KR20210039235A - A method for preventing leakage of display by recapturing the display in a polarized 3d system - Google Patents

Abstract

According to one embodiment of the present invention, provided is a method for preventing re-photographing of a secret image in a polarized 3D system, which comprises the steps of: generating a first image including a plurality of rows by encrypting a secret image to be prevented from re-photographing by a digital device in a block unit; complementing the secret image; generating a second image including a plurality of rows by encrypting the complemented secret image in the block unit; and generating an interlaced image by alternately arranging each of the rows included in the first image and each of the rows included in the second image.

Description

How to prevent screen leakage due to re-taking in a polarized 3D system {A METHOD FOR PREVENTING LEAKAGE OF DISPLAY BY RECAPTURING THE DISPLAY IN A POLARIZED 3D SYSTEM}

The present invention relates to a method of preventing leakage of a screen due to rephotographing in a polarized 3D system.

As 3D displays are developed and popularized, 3D contents can be enjoyed not only in theaters but also at home. In order to allow viewers to feel a 3D stereoscopic effect from 3D content composed of 2D images, the 3D display system has different characteristics from the 2D display system.

There are various 3D display methods for reproducing the sense of depth of 3D scenes. The 3D display method can be classified into a spectacle type method and a non-glass type method depending on whether or not glasses are required.The spectacle type method is in the stage of practical use because it is relatively easy to implement, but the non-glass type method is relatively difficult to implement and is still in the prototype stage. The eyeglass method includes a color multiplexed method, a polarization multiplexed method, and a time multiplexed method.

In the color multiplexed method, anaglyph, which uses two filters of different colors, is simple and inexpensive to implement, but it has the disadvantage that color distortion and ghosting may occur in the filtered image. Not used.

The time multiplexed method uses shutter glasses that interact with the display. When the left-eye image and the right-eye image intersect in time and are displayed on the screen, the shutter glasses interact with the display so that one lens passes the image and the other lens blocks light. The user can perceive the 3D stereoscopic effect by alternately viewing the left-eye image and the right-eye image.

The polarization multiplexed method uses polarizing glasses composed of two polarizing filters that can polarize light in different directions. When a left-eye image and a right-eye image polarized in different directions are displayed on the screen, only the left-eye image is visible to the user's left eye and only the right-eye image is visible to the right eye by polarizing glasses. Compared to shutter glasses, polarized glasses are cheaper and do not require additional synchronization, so the polarized multiplexed method is mainly used in theaters and home theaters.

Meanwhile, due to the spread of digital cameras and smartphones, it is now possible to easily shoot high-quality images. Accordingly, it has become easier to illegally photograph and distribute content without the permission of the content provider. If the contents photographed without the consent of the contents provider are illegally leaked, serious mental and economic damage may occur to the contents provider. Therefore, a method of preventing illegal contents recording is needed.

The problem to be solved by the present invention is to provide a method of preventing leakage of a screen due to re-taking of the screen in a 3D polarization system.

However, the problem to be solved by the present invention is not limited to those mentioned above, and another problem to be solved that is not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description. will be.

A method of preventing retaking of a secret image in a polarized 3D system according to an embodiment of the present invention includes a plurality of rows by encrypting a secret image to be prevented from being retaken by a digital device in block units. Generating a first image; Complementing the secret image; Generating a second image including a plurality of rows by encrypting the conserved secret image in block units; And generating an interlaced image by intersecting each of the plurality of rows included in the first image and each of the rows included in the second image.

The expected value for the pixel value of the block included in the interlaced image is constant regardless of the pixel value of the first image.

Expected values for average pixel values of each of a plurality of rows included in a specific block in the interlaced image are the same.

Among the first images included in the interlaced image, the difference between the expected value for the average pixel value of the block in which the secret image is white and the expected value for the average pixel value in the block in which the secret image is black is greater than a threshold value, wherein , The threshold means the minimum value that humans can distinguish between white and black.

The first image is confirmed only through polarized glasses.

The polarizing glasses include two polarizing filters having the same direction.

According to another embodiment of the present invention, a method of preventing retaking of a secret image in a polarized 3D system includes: generating a first image including a plurality of rows by encrypting the secret image in block units; Generating a second image including a plurality of rows by encrypting the public image in block units using the first image; And generating an interlaced image by intersecting each of the plurality of rows included in the first image and each of the rows included in the second image.

The expected value of the average pixel value of the interlaced image according to the pixel value of the public image corresponding to the second image is constant regardless of the pixel value of the first image.

The distribution value of the average pixel value of the interlaced image according to the pixel value of the public image corresponding to the second image is constant regardless of the pixel value of the first image.

