JP2009076990A - Image processing method, image processing apparatus, image processing program and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method capable of more correctly determining falsification of image data, an image processing apparatus, and to provide an image processing program and a storage medium. <P>SOLUTION: The image processing method is used to determine whether image data having embedded gray-coded electronic watermark data of a predetermined bit length have been tampered. The processing method has: a means for extracting the electronic watermark data from the image data which are tampered or not tampered; and a comparison processing step for determining that the image data are not tampered at arbitrary one bit if the arbitrary one bits do not match to each other in comparison between the extracted electronic watermark data and the electronic watermark data of a predetermined bit length, and determining that the image data have been tampered if arbitrary two or more bits do not match. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing method, an image processing apparatus, an image processing program, and a recording medium.

  Conventionally, digital information can be easily copied by a computer or the like without being deteriorated, but conversely has a feature that it can be easily altered such as rewriting. For this reason, digital information is easily copied and reused without permission by simple processing and operations, or part of the digital information is easily altered so that it cannot be used for evidence photographs.

  Methods for preventing this include methods called digital watermarking and data hiding. The digital watermarking method is a method of adding information that cannot be seen when digital content such as a digital image is normally reproduced to the digital image.

The method of embedding a digital watermark can be broadly classified into the following two. That is,
(1) A method of directly embedding in a sample value of content data (2) A method of embedding in a frequency component, and a technique of embedding a digital watermark directly in a sample value of content data as in (1) is called a spatial domain type. A technique for embedding a digital watermark in a frequency component in a transform domain obtained by transforming image data such as discrete Fourier (DFT), discrete cosine (DCT), or discrete wavelet (DWT) as shown in FIG.

  In general, the spatial domain type (1) has an advantage that the watermark embedding process can be executed at a high speed because the conversion process is unnecessary, but the amount of information that can be embedded is small, and the image is embedded in an image in which a digital watermark is embedded. There is a drawback that the watermark is easily altered or lost when the processing is performed. On the other hand, the transform domain type (2) has the opposite characteristics to the spatial domain type.

  That is, in the space area type method (1), when processing such as processing or compression is performed, embedded data is easily lost, but processing is light. In the case of the spatial domain type (1), since the digital watermark is directly embedded in the sample value of the content data of the digital image, the digital image is subjected to processing such as processing, scaling, compression, etc. Influencing it will damage the watermark as it is.

  On the other hand, the conversion area type method (2) is strong in processing such as processing and compression, but has a characteristic that processing of embedding and extraction is heavy. In the case of the conversion area type (2), since the digital watermark is embedded in the frequency domain data obtained by converting the content data of the digital image into the frequency domain, a scaling process that does not change the contents of the image. There is an advantage that the digital watermark is not damaged by processing that does not affect the frequency of the image, such as processing that gives a slight change to each pixel.

  As described above, the digital watermarking method can be used to record copyright information, track illegal copy information, record IP address history, prevent illegal copying (invisible / highly resistant type), and prevent tampering (invisible / Low tolerance), authentication, secret communication, embedding digital content annotations and labels (visible / irreversible type, owner's display), and enabling watermark removal (visible / reversible type, content distribution).

  Among them, for example, as an application to a digital camera, there has been proposed a method in which a camera is provided with a mechanism for embedding a camera serial number and date / time in a photographed image and at the same time creating an electronic signature ( (See Non-Patent Documents 1 and 2). As a result, in addition to detection of alteration of the ID photo, it is possible to identify the shooting camera and check the shooting date and time. Tampering detection is possible only with the digital signature technology, but by using the watermark technology, it is possible to specify the shooting camera and the shooting date and time, and it works effectively by preventing tampering. Furthermore, by increasing the amount of information embedded in the digital watermark, the accuracy of specifying the falsification location is improved. In addition, if a lot of information can be embedded in the watermark for copyright protection, it becomes easier to extract the information when analyzing the embedded information, and the effectiveness becomes high.

  However, it is common on a daily basis to process the created digital content according to the intended use. In the case of digital content in which a digital watermark is embedded, the internal data changes, so there is no intention of falsification. Even if it is not, it is easy to judge that it has been altered.

  By the way, the human visual ability is biased rather than accepting the whole natural light as it is, so that information that does not affect the visual sense can be cut to reduce the amount of memory. In addition, in JPEG and the like, in which the result of frequency analysis of the pixel position and pixel value in the image (in the plane) is stored data, the high frequency information has a small amplitude (characteristic of natural image), and human vision Since the sensitivity is low, even if the stored information is limited to coarse information (represented by a small number of bits), the function is such that the visual effect is small when the image is restored. By cutting information that has little effect on the visual ability, strictly speaking, an image slightly different from the original image is obtained.

  Examples of such cases include image scaling, image compression, and other image modification processes (noise removal, dithering, edge enhancement, blurring process, etc.). In particular, complex image compression is described below.

  Monochrome digital copy, FAX, black and white printing of newspapers, etc. use black and white binary images, and the original images such as MH, MR, MMR are missing in the International Telecommunications Union (ITU-T) G3, G4 standards, etc. An image compression method that can be restored without loss (lossless) is recommended and generalized. However, in these methods, halftone processed images and error diffusion processed images have poor encoding efficiency, and in many cases cannot be compressed. A method for solving these problems has been attracting attention as an arithmetic coding method, which is a method of performing coding based on the entropy of an image. JBIG, a group that is studying an international standard for a new encoding scheme for binary images, employs an arithmetic encoding scheme called QM-Coder and is recommended as an ITU-T standard.

  Also, in products such as digital color images and multi-valued images such as grayscale images, digital still cameras and digital video cameras emphasize the compression effect at the time of storage at the expense of slight image quality degradation. This employs a compression technique that loses fine information of the original image such as JPEG and MPEG using frequency conversion by (lossy).

Furthermore, JPEG2000 is a successor standard of this JPEG, that is, unified encoding of Lossy encoding method and Loss-Less encoding method, and unified encoding method of binary data and multi-value data. JPEG2000 uses Wavelet transform to reduce image quality degradation during high compression, and similar to JBIG's QM-Coder, and applies MQ-Coder also adopted by JBIG2 to increase the compression rate. It is useful for.
Research report on digital watermarking technology, March 1999, edited by Japan Electronics Industry Promotion Association Nikkei Business, Prevention of Unauthorized Copying of Electronic Information, February 23, 1998 pp. 68-70 (1998)

  By the way, as described above, since digital content such as a digital image to be embedded with digital watermarks changes its internal data even if it is not intended to be altered due to image scaling, image compression, and other image modification processing. Easy to judge.

  However, since the conventional technique cannot accurately determine the difference between the change in the internal data and the alteration of the image data, the detection capability for the alteration in the image is weakened in any case of the internal data change, and sufficient There was a problem that the prevention function was not realized.

  The present invention has been invented in order to solve this problem in view of the above points, and provides an image processing method, an image processing apparatus, an image processing program, and a recording medium for more accurately determining falsification of image data. The purpose is to provide.

  In order to achieve the above object, an image processing method according to the present invention performs an image processing for determining whether or not image data embedded with gray-coded digital watermark data having a predetermined bit length has been falsified. A digital watermark data extracting means for extracting the digital watermark data from the image data that has been tampered with or not tampered with, the extracted digital watermark data, and the digital watermark data having a predetermined bit length. A comparison processing step of determining that no alteration has occurred according to the position of the arbitrary 1 bit when any 1 bit is inconsistent, and determining that there has been tampering when any 2 or more bits are inconsistent. It can be configured to have.

