KR20220136103A - Image encryption method using line interlacing and image decryption apparatus therefor - Google Patents

Abstract

An image encryption method based on line interlacing characteristics according to one embodiment of the present invention comprises: a step of adjusting an intensity range to the same range for each RGB channel of a secret image (S) to generate an adjusted secret image (S'); a step of repeating pixel modulation on the adjusted secret image (S') in a block unit to generate a modulated image (M_S); and a step of interlacing an odd row or even row of the adjusted secret image (S') and an even row or odd row of the modulated image (M_S) step to generate an interlaced image (I). According to the present invention, in a polarized 3D system, the viewing rights of the secret images can be controlled by using polarized glasses, and the secret images can be decoded by using masking even on paper such as ID cards, banknotes, and documents.

Description

Image encryption method and image decryption apparatus based on line interlacing characteristics

The present invention relates to an image encryption method based on line interlacing characteristics and an image decoding apparatus for decrypting an image encrypted according to the method.

With the rapid development of photographing devices and the spread of the Internet, illegal leakage of digital contents due to re-photography has become a problem. High-quality digital content can be easily leaked without the consent of the copyright holder by re-photographing the display on which the digital content is being scanned using a photographing device. If re-recorded content is illegally distributed over the Internet, it is almost impossible to protect copyright. Since re-capturing using such a photographing device occurs externally, unlike capturing in a computer system, such as a screenshot, it is difficult to control or prevent re-shooting. Therefore, there is a need for a technique capable of preventing unauthorized re-photographing using a photographing device.

In order to protect the copyright of content from illegal leakage by re-shooting, three methods have been proposed: digital watermarking, image recapture detection, and image recapture prevention. First, digital watermarking verifies the copyright of the content by inserting a watermark, which is copyright information, into the content and detecting it in the re-photographed content. Second, image recapture detection controls the distribution of re-captured content by determining whether a suspicious image has been re-photographed using traces generated in the re-capture process.

However, these two methods have been proposed to protect copyright after content has been leaked, and cannot fundamentally prevent re-shooting itself. Finally, the image re-shooting prevention technique prevents or prevents the re-shooting of content scanned from the display using the imaging equipment under certain conditions, such as security film, image encryption-based technique, infrared device-based technique, software-based technique, and 3D display-based technique. It protects content from illegal leaks by preventing it. However, these techniques have limitations in partially or limitedly preventing re-photography due to limited conditions. Therefore, there is a need for a technique capable of preventing illegal content leakage from re-photographing using a photographing device.

(Patent Document 1) Registered Patent Publication No. 10-1602803, published on March 16, 2016.

An object of the present invention is to provide an image encryption method for generating an interlaced image in which a secret image is encrypted based on a line interlacing characteristic.

Another object of the present invention is to provide an apparatus for decrypting a secret image encrypted in an interlaced image based on a line interlacing characteristic.

However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems to be solved that are 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.

An image encryption method based on a line interlacing characteristic according to an embodiment of the present invention includes generating an adjusted secret image (S′) by adjusting an intensity range to the same range for each RGB channel of the secret image (S); Generating a modulated image (MS ) by repeating pixel modulation on the adjusted secret image ( _S ′) in block units, and odd lines of the adjusted secret image (S′) and the modulated image An interlaced image (I) was obtained by interlacing the even lines of ( _MS ) or by interlacing the even lines of the adjusted secret image ( _S ′) with the odd lines of the modulated image (MS ). comprising the steps of creating

Here, the step of generating the adjusted secret image S' by adjusting the intensity range includes a distance of the same intensity intensity t from the expected value E of a random variable representing the pixel value of the secret image S. The range of the pixel values may be adjusted to have .

Here, the generating of the modulated image M _S includes calculating a pixel value of an arbitrary block located in a preset range in the adjusted secret image S', and a pixel value of the arbitrary block based on , performing pixel modulation for each block of the adjusted secret image S'.

Here, in the step of performing pixel modulation for each block of the adjusted secret image S', each of the pixel values of any block located in the preset range is included within the target set average range. Pixel modulation may be performed for each block.

In the image encryption method based on the line interlacing characteristic according to an embodiment of the present invention, the secret image (S) and the public image (P) are each adjusted by adjusting the intensity range to the same range for each RGB channel secret image (S') Generating a public image ( _P ') adjusted with and interlacing the odd lines of the adjusted secret image S' and the even lines of the modulated image M _S,P or the modulation with the even lines of the adjusted secret image S'. and generating an interlaced image (I) by interlacing odd lines of the image (MS _,P ).

Here, the public image P may have an image enhancement technique applied to enhance an edge component.

Here, the generating of the modulated image (MS, _P ) includes applying an inverse error spreading technique to the previously generated first modulated image (MS _,P ) to obtain a second modulated image ( M' _S,P ).

Here, the step of generating an adjusted secret image (S') and an adjusted public image (P') by adjusting the intensity range includes the intensity intensity t _p of the secret image S and the public image P ), the range of pixel values may be adjusted in consideration of the correlation between the intensity intensity t _s .

Here, the step of generating the modulated image (MS _,P ) includes the pixel values of arbitrary blocks located in a preset range in the adjusted secret image (S') and the adjusted public image (P'). and performing pixel modulation for each block of the adjusted secret image (S') and the adjusted public image (P') based on the pixel values of the calculating and the arbitrary block.

Here, in the step of performing pixel modulation for each block of the adjusted secret image (S') and the adjusted public image (P'), an average of pixel values of any block located in the preset range is the target. Pixel modulation may be performed for each block to be included within the average range set by .

An image decoding apparatus according to an embodiment of the present invention includes a decryption screen that can be disposed between an encryption object including an interlaced image and a viewing position, wherein the interlaced image is RGB of a secret image (S) generating an adjusted secret image (S') by adjusting an intensity range to the same range for each channel; generating a modulated image (MS ) by repeating pixel modulation on the adjusted secret image ( _S ′) in block units; and interlacing odd lines of the adjusted secret image S′ and even lines of the modulated image M _S or even lines of the adjusted secret image S′ and the modulated image M _S . It is created by interlacing odd lines of

Here, the decryption screen may decrypt the adjusted secret image S' encrypted by the even or odd lines of the interlaced image.