Among the first images included in the interlaced image, a difference between an expected value for an average pixel value of a block in which the secret image is white and an average pixel value in a block in which the secret image is black is greater than a threshold, the An expected value of an average pixel value of a block representing white among blocks included in a public image corresponding to the second image included in an interlaced image, and an average pixel of a block representing black color among blocks included in the public image The difference between the expected value and the value is greater than the threshold value, and the threshold value means a minimum value at which a human can distinguish between white and black.

The first image is viewed only through polarized glasses, but a public image corresponding to the second image is viewed without polarizing glasses.

The polarizing glasses include two polarizing filters having the same direction.

According to an embodiment of the present invention, by generating an interlaced image based on a limited viewing technique or a selective viewing technique proposed in the present invention, it is possible to prevent re-taking of a secret video by a digital device.

1 shows a polarization multiplexed method using an interlaced image among 3D display methods.
2 shows an example of circular polarization using polarizing glasses.
3 shows an example of 3D content formats for expressing 3D stereoscopic content.
4 shows an example of an interlaced block.
5 illustrates a limited viewing technique for preventing re-taking by a digital device according to an embodiment of the present invention.
6 shows a contrast value according to m in m-RVS according to an embodiment of the present invention.
7 is a block diagram illustrating a process of performing a limited viewing technique according to an embodiment of the present invention.
8 shows an example of a secret image generated using 4-RVS according to an embodiment of the present invention.
9 illustrates a selective viewing technique for preventing re-taking by a digital device according to another embodiment of the present invention.
10 shows a contrast value according to m in m-SVS according to another embodiment of the present invention.
11 is a block diagram illustrating a process of performing a selective viewing technique according to another embodiment of the present invention.
12 shows an example of a secret image generated using 4-SVS (α=1) according to another embodiment of the present invention.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments make the disclosure of the present invention complete, and the general knowledge in the technical field to which the present invention pertains. It is provided to completely inform the scope of the invention to the possessor, and the invention is only defined by the scope of the claims.

In describing embodiments of the present invention, if it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted. In addition, terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to the intention or custom of users or operators. Therefore, the definition should be made based on the contents throughout the present specification.

1 shows a polarization multiplexed method using an interlaced image among 3D display methods.

Referring to FIG. 1, a polarization 3D system 1 to which a polarization multiplexed display is applied includes a polarization display 10, polarization glasses 20, and 3D content 30. The 3D (S3D) content 30 may be composed of a left-eye image and a right-eye image. When the 3D (S3D) content 30 is rendered and displayed on the polarized 3D display 10, the user can perceive the depth of the 3D content 30 by viewing the S3D content 30 using the polarized glasses 20. have.

According to the polarized 3D display 10, the polarized 3D system 1 can be classified into two types. The first is a system that uses two projectors and a silver screen. Two images with polarizations in different directions are transmitted through the two projectors using the projector's filter and superimposed on a silver screen. Since the polarization of the reflected light is preserved on the silver screen that maintains the polarization direction, the two images can be separated through polarizing glasses. The second is a system using an interlaced display in which two polarization filters having different directions are arranged for each line in a vertical direction. The first is suitable for use in a theater because the screen size can be easily expanded, and the second is suitable for use in a 3D TV or home theater using a monitor because the installation cost is low.

2 shows an example of circular polarization using polarizing glasses.

Circular polarization is the most used type of polarization in polarized 3D systems. Circular polarizers called circular polarizing filters that include a linear polarizer and a quarter-wave plate convert unpolarized light into circularly polarized light. By adjusting the direction of the quarter wave plate, the light is circularly polarized in a clockwise or counterclockwise direction. In a display, two circular polarizers are arranged for each line in the vertical axis direction on a pixel-by-pixel basis. The analyzer is composed of two polarization filters, and can pass only circularly polarized light in a clockwise or counterclockwise direction. The analyzer configures the polarizing glasses. When a user sees a line interlaced display using polarized glasses, one eye passes through one type as shown in FIG. 2.

3 shows an example of 3D content formats for expressing 3D stereoscopic content.

Referring to FIG. 3, the 3D content format includes a top-and-bottom (TAB), side by side (SBS), a sequential frame, and a checker board. .

Referring to FIGS. 3A and 3B, TAB and SBS include two views (left image and right image) in one frame. Since the TAB performs sub-sampling in the vertical direction and the SBS performs sub-sampling in the horizontal direction, there is a disadvantage in that the resolution is halved in the vertical or horizontal direction in TAB and SBS. In TAB format 3D content, two images are line interlaced vertically on the screen, and in SBS format 3D content, two images are horizontally line interlaced on the screen.

