JP4662367B2 - Information symbol encoding method and apparatus, information symbol decoding method and decoding apparatus - Google Patents

Description

  The present invention relates to an information symbol encoding method and apparatus, and an information symbol decoding method and apparatus, and more particularly to an encoding method and apparatus for encoding information symbols arranged in a two-dimensional frequency space, and The present invention relates to a decoding method and apparatus for decoding information symbols arranged in a two-dimensional frequency space.

  A method of displaying a barcode on a printed matter or a homepage, photographing the barcode with a camera, and obtaining data such as a URL based on the photographed barcode is widely used. The code will reduce the appearance of printed materials and websites.

  In order to solve such a problem, a method of inserting a digital watermark representing data into an image has been proposed. If this method is used, data can be obtained from the captured image, so that a barcode is not necessary.

As an invention relating to such a method, the insertion device sets a data pattern at a position to be combined by insertion data among an enlargement / reduction ratio detection pattern, a rotation angle detection pattern, and candidate positions, and reverses all patterns together. The Fourier transform is performed, the image obtained by the transform is added to the original image, and the detection device divides the image into blocks, Fourier transforms the data of each block to obtain the amplitude of each frequency component of each block, and each frequency Add component amplitude between blocks to obtain total amplitude for each frequency, detect image enlargement / reduction ratio with enlargement / reduction ratio detection pattern, detect rotation angle of image with rotation angle detection pattern, Data is detected based on a combination of positions of a predetermined number of total amplitudes that indicate a relatively large value among the total amplitudes at which the enlargement / reduction ratio and rotation angle are corrected and that are at candidate positions. There is an invention (see, for example, Patent Document 1). In the present invention, particularly when an image is taken with a camera, the scale of the image is changed and the image is rotated. In order to solve the problem that the image cannot be detected, a digital watermark for detecting the enlargement / reduction ratio and rotation angle of the image is embedded in the image.
JP 2004-15396 A

  According to the invention described in Patent Document 1, the possibility that data is erroneously detected is reduced by setting a data pattern at a position that is combined with insertion data among candidate positions. May be sufficient. For example, if data is erroneously detected, content that has nothing to do with the image taken by the user may be provided, which may reduce the trust of the organization that operates the content provision.

  Therefore, the present invention provides an information symbol encoding method and apparatus, an information symbol decoding method, and an information symbol decoding method capable of reducing the possibility that data inserted in the form of a digital watermark is erroneously detected. An object of the present invention is to provide a decoding device.

  According to the first aspect of the present invention, an intermediate inspection value calculation step for obtaining an intermediate inspection value by performing a predetermined operation on a numerical value represented by a plurality of information symbols; An intermediate symbol generation step represented by a symbol, an error codeword generation step of generating an error correction codeword by adding a check symbol to the plurality of intermediate symbols, and outputting the plurality of information symbols and the error correction codeword And an output step. An encoding method is provided.

  According to a second aspect of the present invention, in the encoding method according to the first aspect of the present invention, in the intermediate check value calculation step, the plurality of information symbols are weighted to represent a numerical value represented by an N-ary number. Encoding characterized in that it is treated as a bit, and the numerical value is divided by a numerical value for obtaining a plurality of intermediate symbols constituting the error correction codeword, and a remainder obtained by the division is used as the intermediate check value A method is provided.

  According to a third aspect of the present invention, in the encoding method according to the first aspect of the present invention, in the intermediate check value calculation step, a hash function is obtained by applying a hash function to the plurality of information symbols. Is provided as the intermediate check value.

  According to a fourth aspect of the present invention, in the encoding method according to the first aspect of the present invention, in the output step, an odd number of three or more information symbols are output in an overlapping manner. Is provided.

  According to a fifth aspect of the present invention, in the encoding method according to the first aspect of the present invention, the information symbol, the intermediate symbol, and the check symbol are binary symbols, and the information symbol has a value of 1 In the output step, each of a predetermined number of information symbols with a value of 1 is output as one data so that the number of data with a value of 1 is a fixed number, and the error An encoding method is provided that outputs each intermediate symbol and each check symbol included in the correction codeword as a pair of data having complementary data values.