Here, the decoding screen may include a mask that prevents viewing with respect to a position corresponding to an even line or an odd line of the interlaced image.

Here, the mask may include a polarizing filter or a light blocking filter.

An image decryption apparatus according to an embodiment of the present invention includes a decryption screen that can be disposed between an encryption object including an interlaced image and a viewing position, and the interlaced image is a secret image (S) and a public image generating an adjusted secret image (S') and an adjusted public image (P') by adjusting the intensity range to the same range for each RGB channel of the image (P); generating a modulated image (MS _,P ) by repeating pixel modulation on the adjusted secret image (S') and the adjusted public image (P') in block units; and interlacing odd lines of the adjusted secret image S′ and even lines of the modulated image M _S,P or even lines of the adjusted secret image S′ and the modulated image M It is created by interlacing odd lines of _S,P ).

Here, the decryption screen may decrypt the adjusted secret image S' encrypted by the even or odd lines of the interlaced image.

Here, the decoding screen may include a mask that prevents viewing with respect to a position corresponding to an even line or an odd line of the interlaced image.

Here, the mask may include a polarizing filter or a light blocking filter.

The computer readable recording medium storing the computer program according to an embodiment of the present invention, when the computer program is executed by a processor, adjusts the intensity range to the same range for each RGB channel of the secret image S generating a secret image (S'); generating a modulated image (MS ) by repeating pixel modulation on the adjusted secret image ( _S ′) in block units; and interlacing odd lines of the adjusted secret image S′ and even lines of the modulated image M _S or even lines of the adjusted secret image S′ and the modulated image M _S . generating an interlaced image (I) by interlacing odd lines of

A computer readable recording medium storing a computer program according to an embodiment of the present invention, when the computer program is executed by a processor, the secret image (S) and the public image (P) in the same range for each RGB channel generating an adjusted secret image (S') and an adjusted public image (P') by adjusting the intensity range; generating a modulated image (MS _,P ) by repeating pixel modulation on the adjusted secret image (S') and the adjusted public image (P') in block units; and interlacing odd lines of the adjusted secret image S′ and even lines of the modulated image M _S,P or even lines of the adjusted secret image S′ and the modulated image M Interlacing odd lines of _{S, P} ) to generate an interlaced image (I).

According to an embodiment of the present invention, it is possible to express various colors of a color image while minimizing the deterioration of the image quality of the secret image, unlike previous techniques that express limited colors, require a color analyzer, or generate distortion such as noise. method, and it is possible to prevent leakage of the screen due to re-shooting of the screen in the 3D polarization system.

In addition, in the polarized 3D system, viewing rights of secret images can be controlled by using polarized glasses, and secret images can be decoded using masking even on paper such as ID cards, banknotes, and documents.

In addition, compared with the prior art, such as a document confirmation number, voice barcode, authenticity confirmation barcode, etc. used to verify the authenticity of a document in public institutions, there are the following effects. The prior art requires a separate system access or an expensive scanner device. However, the embodiment of the present invention enables real-time verification and authentication of ID cards, passports, banknotes, documents, etc. through a low-cost and simple masking-based image encryption technique. In addition, since secret images and public images are encrypted on a pixel-based basis through image encryption, synchronization failure occurs when scanning and copying encrypted images. Accordingly, there is an effect that the integrity of the document can be verified.

1 is a diagram showing the configuration of a polarized 3D system according to an embodiment of the present invention.
2 illustrates a view through polarized glasses in a general polarized 3D system and a polarized 3D system for preventing image recapture according to an embodiment of the present invention.
3 is a flowchart illustrating an image encryption method based on line interlacing characteristics according to an embodiment of the present invention.
4 is a diagram for explaining a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention.
5 is a diagram illustrating an upper bound of a standard deviation according to an average for adjusting an intensity range in a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention; FIG. to be.
6 is a diagram illustrating graphs according to lower and upper limits of standard deviation in a restricted viewing scheme of an image encryption method based on line interlacing characteristics according to an embodiment of the present invention.
7 is a diagram illustrating images of a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention.
8 is a flowchart illustrating an image encryption method based on line interlacing characteristics according to another embodiment of the present invention.
9 is a diagram for explaining a selective viewing scheme of an image encryption method based on a line interlacing characteristic according to another embodiment of the present invention.
10 is a diagram illustrating graphs according to lower and upper limits of standard deviation in a selective viewing scheme of an image encryption method based on line interlacing characteristics according to another embodiment of the present invention.
11 is a diagram illustrating an effect of applying inverse error spreading in a selective viewing scheme of an image encryption method based on a line interlacing characteristic according to another embodiment of the present invention.
12 is a diagram illustrating selective viewing scheme images of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention.
13 is a view for explaining an image decoding apparatus capable of decoding a secret image included through printing on paper such as an identification card, banknote, or document using masking according to an 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 in conjunction 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 allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains. It is provided to fully inform the possessor of the scope of the invention, and the present invention is only defined by the scope of the claims.

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

In this specification, in order to describe image encryption and image decryption based on line interlacing characteristics, interlacing odd lines (or even lines) of the first image and even lines (or odd lines) of the second image is exemplified to explain Here, the line may be any one of a line virtually extending at least some of the pixels in the image in a row direction, a line extending virtually in a column direction, or a line virtually extending in a diagonal direction. Among them, a line virtually extending in all directions of at least some of the pixels in the image will be mainly exemplified.

1 is a diagram showing the configuration of a polarized 3D system according to an embodiment of the present invention.

An image encryption method based on line interlacing characteristics according to an embodiment of the present invention relates to an image encryption method capable of preventing re-photographing of a color image using line interlacing, and a polarized 3D system (1) commercialized without additional hardware. ) to prevent illegal content leakage from image re-shooting using a photographing device.

An image encryption method based on line interlacing characteristics according to an embodiment of the present invention may include two types of secure display schemes: a restricted viewing scheme (RVS) and a selective viewing scheme (SVS). .