Referring to (c) of FIG. 3, the sequential frame is a format in which two views are alternately positioned in time. Although there is no loss of resolution in sequential frames, there is a disadvantage in that the frame rate is lowered. Referring to FIG. 3D, the checker board is a format in which two views are displayed in one frame by uniformly subsampling an image like a chess board.

4 shows an example of an interlaced block.

In a spatial division-based polarization 3D system, a left-eye image and a right-eye image may be combined into one interlaced image. In this process, the left-eye image and the right-eye image are downsampled to half the size in the row direction, and are arranged in odd and even rows of the interlaced image, respectively.

In the present specification, I _I denotes an interlaced image, I _o and I _e denote an image composed of odd and even rows of I _{I , respectively, and I D} denotes an interlaced image (I _E ) represents a decoded image that can be viewed when viewing. In the present specification, for convenience, it is assumed that the secret image S to be protected from re-taking _{is located at I o} for convenience, but is not limited thereto. That is, according to an embodiment, the secret image S may be located _{in I e.}

Further, in the present specification, it is assumed that the circular polarizing film in the clockwise direction is located in odd rows of the interlaced image, and the circular polarizing film in the counterclockwise direction is located in even rows of the interlaced image, but is not limited thereto. That is, according to an exemplary embodiment, the circular polarizing film in the clockwise direction may be located in even rows of the interlaced image, and the circular polarizing film in the counterclockwise direction may be located in odd rows of the interlaced image.

The secret video is down-sampled by half the height and can be encrypted using a limited viewing technique or a selective viewing technique. The encrypted secret video can be located _{in I o.} In addition, the polarized 3D system may place the encrypted secret image in I _e based on the limited viewing technique.

Therefore, I _I can be generated by interlacing I _o into odd rows and I _{e into even rows. When a user views I I} using polarizing glasses composed of two clockwise circular polarizing films, the user sees the decrypted image I in which the encrypted secret image is located in odd rows of the interlaced image and black pixels are located in the even rows. You can see _D.

Referring to FIG. 4, in the limited viewing technique and the selective viewing technique according to an embodiment of the present invention, the number of secret images is m (m = p * q, p and q are integers greater than or equal to 1, m is an integer greater than or equal to 2). Can be encrypted with The m-sized block can represent one color representing black or white.

That the block with the (2p * q) size from the interlaced image I _I B _I, and represent each block consisting of a block composed of odd-numbered rows of the _I B in the even rows of the B _o, B _I to B _e. That is, B _o is a block having a size of p * q among _{I o , and B e} is a block having a size of p * q among _{I e.}

In addition, in the present specification, X is defined as a random variable representing a pixel value between 0 (= black) and 1 (= white). Then, X _I may mean an average pixel value of block B _{I , X o} may mean an average pixel value of block B _o , and X _e may mean an average pixel value of block B _e.

The average pixel value of each i-th row of B _o and B _e is defined _{as X o} ⁱ and X _e ⁱ , and X _I ⁱ _{of B I} is defined as the average pixel value of adjacent odd and even rows. In this case, _{the expected value of X I} ⁱ can be expressed as Equation 1 below.

Hereinafter, a method of preventing recapturing of a secret image by utilizing the characteristics of a polarized 3D display is proposed. In this specification, the secret image may mean a screen to be protected from re-taking.

The 3D content composed of the left eye image and the right eye image may be generated by combining an encrypted secret image and an encrypted reward image or an encrypted public image. In a polarized 3D system, 3D content may be spatially interleaved on a pixel-by-pixel basis.

According to the present invention, a secret image can be viewed only by a person with authority through polarized glasses (that is, a person wearing polarized glasses), and the secret image is hidden in pixels on a 3D display. It is difficult to obtain a secret image by retaking the image.

In this specification, two methods of preventing re-taking are proposed. The first method is a Restricted Viewing Scheme (RVS), in which a secret image can be viewed using polarized glasses, but a meaningless noise image is visible when the polarized glasses are removed, and the second method is using polarized glasses. It is a selective viewing scheme (SVS) where you can view secret images and see a public image when you take off polarized glasses. In the present specification, a public image may refer to a screen that includes specific text and/or pictures, but does not need to be protected from re-taking.

The limited viewing technique and the selective viewing technique described with reference to FIGS. 5 to 8 are based on the use of the interlaced display described in FIG. 1, but are not limited thereto. That is, the limited viewing technique and/or the selective viewing technique may be described using other types of displays in addition to the interlaced display.