  In order to achieve the above object, in the comparison processing step of the present invention, in the comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, one bit of the least significant bit is inconsistent. In this case, it can be configured to determine that there is no tampering.

  In order to achieve the above object, in the comparison processing step according to the present invention, in the comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, the Nth bit from the least significant bit When 1 bit (where 2 ≦ N <bit length) does not match, the Nth bit from the least significant bit is the bit in both the extracted digital watermark data and the predetermined digital watermark data When ON and all of the (N−1) th to the least significant bits from the least significant bit are bits OFF, it can be determined that there is no tampering.

  In order to achieve the above object, in the comparison processing step according to the present invention, in the comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, one bit of the most significant bit is inconsistent. In the case of the above, in the extracted digital watermark data and the digital watermark data of the predetermined bit length, the second bit from the most significant bit is bit ON, and the third to the least significant bit from the most significant bit Can be configured to determine that no tampering has occurred.

  In order to achieve the above object, in the comparison processing step according to the present invention, in the comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, the upper plurality of digits are used as significant digits. It can be constituted as follows.

  In order to achieve the above object, the image processing apparatus according to the present invention performs determination processing as to whether or not image data embedded with gray-coded digital watermark data having a predetermined bit length has been falsified. An image processing apparatus, a digital watermark data extracting means for extracting the digital watermark data from the image data that has been tampered with or not tampered with, the digital watermark data that has been extracted, and a digital watermark having the predetermined bit length In comparison with data, if any one bit does not match, the comparison processing means determines that there is no falsification according to the position of any one bit, and determines that there is falsification if any two or more bits do not match It can comprise so that.

  In order to achieve the above object, the comparison processing means according to the present invention is configured such that one of the least significant bits does not match in the comparison between the extracted digital watermark data and the digital watermark data having a predetermined bit length. In this case, it can be configured to determine that there is no tampering.

  In order to achieve the above object, the comparison processing means according to the present invention is configured to compare the extracted digital watermark data and the digital watermark data having the predetermined bit length with the Nth bit from the least significant bit. When 1 bit (where 2 ≦ N <bit length) does not match, the Nth bit from the least significant bit is the bit in both the extracted digital watermark data and the predetermined digital watermark data When ON and all of the (N−1) th to the least significant bits from the least significant bit are bits OFF, it can be determined that there is no tampering.

  In order to achieve the above object, the comparison processing means according to the present invention is such that one bit of the most significant bit does not match in the comparison between the extracted digital watermark data and the digital watermark data having a predetermined bit length. In the case of the above, in the extracted digital watermark data and the digital watermark data of the predetermined bit length, the second bit from the most significant bit is bit ON, and the third to the least significant bit from the most significant bit Can be configured to determine that no tampering has occurred.

  In order to achieve the above object, the image processing program according to the present invention can be configured to be an image processing program for causing a computer to realize the above image processing method.

  In order to achieve the above object, the recording medium in the present invention can be configured to be a computer readable recording medium on which the above image processing program is recorded.

  According to the present invention, it is possible to provide an image processing method, an image processing apparatus, an image processing program, and a recording medium that more accurately determine falsification of image data.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Example of device configuration)
FIG. 1 is a diagram illustrating an example of an apparatus configuration of an image processing apparatus according to the present embodiment. In FIG. 1, as an example of an image processing apparatus according to the present embodiment, a code generation and analysis decoding apparatus that implements a digital image code (digital watermark embedding) generation and decoding (decoding digital watermark and detecting falsification) method. A configuration example is shown.

  In FIG. 1, an image processing apparatus 100 according to the present embodiment includes an overall control unit 1, an operation input (keyboard, mouse) unit 2, an external storage device 3, a memory 4, an image capturing unit 5, a display unit 6, and an external unit Data input unit 7, digital watermark embedding source data generation unit 8, gray (gray) encoding unit 9, digital watermark embedding unit 10, image reproduction unit 11, digital watermark decoding unit 12, (inverted) display of detected falsification unit The unit 13 and a bus 14 for connecting them are included. Note that an interface unit necessary between these units (or devices) and the bus 14 is not shown.

  The overall control unit 1 is a microcomputer (including a CPU, ROM, RAM, etc., but abbreviated as a CPU) that controls the operation and functions of the entire apparatus. The data input unit 7, the digital watermark embedding source data generation unit 8, the gray encoding unit 9, the digital watermark embedding unit 10, the image reproduction unit 11, the digital watermark decoding unit 12, and the (flip) display unit 13 of the detected falsification unit Each function can also be realized by software processing performed by the CPU based on an image processing program installed in the image processing apparatus 100.

  The operation input unit 2 is for inputting various operation instructions, function selection commands, editing data, and the like, and is a keyboard, a mouse, a touch panel, or the like. In particular, it is used as a secret key input function when encrypting image data in which electronic watermark data is embedded and when decrypting an encrypted electronic watermark.

  The operation input unit 2 further has a function as display selection means, and can change the display state of the display unit 6 described later to a display state desired by the operator. For example, the result of decrypting the digital watermark can be displayed superimposed on the input image image data by key operation, or only one of them can be selected and displayed.

  The external storage device 3 stores the image data captured by the image capturing unit 5, the compressed data embedded with the digital watermark by the digital watermark embedding unit 10, the data of the falsification detected by the digital watermark decoding unit 12, etc. FD) and a magneto-optical disk (OMD), etc., which are stored in a storage medium that can be taken out. The external storage device 3 also functions as a medium for recording program software executed by the overall control unit 1.

  The memory 4 is a large-capacity RAM or hard disk for storing image image data read by the image capturing unit 5, data temporarily stored with an electronic watermark embedded therein, image data read and expanded by the image reproduction unit 11, and the like. It is memory.

  The image photographing unit 5 is an image data input unit that scans a set photograph or form, reads the image, and inputs image image data. The image photographing unit 5 includes an image sensor such as a scanning optical system and a CCD, and a drive circuit thereof. These are known image scanners and digital cameras.

  The display unit 6 performs display on a display such as a touch panel. For example, the result of decoding by the digital watermark decoding unit 12 described later is displayed superimposed on the input image image data, or only one of them is displayed.

The external arbitrary data input unit 7 is means for inputting source information for embedding supplemental information in digital content as a digital watermark, and embedded information for tampering detection and copyright protection. The input data, to send the electronic watermark embedding for the source data generator 8 or Gray coding unit 9, Ru stored in the memory 4.

  The digital watermark embedding source data generation unit 8 encrypts or encodes data input from the external arbitrary data input unit 7 or data encoded by the Gray encoding unit 9. After processing, the data is stored in the memory 4 for transmission to the digital watermark embedding unit 10 or the gray encoding unit 9.

  The gray coding unit 9 performs gray coding by using the data input from the external arbitrary data input unit 7 or the data encrypted and encoded by the digital watermark embedding source data generation unit 8 as an input, and for embedding the digital watermark The data is stored in the memory 4 to be sent to the source data generation unit 8 or the digital watermark embedding unit 10.

  The digital watermark embedding unit 10 encrypts and encodes the data processed by the arbitrary data input unit 7 from the external data by the digital watermark embedding source data generation unit 8 or the gray encoding by the gray encoding unit 9. The data stored in the memory 4 is embedded as a digital watermark.

  The image reproduction unit 11 performs control for reading data stored in the external storage device 3 or the like after the digital watermark is embedded by the digital watermark embedding unit 10. The read image is stored in the memory 4.

