, it is used to output 1 if the luminance level of each pixel in the block of the input image exceeds the threshold value of the corresponding dither matrix, and if it is below the threshold value. Outputs 0. To explain with the schematic diagram of the systematic dither method in FIG. 14, FIG. 14 (a) uses the Bayer dither matrix. The input image (b) is compared with the dither matrix as a threshold, and is quantized into two values. (C) is the output image quantized to binary.

By repeating the above procedure for each pixel in each block, an image with a pseudo gray scale display based on the systematic dither method in which the information of the pseudo computer website is embedded is synthesized. When extracting the secret image, the embedded image is considered to be a Fourier transform (or Hadamard transform) hologram, and a complex Fourier transform (or complex Hadamard transform) is performed. The embedded secret image (reproduced image of the computer hologram of the secret image) can be extracted by displaying the magnitude of the obtained complex amplitude distribution in grayscale.

In this method, two types of dither matrices are used. Depending on how the dither matrices are combined, the quality and texture of the output image and the quality of the reconstructed image differ. Here, we compared what images can be obtained by combining various dither matrices.

'Fig. 15 and Fig. 16 are explanatory diagrams showing combinations of dither matrices. D 1 and D O in the table are dither matrices used when the hologram is 1 (white) and 0 (black) as shown above. Fig. 15 (a) is the Bayer type (1), Fig. 15 (b) is the Bayer type (2), Fig. 15 (c) is the magic formation, and Fig. 16 (a) is the halftone dot. Figure (1), Fig. 16 (b) shows an example of halftone dot type (2), and Fig. 16 (c) shows an example of halftone dot type (3).

Thus, by using two dither matrices, a small shape error is generated between each block, and the hologram is embedded accordingly. For this reason, in the dither matrix that is greatly different, the shape of the hologram appears strongly, and in a similar dither matrix, it appears weakly. Therefore, the closer the two types of matrix are, the better the image quality.

Next, optical reproduction of embedded information will be described. Since the image itself, which is displayed in pseudo gray by the dither method, has the hologram shape inside, it is secretly reproduced by optically reproducing it like a normal computer hologram without performing digital processing on the computer. The image can be confirmed. That is, if the embedded image itself is considered as a Fourier transform type hologram, and the reproduction light is irradiated with a laser or the like, the secret image is reproduced due to the light diffraction phenomenon.

FIG. 17 is an explanatory diagram showing an example of a hologram reproducing optical system. In FIG. 17, the focal plane is obtained by installing a computer hologram 4 between the He—Ne laser 1 of the optical system laser, the beam expander 2, and the two lenses 3 a and 3 b. The playback image (playback image) is output to 5. That is, In order to reproduce the embedded image as a computer generated hologram 4, a sculpture is taken with a photograph, and the image is reconstructed after being reduced to the size of the film. This is because laser 1 is used for reproduction. The created film is irradiated with laser 1, and a video camera is installed on the lens focal plane (focal plane) 5 to observe the reconstructed image.

The laser uses a helium-neon (H e—N e) laser 1 and lenses 3 a and 3 b with a focal length f = 400 [mm]. The secret image computer hologram 4 uses an error diffusion type hologram and embeds the hologram using the halftone dot type (1) dither matrix shown in Fig. 16 (a). The use of such an optical system is used only for confirmation of an image by a creator or the like, and the embodiment of the present invention is characterized in that a pseudo-computer hologram by complex transformation is used as described above. Yes, secret images can be played back regardless of the optical system.

FIG. 18 to FIG. 21 are explanatory diagrams showing that attack resistance is excellent in the present invention. Note that FIG. 20 and FIG. 21 (b) showing examples of image reproduction are displayed with black and white reversed in order to clarify the characteristics. In other words, the character “A”, which is confidential information, is originally displayed in black. In Fig. 18 to Fig. 21, we created a dither image in which a pseudo computer hologram was embedded and a reconstructed image from which secret information was extracted. As an external attack, enlargement / reduction of image 'Partial deletion of information-filtering' Explains how to extract information when an attack related to image rotation is performed.

For the enlargement of the information in Fig. 18 (a), the image enlargement process is performed to erase the portion that protrudes from the 5 1 2 X 5 1 2 pixels. Even in this case, it can be seen that the secret information A is displayed as shown in FIG. However, due to the nature of scaling in the Fourier transform, the size of the letter A is shrunk according to the enlargement ratio.

In the case of information reduction shown in Fig. 18 (b), it is assumed that the information is compressed and crushed by reading it with a low-resolution scanner. In this case, the extraction of the secret image is shown when the image is reduced to 400 pixels × 400 pixels and arranged in the region of 5 1 2 × 5 12 pixels. In this case, the dither shape is considerably crushed, but it is still possible to extract the letter A as shown in Fig. 20 when trying to extract the secret image. However, Fourier transformation Due to the nature of scaling in conversion, the size of the letter A is enlarged according to the reduction ratio.