In addition, TAB and SBS described in FIG. 2 are mainly used in a polarization 3D system using a line interlacing display. In stereoscopic 3D, horizontal disparity is more important than vertical disparity, so in order to minimize the loss of horizontal disparity, the line interlacing display arranges two views in a vertical direction rather than a horizontal direction. . For this reason, the TAB format is more suitable than the SBS format in line interlaced displays. Accordingly, the limited viewing technique and the selective viewing technique proposed using FIGS. 5 to 8 are described based on the TAB format, but are not limited thereto. That is, the limited viewing technique and/or the selective viewing technique may be described using a format other than the TAB format.

5 shows a limited viewing technique for preventing re-taking by a digital device according to an embodiment of the present invention, and FIG. 6 shows a contrast value according to m in m-RVS.

The limited viewing technique is a technique in which users with polarized glasses (i.e., authorized) can view 2D images, but users who do not wear polarized glasses (i.e., without authorization) see any information.

The polarizing glasses 20 used in the limited viewing technique may be composed of two polarizing filters in the same direction, unlike conventional polarizing glasses composed of two polarizing filters in different directions. When wearing the polarizing glasses 20 proposed in the present specification, the user can view only one of the left-eye image or the right-eye image. That is, the authorized user can view the secret image S to be protected from re-shooting using the polarized glasses 20 on a limited basis.

The limited viewing technique should satisfy Equations 2 to 4 below.

Here, X _S denotes an average pixel value in the block B _S of S, and w and b denote a white pixel and a black pixel, respectively.

Equations 2 and 3 are conditions for ensuring that the secret image S is not visible in the interlaced image, and Equation 4 provides an appropriate contrast value for visibility of the secret image S in the decoded image. It is a condition indicating that it should be guaranteed.

Equation 2 is a secret image (S) expected value of X _I in the case of the pixel values of white _{(E [X I | X S} = w]) and if the pixel value is a black saekil of X _I expected value (E [X _I of This could mean that |X _S =b]) must be the same. That is, Equation 2 may indicate that the expected value _{of X I} should be constant regardless of the pixel value of the secret image S.

_{Equation 3 is the expected value (E[X I} ^k ]) of the average pixel value of the k-th row (k is an integer of 1 or more and 2p-1 or less) in the interlaced image and the average pixel value of the (k+1)-th row It may mean that the expected value of (E[X _I ^k+1 ]) should be the same as each other. This means that, the visible differences between the expression (3) is expected value of X _I in the B _I generated by the modulation (E [X _I]) is as shown should be constant for each row, a row of the interlaced image (I _I) It can mean that it doesn't exist.

Equation 4 indicates _{that in order to recognize the secret image S in the decoded image I D} , the difference between the expected value representing the white and black pixels of the secret image must be greater than _{the threshold value c th based on the cognitive perception system.} It can mean that. That is, when a user _{views an interlaced image (I I} ) through polarized glasses, the expected value of the average pixel value representing white in I _o in the interlaced image (I _{I ) (E[X o} |X _S =w]) It may mean that the difference (c) between the expected value (E[X _o |X _S =b]) of the average pixel value representing black color in and I _o must be greater than a _{specific threshold value (c th ).} That is, Equation 4 may mean that the contrast between white and black must be sufficiently greater than the threshold value so that the user can recognize the secret image. The threshold may mean a value of a degree at which a human can distinguish between white and black in the human visual system.

When satisfies the Equation 2 to Equation 4, the only can hide the secret image (S) in the interlaced image (I _I) that, through an interlace the polarized glasses 20, the image secret image in the (I _I) (S) can be seen.

The restricted viewing technique consists of two collections, C _w and C _b , which are composed of m-dimensional Boolean vectors. All vectors in C _w represent white, and all vectors in _{C b represent black.} C _w and C _b are composed of a basis vector V _m ^r , and V _m ^r is r unit vectors such that the hamming distance is r as shown in Equation 5 below. It may mean a set of summation m-dimensional vectors. That is, X, which is an average pixel value of _{V m} ^{r, may be set to be r.}

In Equation 5, e _i means a unit vector in which 1 is located in the i-th row (or column) and 0 is located in the remaining rows (or columns), and e ^T means a transpose of the vector e, b _i is a scalar having a value of 0 or 1, and V _m ^r may be a set of vectors in which the sum of b _{i is r.} Ideally for m-dimensional constrained viewing techniques, E[X _o |B _S =w] can be close to 1, E[X _o |B _S =b] is close to 0, and E[X _I ] can be 0.5. have. Therefore, in order to be the sum of the average pixel value of C _w and the average pixel value of C _b to a monovalent C _w and C _b set C _w and C _b can have a symmetry with each other as shown in Equation 6 below.

For example, in 4-RVS (that is, a restricted viewing technique of m=4), _{C w} and C _b composed of _{V 4} ^r may be expressed as Equation 7 below.