  The digital watermark decrypting unit 12 embeds a digital watermark by the digital watermark embedding unit 10 stored in the memory 4, and decrypts the digital watermark from the image data reproduced by the image reproducing unit 11, and the possibility of decryption It is determined whether the falsification of the image and the copyright protection information are valid according to the restoration level by the gray code analysis.

  The detected (inverted) display unit 13 of the tampered portion has a function of displaying the corresponding region by inverting display or black-colored display when it can be determined that there is tampering as a result of decoding by the digital watermark decoding unit 12. Have.

  With the above apparatus configuration, in the image processing apparatus 100 according to the present embodiment, first, as a contrivance for catching tampering of image data sensitively, the source data of the digital watermark embedded in the image data is for digital watermark embedding. Generated by the source data generation unit 8 based on the image data. According to this method, even if either the digital watermark data generation source or the embedding destination is tampered with, the logical meaning does not match, so the probability of finding tampering increases. The source data of the digital watermark for embedding “generated based on the image data” mentioned here may be, for example, the pixel value itself or a value obtained by randomizing the pixel value. . In addition, as a value that hardly changes, for example, statistical data such as a pixel average value and a variance value of a small image area can be considered.

  Next, a contrivance point for preventing the deterioration of internal data due to image compression or image scaling from being falsified is that the embedded data (digital watermark data) is gray-coded. For example, the average value of the pixel values is as small as a minute error and does not change greatly if the block size of the image area is also changed. In addition, since this change changes not only the source data of the digital watermark to be embedded but also the data of the embedding destination, these two approximations are important. The reason why the embedded data is gray-coded is that the process of identifying the approximated data can be realized at high speed.

  In general, as a method of converting a decimal value into a Gray code, an exclusive OR is performed on a bit string in which a decimal number is represented by a binary code with a bit adjacent to an upper bit in order from the lower bit. The method is taken.

  The image processing apparatus 100 according to the present embodiment is characterized in that a change in image data is detected using a gray code, and a conversion method to a gray code is not particularly limited. Further, it goes without saying that any coding method can be applied to the present invention even if it is not a Gray code as long as the Hamming distance between codes adjacent to each other expressed as a Gray code is 1. .

(Function configuration example)
FIG. 2 is a block diagram illustrating an example of a functional configuration of the image processing apparatus according to the present embodiment. 2, an image processing apparatus 100 includes an image reading unit 101, a block dividing unit 102, an embedded data calculating unit 103, a gray code encoding unit 104, a watermark data embedding unit 105, an image output unit 106, and a watermark embedded image. A reading unit 111, a block division unit 112, a comparison data calculation unit 113, a gray code encoding unit 114, a comparison processing unit 115, and a result image output unit 116 are provided.

  The image reading unit 101 to the image output unit 106 in FIG. 2 are functions for the image processing apparatus 100 to perform processing for embedding a digital watermark into image data, and the watermark embedded image reading unit 111 to 11 in FIG. The result image output unit 116 is a function for the image processing apparatus 100 to perform a digital watermark reproducibility check (ie, falsification detection) process in the image data.

  A flow of processing that is a basic concept of digital watermark embedding processing and digital watermark reproducibility check processing will be described with reference to FIG.

  First, the digital watermark embedding process will be described.

  First, the image reading unit 101 reads target image data to be embedded with a digital watermark. Next, the block dividing unit 102 divides the image data read by the image reading unit 101 into blocks. Subsequently, the embedded data calculation unit 103 uses the image data divided by the block dividing unit 102 to perform the first half process for generating the digital watermark embedded data in units of blocks. Subsequently, the Gray code encoding unit 104 performs a second half process for generating digital watermark embedded data based on the embedded data calculated for each block by the embedded data calculating unit 103. Subsequently, the watermark data embedding unit 105 embeds a digital watermark in block units after the processing by the embedded data calculation unit 103 and the Gray code encoding unit 104. Finally, the image output unit 106 outputs image data obtained by performing digital watermark embedding processing on all blocks of the image.

  Next, digital watermark reproducibility check processing will be described.

  First, the watermark embedded image reading unit 111 reads image data in which a digital watermark is embedded. Next, the block division unit 112 divides the image data read by the watermark embedded image reading unit 111 into blocks. Subsequently, the comparison data calculation unit 113 generates digital watermark data by the same method as that for embedding in order to compare with the digital watermark embedding data on a block basis using the image data divided by the block division unit 112. The first half of the process is performed. Subsequently, the Gray code encoding unit 114 performs the latter half process for generating the digital watermark data by the same method as that for generating the digital watermark embedded data based on the comparison data calculated in block units by the comparison data calculation unit 113. Do. The comparison processing unit 115 checks the reproducibility of the digital watermark (that is, whether or not there is falsification) for each block after the processing by the comparison data calculation unit 113 and the Gray code encoding unit 114. Finally, the result image output unit 116 outputs the result of applying the digital watermark reproducibility check process to all blocks of the image.

  With the configuration of the functions described above, in the image processing apparatus 110 according to the present embodiment, the image reading unit 101 to the image output unit 106 perform processing for embedding a digital watermark into image data. In addition, the watermark embedded image reading unit 111 to the result image output unit 116 perform reproducibility check (that is, alteration detection) processing of the digital watermark in the image data. Detailed examples of these processes will be described with reference to FIGS.

(Example of digital watermark embedding process)
FIG. 3 is an example of a flowchart showing the digital watermark embedding process according to the present embodiment. Here, an example of the digital watermark embedding process performed by the image processing apparatus 110 will be described in detail with reference to FIGS. In FIG. 3, the encryption process is omitted. Also, processing such as error correction coding for making it difficult to break when embedded information is extracted at the time of embedding a digital watermark is omitted.

  First, a gray coding level value is set (S1). Here, the operation input unit 2 inputs a gray encoding level value (for example, 8 in the case of 8-bit encoding) based on a user key input or the like, and the input level value is a gray encoding level. It is set as a value and stored in the memory 4.

  In step S2, the image reading unit 101 reads image data to be embedded with the digital watermark (S2). Here, the image photographing unit 5 reads a subject to be embedded with a digital watermark as a multi-value image such as a full color and stores it in the memory 4.

  Proceeding to step S3, the block dividing unit 102 divides the image data to be embedded with the electronic watermark into blocks (S3). Here, the image data read in step S2 is divided into blocks (rectangular ((m × m) pixels: m is a power of 2)). The divided adjacent blocks may be partially overlapped or separated from each other. For the method of division and the method of overlapping, for example, the method described in JP-A-2003-204429 may be used.

  Proceeding to step S4, the embedded data calculation unit 103 performs initial setting of variables for performing the process of embedding a digital watermark (the process of steps S5 to S10) for each block divided in step S3 (S4). Here, the variables include an embedding data storage variable X for storing embedding data, a variable indicating the current processing block position of loop processing, and the number of currently processed blocks = 0.

  Subsequently, the process proceeds to step S5, and the embedded data calculation unit 103 determines whether or not the processing related to steps S7 to S10 for all the blocks divided in step S3 is completed (S5). Here, the determination is made by comparing the number of blocks divided in step S3 with the number of currently processed blocks, which is one of the variables set in step S4. Since specific variable setting and determination methods are known, they are omitted.

  If it is determined in step S5 that all the blocks have been processed (S5, YES), the process proceeds to step S6, and the image output unit 106 stores the image data in which the digital watermark is embedded in all the divided blocks. 4 or the external storage device 3 is stored and saved (or output) (S6). If it is determined in step S5 that all the blocks have not been processed (S5, NO), the process proceeds to step S7.

