JP5953869B2 - Program, watermark embedding apparatus and watermark embedding method - Google Patents

Description

  The present invention relates to a program for embedding watermark information in electronic content, a watermark embedding apparatus, and a watermark embedding method.

  Digital watermarking is a technique for embedding additional information in image data and audio data so that humans cannot recognize it. By embedding the copyright information of the content and the purchase information of the user as watermark information, the presence or absence of the copyright information and the source of the leakage can be specified when the content is illegally leaked.

  Further, when an image or moving image content is a watermark embedding target, the digital watermark can be applied to an electronic advertisement (digital signage). For example, it is possible to acquire additional information such as detailed product information by detecting watermark information with a mobile phone with a camera or the like from an advertisement video on a street screen or television.

  As a method for embedding watermark information, there is a technique of repeatedly embedding watermark information of a certain amount of data (for example, 64 bits) as much as possible in an input content as disclosed in Patent Document 1, for example. In this case, the watermark information can be detected by obtaining the head position of each embedded watermark information repeatedly using a synchronization bit and obtaining the majority of each watermark detection information following the synchronization bit.

Special table 2009-508391

  In the prior art, even when correct watermark information cannot be detected with only one detection data due to content quality degradation or the like, there is an increased possibility that watermark information can be detected by majority processing of embedded watermark information.

  However, even if watermark detection is performed by majority embedding by repeatedly embedding watermark information, if a scene where it is difficult to detect watermark information continues at the same watermark embedding position, the watermark information cannot be detected properly.

  In particular, when the content capacity is small and the watermark information can be embedded only a few times, if there is a scene where it is difficult to detect the watermark at the same position in the repetition, the watermark detection may fail. There was a problem of becoming higher.

  Accordingly, the disclosed technology has been made in view of the above-described problems, and when watermark information is repeatedly embedded, the accuracy of watermark information detection is improved by appropriately distributing positions where it is difficult to detect watermark information. It is an object to provide a program, a watermark embedding device, and a watermark embedding method.

  The program according to an aspect of the disclosure calculates a difficulty level of watermark detection for each section in which watermark information is embedded in content, and based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past , Determining an arrangement parameter indicating a parameter for changing the arrangement of the watermark information, rearranging the watermark information according to the arrangement parameter, and causing a computer to execute a process of embedding the rearranged watermark information in the section to be embedded .

  According to the disclosed technology, when the watermark information is repeatedly embedded, the detection accuracy of the watermark information can be improved by appropriately distributing the positions where the watermark information is difficult to detect.

The block diagram which shows an example of a structure of information processing apparatus. FIG. 3 is a block diagram illustrating an example of a watermark embedding function according to the first embodiment. The figure which shows the mode of the repetition process by arrangement | positioning method determination. The figure which shows the example which carries out the cyclic shift of the bit sequence of watermark information. The figure which shows the example which scrambles the bit sequence of watermark information. The figure which shows the example which adds a position detection code to watermark information. The figure which shows an example of the watermark pattern for embedding. The figure which shows the correspondence example of the watermark pattern for embedding, and an expression bit. The figure for demonstrating the example which embeds watermark information using a watermark pattern. The figure for demonstrating the reason why watermark detection becomes difficult. The figure which shows an example of the past difficulty level and the present difficulty level. 5 is a flowchart illustrating an example of a watermark embedding process according to the first exemplary embodiment. FIG. 9 is a block diagram illustrating an example of a watermark detection function according to the second embodiment. The figure for demonstrating calculation of a cyclic shift value. 10 is a flowchart illustrating an example of a watermark detection process according to the second embodiment. The figure which shows an example of the watermark detection result of a prior art. The figure which shows an example of the watermark detection result by an Example.

  Each embodiment will be described below with reference to the accompanying drawings.

[Example 1]
<Configuration>
FIG. 1 is a block diagram illustrating an example of the configuration of the information processing apparatus 1. The information processing apparatus 1 illustrated in FIG. 1 functions as a watermark embedding apparatus that embeds watermark information. The watermark information is also called digital watermark information.

  The information processing apparatus 1 illustrated in FIG. 1 includes a control unit 10, a main storage unit 20, an auxiliary storage unit 30, a communication unit 40, and a recording medium I / F unit 50. Each unit is connected via a bus so that data can be transmitted / received to / from each other.

  The control unit 10 is a CPU (Central Processing Unit) that performs control of each device, calculation of data, and processing in a computer. The control unit 10 is an arithmetic device that executes a program stored in the main storage unit 20 or the auxiliary storage unit 30. The control unit 10 receives data from the communication unit 40 or each storage unit, calculates, processes, and outputs the data. And output to each storage unit.

  The control unit 10 plays a role of a watermark embedding function by executing a program for embedding watermark information stored in the auxiliary storage unit 30, for example.

  The main storage unit 20 is a ROM (Read Only Memory), a RAM (Random Access Memory), or the like, and a storage device that stores or temporarily stores programs and data such as an OS and application software that are basic software executed by the control unit 10. It is.

  The auxiliary storage unit 30 is an HDD (Hard Disk Drive) or the like, and is a storage device that stores data related to application software and the like. The auxiliary storage unit 30 stores electronic content such as video and music acquired from the communication unit 40 and watermark information.

  The auxiliary storage unit 30 may store content and watermark information acquired from the recording medium 60 or the like.