B _o and B _e constituting _{B I} can be encrypted using C _w and C _b. B _o and B _e can be constructed _{according to X S by selecting one vector randomly from C w} and C _b to have a uniform distribution, and transforming the m-dimensional vector into a p * q matrix. Since all vectors with the same r _{are included in V m} ^r , the method of converting the vector to a matrix does not matter. That is, in the present specification, blocks are configured by performing linear scanning in the row direction, but the present disclosure is not limited thereto.

A value of 0 representing a black pixel is converted to 0, a value of 1 representing a white pixel is converted to 255, and the block B _o where the secret image is located can be set to the same color as X _S in B _S. . On the other hand, the block B _{e in} which the secret image is not located may be set opposite _{to B o in} order to hide the secret image in the interlaced image I _I. That is, if the average pixel value of a specific block in the secret image indicates white, B _{o is} also set to indicate white, and if the average pixel value of a specific block in the secret image indicates black, B _o may also be set to indicate black. have. For example, when _{X S, which} is an X value in _{B S} , is less than 0.5, C _b is used _{to represent B o} , and when X _S is greater than or equal to 0.5, C _w can be used _{to represent B o.}

_{In contrast, B e} that does not correspond to the secret image but is _{interlaced with B o} corresponding to the secret image to constitute the interlaced image may be set to be opposite to B _o. That is, if the average pixel value of a specific block in the secret image indicates white, B _e is set to indicate black, and if the average pixel value of a specific block in the secret image indicates black, B _e may be set to indicate white. have. Therefore, when X _S is less than 0.5, C _w is used _{to represent B e} , and when X _S is greater than or equal to 0.5, C _b can be used _{to represent B e.} Depending on the average pixel value of the secret image, _{one vector is randomly selected so that each of C w} and C _b has a uniform distribution, and the size of the vector is transformed into a matrix of size p * q and each B _o And B _e can be inserted.

Accordingly, the expected value (E[X _o ]) of the average pixel value of the encrypted secret image can be expressed as Equation (8).

는 m개의 원소에서 k개를 취하는 조합(combination)을 의미하고, E[X_o|X_S=w]는 비밀 영상 블록 X_S의 픽셀이 흰색을 나타낼 경우, 암호화된 비밀 영상 블록 B_o의 평균 픽셀 값의 기댓값을 의미하며, E[X_o|X_S=b]는 비밀 영상 블록 X_S 의 픽셀이 검은색을 나타낼 경우, 암호화된 비밀 영상 블록 B_o의 평균 픽셀 값의 기댓값을 의미할 수 있다.In Equation 8

Denotes a combination that takes k from m elements, and E[X _o |X _S =w] is the average of the encrypted secret image block B _o when the pixels of the secret image block X _{S are white.} It means the expected value of the pixel value, and E[X _o |X _S =b] can mean the expected value of the average pixel value of the encrypted secret video block B _o when the pixels of the secret video block X _{S are black.} have.

The blocks designed as above may satisfy all of Equations 2 to 4 for the m-dimensional limited viewing technique (m-RVS).

As shown in Equation 9 below, E[X _I |X _S =w] and E[X _I |X _S =b] may have the same value according to the designed block design.

_{In addition, because the sum of E[X o} ] and E[X _e ] is 1 due to the symmetry of the block configuration and combination _{, E[X I} ] may be an ideal value of 0.5 regardless of the secret image. Since ^{all vectors having the same Hamming distance r} _{in V m} r are used to construct a block, vectors that are vertically symmetric in the matrix can also be included in _{V m} ^r. Therefore, as in Equation 10, E[X ^k |C _w ] is equal to E[X ^k+1 |C _w ], and E[X ^k |C _b ] is equal to E[X ^k+1 |C _b ] and It can be the same.

According to Equation 10, as in Equation 11, E[X _I ^k |X _S =w] and E[X _I ^k+1 |X _S =w] may be the same.

Equation 11 _{relates to a case where X S} is white, but Equation 11 can be applied even when _{X S is black.} Therefore, it can be confirmed that Equation 3 above is satisfied.

In order to confirm that Equation 4 is satisfied, when Equation 8 is substituted for Equation 4, the contrast value (c), which is the difference between the expected values of the average pixel value of the encrypted secret image, is defined as Equation 12 below. Can be.

Referring to FIG. 6, the contrast value c tends to decrease as the block size m increases, but it can be seen that c is sufficiently large to distinguish white and black based on the cognitive perception system. . Accordingly, it can be seen that Equation 4 is also satisfied by Equation 12 and FIG. 6.

7 is a block diagram illustrating a process of performing a limited viewing technique according to an embodiment of the present invention, and FIG. 8 shows an example of a secret video generated using 4-RVS.