  When the process proceeds to step S7, the gray code encoding unit 104 performs gray encoding on the value of the embedded data storage variable X (S7). Here, the Gray code encoding unit 104 converts the embedded data storage variable X set in Step S4 or updated in Step S9 into a Gray code code based on the level value of Gray encoding set in Step S1. Turn into.

  A supplementary description will be given of the processing according to step S7 with reference to FIG. FIG. 4 is a diagram for explaining the relationship between divided blocks and information to be embedded (blocks on the information providing side and blocks on the information receiving and embedding side). When the series of iterative processes (steps S7 to S10) for the blocks divided in step S3 are performed from the leftmost block to the right, the digital watermark embedding process for the (n-1) -th block in FIG. Represents the embedding information and embedding destination when the digital watermark embedding process is performed on the nth block.

  For example, it is assumed that the gray encoding level value is set to 8 (= represents that the calculated value to be embedded is an 8-bit expression) in step S1. At this time, when the digital watermark is embedded in the nth block, the pixel average value of the (n-1) th block that has been embedded one before is 128 (decimal number, and the decimal number N is N ( The binary code is 10000000 (binary number, hereinafter, the binary number N is represented by N (2)). At this time, 11000000 (2) obtained by gray-coding this binary code is substituted into an embedding data storage variable (X ′) that is embedding data for the nth block.

  Subsequently, the process proceeds to step S8, where the watermark data embedding unit 105 embeds the digital watermark information, that is, the embedding data storage variable X ′ gray-coded in step S7, in the nth block (S8). In the step, the gray code data calculated in step 7 is embedded as a digital watermark of a block adjacent to the block (the block to be processed next to the loop process). There are many well-known methods for embedding values as digital watermarks, and details thereof are omitted. In addition, by repeating Step S7 and Step S8 described above, processing for embedding a digital watermark for each block is performed.

  Moving to step 9, the embedded data calculation unit 103 updates the embedded data storage variable X (S9). A value (pixel average value, variance value, etc.) calculated from the pixel data value after embedding the digital watermark in the block is substituted for X.

  In step S10, the embedded data calculation unit 103 updates the variable indicating the current processing block position and updates the current processing block number by 1 (S10), moves to step S5, and again for the next block. Performs digital watermark embedding processing.

  Through the processing described above, the image processing apparatus 100 according to the present embodiment performs processing for embedding a digital watermark into image data.

  Regarding the repetitive processing (steps S7 to S10), among the blocks created by dividing the image data, there is no previous block for the first processed block, so the gray to be embedded from the previous block. The sign cannot be obtained. Therefore, a predetermined value is set in the embedded data storage variable X as an initial value. Further, if it is not necessary to determine whether the first block is falsified, it may be omitted.

(Example of digital watermark reproducibility check processing)
FIG. 5 is an example of a flowchart showing a digital watermark reproducibility check (ie, alteration detection) process according to the present embodiment. Here, an example of a digital watermark reproducibility check process performed by the image processing apparatus 100 will be described in detail with reference to FIGS. In FIG. 5, the encryption process is omitted. In addition, processing for decoding error correction coding when the embedded information is error correction coded at the time of embedding the digital watermark is also omitted.

  First, a level value for reproducibility check is set (S31). Here, the operation input unit 2 inputs a level value (C_Level) (for example, 8 in the case of 8-bit encoding) of the reproducibility check based on a user key input or the like, and the input level value is the reproducibility. It is set as a check level value and stored in the memory 4. Note that it is necessary to set a value equal to or lower than the gray coding level value in step S1 of FIG.

  Proceeding to step S32, the watermark embedded image reading unit 111 reads the image data in which the digital watermark to be checked for reproducibility is embedded (S32). Here, the image photographing unit 5 reads the image data in which the digital watermark is embedded as a multi-value image such as a full color and stores it in the memory 4.

  Proceeding to step S33, the block division unit 112 divides the image data to be checked for reproducibility into rectangular blocks (S33). Here, it is necessary to be the same as the method of step S3 of FIG.

  Proceeding to step S34, the comparison data calculation unit 113 performs initial setting of variables for performing processing for checking the digital watermark embedded for each block divided at step S33 (processing of step S35 to step S43). (S34). Here, the variables include an extraction data storage variable Y for storing digital watermark extraction data for extracting a digital watermark, a variable indicating the current processing block position of loop processing, and the number of currently processed blocks = 0, etc. is there.

  Moving to Step S35, the comparison data calculation unit 113 determines whether or not the processing related to Step S37 to Step S43 for all the blocks divided in Step S33 has been completed (S35). Here, the determination is made by comparing the number of blocks divided in step S33 with the number of currently processed blocks which is one of the variables set in step S4. Since specific variable setting and determination methods are known, they are omitted.

  If it is determined in step S35 that all the blocks have been processed (S35, YES), the process proceeds to step S36, and the result image output unit 116 displays the result of analyzing the digital watermark for all the divided blocks. 13 (S36). Here, for example, the block positions determined to have been tampered with in step S41, which will be described later, and stored, are shown in reverse display or filled display. If it is determined in step S35 that all blocks have not been processed (S35, NO), the process proceeds to step S37.

  When the process proceeds to step S37, the gray code encoding unit 114 performs gray code encoding on the value of the digital watermark extraction data storage variable Y (S37). Here, the Gray code encoding unit 114 performs Gray code encoding on the digital watermark extraction data storage variable Y set in Step S34 or updated in Step S42. Note that the digital watermark extraction data storage variable Y subjected to Gray code encoding is stored in a digital watermark extraction data storage variable (Y ′ in this case).

  In step S31, it is assumed that the level value of the reproducibility check is set to 8 (= the calculated value at the time of digital watermark extraction is the same 8-bit representation as in the embedding process, indicating that all bits are valid). Further, it is assumed that 11000000 (2) is embedded in advance in the nth block as the embedded data storage variable X ′. Details are the same as step S7 in FIG.

  Subsequently, the process proceeds to step S38, and the comparison processing unit 115 performs processing for extracting digital watermark information from the block (S38).

  Moving to step 39, the comparison processing unit 115 checks the digital watermark extraction value (S39). Here, based on the level value of the reproducibility check set in step S31, the number of upper significant digits used for the check is determined, and within this range, data obtained by gray-coding the extraction data storage variable Y in step S37 And whether or not the digital watermark information extracted in step 38 has the same value, that is, whether or not the block is falsified.

  That is, the digital watermark information embedded in the n-th block by the digital watermark embedding process shown in FIG. 3 (that is, X ′) and the pixel value of the image data are used for embedding at the time of tampering check by the process in step S39. The extracted data storage variable Y calculated by the same method as the data storage variable X is compared with the gray encoded data Y ′ obtained by performing the gray encoding by the same method as that for embedding the digital watermark.

  At this time, first, it is assumed that the digital watermark information (that is, the above X ′) embedded in the nth block can be restored normally (an error correction code or the like may be used). Next, the pixel average value at the time of extracting the previous (n-1) th block is 127 (10) (the value different from the above 128 is embedded for some reason such as lossy compression processing or tampering) The binary code is 01111111 (2), which is gray-coded, 01000000 (2) is assigned to the digital watermark extraction data storage variable (here Y ') The Based on the above contents, comparing the digital watermark embedding information and the digital watermark extraction information is comparing X ′ and Y ′.