  According to a sixth aspect of the present invention, the plurality of information symbols that are output by the encoding method according to the first aspect of the present invention and that may have been added with errors in the transmission path, and the first of the present invention An input step of inputting the error correction codeword that is output by the encoding method according to the above aspect and that may have been added with an error in a transmission path, and performing error correction processing on the error correction codeword, An error correction step for obtaining a plurality of decoded intermediate symbols; a first intermediate check value calculating step for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols; and the plurality of information symbols. A second intermediate check value calculating step for obtaining a second decoded intermediate check value by performing the predetermined operation on the numerical value, the first decoded intermediate check value and the second decoded intermediate check Comparing the door, when both do not match, the decoding method characterized by comprising the steps of: determining that the remaining error is provided.

  According to a seventh aspect of the present invention, the plurality of information symbols output by the encoding method according to the second aspect of the present invention and possibly including an error added in the transmission path, and the second of the present invention An input step of inputting the error correction codeword that is output by the encoding method according to the above-mentioned viewpoint and that may have been added with an error in a transmission path, and performing error correction processing on the error correction codeword, An error correction step for obtaining a plurality of decoded intermediate symbols; a first intermediate check value calculating step for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols; and the plurality of information symbols. A second intermediate check value calculating step for obtaining a second decoded intermediate check value by performing the predetermined operation on the numerical value, the first decoded intermediate check value and the second decoded intermediate check And in the case where the two do not coincide with each other, it is determined that an error remains. In the second intermediate check value calculation step, each of the plurality of information symbols is represented by an N-ary number. The numerical value is divided by a numerical value for obtaining a plurality of intermediate symbols constituting the error correction codeword, and the remainder obtained by the division is decoded by the second decoding A decoding method is provided that is characterized by an intermediate check value.

  According to an eighth aspect of the present invention, the plurality of information symbols that are output by the encoding method according to the third aspect of the present invention and that may have been added with errors in the transmission path, and the third aspect of the present invention. An input step of inputting the error correction codeword that is output by the encoding method according to the above aspect and that may have been added with an error in a transmission path, and performing error correction processing on the error correction codeword, An error correction step for obtaining a plurality of decoded intermediate symbols; a first intermediate check value calculating step for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols; and the plurality of information symbols. A second intermediate check value calculating step for obtaining a second decoded intermediate check value by performing the predetermined operation on the numerical value, the first decoded intermediate check value and the second decoded intermediate check And in the case where the two do not match, the step of determining that an error remains is included. In the second intermediate check value calculation step, a hash function is applied to the plurality of information symbols. A decryption method is provided in which the hash value obtained thereby is used as the intermediate check value.

  According to a ninth aspect of the present invention, the plurality of information symbols that are output by the encoding method according to the fourth aspect of the present invention and that may have been added with errors in the transmission path, and the fourth aspect of the present invention. An input step of inputting the error correction codeword that is output by the encoding method according to the above aspect and that may have been added with an error in a transmission path, and performing error correction processing on the error correction codeword, An error correction step for obtaining a plurality of decoded intermediate symbols, a first residue calculation step for obtaining a first decoded residue based on the plurality of decoded intermediate symbols, and error correction by majority vote for the information symbols A majority step and a second residue calculation step for obtaining a second decoded residue by performing division on a numerical value represented by the plurality of information symbols error-corrected by the majority vote. And comparing the first decoding residue and the second decoding residue and determining that there is an error if they do not match, A decoding method is provided.