_{Referring to FIG. 7, an encrypted secret image I o} may be generated by reducing the vertical resolution of the secret image by half and using the m-RVS encryption technique (S700).

The secret image whose resolution is half of the resolution may be complemented to generate a complement image, and an encrypted complement image I _e may be generated using the m-RVS encryption technique (S710).

An interlaced image may be generated by line interlacing the encrypted secret image I _o and the encrypted complement image I _{e in a vertical direction (S720).}

When a user wearing polarized glasses views an interlaced image, the user can view a secret image in the interlaced image. On the other hand, when a user who does not wear polarized glasses views an interlaced image, the user cannot view the secret image.

Referring to Figure 8, Figure 8 (a) shows a secret image (S) to be protected from re-shooting, the upper half of Figure 8 (b) is an encrypted secret image (I _o) , the lower _{Half shows the complementary video (I e)} encrypted using m-RVS by placing the complementary video of the secret video.

(C) of FIG. 8 shows an encrypted interlaced image (I _E ) obtained by line-interlacing an encrypted secret image and an encrypted complement image, and (d) is a decryption shown to the user through the polarizing glasses proposed in the present specification. The resulting image (I _D ) is shown.

Therefore, when users who do not wear polarized glasses view the interlaced image, the user sees an image that has no meaning as shown in Fig. 8(c), whereas users who wear polarized glasses view the interlaced image. , The user can view the secret video as shown in Figure 8(d).

9 shows a selective viewing technique for preventing re-taking by a digital device according to another embodiment of the present invention, and FIG. 10 shows a contrast value according to m in m-SVS.

In the selective viewing technique, users with polarized glasses 20 (i.e., authorized) can view secret images, but users who do not wear polarized glasses 20 (i.e., unauthorized) are not secret images. It is a technique that allows you to view only the video.

The polarizing glasses 20 used in the selective viewing technique may be composed of two polarizing filters in the same direction, unlike conventional polarizing glasses including two polarizing filters in different directions. When wearing the polarizing glasses 20 proposed in the present specification, the user can view only one of the left-eye image or the right-eye image. That is, the authorized user may use the polarizing glasses 20 to view a secret image to be protected from re-photographing on a limited basis.

The selective viewing technique should satisfy Equations 13 to 15 below.

Here, P _r denotes a probability, and X _P may denote an average pixel value in _{block B P} of the public image P.

Equation 13 and Equation 14 are conditions for ensuring that the secret image is not visible in the interlaced image, and Equation 15 must ensure an appropriate contrast value for visibility of the public image P in the interlaced image. Is a condition, and Equation 16 is a condition indicating that an appropriate contrast value should be guaranteed for visibility of the secret image S in the decoded image.

Equation 13 may mean that E[X _{I ] is constant for X S} of the secret image S and depends on _{X P} of the public image P. That is, Equation 13 may mean that the interlaced image is not affected by the secret image, but only the public image.

Equation 14 may mean that the distribution of XI in the interlaced image is constant with respect to _{X S} of the secret image S and depends on _{X P of the public image P.} That is, Equation 14 may mean that the secret image cannot be statistically extracted from the retaken image.

Equation 15 is an expected value of the average pixel value when the public image represents white so that the user can recognize the public image P from _{I E} when viewing the encrypted interlaced image I _{E without polarizing glasses 20} The difference between (E[X _I |X _P =w]) and the expected value of the average pixel value (E[X _I |X _P =b]) when the public image is black is the threshold value (c) based on the cognitive perception system. It could mean that it must be greater than _{th ).} In addition, Equation 16 is an average pixel when the secret image represents white so that the user can recognize the secret image S from _{I E} when viewing the _{encrypted interlaced image I E through the polarizing glasses 20.} The difference between the expected value of the value (E[X _o |X _S =w]) and the expected value of the average pixel value (E[X _o |X _S =b]) when the secret image is black It may mean that it should be greater than the threshold (c _{th ).} That is, it may mean that the contrast between white and black must be sufficiently greater than the threshold value so that the user can recognize the public image and the secret image.

When all of Equations 13 to 16 are satisfied, the secret image S _{is hidden in the interlaced image I I} , but can be shown to the user when using the polarized glasses 20, and the public image P Silver can be shown to the user without polarizing glasses 20.

For _{the encryption of I o , the selective viewing technique can construct I o} by encrypting the secret video using the method used in the restricted viewing technique, and configure _{I e} by encrypting the public video based on _{I o} . Unlike the limited viewing technique, only m, which is an even number, can be considered in the selective viewing technique to include _{V m} ^m/2 representing an intermediate color between white and black.