Both techniques are pixel-level encryption techniques that disable the gestalt theory, making it impossible to extract information about the secret image from the re-photographed image on the display.

In RVS, interlaced images with hidden images are expressed as meaningless noise, whereas in SVS, interlaced images are expressed as meaningful public images with an improved technique of RVS. In both techniques, the hidden image is only visible to authorized users with polarized glasses. Unlike previous techniques that express limited colors, require a color analyzer, or generate distortion such as noise, the proposed technique is a software-based technique that can express various colors of a color image while minimizing the deterioration of the image quality of the secret image. .

Through this, the secret image can be visually and statistically hidden while minimizing distortion of the secret image, and it is possible to prevent the secret image from being extracted from the re-photographed image. In addition, the image encryption method based on the line interlacing characteristic according to an embodiment of the present invention can control the viewing right of a secret image by using polarized glasses in a polarized 3D system, and masking even on paper such as identification cards, banknotes, and documents can be used to decrypt the secret image.

In the present specification, a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention will be described with reference to FIGS. 3 to 7 below, and another embodiment of the present invention A selective viewing scheme of an image encryption method based on the line interlacing characteristic according to ? will be described below with reference to FIGS. 8 to 12 .

Referring to FIG. 1 , a polarized 3D system 1 according to an embodiment of the present invention includes a 3D display 10 , polarized glasses 20 , and stereoscopic 3D (S3D) content 30 .

The stereoscopic 3D (S3D) content 30 is composed of a left-eye image and a right-eye image, and the two images are interlaced on a line-by-line basis and scanned on a 3D display. The display area is divided into odd rows and even rows, and a clockwise circular polarization filter and a counterclockwise circular polarization filter are disposed in odd rows and even rows, respectively. A circularly polarized filter is a filter that converts natural light into circularly polarized light. A circularly polarized filter of a different direction blocks light and a circularly polarized filter of the same direction passes light. Finally, clockwise and counterclockwise circular polarization filters are disposed on the two lenses of the polarizing glasses, respectively. Accordingly, the left-eye image and the right-eye image are circularly polarized in different directions through the two circular polarization filters and scanned on the display, and are separated into both eyes through the polarizing glasses 20 .

Polarization glasses 20 according to an embodiment of the present invention include circular polarization filters in the same direction, and the polarization glasses 20 identify a secret image hidden in odd rows of interlaced images.

The polarization glasses 20 will be described in detail with reference to FIG. 2 below.

2 illustrates a view through polarized glasses in a general polarized 3D system and a polarized 3D system for preventing image recapture according to an embodiment of the present invention.

The image encryption method based on the existing line interlacing characteristic assumes that two circular polarization filters in a clockwise direction and a counterclockwise direction are located in odd and even rows of the display, respectively, as shown in FIG. 2A . In addition, it is assumed that two circular polarization filters are located in the left lens and the right lens in the polarizing glasses, respectively. Accordingly, the left eye can see only odd rows of the interlaced image, and the right eye can see only even rows. Therefore, the viewer enjoys 3D content by recognizing the binocular difference between the left-eye image and the right-eye image from a single display.

로 정의하면, I는 수학식 1과 같이 정의된다.L and R are defined as a left-eye image and a right-eye image of size (h×w), respectively. In addition, L _h and R _h are defined as images whose size is (h/2×w) halved in the vertical direction at L and R, respectively. We define I as an image in which two L _h and R _h are vertically interlaced on a line-by-line basis, and I _o and I _e are defined as images composed of odd and even rows of I, respectively. interlacing operator

When defined as , I is defined as in Equation 1.

f _cw (I) and f _ccw (I) are defined as in Equation 2 as views of I seen through f _cw and f _ccw , which are circular polarization filters in clockwise and counterclockwise directions, respectively.

B denotes a black image of size (h/2×w). Therefore, the glasses view V _g and the non-glasses view V _ng for I are the same as in Equation 3.

V _g ^L and V _g ^R denote views through the left and right lenses of polarized glasses, respectively.

The polarized glasses 20 in the polarized 3D system for image recapture prevention according to an embodiment of the present invention are modified to prevent image recapture of the existing polarized 3D system for viewing 3D content.

A polarization 3D system is used to hide the secret image in the interlaced image and to view the secret image in the interlaced image through the polarized glasses 20 . Therefore, it is changed so that it is composed of a circular polarization filter in the same direction as shown in (b) of FIG. 2 .

In FIG. 2 , it is assumed that the modified polarization glasses are composed of only a clockwise circular polarization filter f _cw , but the present invention is not limited thereto.

In the modified polarization 3D system, V _g , which is the glasses view, is Equation (4).

Accordingly, the secret image hidden in the odd rows of the interlaced image as shown in FIG. 2B and the following FIGS. 4 and 9 can be viewed through the modified polarized glasses. In addition, by creating a mask in which odd rows are transparent or empty and even rows are masked with black areas, the same effect as polarizing glasses can be obtained. Therefore, the same conditions can be implemented through the masking technique not only in the polarization 3D system but also in paper such as printed ID cards and banknote documents.

Although it is illustrated that the secret image hidden in the odd-numbered rows of the interlaced image can be viewed in (b) of FIG. 2 , the present invention is not limited thereto, and the image can be viewed at a position where the secret image is hidden among the odd-numbered rows or even-numbered rows.

3 is a flowchart illustrating an image encryption method based on line interlacing characteristics according to an embodiment of the present invention.

FIG. 3 relates to an encryption method using a restricted viewing scheme. Referring to FIG. 3 , the image encryption method based on the line interlacing characteristic according to an embodiment of the present invention is performed in a processor, step S110 , an adjusted secret image S' is generated by adjusting the intensity range to the same range for each RGB channel of the secret image S.

Here, the step of generating the adjusted secret image S′ by adjusting the intensity range ( S110 ) includes the same intensity intensity t from the expected value E of a random variable representing the pixel value of the secret image S. Adjust the range of pixel values to have a distance.

A modulated image (MS ) is generated by repeating pixel modulation on the secret image ( _S ′) adjusted in step S120 in block units.