  Proceeding to step S40, the comparison processing unit 115 determines whether or not tampering has occurred by comparing the digital watermark embedded value with the digital watermark extraction value in step S39 (S40). In step S40, it is determined for each divided block whether or not tampering has occurred. As a result of comparison between the digital watermark embedding information X ′ and the digital watermark extraction information Y ′ in the effective number of digits determined in step 39, the two data are completely matched. If any one bit is inconsistent on the basis of a specific condition (see the specific examples described later and examples of how to use gray code data), the pixel value in the block is falsified. Judge that there is no. If any two or more bits do not match at the same time, it is determined that the pixel value in the block has been tampered with.

  If it is determined in step S40 that the image has not been tampered with (S40, YES), the process proceeds to step 42. If it is determined in step S40 that the block has been tampered with (S40, NO), the process proceeds to step 41, where it is assumed that the block has been tampered with, and the block position is stored in the memory 4 as a block to be tampered with.

  Moving to step 42, the comparison data calculation unit 113 updates the digital watermark extraction data storage variable Y (S42). A value (pixel average value, variance value, etc.) calculated from the pixel data value after digital watermark extraction in the block is substituted for Y.

  In step S43, the comparison data calculation unit 113 updates the variable indicating the current processing block position and updates the current processing block number by one (S43), moves to step S35, and electronically updates the next block. Perform watermark reproducibility check processing.

  Through the processing described above, the image processing apparatus 100 according to the present embodiment performs processing for checking the reproducibility of the digital watermark embedded in the image data.

  Regarding the repetitive processing (steps S35 to S43), among the blocks created by dividing the image data, there is no previous block for the first processed block, so the gray to be embedded from the previous block. The sign cannot be obtained. Therefore, a predetermined value is set in the electronic watermark extraction data storage variable Y as an initial value. Further, if it is not necessary to determine whether the first block is falsified, it may be omitted.

(Concrete example)
Hereinafter, a specific example of the process in step S40 of FIG. 5 will be described with reference to FIGS. FIG. 6 is a diagram for explaining a case where there is no alteration as a result of comparison of gray code data. FIG. 7 is a diagram for explaining a case where tampering occurs as a result of comparison of gray code data.

  Here, in the flowchart showing the digital watermark embedding process of FIG. 3, the gray encoding level value set in step S1 is 4 (bits), and the initial setting value of the embedding data storage variable X set in step S4 is A range of 0 to 15 that is an average value of luminance values of the immediately preceding processing block is used.

  At this time, when the average value of the luminance values of the (n−1) -th block is 12 (10), the gray-coded data is 1010 (2). That is, the digital watermark embedded in the nth block is 4-bit information of 1010 (2).

  The embedded watermark information may be, for example, the gray-encoded data, but may be encoded with a BCH code or a convolutional code that is resistant to error correction with a tolerance to avoid a slight deterioration in image quality. Also good. In that case, the number of embedded bits increases.

  Next, consider a case where internal data changes after embedding digital watermark information (FIG. 6). Here, image degradation will be described as an example. For example, it is assumed that the average value of the luminance values of the (n−1) -th block has changed to 11 (10) due to a slight deterioration (change) in image quality due to the lossy compression process immediately before storing the image data. . If the level value (C_Level) of the reproducibility check is set to 4 when extracting the embedded watermark information, the gray-coded data is 1110 (2), and the original value is a 1-bit value. However, since it can be judged that “this change is small”, it is possible to take measures that are not regarded as tampering.

  On the other hand, consider a case where image data has been tampered with after embedding digital watermark information (FIG. 7). For example, it is assumed that the average value of the luminance values of the (n−1) -th block is changed to 10 (10) after being tampered with after the image data is stored. If the level value (C_Level) of the reproducibility check is set to 4 when extracting the embedded digital watermark information, the gray-coded data becomes 1111 (2), and the original value is a 2-bit value. Therefore, it is understood that the change is larger than the change in image quality due to the compression process, and it becomes easy to recognize that the tampering has occurred.

  However, for example, when the embedded digital watermark information is extracted, if the level value (C_Level) of the reproducibility check is set to 3 (the scale of the processing range is changed from the above 4 bits to the upper 3 bits), the embedded watermark information is embedded. The digital watermark information is 101 (2), the digital watermark extraction information after the change due to the change of the internal data is 111 (2), and the digital watermark extraction information after the change due to the alteration of the image data is 111 (2). That is, the change due to the change in the internal data and the change due to the falsification of the image data have the same result, and are indistinguishable. In this way, by changing the number of bits used for the determination, it is possible to adjust how much change is considered to be falsified.

  As another example, the value obtained by receiving the digital watermark information X for embedding and embedding the digital watermark can be easily prevented from being deteriorated (changed) by the error correction code function. Even if a little occurs, if the image data degradation at the time of image compression does not appear as a change on the embedded information value generation side (luminance average value), the degradation level can be grasped as a difference of 1 bit, for example. it can.

(Example of how to use gray code data)
Next, a method for using gray encoded data in the processing according to step S40 in FIG. 5 will be described. In step S40 of FIG. 5 described above, it has been described that it is determined whether or not falsification has been made based on a comparison between the digital watermark embedding information X ′ and the digital watermark extraction information Y ′. Here, a method of using the gray coded data of the digital watermark embedding information X ′ and the digital watermark extraction information Y ′ will be described with reference to the flowchart of FIG.

  FIG. 8 is an example of a general-purpose flowchart for explaining the comparison process of gray code data. Here, a method of identifying whether two gray coded data X and Y having an arbitrary number of bits are the same value, whether the difference in decimal numbers is 1, or whether the difference in decimal numbers is 2 or more. To express.

  First, the exclusive OR operation result of X and Y is set to Z (S51). Subsequently, based on Z calculated in step S51, the number U of bit values 1 in Z and the position V of bit value 1 in Z are calculated (S52). Here, Z calculated in step S51 is examined in bit units in order from the least significant bit, and the position where bit 1 is found for the first time is taken as V. For example, V = 0 when the least significant bit is 1, and V = 1 when the least significant bit is 0 and the second least significant bit (lowest neighbor) is 1. At the same time, the number of bits 1 is counted as U. For example, if Z = 00010100 bits, U = 2 and V = 2. Since the calculation methods of U and V are known, the description thereof is omitted. Thereafter, in the processing after step S53, X and Y are compared based on the calculation result in step S52.

  Moving to step S53, it is determined whether or not U = 0 (S53). Here, it is determined whether X and Y are the same. If U = 0 (S53, YES), the process moves to step S54 and X = Y is determined (S54). If U = 0 is not satisfied (S53, NO), the process proceeds to step S55.

  When the process proceeds to step S55, it is determined whether or not U> 1 (S55). If U> 1 (S55, YES), the process moves to step S56, and it is determined that the distance (difference) between X and Y is 2 (10) or more (S56). If U <1 (S55, NO), the process proceeds to step S57.

  When the process proceeds to step S57, it is determined whether or not V = 0 (S57). If V = 0 (S57, YES), the process moves to step S58, and the distance (difference) between X and Y is determined to be 1 (10) (S58). If V = 0 is not satisfied (S57, NO), the process proceeds to step S59.

  When the process proceeds to step S59, the gray encoded data X is examined bit by bit from the least significant bit, and the position where bit 1 is found for the first time is defined as Xb. Further, the gray encoded data Y is examined in bit units in order from the least significant bit, and the position where bit 1 is found for the first time is defined as Yb (S59). Since the process according to step S59 is the same as the process when calculating V in step S52, the description thereof is omitted here.