  The communication unit 40 performs wired or wireless communication. The communication unit 40 acquires content such as video and music and watermark information from, for example, a server and stores the content in the auxiliary storage unit 30, for example.

  The recording medium I / F (interface) unit 50 is an interface between the information processing apparatus 1 and a recording medium 60 (for example, a flash memory) connected via a data transmission path such as a USB (Universal Serial Bus).

  A predetermined program is stored in the recording medium 60, and the program stored in the recording medium 60 is installed in the information processing apparatus 1 via the recording medium I / F unit 50. The installed predetermined program can be executed by the information processing apparatus 1.

  If the recording medium 60 is an SD card, for example, the recording medium I / F unit 50 is an SD card slot.

<Watermark information embedding function>
Next, the function of embedding watermark information will be described in detail. FIG. 2 is a block diagram illustrating an example of a watermark embedding function according to the first embodiment.

  In the example illustrated in FIG. 2, the information processing apparatus 1 having a function as a watermark information embedding apparatus includes a difficulty level calculation unit 101, a storage unit 102, an arrangement parameter determination unit 103, a rearrangement unit 104, and an embedding unit 105. And have.

  The difficulty level calculation unit 101, the arrangement parameter determination unit 103, the rearrangement unit 104, and the embedding unit 105 can be realized by the control unit 10 and the main storage unit 20 as a work memory, for example. The storage unit 102 can be realized by the main storage unit 20, for example.

  The difficulty level calculation unit 101 calculates the difficulty level of watermark detection for each section (or position) in which watermark information is embedded for the input content. The content may be content distributed from an external device, or content stored in the auxiliary storage unit 30.

  The section in which the watermark information is embedded is, for example, the amount of content corresponding to the watermark information. For example, the section when the content is a moving image is the number of frames corresponding to the number of bits of the watermark information. The difficulty level calculation unit 101 knows in advance the amount of watermark information to be embedded with reference to the main storage unit 20 or the like.

  The degree of difficulty represents the difficulty of detection when watermark information is embedded. For example, when the content is a moving image and the embedding process changes the difference between the pixel values of the adjacent frames and expresses binary (0 or 1) of the watermark information by the positive or negative of the difference, the difficulty level is, for example, the pixels of the adjacent frames The absolute value of the difference between the values. This is because watermark information cannot be appropriately embedded in a frame having a large difference between the original moving images, making detection difficult.

  In addition, when representing the binary information of the watermark information by changing the pixel value of the moving image in a triangular wave shape at a constant period, it is desirable that the difficulty level is, for example, a Fourier coefficient corresponding to the period of the triangular wave from the pixel value of the moving image. . A large Fourier coefficient indicates that detection is difficult. The difficulty level calculation unit 101 writes the difficulty level indicating the difficulty in detecting watermark information in the storage unit 102 and outputs the difficulty level to the arrangement parameter determination unit 103.

  The storage unit 102 stores the difficulty level of the embedded section of each watermark information obtained by the difficulty level calculation unit 101. The storage unit 102 stores the difficulty level for each section. The stored difficulty level of the past section is used by the arrangement parameter determination unit 103.

  The arrangement parameter determination unit 103 determines an arrangement parameter indicating a parameter for changing the arrangement of the watermark information based on the difficulty level calculated in the section to be embedded and the difficulty levels calculated in the past.

  The placement parameter determination unit 103 is used to determine a placement method so that a difficult-to-detect scene does not overlap the watermark information at the same position in the repetition in the watermark information repetitive embedding process.

  The arrangement method can be determined by iterative processing with a certain length of section as a unit. FIG. 3 is a diagram showing the state of the iterative process by determining the arrangement method. In the example shown in FIG. 3, the arrangement method is determined based on the difficulty level of the current position in the first designated section. The hatched section is the current processing target section.

  In the second and subsequent sections, the arrangement method is determined with reference to the past difficulty level. The length of the section as a unit of repetition can be set, for example, for one watermark information or a plurality of watermark information.

  For example, at least the following two arrangement methods can be considered. FIG. 4 is a diagram illustrating an example of cyclically shifting a bit string of watermark information.

  In the example illustrated in FIG. 3, the arrangement parameter determination unit 103 determines an appropriate cyclic shift shift amount based on the difficulty level of the section in which the watermark information has already been embedded and the difficulty level of the current processing target section. A specific method for calculating the shift amount will be described later.

  Next, the placement parameter determination unit 103 outputs the determined shift amount to the rearrangement unit 104 as a placement parameter.

  FIG. 5 is a diagram illustrating an example of scrambling a bit string of watermark information. In the example illustrated in FIG. 5, the arrangement parameter determination unit 103 determines a scramble method based on the difficulty level of the section in which the watermark information is already embedded and the difficulty level of the section that is currently processed. A method for determining the scramble method will be described later.

  Even when the arrangement method is scrambled, as in the case of the cyclic shift, the arrangement parameter determination unit 103 obtains, based on the degree of difficulty, a scramble method in which difficult-to-detect scenes do not overlap at the same position in repetition. The placement parameter determination unit 103 outputs the obtained scrambling method to the rearrangement unit 104 as a placement parameter.