  According to a tenth aspect of the present invention, the plurality of information symbols output by the encoding method according to the fifth aspect of the present invention and possibly including an error added in the transmission path, and the fifth aspect of the present invention An input step of inputting data representing the error correction codeword that may have been added with an error in the transmission path, and a data having a single value among the input data If the number is not the fixed number, an error ending step for ending the process in error, an error correction step for obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword, A first residue calculating step for obtaining a first decoded residue based on the decoded intermediate symbols, and dividing the numerical values represented by the plurality of information symbols into a second recovery A second residue calculating step for obtaining a residue, and a step of comparing the first decoding residue and the second decoding residue and determining that an error remains if they do not match. And a decoding method characterized by comprising:

  In the decoding method according to any one of the sixth to tenth aspects of the present invention, the error correction step may further include an error ending step for ending the processing in error when error correction cannot be performed. Good.

  According to the present invention, it is possible to reduce as much as possible the possibility of erroneously detecting data inserted in the form of a digital watermark. If there is a possibility of erroneous detection, a detection error is assumed. Then, the user can start again from taking an image, and as a result, there is a possibility that data can be detected correctly next time.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

[Embodiment 1]
In the present embodiment, the digital watermark insertion device inserts a digital watermark corresponding to the ID into the original image.

  There are a total of 38 information bits representing ID, which are A-1 to A6, B1 to B6, C1 to C6, D1 to D6, E1 to E6, F1 to F6, G1 and G2. As shown in FIG. 1, one information bit corresponds to three points on a semicircle in the frequency space (for example, points 0, 1, and 0 of circle 7 for information bit A-1). 2 corresponds). When the value of the information bit is 1, all three points have a predetermined value (data is 1 value), and when the value of the information bit is zero, the amplitude of all three points is zero. It is.

  Also, a total of 38 information bits are divided into two groups. For example, the information bits belonging to the first group are 19 information bits of A1 to A3, B1 to B3, C1 to C3, D1 to D3, E1 to E3, F1 to F3 and G1, and the second group The information bits belonging to are 19 bits of A4 to A6, B4 to B6, C4 to C6, D4 to D6, E4 to E6, F4 to F6 and G2.

  Four intermediate bits belonging to the first group are generated based on the 19 information bits belonging to the first group. Then, by adding three check bits to the four intermediate bits, a first Hamming codeword having 1 error correction and 2 error detection capabilities is generated.

  Similarly, four intermediate bits belonging to the second group are generated based on 19 information bits belonging to the second group. Then, by adding three check bits to the four intermediate bits, a second Hamming codeword having 1 error correction and 2 error detection capabilities is generated.

  In FIG. 1, points within the frame of C 1-1 to C 1-7 are points corresponding to the first Hamming codeword. Two points in each frame correspond to each bit of the first Hamming codeword. For example, two points in the frame of Ha 1-1 correspond to the first intermediate bit of the first Hamming codeword, and two points in the frame of Ha 1-2 are the first Hamming. The two points corresponding to the second intermediate bit of the codeword and within the frame of C1-3 correspond to the third intermediate bit of the first Hamming codeword and are within the frame of C1-4. Two points correspond to the fourth intermediate bit of the first Hamming codeword, and two points within the frame of Ha-1-5 correspond to the first check bit of the first Hamming codeword The two points in the frame 1-6 correspond to the second check bits of the first Hamming codeword, and the two points in the frame 1-7 are the first Hamming Corresponds to the third check bit of the codeword.

  The two points within each frame have complementary values. For example, if the value of the first intermediate bit of the first Hamming codeword is zero, the value of the first point of the two points in the frame c 1-1 is zero, while the other The value of the point is a predetermined value (data is a value of 1). On the other hand, when the value of the first intermediate bit of the first Hamming codeword is 1, the value of the first point of the two points in the frame c 1-1 is a predetermined value (data is 1) and the value of the other point is zero. The same applies to other points.