Here, the step of generating the modulated image M _S ( S120 ) calculates the pixel value of any block located in a preset range in the adjusted secret image S', and the arbitrary block Based on the pixel value of , pixel modulation is performed for each block of the adjusted secret image S'.

Specifically, pixel modulation is performed for each block so that the average of pixel values of any block located in the preset range is included within the target average range.

In step S130, an interlaced image (I) is obtained by interlacing odd rows or even rows of the adjusted secret image ( _S ') and even rows or odd rows of a modulated image (MS ). create

A Restricted viewing scheme will be described in more detail below in FIG. 4 .

4 is a diagram for explaining a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention.

Restricted viewing technique (RVS) is a technique that shows a meaningless noise image in the glasses-free view and allows a limited view of a secret image through polarized glasses. Therefore, as follows, the secret image S' with the autostereoscopic view V _ng adjusted and the modulated image M _s approximate the interlaced random image R, and the spectacles view V _g approximates the secret image S. and is the same as Equation 5.

Here, R denotes a random image in which pixel values follow a uniform distribution.

It is assumed that the statistical properties of the interlaced image should be similar to the random image R following a uniform distribution for the restricted viewing technique under restricted viewing conditions. The mean μ _R and standard deviation σ _R of pixel values in R are calculated as in Equation 6.

x _i means a pixel value having the value of i. P _r (x) means the probability mass function of x, and since xi follows a uniform distribution, the value is the same for all x _i .

To adjust the distribution of the interlaced image I, the adjustment of I _o and I _e is essential. According to an embodiment of the present invention, it is based on a block unit in order to follow the target distribution.

와 X_I의 표준편차인 σ_I 는 수학식 7과 같이 표현된다.Divide I of size (h×w) into blocks of size (2m×n) so that they do not overlap, and define this as B _I. In B _I , blocks of size (m×n) composed of odd and even rows are defined as B _o and B _e , respectively. X is defined as a random variable representing pixel values between 0 and 255, and pixel values of blocks B _I , B _o , and B _e are defined as X _I , X _o , X _e , respectively. Then, the average of X _I

σ _I , which is the standard deviation of and X _I , is expressed as in Equation 7.

는 X 의 평균을 의미하며, σ_o와 σ_e는 각각 X_o와 X_e의 표준편차를 의미한다. 따라서, X_I 의 분포는 수학식 8과 같이 R의 분포를 따라야 한다.

is the mean of X , and σ _o and σ _e are the standard deviations of X _o and X _e , respectively. Therefore, the distribution of X _I must follow the distribution of R as in Equation (8).

As such, to adjust the distribution of X _I , it is essential to adjust X _o and X _e . Therefore, it is necessary to construct X _I by generating X _e to hide the secret image while minimizing the deformation of X _o representing the secret image.

To this end, the intensity range is adjusted in the same range for each RGB channel of the secret image S through intensity adjustment.

The lower limit of σ _X , which is the standard deviation of pixel values, is 0 when all pixel values are the same, and the upper limit is calculated as in Equation (9).

Here, E means an expected value (expectation). Considering the range of pixel values, the upper limit tighter than Equation 9 may be calculated as Equation 10.

here,

N means the size of the block, and mod means the remainder operation. The upper limit of the standard deviation σ _X of x according to X using Equation 10 is as shown in FIG. 5 below. It can be seen that for σ _X to reach σ _R , X must be greater than 43 and less than 212 . As such, since the range of standard deviation is determined according to the average of pixel values, it is inevitable to adjust the range of pixel values in order to reach the target standard deviation σ _R .

For the target standard deviation, the range of I _o representing the secret image is adjusted, while the range of I _e for hiding the secret image is not adjusted to increase the entropy of pixel values and to cover a wider range of standard deviations. The upper limit of σ _X is symmetric with respect to E(X) as shown in FIG. 5 . At this time, it is important not to bias the distribution of pixel values due to adjustment of the pixel value range. Therefore, the range of pixel values is adjusted from [0, 255] to [E(X)-t, E(X)+t] so that the upper and lower limits have the same distance of t from E(X). We define t as the intensity strength that controls the range of pixel values of the image, and the range of t is [0, 255 - E(X)].

Define X _o (i) and X _e (i) as the i-th pixel value in X _o and X _e , respectively. Then, X _o (i) and X _e (i) are defined as in Equation 11.

α _i ∈ [-t, t] and β _i ∈ [-E(X), 255-E(X)]. Assuming that the size of B _I is 2N, the sizes of B _o and B _e are N, respectively.

= μR을 만족시키기 위해 Σα_i+Σβ_i는 0이어야 한다. Σα_i = k라고 하면, k의 범위는 [-Nt, Nt]이다. k가 양의 정수인 [0, N·t]의 경우, t와 k에 따른 표준편차 σ_I 의 상한과 하한은 수학식 12와 같이 계산된다.

= μR, Σα _i +Σβ _i must be zero. If Σα _i = k, the range of k is [-Nt, Nt]. In the case where k is a positive integer [0, N·t], the upper and lower limits of the standard deviation σ _I according to t and k are calculated as in Equation 12.

= 2·[k/2t]+1이며, ø = 2·[k/2m]+1이다. 그리고 N 은 2의 배수이며, m은 E(X)와 같다. k가 음의 정수인 경우에도 상한과 하한은 동일하다. N = 4인 경우, t와 k에 따른 표준편차 σ_I 의 상한과 하한은 하기 도 6과 같다.

= 2·[k/2t]+1, and ø = 2·[k/2m]+1. And N is a multiple of 2, and m is equal to E(X). Even when k is a negative integer, the upper and lower bounds are the same. When N = 4, the upper and lower limits of the standard deviation σ _I according to t and k are as shown in FIG. 6 below.

The region of σ _I less than σ _R is denoted as the region under the line. Inf σ _I , the inmum of σ _I , is t when k = ±Nt. Since inf σ _I must be less than σ _R , t must be less than σ _R . The secret image with the range of pixel values adjusted in this way is defined as the adjusted secret image S'.

Thereafter, a modulated image (MS ) is generated by repeating pixel modulation on the adjusted secret image ( _S ′) in block units.