  Returning to FIG. 2, the rearrangement unit 104 rearranges the watermark information according to the arrangement parameter acquired from the arrangement parameter determination unit 103. Rearrangement refers to changing the bit position of the watermark information by shifting, rearranging, or rearranging, for example. The rearrangement unit 104 acquires watermark information distributed from an external device, or acquires watermark information stored in the auxiliary storage unit 30.

  The watermark information includes, for example, copyright information of the content to be embedded, store information, purchaser information, and the like, and is expressed by binary information of 0 and 1.

  FIG. 6 is a diagram illustrating an example of adding a position detection code to watermark information. In the example shown in FIG. 6, a position detection code representing the head position of the watermark information is added to the watermark information. For example, a 16-bit bit string such as “1111111100000000” is set as the position detection code.

  The watermark information can also be expressed by a code having an error correction and error detection function. A CRC (Cyclic Redundancy Checking) code or the like can be used as the error detection code, and a Reed-Solomon code or an LDPC (Low Density Parity Check) code can be used as the error correction code.

  As shown in FIG. 6, when the position detection code is included in the watermark information, only the portion related to the net watermark information is to be rearranged. Since the position detection code is a code representing the head position of the watermark information, it is not a target for rearrangement.

  When the arrangement method is cyclic shift, the shift amount of the cyclic shift is obtained from the arrangement parameter determination unit 103, and the watermark information is rearranged by cyclically shifting the watermark information as shown in FIG.

  When the arrangement method is scramble, the scramble method is acquired from the arrangement parameter determination unit 103, and the watermark information is scrambled as shown in FIG.

  Returning to FIG. 3, the embedding unit 105 embeds the watermark information rearranged by the rearrangement unit 104 in a section where content is to be embedded. For example, at the time of embedding, the embedding unit 105 converts the watermark information including the position detection code into a watermark pattern for embedding in the input content.

  FIG. 7 is a diagram illustrating an example of a watermark pattern for embedding. In the example illustrated in FIG. 7, the watermark pattern includes a plurality of watermark blocks, and the pixels included in each watermark block have a negative value, for example, “−2”. Therefore, each watermark block has a shadow shape. As a result, pixels included in the watermark pattern are superimposed, so that the value of the superimposed pixel is lower than the original pixel value.

  In FIG. 7, nine images that are continuous in time from time t to time (t + 8) are shown. A rectangular watermark pattern A11 is superimposed on the image A01 at time t. Then, from the time t to the time (t + 4), the number of the watermark blocks A12 is reduced, so that the area of the watermark pattern superimposed on the image is reduced. Then, the watermark pattern disappears in the image A02 at time (t + 4). In addition, after the time (t + 4), the area of the watermark pattern increases, and the area of the watermark pattern is maximized again in the image A03 at the time (t + 8).

  With respect to the watermark pattern generated by this example, the temporal change in the average pixel value of each frame is triangular as shown in FIG. FIG. 8 is a diagram illustrating a correspondence example between a watermark pattern for embedding and an expression bit. FIG. 8 shows an example of the relationship between the elapsed time of the watermark pattern and the value of the embedded bit. In FIG. 8, the horizontal axis of each of the upper, middle, and lower graphs represents time, and the vertical axis represents the average pixel value in the reference area. Graphs B01 and B02 represent the variation of the average pixel value in the reference region with respect to the passage of time when the bit value is “0” or “1”, respectively. In this example, the cycle T1 when the bit value is “0” is twice the cycle T2 when the bit value is “1”. In order to facilitate detection of the embedded value, the length of the section in which one bit is embedded is preferably the same regardless of the bit value. For example, when the bit value is “0”, one interval includes a change in the average pixel value for one period. On the other hand, when the bit value is “1”, one interval includes 2 Variations in the average pixel value of the period are included.

  FIG. 9 is a diagram for explaining an example of embedding watermark information using a watermark pattern. In the example shown in FIG. 9, it is assumed that the bit string of the watermark information including the position detection code is “0101. Next, the binary data of the watermark information is converted into a watermark pattern.

  As shown in FIG. 9, a watermark pattern is embedded for each section of content corresponding to the cycle of the watermark pattern. For example, the embedding unit 105 adds the pixel value on the peak side of the watermark pattern to the average pixel value of each frame of the original moving image content, and subtracts the pixel value on the valley side, so that the original pixel value is not changed as much as possible. Can be embedded with a watermark pattern. As the value to be added to or subtracted from the pixel value, an appropriate value may be set in advance through experiments or the like.

  Note that the embedding process of the embedding unit 105 is not limited to the above process. For example, the embedding unit 105 sets the luminance value of the pixel at each predetermined position of each image to a luminance value corresponding to the value of the bit in order from the first bit of the watermark information. Note that the predetermined position can be, for example, any one of the pixels at the four corners of the image. Therefore, in the embodiment, a method for embedding a watermark in content is not particularly limited, and various methods can be applied.

  The series of watermark embedding processes can be repeatedly applied until the watermark information (or watermark pattern) is embedded in all areas of the input content. For example, if the input target content is a moving image of 10 minutes and it takes 2 minutes to embed a set of watermark information, the watermark embedding process is repeated 5 times with a 2 minute watermark as a unit. Therefore, by performing this processing, it is possible to embed a watermark in the entire area of 10 minutes of moving image content.