  In FIG. 1, points within the frames of C2-1 to C2-7 correspond to the second Hamming codeword. Two points in each frame correspond to each bit of the second Hamming codeword. For example, two points within the frame of Ha 2-1 correspond to the first intermediate bit of the second Hamming codeword, and two points within the frame of Ha 2-2 are the second Hamming code. The two points corresponding to the second intermediate bit of the word and in the frame of C2-3 correspond to the second intermediate bit of the second Hamming codeword and the two points in the frame of C2-4 The point corresponds to the fourth intermediate bit of the second Hamming codeword, and the two points within the frame of Ha-2-5 correspond to the first check bit of the second Hamming codeword, The two points within the -6 frame correspond to the second check bit of the second Hamming codeword, and the two points within the frame 2-7 correspond to the second Hamming codeword. Corresponds to 3 check bits.

  The two points within each frame have complementary values. For example, when the value of the first intermediate bit of the second Hamming codeword is zero, the value of the first point out of the two points in the frame c 2-1 is zero, The value of the point is a predetermined value (data is a value of 1). On the other hand, when the value of the first intermediate bit of the second Hamming codeword is 1, the value of the first point of the two points in the frame c 2-1 is a predetermined value (data is 1 The value of the other point is zero. The same applies to other points.

  Next, a method for generating intermediate bits from information bits and further generating a Hamming codeword will be described.

  N information bits are represented as follows.

x _N-1 ,... x ₃ , x ₂ , x ₁ , x ₀
In this case, the numerical value that is the basis of the intermediate bit is expressed as follows.

y = MOD ((x _N-2 × 2 ^N-2 +... + x ₂ × 2 ² + x ₀ × 2 ⁰ ) / 16)
z = MOD ((x _N-1 × 2 ^N-1 +... + x ₃ × 2 ³ + x ₁ × 2 ¹ ) / 16)
That is, every other bit is divided into group 1 and group, and for each group, the total value of the values obtained by multiplying each bit by a power of 2 is taken, and the remainder obtained by dividing this by 16 is used as the base of the intermediate bits. It becomes the numerical value. Here, the power value is the bit number of each bit of each group. Since the base of the intermediate bits and the numerical value that is the numerical value is the remainder of division by 16 (= 2 ⁴ ), it can be expressed in binary as 4 bits as shown below.

y = y ₃ × 2 ³ + y ₂ × 2 ² + y ₁ × 2 ¹ + y ₀ × 2 ⁰
z = z ₃ × 2 ³ + z ₂ × 2 ² + z ₁ × 2 ¹ + z ₀ × 2 ⁰
The first intermediate bits are y ₃ , y ₂ , y ₁ , y ₀ . The second intermediate bits are z ₃ , z ₂ , z ₁ , z ₀ . On the other hand, by adding check bits p ₁ , p ₂ , p ₃ , q ₁ , q ₂ , q ₃ by a predetermined generator polynomial, the first Hamming codeword (y ₃ , y ₂ , y ₁ , y _{0, p 1, p 2,} p 3)
Second Hamming codeword (z ₃ , z ₂ , z ₁ , z ₀ , q ₁ , q ₂ , q ₃ )
Get.

Referring to FIG. 1, for the first group, intermediate bit y ₃ corresponds to frame c 1-1, intermediate bit y ₂ corresponds to frame c 1-2, and intermediate bit y ₁ corresponds to frame c 1 -3, intermediate bit y ₀ corresponds to frame c 1-4, check bit p ₁ corresponds to frame c 1-5, and check bit p ₂ corresponds to frame c 1-6. , check bit _{p 3} corresponds to Wakuha 1-7.

Similarly, for the second group, intermediate bit z ₃ corresponds to frame c 2-1, intermediate bit z ₂ corresponds to frame c 2-2, and intermediate bit z ₁ corresponds to frame c 2-3. The intermediate bit z ₀ corresponds to frame c 2-4, the check bit q ₁ corresponds to frame c 2-5, the check bit q ₂ corresponds to frame c 2-6, and the check bit q ₃ corresponds to Wakuha 2-7.

  Next, a digital watermark insertion apparatus that inserts a digital watermark corresponding to an ID into an original image will be described with reference to FIG. Note that the digital watermark insertion apparatus shown in FIG. 2 can be configured by hardware, software, or a combination thereof.