  Subsequently, the process proceeds to step S60, and it is determined whether Xb = Yb and V = Xb + 1 are satisfied (S60). If Xb = Yb and V = Xb + 1 (S60, YES), the process moves to step S58, and the distance (difference) between X and Y is determined to be 1 (10). When Xb = Yb and V = Xb + 1 is not satisfied (S60, NO), the process proceeds to step S56, and it is determined that the distance (difference) between X and Y is 2 (10) or more.

  Through the processing described above, in the image processing apparatus 100 according to the present embodiment, the two gray encoded data X and Y having an arbitrary number of bits have the same value, the difference in decimal numbers is 1, or 10 It identifies whether the difference in the decimal number is 2 or more.

  A specific example will be described with reference to FIGS. 9, 10, and 11, where Gray encoded data X and Y are 4 bits, 3 bits, and 2 bits, respectively. First, the case where the gray encoded data X and Y are 4 bits will be described. Next, a general N bit case will be described with reference to a case where X and Y are 4 bits. Finally, the case where X and Y are 3 bits and 2 bits will be described. In addition, the flowchart shown in FIG. 8 has shown the process in the case of a general purpose N bit.

(When gray coded data X and Y are 4 bits)
FIG. 9 is a diagram for explaining an XOR operation result when the gray code data is expressed in 4 bits. Each of the horizontal and vertical axes in FIG. 9 indicates X and Y expressed in 4 bits, and each element in FIG. 9 indicates an exclusive OR (XOR operation value) value of X and Y. Has been.

  At this time, referring to FIG. 9, the XOR operation value of adjacent gray code data values (with a distance of 1) (for example, X = 0000 (2), Y = 0001 (2)) is only a predetermined 1 bit. On (1 or “true”), bit OFF (0 or “false”) is calculated for other cases (underlined numbers in FIG. 9). In addition, the XOR operation value (for example, X = 0000 (2), Y = 0011 (2)) with the gray code data value next to another (distance is 2) is the bit ON only for the predetermined 2 bits. In other cases, bit OFF is calculated (framed numbers in FIG. 9).

  This property makes it possible to use the following Gray code data. Here, all the embedded data is assumed to be gray code data.

  (A) On the number of gradation levels, the process for discriminating whether there is a mismatch with the adjacent value or a mismatch with a value slightly larger than the adjacent value is simple (XOR between the correct value and the extracted embedded value) If the number of bit ONs in the calculation result is 1, the value is the adjacent value, and if it is 2, the value can be determined as the adjacent value.

  (B) In the process of bit-decomposing the source data and embedding the watermark, “Even if any one bit is degraded after embedding the digital watermark, it is effective, but when any two bits are degraded at the same time, I want to invalidate it.” In this case, a simple process (XOR operation between the correct value and the extracted embedded value is performed, and if the number of bit ONs of the operation result is 1 or less, the extracted value is valid, and if it is 2, the extracted value can be determined invalid) realizable.

  The utilization method of the Gray code data shown in the above (A) and (B) becomes possible. However, as indicated by the encircled numbers in FIG. 9, there is one bit ON in the calculation result, but the gray code data X and Y as the calculation source are not adjacent values (distance is 1). There is something. It is necessary to distinguish these from the XOR operation result of adjacent values (that is, the underlined numbers in FIG. 9). The identification method is performed as follows.

In the case where the gray code data is 4 bits, as in the underlined numbers and circled numbers in FIG. 8, the case where one bit ON exists in the operation result is 0001 bits, 0010 bits, 0100 bits, 1000 There are four types of bits. Therefore, when analyzed in each case, the following results (1) to (4) are obtained.
(1) For 0001 bit:
All correspond to underlined numbers (in the example of FIG. 9, for example, [X, Y] = [0000 (2), 0001 (2)], etc.).
(2) For the 0010 bit:
(2-A) When the least significant bit of the gray encoded data X is bit ON (X = ??? 1 (2), “?” Is 1 bit and can be either 0 or 1), all Corresponds to underlined numbers (in the example of FIG. 9, for example, [X, Y] = [0001 (2), 0011 (2)], etc.).

(2-B) When the least significant bit of the gray encoded data X is bit OFF (X = ??? 0 (2)), all correspond to the circled numbers (in the example of FIG. 9, for example, [X , Y] = [0000 (2), 0010 (2)], etc.).
(3) For 0100 bits:
(3-A) When the second least significant bit of gray encoded data X is bit ON and the least significant bit is OFF (X = ?? 10 (2)), all correspond to underlined numbers. (In the example of FIG. 9, for example, [X, Y] = [0010 (2), 0110 (2)]).

(3-B) When other than (3-A) above (X = ?? ** (2), "**" is any 2 bits other than "10"), all correspond to circled numbers (In the example of FIG. 9, for example, [X, Y] = [0000 (2), 0100 (2)]).
(4) For 1000 bits:
(4-A) When the third least significant bit of gray encoded data X is bit ON, and both the least significant and second least significant bit are bit OFF (X =? 100 (2)) , All correspond to underlined numbers (in the example of FIG. 9, [X, Y] = [0100 (2), 1100 (2)]).

  (4-B) In cases other than the above (4-A), all correspond to the circled numbers (in the example of FIG. 9, for example, [X, Y] = [0000 (2), 1000 (2)], etc. 7 ways).

  From the results of (1) to (4) above, when the Gray code data is 4 bits, among the 32 (= 8 + 4 + 4 + 2 + 6 + 1 + 7) ways in which one bit ON exists in the operation result, There are 15 (= 8 + 4 + 2 + 1) numbers (underlined numbers), that is, 15/32 = about 47%.

(When gray coded data X and Y are N bits)
From the above, the case where the Gray code data X and Y are expressed in N bits is as follows. As described above, the flowchart shown in FIG. 8 shows general-purpose processing when the Gray code data X and Y are expressed in N bits.
(1) From the analysis of Z (Z = XxorY), which is an exclusive OR operation result between the Gray code data X and Y, (2) the following is determined. Here, 'xor' is an exclusive OR operator.
(2) The following determination is performed on the bit data of the Gray code data Z calculated in (1) above.
(2-1) If the number of bits ON is 0, X = Y is considered.
(2-2) When the number of bit ON is 1, the contents of (3) are as follows.
(2-3) When the number of bits ON is 2 or more, the difference between the values represented by the Gray code data X and Y is considered to be 2 or more.
(3) When the number of bit ONs of the Gray code data Z calculated in (1) is 1, there are N types of bit ON positions (00... 001 (2), 00. ... 010 (2), ..., 10 ... 000 (2)). These are organized as follows.

(3-1) When the least significant bit is 1:
It can be seen that all the numbers correspond to underlined numbers, and the difference between the values of the gray code data X and Y is 1 (10).

(3-2) When the second least significant bit is 1:
(3-2-A) When the gray coded data X and Y are both combinations in which the least significant bit is the bit ON, they all correspond to underlined numbers. That is, X and Y are a combination of the least significant bit and the second least significant bit being 1, the least significant bit being 1 and the second least significant bit being 0 (assignment of X and Y is arbitrary) Yes, the code content existing in the underlined numbers (the difference between the values represented by the Gray code data X and Y is 1). For example, gray codes “1011 (2)” and “1001 (2)” represent 13 (10) and 14 (10), respectively, and the difference is 1 (10).