<Detailed processing of each part>
Next, each process of the watermark embedding process will be described in detail. In the example shown below, it is assumed that the input content is a moving image and a watermark pattern that changes the pixel value of each frame in a triangular wave shape is embedded by the method shown in FIGS. Further, it is assumed that watermark information is repeatedly embedded with one watermark information as a unit. Regarding rearrangement, first, an example of performing cyclic shift will be described.

《Circular shift》
The variables used in this example are defined as follows:
R: Number of times watermark information is repeatedly embedded N: Bit length of watermark information C [n]: Value of nth bit of watermark information (0 or 1)
C ^′ [r] [n]: value (0 or 1) corresponding to the nth bit after the watermark information to be embedded at the rth time is rearranged
F [r] [i]: After adding watermark information to the pixel average value FW [r] [i]: F [r] [i] of the i-th frame in the moving image region where the watermark information is embedded at the r-th time Pixel average value D [r] [n]: Difficulty level of the position where the nth bit watermark pattern is embedded in the moving image area where the watermark information is embedded at the rth time T: Period W [0] [t] of the embedded watermark pattern: Watermark pattern representing bit 0 W [1] [t]: Watermark pattern representing bit 1

  Here, W [0] [t] is a triangular wave with a period T1, and W [1] [t] is a triangular wave with a period T2, each represented by the following expression. “A” in the equation represents the embedding strength of the watermark.

(Difficulty calculation)
When embedding a watermark pattern by changing pixel values in a triangular wave shape, if a moving image includes a scene having a change in the average pixel value of the same period (T1 or T2) as the watermark pattern, it is difficult to detect the watermark pattern. .

  FIG. 10 is a diagram for explaining the reason why watermark detection becomes difficult. A vertical line shown in FIG. 10 indicates a frame, and a line segment indicates a line connecting pixel average values of each frame. FIG. 10A shows a case where the change in the pixel average value of each frame in the period T1 becomes a triangular wave having an antiphase. Assume that a watermark pattern indicating “0” is embedded in the average pixel value of each frame shown in FIG.

  FIG. 10B shows a pixel average value as a result of embedding a watermark pattern of “0”. 10A includes an antiphase triangular wave having a larger amplitude than the watermark pattern of “0”, the pattern of FIG. 10B to which the watermark pattern is added is also an antiphase triangular wave. End up.

  Therefore, as shown in FIG. 10A, when the change in the pixel average value of each frame in the period T1 is a triangular wave, watermark detection is difficult at the position of each frame. The same can be said for a triangular wave with a period T2 which is a watermark pattern corresponding to “1”.

  Therefore, the difficulty level calculation unit 101 calculates the sum of the magnitudes of Fourier coefficients corresponding to the periods T1 and T2 of the input moving image as the difficulty level. The degree of difficulty D [r] [n] is obtained by the following equation.

(Determining placement parameters)
The arrangement parameter determination unit 103 determines the shift amount of the cyclic shift as a watermark arrangement method so that a scene that is difficult to detect at the same position as the already embedded watermark information does not overlap. The same position means that the position where the binary data of watermark information embedded in the past is embedded and the position where the binary data of watermark information to be embedded is embedded are the same position.

  As the evaluation value, a correlation value between the difficulty level calculated in the past and the difficulty level after rearranging the watermark information at the current embedding target position can be used. The correlation value is high when scenes that are difficult to detect after rearrangement overlap at the same position, and conversely, the correlation value is low when scenes that are difficult to detect are distributed at each watermark embedding position.

  FIG. 11 is a diagram illustrating an example of the past difficulty level and the current difficulty level. In the example illustrated in FIG. 11, D [1] [n] indicates the past difficulty level, and D [2] [n] indicates the current difficulty level. Here, the degree of difficulty D [1] [3] having a large value and the degree of difficulty D [2] [3] are highly correlated at the same position. That is, if the watermark information is embedded as it is, the watermark detection becomes difficult for the third bit of the watermark information.

Therefore, the arrangement parameter determination unit 103 uses the property of the correlation value to obtain the cyclic shift value S ^* [r] of the watermark information in each repetitive embedding according to the following procedure. r represents the number of repetitions of the current position of watermark embedding.

(A) In the first embedding process (r = 1), no cyclic shift is performed, and the cyclic shift value S ^* [1] is set to 0. Further, E [r] [n] is set as the cumulative value of the difficulty level, and the cumulative value is initialized by the equation (5).

(B) In the second and subsequent (2 ≦ r <R) embedding processes, the correlation value Q [s] at each shift value s is obtained by Expression (6), and the shift amount that minimizes the correlation value by Expression (7) S ^* [r] is obtained. In addition, E [r] [n] is updated by Expression (8).

(Relocation)
The rearrangement unit 104 uses the cyclic shift value S ^* [r] obtained by the arrangement parameter determination unit 103 to cyclically shift the watermark information C [n] using Equation (9) and rearrange the watermark information C ^′. [R] [n] is obtained.

(embedded)
The embedding unit 105 uses the pixel average value F [r] [i] of the input moving image as the pixel average value according to Expression (10) using the watermark patterns W [0] [t] and W [1] [t]. A watermark is added by changing.

Here, n and t in equation (10) are calculated by the following equation using i.