와 σ_I 를 달성하기 위해 픽셀 변조를 하여 I_e를 구성한다. 조정된 비밀 영상 S'가 위치한 I_o에서 B_o의 평균

와 표준편차 σ_o는 수학식 13과 같다.Specifically, after adjusting the intensity of the secret video, the target

We construct I _e with pixel modulation to achieve and σ _I . Average of B _o in I _o where the adjusted secret image S' is located

and standard deviation σ _o are the same as in Equation 13.

와 σ_e의 목표인

와 σ_e ^T 는 수학식 14와 같다.By Equation 11 and Equation 12

and σ _e is the target

and σ _e ^T are the same as in Equation 14.

By random sampling of Y of size N having a uniform distribution in the range [0, 1], X _e is configured as in Equation 15.

-

·σ_e ^T /σ_Y 이다. X_e를 (m×n) 크기의 블록 B_e로 변환한 후 두 블록 B_o와 B_e를 서로 라인 인터레이싱하여 B_I 를 구성한다. 그 다음, 하기 수학식 16과 같이 X_I의 평균

와 표준편차 σ_I 가 사전에 정의된 임계치의 범위 내에 있는지 체크한다.Y to U(0, 1), where q = σ _e ^T /σ _Y , r =

-

σ _e ^T /σ _Y . After converting X _e into a block B _e of size (m×n), B _I is constructed by line interlacing two blocks B _o and B _e with each other. Then, the average of X _I as shown in Equation 16 below

and standard deviation σ _I are within the predefined threshold range.

와 σ_I 가 범위를 벗어난다면, 범위 내에 존재할 때까지 B_e를 픽셀 변조를 반복한다. 이렇게 픽셀 변조를 이용하여 생성한 이미지 I_e를 변조된 이미지 M_s로 정의한다.what if

If and σ _I are out of range, _repeat pixel modulation of Be until they are within range. An image I _e generated using pixel modulation is defined as a modulated image M _s .

That is, when explaining the overall process of RVS, first, the intensity range is adjusted to the same range for each RGB channel of the secret image S. Then, an adjusted image M _s is generated by repeating pixel modulation block by block based on the adjusted secret image S'. Finally, an interlaced image I, which visually hides the secret image, is obtained by line interlacing S' and M _s with each other.

5 is a diagram illustrating an upper bound of a standard deviation according to an average for adjusting an intensity range in a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention; FIG. to be.

6 is a diagram illustrating graphs according to lower and upper limits of standard deviation in a restricted viewing scheme of an image encryption method based on line interlacing characteristics according to an embodiment of the present invention.

Specifically, FIG. 6 shows the lower and upper limits of the standard deviation of X _I according to t and k in the limited viewing technique, and FIG. 6 (a) is a graph of the lower limit, and FIG. 6 (b) is a graph of the upper limit.

7 is a diagram illustrating images of a restricted viewing scheme of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention.

B 영상이다.Figure 7 (a) shows the original secret image S and the black image B are line interlaced S

B is a video.

In (b) of FIG. 7 , the upper half represents the adjusted secret image S', and the lower half represents the modulated image M _s . FIG. 7(c) shows the autostereoscopic view V _ng where S' and M _s are line interlaced images in FIG. 7(b), and FIG. 7(d) shows the polarization glasses represents the glasses view V _g through .

8 is a flowchart illustrating an image encryption method based on line interlacing characteristics according to another embodiment of the present invention.

Referring to FIG. 8 , an image encryption method based on line interlacing characteristics according to another embodiment of the present invention is performed in a processor, and in step S210, a secret image (S) and a public image (P) have the same range for each RGB channel. An adjusted secret image (S') and an adjusted public image (P') are generated by adjusting the intensity range.

Here, the public image P is an image enhancement technique applied to enhance an edge component.

Here, the step S210 of generating an adjusted secret image S' and an adjusted public image P' by adjusting the intensity range includes the intensity intensity t _p of the secret image S and the public image P ), the range of pixel values is adjusted in consideration of the correlation between the intensity intensity (t _s ).

In step S220, a modulated image (MS _,P ) is generated by repeating pixel modulation on the adjusted secret image (S') and the adjusted public image (P') in block units.

Here, the step (S220) of generating a modulated image (MS, _P ) is performed by applying an inverse error spreading technique to a pre-generated first modulated image (MS _,P ). and generating (S221) a second modulated image (M' _S,P ) with improved image quality.

Here, the step (S220) of generating a modulated image (MS _,P ) by repeating pixel modulation on the adjusted secret image (S') and the adjusted public image (P') in block units (S220), Calculate the pixel value of any block located in a preset range from the adjusted secret image (S') and the adjusted public image (P'), and based on the pixel value of the arbitrary block, the adjusted secret image S ') and pixel modulation for each block of the adjusted public image (P').

Specifically, pixel modulation is performed for each block so that the average of pixel values of any block located in the preset range is included within the target average range.

In step S230, the odd rows or even rows of the adjusted secret image S' and the even rows or odd rows of the modulated image M _S,P are interlaced to form an interlaced image (I ) is created.

A selective viewing scheme will be described in more detail below with reference to FIG. 9 .

9 is a diagram for explaining a selective viewing scheme of an image encryption method based on a line interlacing characteristic according to another embodiment of the present invention.

In the selective viewing technique (SVS), since an autostereoscopic view represents a public image, a secret image and a public image can be selectively viewed using polarized glasses. As a result, as shown in Equation 17 below, the glasses-free view approximately expresses the public image and the glasses view approximately expresses the secret image.

Here, P denotes a public image that anyone can see without polarized glasses.

와 표준편차 σ_R을 따르도록 수정되어야 한다.For selective viewing conditions, the restrictive viewing technique is modified so that the average of block B _I in the interlaced image follows the average of block B _p in the public image. That is, as in Equation 18, the distribution of X _I is the mean X _I and the standard deviation σ _I is the average

and standard deviation σ _R .

Assume that I and P have the same size. B _p means a block of the same size as block B _I in the public image P, and X _p means a pixel value of B _p . Therefore, in order to follow the targeted distribution, X _I must be constructed by generating X _e to express public images while hiding secret images while minimizing the deformation of X _o , as in the limited-view technique.