  Referring to FIG. 2, the ID input unit 11 inputs an ID. For example, the ID corresponds to a URL or represents identification information of a related image.

The information bit generation unit 13 generates information bits based on the ID. Referring to FIG. 1, since a group of three points corresponds to one information bit, there are 6 information bits for circle 2, 6 information bits for circle 3, For 4 there are 6 information bits, for circle 5 there are 6 information bits, for circle 6 there are 6 information bits, for circle 7 there are 8 information bits. The In each circle, the number of information bits whose value is 1 is equal to the number of information bits whose value is zero. Thus, possible values of ID _{becomes ^{(6 C 3) 5 × 8}} C 4 = 224000000 ways.

  The overlapping point generator 15 generates three points for one information bit. However, the number of points may be an odd number such as 5 or 7 in addition to 3. Specifically, for circles 2-6, 6 × 3 = 18 points are generated for 6 information bits, respectively, and for circle 7, 8 information bits are generated. 8 × 3 = 24 points are generated. If the value of the information bit is 1, the amplitude of the point is a predetermined value, and if the value of the information bit is zero, the amplitude of the point is zero.

  The intermediate bit generation unit 17 generates intermediate bits based on the information bits by the method described above.

  The check bit generation unit 19 generates a check bit of a Hamming codeword using a predetermined generator polynomial based on the intermediate bit, and outputs a Hamming codeword composed of the intermediate bit and the check bit.

  The complementary point generator 21 generates two complementary points for each intermediate bit and each check bit. If the value of the intermediate bit or check bit is zero, the value of one of the corresponding complementary points is zero and the other value is a predetermined value. On the other hand, if the value of the intermediate bit or the check bit is 1, one of the complementary points corresponding thereto is a predetermined value, and the other value is zero.

  The correction point generation unit 23 performs the rotation angle detection and enlargement / reduction ratio detection points (11 points of the circle 1, points 3 and 16 of the circle 3, points 3 and 6 of the circle 6 shown in FIG. ) Is generated.

  The synthesizer 25 adds the points from the overlapping point generator 15, the complementary point generator 21, and the correction point generator 23 in the two-dimensional frequency space. Specifically, a frequency component of a predetermined level is arranged at a point where the data value is 1 in the two-dimensional frequency space.

  The inverse Fourier transform unit 27 performs inverse Fourier transform on the output of the synthesis unit 25. The number of points in the inverse Fourier transform may be equal to the number of points in the original image, but may be smaller than the original image and the same pattern may be continuous. For example, if the size of the original image is 2048 × 2048, the size of the inverse Fourier transform may be 2048 × 2048, but for example, 128 × 128, and 16 patterns of 128 × 128 are continuously arranged vertically and horizontally, You may make it cover the area | region of 2048x2048.

  The adding unit 31 adds the output from the inverse Fourier transform unit 27 to the original image input by the image input unit 29 to generate a digital watermarked image.

  Next, an error detection and correction method will be described with reference to FIGS. 3, 4, and 5. FIG. Note that the digital watermark detection apparatus shown in FIG. 3 can be configured by hardware, software, or a combination thereof.

  First, the Fourier transform unit 51 performs a Fourier transform on the read image (step S101). Next, the absolute value calculation part 53 calculates | requires the absolute value of each frequency component (step S103). Next, the correcting unit 55 corrects the rotation angle and the scale using the rotation angle detection point and the enlargement / reduction ratio detection point (step S105).

  Next, the point detection part 57 detects whether the value of each point is zero or 1 (step S107). For this detection, a window is provided at a point where a signal having a level equal to or higher than the threshold may be embedded (a point where the data value may be 1), and out of the frequency components that have passed through the window. It is assumed that the value of a predetermined number of points in descending order of the level among points whose absolute value level is equal to or greater than the threshold value is 1. If the number of points whose absolute value level is greater than or equal to the threshold value among the frequency components that have passed through the window does not reach the predetermined number, the threshold value is lowered and the absolute value level of the frequency component that has passed through the window is greater than or equal to the threshold The number of points reaches a predetermined number, but if the number of points whose absolute value level is equal to or greater than the threshold value among the frequency components that have passed through the window does not reach the predetermined number even if it is lowered to a certain level, control is performed. The unit 67 sets an error flag and ends the error.