In order to encrypt the secret image S with I _o , the selective viewing technique may use two collections C _w and C _b composed of m-dimensional Boolean vectors. In addition, in order to encrypt the public video (P) with I _e , the selective viewing technique is _{C w} ^r , which is two collections composed of m-dimensional Boolean vectors according to the vectors V _m ^r _{and P used in I o.} C _b ^r can be used. C _w ^r and C _b ^r may be defined as in Equation 17 below.

Here, α is an integer greater than or equal to 1 and less than or equal to m/2, and in this case, α may mean an intensity that adjusts the visibility of the public image P.

When representing a particular block (B _S) in the secret white image, _w C it may be encrypted by using a B _o C _w containing vector to V _m ^m _m ^m in V ^{/ 2.} When _{V m} ^r of r≠m/2 is selected _{in C w , B e} can be configured by selecting _{V m} ^mr regardless of the pixel value of the public image in order to guarantee the invisibility of the secret image in _{I e.} .

On the other hand, when _{V m} ^r with r = m/2 in _{C w} is selected, the _invisibility of the secret image in I e can be satisfied. Therefore, to secure the visibility of the public image, V _m ^m/2+α _{is selected when the pixel value of the public image is white, and V m} ^m/2-α is selected when the pixel value of the public image is black. By doing so, you can encrypt _{B e.}

As derived from Equation 18 below, E[X _I |X _P =w, X _S =w] is the same as E[X _I |X _P =w, X _S =b], and E[X _I |X _P =b, X _S =w] may be the same as E[X _I |X _P =b, X _S =b].

Therefore, since E[X _I ] is not affected by the secret image, it is proved that Equation 13 is satisfied in the selective viewing technique.

Since I _o is constructed by selecting a vector to have a uniform distribution in _{C w} and C _b , if the average pixel value (X _{P ) in the block B P} of the public image (P) represents white, then for X _S The probability of X _I can be expressed as in Equation 19.

Equation 19 can be equally applied even when the average pixel value X _P in the block B _{P of the public image P represents black.} Therefore, since the distribution of _{X I} with respect to _{X P is constant regardless of X S} , it can be seen that Equation 14 is also satisfied.

In addition, the expected value E[X _{I ] for X P} may be expressed as Equation 20 below.

_{The contrast value (c s} ), which is a difference between the expected value of the average pixel value of the encrypted image according to the pixel value of the secret image, may be the same as the limited viewing technique. _{Therefore, when Equation 20 is substituted into Equation 15, the contrast value (c p} ), which is the difference between the expected value of the average pixel value of the encrypted image according to the pixel value of the public image, can be defined as in Equation 21 below. I can.

Referring to FIG. 10, the contrast value c _p increases as α increases, but tends to decrease as m increases. However, it can be confirmed that _{c p} is large enough to distinguish between white and black based on perceived vision. Accordingly, it can be seen that Equation 15 is also satisfied by Equation 21 and FIG. 10.

11 is a block diagram showing a process of performing a selective viewing technique according to another embodiment of the present invention, and FIG. 12 is a secret image generated using 4-SVS (α=1) according to another embodiment of the present invention. Shows an example of.

Referring to FIG. 11, the polarization display device may reduce the vertical resolution of the secret image S by half and generate an encrypted secret image I _o using the m-RVS encryption technique ( S1100).

_{The polarization display apparatus may generate an encrypted public image I e} based on an encrypted secret image for the public image P and using an m-dimensional selective viewing technique (m-SVS) encryption technique. (S1110).

The polarization display device may generate an encrypted interlaced image I _{E by line interlacing the encrypted secret image I o} and the encrypted public image I _e in a vertical direction (S1120). .

Here, it has been described that the polarization display device performs a series of processes for generating the _{encrypted interlaced image I E, but is not limited thereto.} That is, according to an embodiment, a device other than a polarization display device (or a program in another device _{) performs a series of processes for generating an encrypted interlaced image I E} , and the polarization display device generates the generated interlaced image. It is also possible to perform only the process of receiving and displaying the image I _E.

Referring to FIG. 12, FIGS. 12A to 12D illustrate interlaced images generated using 4-SVS (α=1). Figure 12 (a) shows the public video (P), the upper half of Figure 12 (b) shows the encrypted secret video (I _o ), the lower half shows the encrypted public video (I _e ). . _{12(c) shows an encrypted interlaced image I E} generated by interlacing an encrypted secret image and an encrypted public image, and FIG. 12(d) shows the polarization glasses proposed in the present specification. It represents the decoded image (I _{D) visible to the user.}

Accordingly, when a user wearing polarizing glasses views an interlaced image, the user can view a secret image in the interlaced image as shown in FIG. 12D. On the other hand, when a user who does not wear polarized glasses views the interlaced image, the user cannot see the secret image but can only view the public image as shown in FIG. 12C.