    (3-2-B) When the gray encoded data X and Y are both combinations in which the least significant bit is bit OFF, they all correspond to the circled numbers (the difference between the values represented by X and Y is 2 or more). That is, the gray coded data X and Y are a combination of numerical values (X is the least significant bit is 0 and the second least significant bit is 1, and the least significant bit is 0 and the second least significant bit is 0 (X , Y is arbitrary), which is a code corresponding to a circled number. For example, the Gray code “1010 (2)” and “1000 (2)” bits represent 12 (10) and 15 (10), respectively, and the difference is 3 in decimal notation.

(3-3) When the Nth bit (N ≧ 3) from the least significant bit is 1 (not including the case where the most significant bit is 1):
(3-3-A) In the gray coded data X and Y, the Nth bit from the least significant bit is ON, and all the (N-1) th to least significant bits from the least significant bit are OFF. In the case of the combination, all correspond to underlined numbers (the difference between the values represented by the Gray code data X and Y is 1). That is, the gray encoded data X and Y are a combination of “? →? 010-- → 0 (2)” and “? →? 110-- → 0 (2)” (assignment of X and Y is arbitrary). Yes, the code content corresponding to the underlined number (the difference between the values represented by the Gray codes X and Y is 1 (10)). For example, gray codes “0010 (2)” and “0110 (2)” with N = 3 represent 3 (10) and 4 (10), respectively, and the difference is 1 (10).

    (3-3-B) When other than the above (3-3-A), it corresponds to a circled number (the difference between the values represented by the Gray codes X and Y is 2 or more). That is, Gray code data X and Y are a combination of “? →? 0 *-→ * (2)” and “? →? 1 *-→ * (2)” (assignment of X and Y is arbitrary) The code content corresponds to a circled number. For example, gray codes “1001 (2)” and “1101 (2)” with N = 3 represent 14 (10) and 9 (10), respectively, and the difference is 5 (10).

(3-4) When the most significant bit is 1:
(3-4-A) In the gray encoded data X and Y, both the most significant (second) bit is bit ON, and all the third to least significant bits counted from the most significant bit are OFF. In the case of combinations, the code contents corresponding to the underlined numbers are all (the difference between the values represented by the Gray codes X and Y is 1 (10)). That is, the gray encoded data X and Y are a combination of “010... → 0 (2)” and “110... → 0 (2)” (assignment of X and Y is arbitrary) and corresponds to an underlined number. The code content (the difference between the values represented by the Gray codes X and Y is 1 (10)). For example, gray codes “0100 (2)” and “1100 (2)” represent 7 (10) and 8 (10), respectively, and the difference is 1 (10).

    (3-4-B) When other than (3-4-A), it corresponds to a circled number (the difference between the values represented by the Gray codes X and Y is 2 or more). That is, Gray code data X and Y are a combination of “0 *-→ * (2)” and “1 *-→ * (2)” (assignment of X and Y is optional), The code content corresponding to. For example, gray codes “0111 (2)” and “1111 (2)” represent 5 (10) and 10 (10), respectively, and the difference is 5 (10).

  The flow chart shown in FIG. 8 summarizes the processing in the case where the Gray code data X and Y described above are represented by N bits.

(When gray coded data X and Y are 3 bits)
FIG. 10 is a diagram for explaining an XOR operation result when the gray code data is expressed in 3 bits. Each of the horizontal axis and the vertical axis in FIG. 10 indicates X and Y expressed in 3 bits, and each element in FIG. 10 indicates an exclusive OR (XOR operation value) value of X and Y. Has been.

  Here, for example, an operation result focusing on only the upper 3 bits of FIG. 9 is shown.

  At this time, as shown in FIG. 10, the XOR operation value of adjacent gray code data values (with a distance of 1) (for example, X = 000 (2), Y = 001 (2)) is only a predetermined one bit. On (1 or “true”), bit OFF (0 or “false”) is calculated otherwise (underlined numbers in FIG. 10). In addition, the XOR operation value (for example, X = 000 (2), Y = 011 (2)) with the gray code data value next to another (distance is 2) is the bit ON when only the predetermined 2 bits are ON. In other cases, bit OFF is calculated (framed numbers in FIG. 10).

  This property makes it possible to use the gray code data described above. Here, all the embedded data is assumed to be gray code data. However, as indicated by the encircled numbers in FIG. 10, there is one bit ON in the calculation result, but the gray code data X and Y as the calculation source are not adjacent values (distance is 1). There is something. It is necessary to distinguish these from the XOR operation result of adjacent values (that is, the underlined numbers in FIG. 10). The identification method is performed in the same manner as in the case where the gray encoded data X and Y are N bits.

  As in the case of underlined numbers and circled numbers in FIG. 10, when the Gray code data is 3 bits, the case where one bit ON exists in the operation result is 001 bits, 010 bits, 100 bits 3 There are types. The description will be made by applying (3) in the description of the case where the gray encoded data X and Y are N bits.

(1) When the least significant bit is 1 (here, 001 bit):
It can be seen that all of the numbers are underlined numbers and the difference between the values of the gray code data X and Y is 1 (10) (in the example of FIG. 10, for example, [X, Y] = [000 ( 2), 001 (2)], etc.).
(2) When the second least significant bit is 1 (here, 010 bits):
(2-A) When the gray encoded data X and Y are both combinations in which the least significant bit is the bit ON, they all correspond to underlined numbers (in the example of FIG. 10, for example, [X, Y] = [001 ( 2), 011 (2)], etc.).

(2-B) When the gray coded data X and Y are both combinations in which the least significant bit is bit OFF, they all correspond to circled numbers (in the example of FIG. 10, for example, [X, Y] = [000 ( 2), 010 (2)], etc.).
(3) is not considered here.
(4) When the most significant bit is 1 (100 bits here):
(4-A) Gray coded data X and Y are combinations in which the most significant next (second) bit is bit ON, and the third to least significant bits counted from the most significant bit are all bit OFF. All correspond to underlined numbers (in the example of FIG. 10, [X, Y] = [010 (2), 110 (2)]).

  (4-B) Other than the above (4-A), it corresponds to a circled number (in the example of FIG. 10, for example, three types such as [X, Y] = [011 (2), 111 (2)]) ).

  From the results of (1) to (4) above, when the gray code data is 3 bits, there are 12 (= 4 + 2 + 2 ++ 1 + 3) ways in which one bit ON exists in the operation result, There are 7 (= 4 + 2 + 1) numerical values (underlined numbers), that is, 7/12 = about 58%.

(When gray coded data X and Y are 2 bits)
FIG. 11 is a diagram for explaining an XOR operation result when the gray code data is expressed in 2 bits. In each of the horizontal axis and the vertical axis in FIG. 11, X and Y expressed by 2 bits are shown, and each element in the figure shows an exclusive OR (XOR operation value) value of X and Y. Has been.

  Here, for example, the calculation result focusing on only the upper 2 bits of FIG. 10 is shown.

  At this time, as shown in FIG. 11, the XOR operation value of adjacent gray code data values (with a distance of 1) (for example, X = 00 (2), Y = 01 (2)) is a bit of only one predetermined bit. On (1 or “true”), bit OFF (0 or “false”) is calculated otherwise (underlined numbers in FIG. 11). In addition, the XOR operation value (for example, X = 00 (2), Y = 11 (2)) with the gray code data value next to another (distance is 2) is the bit ON only for the predetermined 2 bits. In other cases, bit OFF is calculated (framed numbers in FIG. 11).