As for the partial erasure of information in Fig. 18 (c), about 40% of the number of display pixels is erased. Even when secret information is extracted from such a watermark-embedded image, the letter A, which is secret information, appears as shown in FIG. In this way, the reproduction of secret information even when information is partially erased means that the secret information is retained even if the recording medium is externally damaged. In other words, it can be seen that it is durable when embedded as a substitute for a hologram or IC chip on a card or the like.

Furthermore, for information filtering attacks, it is assumed that smoothing filtering (blurring) is added to the image in which the watermark generated as shown in Fig. 19 is embedded. Also in this case, as shown in FIG. 20, the secret image is extracted as long as the dither shape remains, and the character A, which is the secret information, is reproduced. In this case, the watermark embedded image is a binary image, indicating that it is robust against filtering. Figure 21 (a) shows an example of rotating the image, and the protruding part is cut off. Also in this case, as shown in Fig. 21 (b), the character A, which is the secret information, is reproduced. In other words, when the image is rotated, there is no practical problem because only the shaft is rotated, and the extracted image is only rotated when extracting the secret image.

As you can see, the holograms are used in the extraction of information, indicating that they are resistant to “attacks” that cause problems in digital watermarking, such as scaling up and down of information and partial erasure. Conventional watermarking methods are known to have poor tolerance for geometric transformation (enlargement / reduction of images) and partial deletion of information, and the embodiments of the present invention are greatly improved in this respect. It has become a method that can improve resistance to attacks.

In the embodiment of the present invention, various applications can be considered. As an example, a means for embedding a secret image in an IC card or the like will be described. Figure 24 shows image information for creating an IC card in which the secret image is embedded by X-ray lithography. 3 is an explanatory diagram showing a schematic configuration of a creation device 3 1. FIG. In FIG. 24, 3 2 is an electron gun that irradiates a line 3 8, 3 3 is an acceleration coil for X-ray 3 8, 3 4 is a diaphragm member, and 3 5 is a deflection coil.

Prepare cover image 4 1 and secret image 4 2 as described in Fig. 4 and so on. The arithmetic unit 43 performs arithmetic operations such as the complex transformation. Further, the image generation device 44 generates an image in which the secret image 42 is embedded in the cover image 41 by the calculation of the calculation device 43. The control device 45 forms control signals Da to Dc based on the image generated by the image generation device 44. These control signals D a to D c are given to the acceleration coil 3 3 and the deflection coil 35 to control the X-ray lithography.

An X-ray mask and a resist layer (not shown) are provided on the IC substrate 36, and the image generated by the image generation device 44 is absorbed by the X-ray mask and resisted. Transferred to the layer.

In FIG. 24, the image information creation apparatus 31 that creates the IC force pad in which the secret image is embedded by X-ray lithography has been described. However, the present invention is not limited to such an embodiment. For example, an electron beam lithography system, an electron beam lithography system, a focused ion beam lithography system, or other semiconductor process equipment similar to these is applied as an image information creation system that creates an IC card in which a secret image is embedded. be able to.

In this manner, image information in which the secret image is embedded is formed on the depiction surface 37 of the IC substrate 36. Since the image information embedded with the secret image of the present invention is excellent in resistance to various external attacks, it is also effective as a defense against skimming.

According to the image information creating apparatus and the image information creating method of the present invention, the following special effects can be obtained.

(1) The image information (secret image) to be protected is set as a pseudo computer hologram, the dummy computer hologram is embedded in a dummy image (cover image) to generate an embedded image, and the secret image is reproduced from the embedded image. Information (secret images) can be protected. Image quality can be improved by adding a random phase to the image information. In the present invention, block division as seen in DCT is not necessarily required. (2) In addition, by making copyright information (secret image) into the form of a pseudo computer hologram, it has robustness against modification operations that are performed by malicious tamperers to erase copyright information. It becomes like this. Also, if you want to use 3D information as a watermark, it can be expressed in 2D by making it a computer generated hologram.

(3) In addition, pseudo computer holograms are highly redundant, so that information will not be lost if there is a slight deterioration, and even if the secret image is three-dimensional, if it is made into a pseudo computer hologram, it will be two-dimensional. Can be expressed as The reason why 3D images can be handled as secret images is that the data handled by the pseudo-computer hologram is a complex number and has both the amplitude and phase of the wavefront. In addition, since the pseudo-computer hologram cannot grasp the contents of the information unless it continues the reproduction including the optical means, it is excellent in safety from the viewpoint of information leakage, and the pseudo-computer hologram. Due to the complexity of the hologram shape itself, it is difficult to recognize that it has been embedded.

(a) Effects of noise mixing: Regarding the effects of adding noise to the embedded image, the effect of noise is not a serious problem because the embedded image is a binary image. (B) Effect of JPEG compression: Even if JPEG compression is performed, if the binary image can be accurately restored, it is not necessary to consider the influence of JPEG compression on the embedded image. (C) Influence of median filter: Since binary images are targeted, only binary values can be obtained when the median filter is applied, so it is possible to think in the same way as when noise is superimposed on a binary image. it can. Therefore, even in the case of the influence of a median filter, attack resistance is strong. (D) Effect of smoothing filter: Since the image with embedded watermark is a binary image, it is robust against filtering.