  As a result, when using a cyclic shift for the rearrangement method, even if there is a scene that is difficult to detect at the same position in the repetition, it is possible to distribute the difficult detection scene in the repetition by appropriately shifting the watermark information cyclically. Can do. Therefore, the accuracy of watermark detection can be improved.

"scramble"
Next, a case where a scramble method is used as a rearrangement method will be described. Since the watermark embedding procedure other than the rearrangement determination method and the rearrangement method is the same as in the case of the cyclic shift, the description thereof is omitted.

  All combinations that scramble the watermark information are in the factorial order of the bit length of the watermark information. For example, in the case of 64-bit watermark information, all combinations of scramble are 64! Street.

  It is not realistic from the viewpoint of computational complexity to consider all the scramble methods. Therefore, in the example shown below, the number of scrambling methods to be considered is limited.

Here, in addition to the variables used in the cyclic shift, the following variables are defined. The other variables have the same meaning as the variables used in the cyclic shift.
M: Number in case of scrambling method Scr [m] [n]: Bit position after rearrangement of n-th watermark information in m-th scrambling method, where 0 ≦ m <M, 0 ≦ n <N If i ≠ j, then Scr [m] [i] ≠ Scr [m] [j]. That is, the scrambled position of each bit after rearrangement is a different position.

(Determining placement parameters)
When scramble is used as the rearrangement method, the placement parameter determination unit 103 calculates the difficulty calculated in the past and the difficulty after rearranging (scrambled) the watermark information at the current position in the same manner as the cyclic shift. Determined using correlation value. The arrangement parameter in this case indicates which scramble method among a plurality of scramble methods.

Here, if the scrambling method determined in each repetitive embedding process is Scr ^* [r] (= Scr ^* [r] [0], Scr ^* [r] [1]...), Scr ^* [r] is It is obtained by the following procedure.

  (A) The first embedding process (r = 1) does not scramble (formula (13)). Further, E [r] [n] is set as the cumulative value of the difficulty level, and the cumulative value is initialized by the equation (14).

(B) In the second and subsequent embedding processes (2 ≦ r <R), the correlation value Q [m] in each scramble method Scr [m] is obtained by Expression (15), and the correlation value is obtained by Expressions (16) and (17) The scramble method Scr ^* [r] that minimizes is obtained. In addition, E [r] [n] is updated by Expression (18).

(Relocation)
The rearrangement unit 104 uses the scrambling method Scr ^* [r] obtained by the arrangement parameter determination unit 103 to scramble the watermark information C [n] according to the equation (19) and rearrange the watermark information C ^′ [r ] [N] is obtained.

  Here, IScr [r] [n] in equation (19) represents the inverse transformation of Scr [r] [n], and satisfies the property of equation (20).

  Thus, when scrambling is used for the rearrangement method, even if there is a scene that is difficult to detect at the same position in the repetition, it is possible to disperse the scene that is difficult to detect in the repetition by appropriately scrambling the watermark information. . Therefore, the accuracy of watermark detection can be improved.

  In the above two examples, the position detection code and the error correction code are not considered for the watermark information C [n]. However, if the watermark information includes the position detection code or the error correction code, the position detection code It is only necessary to rearrange the watermark information other than those (cyclic shift or scramble) (see FIG. 6).

<When the input content is audio data>
Next, the case where the input content is audio data will be described. In the first embodiment, watermark information can be embedded in audio data. The information processing apparatus 1 according to the first embodiment can embed watermark information in audio data in the same manner as the above-described moving image watermark embedding process (cyclic shift and scramble).

  For example, watermark information can be expressed by embedding sine waves having different frequencies between bit 0 and bit 1 in audio data. The specific frequency for embedding the watermark information is desirably set to a band that cannot be heard by the human ear (for example, 20 KHz or more).

  As a result, even if the input content is audio data, it is possible to disperse a scene that is difficult to detect and repeatedly embed watermark information.

<Operation>
Next, the operation of the information processing apparatus 1 in the first embodiment will be described. FIG. 12 is a flowchart illustrating an example of the watermark embedding process according to the first embodiment. In step S101 illustrated in FIG. 12, the difficulty level calculation unit 101 determines whether there is an area in which watermark information is not inserted in the input content. If there is an uninserted area (step S101—YES), the process proceeds to step S102, and if there is no uninserted area (step S101—NO), the watermark embedding process is terminated.

  In step S102, the difficulty level calculation unit 101 designates a section in which watermark information is embedded from the input content. The difficulty level calculation unit 101 holds the data amount of watermark information to be embedded.

  In step S <b> 103, the difficulty level calculation unit 101 obtains a difficulty level indicating the difficulty in detecting a watermark for each watermark embedding position in the designated section.

  In step S <b> 104, the storage unit 102 stores the difficulty level obtained by the difficulty level calculation unit 101.

  In step S <b> 105, the arrangement parameter determination unit 103 determines the arrangement parameter of the watermark information of the target section based on the past difficulty level stored in the storage unit 102 and the difficulty level of the current section to be embedded.

  In step S106, the rearrangement unit 104 rearranges the watermark information according to the determined arrangement parameter.

  In step S107, the embedding unit 105 embeds the rearranged watermark information in the target section of the input content. When this process ends, the process returns to step S101 to embed watermark information repeatedly.

[Example 2]
Next, an information processing apparatus according to the second embodiment will be described. The information processing apparatus according to the second embodiment functions as a watermark detection apparatus and detects watermark information embedded by the watermark embedding apparatus according to the first embodiment.