An image encryption method based on line interlacing characteristics according to another embodiment of the present invention generates an adjusted secret image (S') and an adjusted public image (P') by adjusting an intensity range, The range of pixel values is adjusted in consideration of the correlation between the intensity intensity t _p of the image S and the intensity intensity t _s of the public image P.

Since only σ _e is variable in Equation 7, the upper and lower limits of σ _I are expressed as Equation 19.

는 상기 수학식 10에서 max

인 경우와 동일하다.max

is max in Equation 10

same as in the case of

= 127.5인 경우와

= 202.5인 경우에 평균

과 표준편차 σ_o에 따른 표준편차 σ_I 의 상한과 하한을 나타낸다. 도 10에서 빨간 영역은 σ_I 가 σ_R보다 작은 영역을 나타낸다. 하한의 그래프에서 빨간 영역은 σ_I 가 σ_R에 도달할 수 있는 X_o의 영역인 커버리지 영역(coverage area)을 의미한다. 반면, 상한의 그래프에서 빨간 영역은 σ_I 가 σ_R에 도달할 수 없는 X_o의 영역인 홀 영역(hole area)을 의미한다. X_I 가 127.5에서 멀어질수록 커버리지 영역이 감소하며 홀 영역이 증가하는 것을 알 수 있다. 따라서 선택적 시청 조건을 위해 X_I 의 범위가 제한되도록 X_p의 범위가 조정되어야 한다.10 below is

= 127.5 and

= 202.5 mean

and the upper and lower limits of the standard deviation σ _I according to the standard deviation σ _o . A red region in FIG. 10 indicates a region in which σ _I is smaller than σ _R . In the graph of the lower bound, the red area means the coverage area, which is the area of X _o where σ _I can reach σ _R . On the other hand, in the graph of the upper limit, the red area means the hole area, which is the area of X _o where σ _I cannot reach σ _R . It can be seen that as X _I is further away from 127.5, the coverage area decreases and the hole area increases. Therefore, the range of X _p should be adjusted so that the range of X _I is limited for selective viewing conditions.

The range of X _s is adjusted as in Equation (20) in the same way as for the limited viewing technique.

t _s ∈ [0, 127.5] is the intensity intensity of the secret image S. In order to prevent the pixel value bias, the range of the public image P is adjusted as in Equation 21 like the modified secret image S'.

t _p ∈ [0, 127.5] is the intensity intensity of the public image P. Since X _s ' and X _p ' are the same as X _o and X _I , respectively, the range of X _e is expressed as Equation (22).

Since the range of pixel values is limited to [0, 255], the relationship between t _p and t _s can be derived as in Equation 23 using Equation 22 above.

σ _e can be expressed as X _p' and X _s' using Equation 7 above, which can be expressed again as Equation 24 with t _p and t _s .

σ _e defined as above must satisfy Equation 25.

이다.Because of,

to be.

Therefore, for the selective viewing condition, t _p and t _s must be set to satisfy the two conditions, Equations 23 and 25.

Thereafter, a modulated image (MS _,P ) is generated by repeating pixel modulation on the adjusted secret image (S') and the adjusted public image (P') in block units.

와 σ_I 를 달성하기 위해 픽셀 변조를 함으로써 I_e를 구성한다. RVS 기법과 동일하게, B_o의 평균

와 표준편차 σ_o는 상기 수학식 13과 같다.Specifically, after adjusting the intensity of the secret video and the public video, the target

Construct I _e by pixel modulation to achieve σ I and σ _I . As with the RVS technique, the average of B _o

and standard deviation σ _o are the same as in Equation 13 above.

와 σ_e ^T 을 이용하여 상기 수학식 15처럼 X_e를 랜덤하게 샘플링한다.To satisfy optional viewing conditions,

and σ _e ^T are used to randomly sample X _e as in Equation 15 above.

와 σ_I 가 사전 정의된 임계치인 τ_μ와 τ_σ 의 범위 내에 있는지 체크한다. 만약

와 σ_I 가 범위를 벗어난다면, 범위 내에 존재할때까지 픽셀 변조를 반복한다. 이렇게 픽셀 변조를 통해 생성한 영상 I_e를 변조된 영상 M_s,p로 정의한다.next,

and σ _I are within the range of predefined thresholds τ _μ and τ _σ . what if

If and σ _I are out of range, repeat pixel modulation until they are within range. The image I _e generated through pixel modulation is defined as the modulated image M _s,p .

Here, a second modulated image (M' _S,P ) with improved image quality is generated by applying an inverse error diffusion technique to the pre-generated first modulated image (M _S ,P ) can do.

Specifically, since the SVS technique approximates the public image in block units to hide the secret image, the image quality of the interlaced image representing the public image deteriorates. Therefore, in an embodiment of the present invention, inverse error diffusion (IED) may be used to improve the image quality of the interlaced image.

First, the error diffusion technique is a simple and efficient image dithering algorithm proposed to improve image quality degradation that occurs in image quantization. As shown in Equation 26 below, the quantization error of the pixel value is propagated to adjacent pixels, and the corrected pixel value is fed back to the input, and the error is propagated in the lower right direction.

x and y denote pixel values of an input image and an output image, respectively, h denotes an error filter of size (k×l), and e denotes a quantization error of e = x - y. Since this technique reduces the distortion of the low-frequency component of the input image, it is possible to effectively improve the image quality degradation due to image quantization.

In the IED technique according to an embodiment of the present invention, an inverse error converted to an inverse error is applied instead of the quantization error of the existing error spreading technique.

Thus, rather than reducing the difference in low-frequency components between the input image and the output image, the difference is increased to smooth the range of pixel values while hiding the secret image. In addition, unlike the existing error spreading technique, the inverse error is propagated only in I _e to prevent deterioration of the image quality of the secret image. The modulated image M' _s,p generated through the inverse error spreading technique is calculated as in Equation 27.

here,

P _o and P _e denote an image composed of only odd and even rows of P, respectively, and h denotes an error filter. e _o is the inverse error of I _o and P _o , and e _e is the inverse error of M _s,p and P _e . 11 shows an effect of improving the quality of an interlaced image expressing a public image while maintaining the confidentiality of the secret image by applying the IED.