(e) Impact of cropping attack: When a cropping attack that performs processing to crop a part of an image is added to the embedded image (cutting attack), a malicious tamper erases the confidential information embedded in the image. For this purpose, a part of the embedded image may be cut out. In order to be effective as a digital watermark, it is required that copyright information is not lost even if the image is cropped. It has been In the present invention in which the pseudo computer generated hologram is embedded, the secret information is spread over the entire image, and even if a part is lost, the secret information is not lost. Therefore, the method of embedding a pseudo computer generated hologram according to the present invention has an excellent resistance to a cutting attack. (F) Enlargement / reduction 'Effects of geometric transformations such as rotation: Secret images can be extracted without any problem even when image enlargement / reduction processing is performed. Also, even if the image is rotated, there is no practical problem because only the rotation of the axis seen in the Fourier transform is performed, and the extracted image is only rotated when extracting the secret image.

(4) In this way, it has excellent resistance to external attacks, so it is effective as a defensive measure against skimming in an application example in which a secret image is embedded in the I C cover plate.

Although the image information creating apparatus and the image information creating method of the present invention have been described above, the present invention can be applied to an ID card and an electronic key. It can also be applied to watermarks such as banknotes and securities. With the conventional IC card, confidential information embedded due to scratches or breakage can no longer be used, but in the present invention, it can be embedded in multiple places, so it is highly resistant to scratches and breakage. Also, if an embedded image is created by embedding a secret image in a copyrighted work, if the embedded image (copyrighted work) is copied, the secret image is also copied, so it is easy to prove unauthorized copying of the copyrighted work. it can.

Claims

The scope of the claims

1. means for creating a cover image for embedding a secret image; means for creating a secret image to be protected; means for performing a first complex transformation process on the secret image; and performing the complex transformation process. Means for synthesizing a pseudo-computer hologram with the secret image, means for embedding the synthesized pseudo-computer hologram in the cover image to create an embedded image, means for subjecting the embedded image to a second complex transformation process, An image information creation device comprising: means for reproducing the secret image. .

2. The image information creation device according to claim 1, wherein the first and second complex transformation processes are complex Fourier transform or complex Hadamard transformation.

3. The image information creation device according to claim 1, wherein a random phase is added to the image information during the first and second complex transformation processes. ,

4. The image information according to claim 1, wherein black and white binarization processing is performed on the complex image information during the first and second complex conversion processing. Creation device.

5. The image information creating apparatus according to claim 4, wherein the black-and-white binarization processing is any one of a Roman hologram, a Lee hologram, a binary phase hologram, and an error diffusion hologram.

6. The image information according to any one of claims 1 to 5, wherein in the process of creating the embedded image, the synthesized pseudo computer generated hologram is embedded in the cover image using a systematic dither. Creation device.

7. means for creating a cover image for embedding the secret image, means for creating a secret image to be protected, means for performing a complex transformation process on the secret image, and a secret image subjected to the complex transformation process Means for synthesizing a pseudo computer hologram; means for embedding the synthesized pseudo computer hologram in the cover image to create an embedded image; an X-ray lithography apparatus; an electron beam lithography apparatus; an electron beam drawing apparatus; A converging ion beam drawing apparatus, a semiconductor process apparatus similar to these, and a control apparatus. An image information creating apparatus characterized by controlling the position to form the embedded image on an IC substrate.

8. A step of creating a cover image for embedding the secret image, a step of creating a secret image to be protected, a step of performing a first complex transformation process on the secret image, and performing the complex transformation process A step of synthesizing a pseudo computer hologram with the secret image, a step of embedding the synthesized pseudo computer hologram in the cover image to create an embedded image, a step of performing a second complex transformation process on the embedded image, An image information creating method comprising: a step of reproducing the secret image.

9. The image information creating method according to claim 8, wherein the first and second complex transformation processes are two-dimensional complex transformation processes by complex Fourier transformation or complex Hadamard transformation.

10. The spatial frequency amplitude is made constant by adding a random phase to the image information in the first and second complex transformation processes, wherein the spatial frequency amplitude is constant. Image information creation method.

11. The black-and-white binarization process is performed on the complex image information of at least 4 × 4 pixels in the first and second complex conversion processes. The image information creation method according to any one of the above.

12. The image information according to claim 11, wherein the black-and-white binarization processing is any one of a Roman hologram, a Lee hologram, a binary phase hologram, and an error diffusion hologram. How to make.

1 3. The process of creating the embedded image has a procedure of selecting a systematic dither in the cover image and a process of embedding the synthesized simulated computer hologram using the selected systematic dither. The image information creation method according to claim 8, characterized in that:

14. Creating a cover image for embedding a secret image, creating a secret image to be protected, performing a first complex transformation process on the secret image, and performing the complex transformation process A step of synthesizing a pseudo-computer hologram with a secret image; a step of embedding the synthesized pseudo-computer hologram into the cover image to create an embedded image; and an X-ray lithography apparatus by a controller Forming an embedded image on an IC substrate by controlling an electron beam lithography apparatus, an electron beam lithography apparatus, a focused ion beam lithography apparatus, and other similar semiconductor process apparatuses. Information creation method.