<Configuration>
Since the information processing apparatus in the second embodiment is the same as the information processing apparatus 1 in the first embodiment, the description thereof is omitted. In the description of the configuration of the information processing apparatus according to the second embodiment, the same reference numerals as those illustrated in FIG. 1 are used.

<Watermark information detection function>
Next, the function of detecting watermark information will be described in detail. FIG. 13 is a block diagram illustrating an example of a watermark detection function according to the second embodiment. The information processing apparatus illustrated in FIG. 13 includes a feature amount extraction unit 201, a position detection code detection unit 202, a rearrangement parameter calculation unit 203, a restoration unit 204, a detection data generation unit 205, and a watermark information detection unit 206. And have.

  Note that the feature quantity extraction unit 201, the position detection code detection unit 202, the rearrangement parameter calculation unit 203, the restoration unit 204, the detection data generation unit 205, and the watermark information detection unit 206 are, for example, the control unit 10 And the main storage unit 20 as a work memory.

  The feature amount extraction unit 201 extracts a feature amount for watermark detection from the content in which the watermark information is embedded. The feature amount used depends on the watermark information embedding method. For example, when the pixel average value of the moving image is embedded in a triangular wave shape as in the first embodiment, the feature amount extraction unit 201 calculates a Fourier coefficient corresponding to the period of the triangular wave from the pixel average value of the moving image. The magnitude (absolute value) can be used as a feature amount. Note that the feature amount extraction unit 201 may convert the obtained Fourier coefficient into binary data “0” or “1” by threshold processing, and use this binary data as the feature amount.

  The position detection code detection unit 202 detects a position detection code representing the head position of each piece of watermark information. Assume that the position detection code is expressed by fixed binary data as shown in the watermark embedding process. In this case, the position detection code detection unit 202 performs pattern matching between the ideal feature amount when there is a position detection code and the feature amount obtained from the moving image, and detects the position detection code from the position where the matching value becomes large. can do.

  The rearrangement parameter calculation unit 203 calculates rearrangement parameters in which watermark information is rearranged in the watermark embedding process in each section delimited by the detected position detection code. For example, when the cyclic shift is used as the arrangement method, the rearrangement parameter calculation unit 203 may obtain the cyclic shift value as the rearrangement parameter.

  In order to obtain the cyclic shift value of each section as a rearrangement parameter, the rearrangement parameter calculation unit 203 calculates the feature amount of the section in which the watermark information is embedded in the first time and the feature amount of the current section. A correlation value is obtained from a sequence cyclically shifted by the value.

  This is because, when the cyclic shift value matches the cyclic shift value at the time of watermark embedding, the feature values at the respective positions in both sections match, and as a result, the correlation value becomes maximum. The rearrangement parameter calculation unit 203 uses the cyclic shift value that maximizes the correlation value as the rearrangement parameter. In addition, when a scramble method is used as an arrangement method, a value indicating which scramble method is used as a rearrangement parameter.

  The restoration unit 204 restores the position of the watermark information of each section rearranged at the time of embedding using the rearrangement parameter calculated by the rearrangement parameter calculation unit 203. When the rearrangement of the watermark information is realized by cyclic shift, the restoration unit 204 cyclically shifts the watermark information in the direction opposite to that at the time of embedding using the cyclic shift value obtained in each section. Do.

  The detection data generation unit 205 adds (majority decision) the feature amount of the watermark information of each section restored by the restoration unit 204 at the same position in repetition, and generates data for watermark detection.

  The watermark information detection unit 206 detects watermark information from the watermark detection data generated by the detection data generation unit 205. When the watermark information includes an error correction code or an error detection code, the accuracy and accuracy of watermark detection can be improved by using these codes.

<Outline of watermark detection>
Next, an outline of watermark detection in the second embodiment will be described. In the following example, an example in which a cyclic shift is used as an arrangement method will be described, but the arrangement method is not limited to a cyclic shift.

FIG. 14 is a diagram for explaining the calculation of the cyclic shift value. In the example shown in FIG. 14, a horizontally long rectangle on the right side of G [i], G ′ [i], and G ^* [i] represents a bit string of each code. The bit string is also called a code sequence.

In the example illustrated in FIG. 14, the rearrangement parameter calculation unit 203 obtains S [1] corresponding to the difference between the cyclic shift amounts of G ^* [0] and G [1] as the correlation value. As shown in FIG. 14, when the graph of the shift amount and the correlation value is viewed, a peak of the correlation value appears at the shift amount S [1].

The restoration unit 204 reversely shifts G [1] by S [1] to generate G ′ [1]. Then, rearrangement parameter calculation unit ^{203, G * [1] = G} * [0] + G ' Request ^G * [1] by [1].

As illustrated in FIG. 14, the rearrangement parameter calculation unit 203 generates the code sequence G ^* [N−1] in which G [i] is accumulated according to the peak position of the correlation value by repeating the above processing. be able to. Each element g ^* [N−1] [k] of G ^* [N−1] is obtained by adding bit information at the same position of the codeword before cyclic shift.

  The above watermark detection method is the same as the watermark detection method described in Japanese Patent Application Nos. 2010-294032 and 2011-261051 filed by the first inventor, for example. Refer to that for details of the watermark detection method in the second embodiment.