That is, to describe the overall process of the SVS technique, first, image enhancement is applied to the public image P to enhance an edge component. The intensity range is adjusted to the same range for each RGB channel of the secret image S and the public image P. Then, a modulated image M _s,p is generated by repeating pixel modulation in units of blocks based on S' and P'. In order to improve the picture quality of P _, M' _s,p is generated by applying the inverse error spreading technique to M s,p. Finally, an interlaced image I expressing P while hiding S is obtained by line interlacing S' and M _s,p .

10 is a diagram illustrating graphs according to lower and upper limits of standard deviation in a selective viewing scheme of an image encryption method based on line interlacing characteristics according to another embodiment of the present invention.

= 127.5인 하한과 상한의 그래프이고, 도 10의 (c)와 도 10의 (d)는

= 170인 하한과 상한의 그래프이다.10 shows the lower and upper limits of the standard deviation of X _I according to the average of X _o in the selective viewing technique, and FIGS. 10 (a) and 10 (b) are

= 127.5 is a graph of the lower limit and the upper limit, (c) and 10 (d) of FIG.

= 170 is a graph of the lower and upper limits.

11 is a diagram illustrating an effect of applying inverse error spreading in a selective viewing scheme of an image encryption method based on a line interlacing characteristic according to another embodiment of the present invention.

11(a) is a modulated image, and FIG. 11(b) is a modulated image to which an inverse error spreading technique is applied. 11(c) and 11(e) are enlarged blocks of FIG. 11(a), and FIGS. 11(d) and (f) show the enlarged blocks of FIG. 11(b).

12 is a diagram illustrating selective viewing scheme images of an image encryption method based on a line interlacing characteristic according to an embodiment of the present invention.

12 shows an example generated by the SVS technique. 12 (a) is the original public image P, in (b) the upper half is the adjusted secret image S', and the lower half shows the image M' _s,p modulated by applying the inverse error spreading technique. FIG. 12(c) shows an autostereoscopic view _Vng in which S' and M' _s,p are line interlaced images in FIG. 12(b), and FIG. 12(d) is FIG. represents the glasses view V _g seen through polarized glasses.

13 is a view for explaining an image decoding apparatus capable of decoding a secret image included through printing on paper such as an identification card, banknote, or document using masking according to an embodiment of the present invention. 13 (a) is an encryption object including an interfaced image, (b) is a decryption screen 40 that can be disposed between the encrypted object and the viewing position.

As shown in FIG. 13 , the decoding screen 40 may include a mask 41 that prevents viewing with respect to a position corresponding to an even line or an odd line of the image. Here, the interlaced image included in the encryption object shown in (a) may be an interlaced image generated by the image encryption method described with reference to FIG. 3 or the image encryption method described with reference to FIG. 8 .

13 , the mask 41 may be a light blocking filter, and the mask 41 may be integrally formed through a technique such as printing on the back side of the encrypted object shown in (a). In this case, (a) may indicate an interface image included on the front side of the encryption object integrated with the screen 40, and (b) is a light blocking image included on the back side of the screen 40 integrated with the encryption object. It may indicate a filter. When viewing the front of the encrypted object with the light source positioned behind the encrypted object for decryption, some lines of the interfaced image included in the encrypted object are masked by the light blocking filter and only the remaining unmasked lines are viewed. can do. This can be said to be the decrypted secret image.

As another embodiment of FIG. 13 , the mask 41 may be a light blocking filter, and the mask 41 may be formed through a technique such as printing on the front side or the back side of the transparent material film. In this case, (a) may indicate an interface image included on the front side of the encryption object formed separately from the screen 40, and (b) is on the front or back side of the screen 40 formed separately from the encryption object. It may indicate an included light-blocking filter. For decryption, when the encrypted object is viewed through the transparent film in the overlapped state through line alignment with respect to the encrypted object and the transparent film, some lines of the interfaced image included in the encrypted object are masked by the light blocking filter and Only the remaining unmasked lines are visible. This can be said to be the decrypted secret image.

Comparing the image decoding apparatus according to the embodiment of FIG. 13 with the polarization 3D system 1 of FIG. 1 , it can be seen that the 3D display 10 corresponds to the encryption object a shown in FIG. 13 (a) and , it can be seen that the polarized glasses 20 correspond to the decoding screen 40 . In the case of including a circular polarization filter in place of the light blocking filter of the decryption screen 40, the encryption object shown in (a) may be referred to as the stereoscopic 3D content 30 shown in FIG.

According to an embodiment of the present invention, the proposed method of encrypting an image using the line interlacing characteristic can prevent illegal content leakage from re-photographing of the screen using a photographing device, and can also be applied as a security display method. In addition, the proposed techniques can be applied to contents that need protection from unauthorized re-shooting in public places such as public presentations and exhibitions, and can be applied to situations where two contents are displayed from a single display at the same time, such as a dual display. have. Additionally, it can be applied as an image encryption technique for authentication and integrity verification of documents such as identification cards, banknotes, and documents.

Also, it is possible to provide a computer program stored in a computer-readable recording medium for executing an image encryption method based on line interlacing characteristics.

In addition, it is possible to provide a computer-readable recording medium in which a program for executing an image encryption method based on line interlacing characteristics is recorded.

Combinations of each block in the block diagram attached to the present invention and each step in the flowchart may be performed by computer program instructions. These computer program instructions may be embodied in an encoding processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, such that the instructions executed by the encoding processor of the computer or other programmable data processing equipment may correspond to each block of the block diagram or Each step of the flowchart creates a means for performing the functions described. These computer program instructions may also be stored in a computer-usable or computer-readable memory that may direct a computer or other programmable data processing equipment to implement a function in a particular way, and thus the computer-usable or computer-readable memory. The instructions stored in the block diagram may produce an article of manufacture containing instruction means for performing the functions described in each block in the block diagram or in each step in the flowchart. The computer program instructions may also be mounted on a computer or other programmable data processing equipment, such that a series of operational steps are performed on the computer or other programmable data processing equipment to create a computer-executed process to create a computer or other programmable data processing equipment. It is also possible that instructions for performing the processing equipment provide steps for performing the functions described in each block of the block diagram and each step of the flowchart.