Combinations of each block of the block diagram attached to the present invention and each step of the flowchart may be performed by computer program instructions. Since these computer program instructions can be mounted on the encoding processor of a general purpose computer, special purpose computer or other programmable data processing equipment, the instructions executed by the encoding processor of the computer or other programmable data processing equipment are each block of the block diagram or Each step in the flow chart will create a means to perform the functions described. These computer program instructions can also be stored in computer-usable or computer-readable memory that can be directed to a computer or other programmable data processing equipment to implement a function in a particular way, so that the computer-usable or computer-readable memory. It is also possible to produce an article of manufacture in which the instructions stored in the block diagram contain instruction means for performing the functions described in each block of the block diagram or each step of the flowchart. Since computer program instructions can also be mounted on a computer or other programmable data processing equipment, a series of operating steps are performed on a computer or other programmable data processing equipment to create a computer-executable process to create a computer or other programmable data processing equipment. It is also possible for the instructions to perform the processing equipment to provide steps for executing the functions described in each block of the block diagram and each step of the flowchart.

In addition, each block or each step may represent a module, segment, or part of code that contains one or more executable instructions for executing the specified logical function(s). In addition, it should be noted that in some alternative embodiments, functions mentioned in blocks or steps may occur out of order. For example, two blocks or steps shown in succession may in fact be performed substantially simultaneously, or the blocks or steps may sometimes be performed in the reverse order depending on the corresponding function.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential quality of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

1: polarized 3D system
10: polarized display
20: polarized glasses
30: 3D content

Claims (14)

Generating a first image including a plurality of rows by encrypting a secret image to be prevented from being retaken by a digital device in block units;
Complementing the secret image;
Generating a second image including a plurality of rows by encrypting the conserved secret image in block units; And
And generating an interlaced image by intersecting each of the plurality of rows included in the first image and each of the rows included in the second image.
How to prevent retake of secret images in a polarized 3D system. The method of claim 1,
The expected value for the pixel value of the block included in the interlaced image is constant regardless of the pixel value of the first image.
How to avoid retaking secret images in polarized 3D systems. The method of claim 1,
Expected values for the average pixel values of each of a plurality of rows included in a specific block in the interlaced image are the same
How to avoid retaking secret images in polarized 3D systems. The method of claim 1,
Among the first images included in the interlaced image, a difference between an expected value for an average pixel value of a block representing white and an expected value of an average pixel value of a block representing black is greater than a threshold value,
The threshold means the minimum value at which a human can distinguish between white and black.
How to avoid retaking secret images in polarized 3D systems. The method of claim 1,
The first image is confirmed only through polarized glasses
How to avoid retaking secret images in polarized 3D systems. The method of claim 5,
The polarizing glasses include two polarizing filters having the same direction.
How to avoid retaking secret images in polarized 3D systems. Generating a first image including a plurality of rows by encrypting the secret image in block units;
Generating a second image including a plurality of rows by encrypting the public image in block units using the first image; And
And generating an interlaced image by intersecting each of the plurality of rows included in the first image and each of the rows included in the second image.
How to prevent retake of secret images in a polarized 3D system. The method of claim 7,
The expected value of the average pixel value of the interlaced image according to the pixel value of the public image corresponding to the second image is constant regardless of the pixel value of the secret image.
How to prevent retake of secret images in a polarized 3D system. The method of claim 7,
The distribution value of the average pixel value of the interlaced image according to the pixel value of the public image corresponding to the second image is constant regardless of the pixel value of the secret image.
How to prevent retake of secret images in a polarized 3D system. The method of claim 7,
Among the first images included in the interlaced image, a difference between an expected value for an average pixel value of a block representing white and an expected value of an average pixel value of a block representing black is greater than a threshold value,
An expected value of an average pixel value of a block representing white among blocks included in a public image corresponding to the second image included in the interlaced image, and an average of a block representing black color among blocks included in the public image The difference between the expected value for the pixel value is greater than the threshold,
The threshold is the minimum value at which a human can distinguish between white and black.
How to avoid retaking secret images in polarized 3D systems. The method of claim 7,
The first image is confirmed only through polarized glasses, but the public image corresponding to the second image is confirmed without polarized glasses.
How to avoid retaking secret images in polarized 3D systems. The method of claim 7,
The polarizing glasses include two polarizing filters having the same direction.
How to avoid retaking secret images in polarized 3D systems. In the polarized 3D system according to any one of claims 1 to 12, a method for preventing re-taking of a secret image is performed.
A computer program stored on a computer-readable recording medium. In the polarized 3D system according to any one of claims 1 to 12, a program for executing a method for preventing re-taking of a secret image is recorded.
Computer-readable recording medium.

Images