  Thereby, since the watermark information is embedded so that scenes that are difficult to detect do not overlap at the same position of the bits of the watermark information in the repetition, the detection accuracy of the watermark information is improved.

<Operation>
Next, the operation of the information processing apparatus according to the second embodiment will be described. FIG. 15 is a flowchart illustrating an example of a watermark detection process according to the second embodiment. In step S201 shown in FIG. 15, the feature amount extraction unit 201 extracts a feature amount for watermark detection from the content in which the watermark information is embedded. The feature amount used depends on the watermark information embedding method.

  In step S202, the position detection code detection unit 202 detects a position detection code representing the head position of each piece of watermark information.

  In step S203, the rearrangement parameter calculation unit 203 calculates rearrangement parameters in which watermark information is rearranged by watermark embedding processing in each section delimited by the detected position detection code. For example, when the cyclic shift is used as the arrangement method, the rearrangement parameter calculation unit 203 may obtain the cyclic shift value as the rearrangement parameter.

  In step S204, the restoration unit 204 restores the position of the watermark information of each section rearranged at the time of embedding using the rearrangement parameter calculated by the rearrangement parameter calculation unit 203. When the rearrangement of the watermark information is realized by cyclic shift, the restoration unit 204 cyclically shifts the watermark information in the direction opposite to that at the time of embedding using the cyclic shift value obtained in each section. Do.

  In step S <b> 205, the detection data generation unit 205 adds (majority decision) the feature amount of the watermark information of each section restored by the restoration unit 204 at the same position in the iteration to generate data for watermark detection.

  In step S206, the watermark information detection unit 206 detects watermark information from the watermark detection data generated by the detection data generation unit 205.

<Comparison between Example and Conventional Technology>
The detection accuracy of watermark information embedded in content by the watermark embedding method according to the disclosed embodiment will be described with reference to FIGS. 16 and 17. In the conventional technology, it is assumed that watermark information is repeatedly embedded in content without rearranging.

  FIG. 16 is a diagram illustrating an example of a watermark detection result of the prior art. In the example shown in FIG. 16, the watermark information is detected from the content in which the watermark information is repeatedly embedded in the prior art. FIG. 16A shows content in which watermark information is embedded. FIG. 16B shows feature amounts extracted from each section. FIG. 16C shows watermark information detected by majority from each feature quantity.

  First, the watermark feature amount of each time as shown in FIG. 16B is extracted from the content as shown in FIG. A portion indicated by P11 in FIG. 16B represents a region where it is difficult to detect a watermark. As shown in FIG. 16B, it can be seen that there is a portion where a region that is difficult to detect is overlapped in each repetition.

  When the watermark information is detected by majority vote from the feature values of each time shown in FIG. 16B, a detection result as shown in FIG. 16C is obtained. A portion indicated by P12 in FIG. 16C represents a portion with high detection reliability. A portion indicated by P13 in FIG. 16C represents a portion with low detection reliability. Even if the watermark information is detected by majority decision, the P13 portion occupies more than half of the P11 portion, so the reliability of the detected watermark information is lower than the P12 portion.

  FIG. 17 is a diagram illustrating an example of a watermark detection result according to the embodiment. In the example shown in FIG. 17, the watermark information is detected from the content in which the watermark information is repeatedly embedded in the embedding process of the first embodiment.

  As shown in FIG. 17, in the watermark embedding process according to the first embodiment, the arrangement of the watermark information is changed in advance as shown in FIG. 17A so that scenes that are difficult to detect the watermark do not overlap at the same position.

  FIG. 17A shows content in which watermark information is embedded. FIG. 17B shows feature amounts extracted from each section. FIG. 17C shows each feature amount restored to the original position. FIG. 17D shows watermark information detected by majority vote from each feature quantity after restoration.

  First, the watermark feature amount at each time as shown in FIG. 17B is extracted from the content as shown in FIG. Thereafter, as shown in FIG. 17C, the rearranged feature amounts are restored to their original positions. In this example, the rearrangement is a cyclic shift. At this time, in the second embodiment, after restoration of the bit position of the watermark information, the area of the scene P11 where it is difficult to detect the watermark is arranged so as not to overlap each time.

  As shown in FIG. 17D, watermark information is detected by deciding the majority of each restored feature quantity. Unlike the detection result of FIG. 16C, the detection result in FIG. 17D can be said to have high detection reliability at all positions.

  As a result, in the second embodiment, even if there is a location that is difficult to detect (P11 region), watermark information can be detected by majority decision of each feature amount, and the detection accuracy is improved.

  As described above, according to the second embodiment, it is possible to accurately detect the watermark information embedded by the watermark embedding process according to the first embodiment.

[Modification]
In addition, by recording a program for realizing the watermark embedding process and the watermark detection process described in each of the above-described embodiments on a recording medium, the computer performs the watermark embedding process and the watermark detection process in each embodiment. Can do. For example, the above-described watermark embedding process and watermark detection process can be realized by recording the program on a recording medium and causing the computer or portable device to read the recording medium on which the program is recorded.

  The recording medium is a recording medium for recording information optically, electrically or magnetically, such as a CD-ROM, flexible disk, magneto-optical disk, etc., and information is electrically recorded such as ROM, flash memory, etc. Various types of recording media such as a semiconductor memory can be used.