Further, each block or each step may represent a module, segment, or portion of code that includes one or more executable instructions for executing the specified logical function(s). It should also be noted that in some alternative embodiments it is also possible for the functions recited in blocks or steps to occur out of order. For example, it is possible that two blocks or steps shown one after another may in fact be performed substantially simultaneously, or that the blocks or steps may sometimes be performed in the reverse order according to the corresponding function.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations will be possible without departing from the essential quality of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed 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.

Claims (20)

generating an adjusted secret image by adjusting an intensity range to the same range for each RGB channel of the secret image;
generating a modulated image by repeating pixel modulation on the adjusted secret image in block units; and
An interlaced image by interlacing odd lines of the adjusted secret image and even lines of the modulated image M _S or by interlacing even lines of the adjusted secret image and odd lines of the modulated image ) generating an image encryption method comprising a. According to claim 1,
The step of generating an adjusted secret image by adjusting the intensity range comprises:
An image encryption method of adjusting the range of the pixel value to have a distance of the same intensity intensity from an expected value of a random variable representing the pixel value of the secret image. 3. The method of claim 2,
The step of generating the modulated image comprises:
calculating a pixel value of an arbitrary block located in a preset range in the adjusted secret image; and
and performing pixel modulation for each block of the adjusted secret image based on the pixel value of the arbitrary block. 4. The method of claim 3,
The step of performing pixel modulation for each block of the adjusted secret image comprises:
An image encryption method of performing pixel modulation for each block so that an average of pixel values of any block located in the preset range is included within a target average range. generating an adjusted secret image and an adjusted public image by adjusting an intensity range to the same range for each RGB channel of the secret image and the public image;
generating a modulated image by repeating pixel modulation on the adjusted secret image and the adjusted public image in block units; and
generating an interlaced image by interlacing odd lines of the adjusted secret image and even lines of the modulated image or interlacing even lines of the adjusted secret image and odd lines of the modulated image; video encryption method. 6. The method of claim 5,
The public image is an image encryption method to which an image enhancement technique is applied to enhance an edge component. 6. The method of claim 5,
The step of generating the modulated image comprises:
An image encryption method comprising the step of generating a second modulated image with improved image quality by applying an inverse error spreading technique to the previously generated first modulated image. 6. The method of claim 5,
generating an adjusted secret image and an adjusted public image) by adjusting the intensity range,
An image encryption method for adjusting a range of pixel values in consideration of a correlation between intensity intensity of the secret image and intensity intensity of the public image. 6. The method of claim 5,
The step of generating the modulated image comprises:
calculating a pixel value of an arbitrary block located in a preset range in the adjusted secret image and the adjusted public image; and
and performing pixel modulation for each block of the adjusted secret image and the adjusted public image based on the pixel value of the arbitrary block. 10. The method of claim 9,
The step of performing pixel modulation for each block of the adjusted secret image and the adjusted public image comprises:
An image encryption method of performing pixel modulation for each block so that an average of pixel values of any block located in the preset range is included within a target average range. A decryption screen that can be disposed between an encryption object comprising an interlaced image and a viewing position;
The interlaced image is
An adjusted secret image is generated by adjusting the intensity range to the same range for each RGB channel of the secret image, and a modulated image is generated by repeating pixel modulation on the adjusted secret image in block units, and the odd number of the adjusted secret image generated by interlacing lines and even lines of the modulated image or interlacing even lines of the adjusted secret image and odd lines of the modulated image;
video decoding device. 12. The method of claim 11,
The decryption screen,
Decrypting the adjusted secret image encrypted by even lines or odd lines of the interlaced image
video decoding device. 13. The method of claim 12,
The decryption screen,
A mask that interferes with viewing is included in the position corresponding to the even or odd lines of the interlaced image.
video decoding device. 14. The method of claim 13,
The mask includes a polarizing filter or a light blocking filter
video decoding device. A decryption screen that can be disposed between an encryption object comprising an interlaced image and a viewing position;
The interlaced image is
An adjusted secret image and an adjusted public image are generated by adjusting the intensity range to the same range for each RGB channel of the secret image and the public image, and the adjusted secret image and the adjusted public image are repeatedly modulated by pixel modulation in blocks. generated by interlacing odd lines of the adjusted secret image and even lines of the modulated image, or interlacing even lines of the adjusted secret image and odd lines of the modulated image,
video decoding device. 16. The method of claim 15,
The decryption screen,
Decrypting the adjusted secret image encrypted by even lines or odd lines of the interlaced image
video decoding device. 17. The method of claim 16,
The decryption screen,
A mask that interferes with viewing is included in the position corresponding to the even or odd lines of the interlaced image.
video decoding device. 18. The method of claim 17,
The mask includes a polarizing filter or a light blocking filter
video decoding device. As a computer-readable recording medium storing a computer program,
The computer program, when executed by a processor,
generating an adjusted secret image by adjusting an intensity range to the same range for each RGB channel of the secret image;
generating a modulated image by repeating pixel modulation on the adjusted secret image in block units; and
generating an interlaced image by interlacing odd lines of the adjusted secret image and even lines of the modulated image or interlacing even lines of the adjusted secret image and odd lines of the modulated image; A computer-readable recording medium comprising instructions for causing the processor to perform an image decoding method. As a computer-readable recording medium storing a computer program,
The computer program, when executed by a processor,
generating an adjusted secret image and an adjusted public image by adjusting an intensity range to the same range for each RGB channel of the secret image and the public image;
generating a modulated image by repeating pixel modulation on the adjusted secret image and the adjusted public image in block units; and
generating an interlaced image by interlacing odd lines of the adjusted secret image and even lines of the modulated image or interlacing even lines of the adjusted secret image and odd lines of the modulated image; A computer-readable recording medium comprising instructions for causing the processor to perform an image encryption method.

Images