  This property makes it possible to use the gray code data described above. Here, all the embedded data is assumed to be gray code data. However, as indicated by the encircled numbers in FIG. 11, there is one bit ON in the calculation result, but the gray code data X and Y as the calculation source are not adjacent values (distance is 1). There is something. It is necessary to distinguish these from the XOR operation result of adjacent values (that is, the underlined numbers in FIG. 10). The identification method is performed in the same manner as in the case where the gray encoded data X and Y are N bits.

  As in the underlined numbers and circled numbers in FIG. 11, when the Gray code data is 2 bits, there are two cases of one bit ON in the operation result, 01 bits and 10 bits. The description will be made by applying (3) in the description of the case where the gray encoded data X and Y are N bits.

(1) When the least significant bit is 1 (here, 01 bit):
It can be seen that all of the numbers are underlined numbers and the difference between the values of the gray code data X and Y is 1 (10) (in the example of FIG. 11, for example, [X, Y] = [00 ( 2), 01 (2)], etc.).
(2) and (3) are not considered here.
(4) When the most significant bit is 1 (here 10 bits):
(4-A) Gray coded data X and Y are combinations in which the most significant next (second) bit is bit ON, and the third to least significant bits counted from the most significant bit are all bit OFF. All correspond to underlined numbers (in the example of FIG. 11, [X, Y] = [01 (2), 11 (2)], etc.).

  (4-B) When other than the above (4-A), it corresponds to a circled number (in the example of FIG. 11, [X, Y] = [00 (2), 10 (2)], etc.) .

  From the results of (1) to (4) above, when the gray code data is 2 bits, among the 4 (= 2 + 1 + 1) ways in which one bit ON exists in the operation result, There are 3 (= 2 + 1) numerical values (underlined numbers), that is, 3/4 = 75%.

(Other)
As described above, the number of values representing the degree (gradation) such as density values using the same source data is reduced (the lower digits are discarded and only the upper digits are left. For example, if the lower 1 bit is reduced, the number of gradations is reduced to 1/2. However, on each tone number level, it is simple to identify whether it is a discrepancy with the adjacent value or a discrepancy with a value slightly larger than the adjoining value.

  This property makes it possible to use the following Gray code data. Here, all the embedded data is assumed to be gray code data.

  (A). When fuzziness is to be expressed in the data to be watermark-embedded based on the data representing the degree such as the density value, the data representing the degree is preliminarily embedded with the maximum accuracy source information → gray code. In the process of extracting embedded information, the level classification for determining the validity of degraded data corresponds to the classification of the number of digits to be validated from the upper digits of the data at the time of watermark embedding.

  (B). If the source data to be embedded is encrypted or otherwise encoded and then embedded by Gray encoding, the source information → Gray As in the case of directly embedding the code data, in the process of extracting the embedded gray code data, the data from the upper digits of the data at the time of watermark embedding is used for leveling to determine the effectiveness of the degraded data. It corresponds by how to divide the number of digits.

  As described above, the present invention has been described based on the embodiments, but the present invention is not limited to the requirements shown here, such as combinations with other elements listed in the above embodiments. With respect to these points, the present invention can be changed within a range that does not detract from the gist of the present invention, and can be appropriately determined according to the application form.

It is a figure which shows an example of the apparatus structure of the image processing apparatus which concerns on this embodiment. It is a block diagram which shows an example of a function structure of the image processing apparatus which concerns on this embodiment. It is an example of the flowchart which shows the digital watermark embedding process which concerns on this embodiment. It is a figure for demonstrating the relationship between the divided | segmented block and the information to embed. It is an example of the flowchart which shows the digital watermark reproducibility check process which concerns on this embodiment. It is a figure for demonstrating the case where there is no falsification as a comparison result of gray code data. It is a figure for demonstrating the case where there exists falsification as a comparison result of gray code data. It is an example of the general purpose flowchart for demonstrating the comparison process of gray code data. It is a figure for demonstrating the XOR operation result in case Gray code data is 4-bit expression. It is a figure for demonstrating the XOR operation result in case Gray code data is 3 bits expression. It is a figure for demonstrating the XOR operation result in case Gray code data is 2 bits expression.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Overall control part 2 Operation input part 3 External storage device 4 Memory 5 Image pick-up part 6 Display part 7 Arbitrary arbitrary data input part 8 Digital watermark embedding source data generation part 9 Gray (gray) encoding part 10 Electronic watermark embedding Unit 11 image reproduction unit 12 digital watermark decoding unit 13 detected (inverted) display unit 14 of detected falsification unit bus

Claims (11)

An image processing method for determining whether or not image data embedded with gray-coded digital watermark data of a predetermined bit length has been falsified,
A digital watermark data extraction step of extracting the digital watermark data from the image data that has been altered or not altered;
In the comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, if any one bit does not match, it is determined that there is no falsification according to the position of the arbitrary one bit, A comparison processing step for determining when two or more bits do not match;
An image processing method characterized by comprising: In the comparison process step,
The comparison between the extracted digital watermark data and the digital watermark data having the predetermined bit length determines that no alteration has been made when one least significant bit does not match. Image processing method. In the comparison process step,
In comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, when the Nth 1 bit (2 ≦ N <bit length) from the least significant bit does not match, In both the extracted digital watermark data and the digital watermark data of the predetermined bit length, the Nth bit from the least significant bit is bit ON, and the (N−1) th to least significant bits from the least significant bit are The image processing method according to claim 1, wherein if all bits are OFF, it is determined that there is no tampering. In the comparison process step,
In the comparison between the extracted watermark data and the digital watermark data having the predetermined bit length, if one most significant bit does not match, the extracted watermark data and the predetermined bit length electronic The watermark data is determined not to be tampered when the second most significant bit is bit ON and the third to least significant bits from the most significant bit are all bit OFF. The image processing method according to any one of claims 1 to 3. In the comparison processing step,
5. The image processing according to claim 1, wherein, in the comparison between the extracted digital watermark data and the digital watermark data having the predetermined bit length, upper digits are set as significant digits. Method. An image processing apparatus that performs a determination process of whether or not image data in which digital watermark data having a predetermined bit length that has been gray-coded is embedded has been tampered with,
Digital watermark data extraction means for extracting the digital watermark data from the image data that has been tampered with or not tampered with;
In the comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, if any one bit does not match, it is determined that there is no falsification according to the position of the arbitrary one bit, A comparison processing means for determining that tampering has occurred when two or more bits do not match;
An image processing apparatus characterized by comprising: The comparison processing means includes
The comparison between the extracted digital watermark data and the digital watermark data having the predetermined bit length determines that no alteration has been made if one least significant bit does not match. Image processing apparatus. The comparison processing means includes
In comparison between the extracted digital watermark data and the digital watermark data of the predetermined bit length, when the Nth 1 bit (2 ≦ N <bit length) from the least significant bit does not match, In both the extracted digital watermark data and the digital watermark data of the predetermined bit length, the Nth bit from the least significant bit is bit ON, and the (N−1) th to least significant bits from the least significant bit are The image processing apparatus according to claim 6, wherein when all bits are OFF, it is determined that there is no falsification. The comparison processing means includes
In the comparison between the extracted watermark data and the digital watermark data having the predetermined bit length, if one most significant bit does not match, the extracted watermark data and the predetermined bit length electronic The watermark data is determined not to be tampered when the second most significant bit is bit ON and the third to least significant bits from the most significant bit are all bit OFF. The image processing apparatus according to any one of 6 to 8.   An image processing program for causing a computer to realize the image processing method according to any one of claims 1 to 5.   A computer-readable recording medium on which the image processing program according to claim 10 is recorded.

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