  The program executed by the information processing apparatus has a module configuration including each unit described in each embodiment. As actual hardware, for example, when the control unit 10 reads a program from the auxiliary storage unit 30 and executes it, one or more of the above-described units are loaded onto the main storage unit 20, and one or more of the units are It is generated on the main storage unit 20.

  Although the embodiments have been described in detail above, the invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope described in the claims. It is also possible to combine all or a plurality of the constituent elements of the above-described embodiments.

In addition, the following additional notes are disclosed regarding each of the above embodiments.
(Appendix 1)
For the content, calculate the degree of watermark detection difficulty for each section where watermark information is embedded,
Based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past, determine an arrangement parameter indicating a parameter for changing the arrangement of the watermark information,
Rearrange the watermark information according to the placement parameters;
A program for causing a computer to execute a process of embedding the rearranged watermark information in the section to be embedded.
(Appendix 2)
The program according to claim 1, wherein the degree of difficulty represents difficulty in detection when the watermark information is embedded.
(Appendix 3)
The process of determining the placement parameter includes:
The program according to claim 1 or 2, wherein the arrangement parameter is determined based on a correlation value between a difficulty level calculated in the section to be embedded and a cumulative value of the difficulty levels calculated in the past.
(Appendix 4)
When the arrangement parameter is a shift amount of a cyclic shift,
The process of determining the placement parameter includes:
The program according to supplementary note 3, wherein a correlation value between the difficulty calculated while shifting in the section to be embedded and the cumulative value is obtained, and a shift amount that minimizes the correlation value is determined.
(Appendix 5)
When the placement parameter indicates which scramble method among a plurality of scramble methods,
The process of determining the placement parameter includes:
The program according to supplementary note 3, wherein a correlation value between the degree of difficulty calculated while being scrambled by the plurality of scrambling methods in the section to be embedded and the cumulative value is obtained, and the scramble method having the smallest correlation value is determined.
(Appendix 6)
For the content, a calculation unit that calculates the difficulty level of watermark detection for each section in which watermark information is embedded;
A determination unit for determining an arrangement parameter indicating a parameter for changing the arrangement of the watermark information based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past;
A rearrangement unit that rearranges the watermark information according to the arrangement parameters;
An embedding unit that embeds the rearranged watermark information in the section to be embedded;
A watermark embedding device.
(Appendix 7)
For the content, calculate the degree of watermark detection difficulty for each section where watermark information is embedded,
Based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past, determine an arrangement parameter indicating a parameter for changing the arrangement of the watermark information,
Rearrange the watermark information according to the placement parameters;
A watermark embedding method in which a computer executes a process of embedding the rearranged watermark information in the section to be embedded.

DESCRIPTION OF SYMBOLS 1 Information processing apparatus 10 Control part 20 Main storage part 30 Auxiliary storage part 40 Communication part 50 Recording medium I / F part 101 Difficulty degree calculation part 102 Storage part 103 Arrangement parameter determination part 104 Relocation part 105 Embedding part 201 Feature quantity extraction part 202 position detection code detection unit 203 rearrangement parameter calculation unit 204 restoration unit 205 detection data generation unit 206 watermark information detection unit

Claims (7)

For the content, calculate the degree of watermark detection difficulty for each section where watermark information is embedded,
Based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past, determine an arrangement parameter indicating a parameter for changing the arrangement of the watermark information,
Rearrange the watermark information according to the placement parameters;
A program for causing a computer to execute a process of embedding the rearranged watermark information in the section to be embedded.   The program according to claim 1, wherein the degree of difficulty represents difficulty in detection when the watermark information is embedded. The process of determining the placement parameter includes:
The program according to claim 1 or 2, wherein the arrangement parameter is determined based on a correlation value between a difficulty level calculated in the section to be embedded and a cumulative value of the difficulty levels calculated in the past. When the arrangement parameter is a shift amount of a cyclic shift,
The process of determining the placement parameter includes:
The program according to claim 3, wherein a correlation value between the degree of difficulty calculated while cyclically shifting the watermark information in the section to be embedded and the cumulative value is obtained, and a shift amount that minimizes the correlation value is determined. When the placement parameter indicates which scramble method among a plurality of scramble methods,
The process of determining the placement parameter includes:
A correlation value between a difficulty level calculated while scrambling the watermark information by the plurality of scrambling methods in the section to be embedded and the cumulative value is obtained, and a scrambling method having the smallest correlation value is determined. 3. The program according to 3. For the content, a calculation unit that calculates the difficulty level of watermark detection for each section in which watermark information is embedded;
A determination unit for determining an arrangement parameter indicating a parameter for changing the arrangement of the watermark information based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past;
A rearrangement unit that rearranges the watermark information according to the arrangement parameters;
An embedding unit that embeds the rearranged watermark information in the section to be embedded;
A watermark embedding device. For the content, calculate the degree of watermark detection difficulty for each section where watermark information is embedded,
Based on the difficulty level calculated in the section to be embedded and the difficulty level calculated in the past, determine an arrangement parameter indicating a parameter for changing the arrangement of the watermark information,
Rearrange the watermark information according to the placement parameters;
A watermark embedding method in which a computer executes a process of embedding the rearranged watermark information in the section to be embedded.