  In the example of FIG. 1, there are 18 points in the circle 2, but a signal having a level at which half of the nine points are equal to or greater than the threshold is embedded. For example, if the number of points whose absolute value level is equal to or greater than the threshold among the points that have passed through the window is 10, it is assumed that 1 is embedded in the nine points in descending order of the absolute value level.

  Similarly, although there are 20 points in the circle 3, a signal having a level at which half of the 10 points is equal to or higher than the threshold value is embedded. For example, if the number of points whose absolute value level is equal to or greater than the threshold among the points that have passed through the window is 12, it is assumed that 1 is embedded in the 10 points in descending order of the absolute value level.

  Similarly, although there are 22 points in the circle 4, a signal having a level at which 11 points of the half are equal to or higher than the threshold is embedded. For example, if the number of points whose absolute value level is equal to or greater than the threshold among the points passing through the window is 12, 1 is embedded in 11 points in descending order of the absolute value level.

  Returning to FIG. 4, as described above, when the value of each point cannot be detected (NO in step S109), the control unit 67 sets an error flag and ends the error. The case where the value of each point cannot be detected is, for example, the case where a predetermined number of points that are equal to or greater than the threshold cannot be detected even if the threshold is lowered to some extent.

  Next, the majority decision unit 59 makes a majority decision based on the points generated by the overlapping point generation unit 15, and sets the result as the value of the information bit (step S111). For example, the value of one information bit is determined based on the points 0, 1, and 2 of the circle 2, but if the value of zero or one of the three points is 1, the value of the information bit If the value of two or three points is 1, the value of the information bit is 1.

  Next, the error correction unit 61 attempts error correction for each of the two Hamming codewords (step S113). If error correction cannot be performed (when there are two or more errors) (NO in step S115), an error flag is set and the process ends with an error.

  Next, the score checking unit 63 checks whether or not the number of information bits whose data value is 1 is correct (step S117). Specifically, it is confirmed whether the number of information bits having a data value of 1 in circles 2 to 6 is 3 and the number of information bits having a data value of 1 in circle 7 is 4 or not. . If not correct (NO in step S117), the process ends in error.

  Next, the first residue calculation unit 65 calculates the first residue using the result of hamming decoding (error correction) by the error correction unit 61 (step S119).

Specifically, the decoded first Hamming codeword is (y ′ ₃ , y ′ ₂ , y ′ ₁ , y ′ ₀ , p ′ ₁ , p ′ ₂ , p ′ ₃ ).
As a decoded second Hamming codeword (z ′ ₃ , z ′ ₂ , z ′ ₁ , z ′ ₀ , q ′ ₁ , q ′ ₂ , q ′ ₃ )
In this case, the first remainders y ′ and z ′ are obtained by the following equation.

y ′ = y ′ ₃ × 2 ³ + y ′ ₂ × 2 ² + y ′ ₁ × 2 ¹ + y ′ ₀ × 2 ⁰
z ′ = z ′ ₃ × 2 ³ + z ′ ₂ × 2 ² + z ′ ₁ × 2 ¹ + z ′ ₀ × 2 ⁰
Next, the second remainder calculation unit 67 calculates the second remainder using the result of majority decision (error correction) by the majority decision unit 59 (step S121).

  Specifically, the second remainders y ″ and z ″ are obtained by the following equations.

y ″ = MOD ((x ′ _N−2 × 2 ^N−2 +... + x ′ ₂ × 2 ² + x ′ ₀ × 2 ⁰ ) / 16)
z ″ = MOD ((x ′ _N−1 × 2 ^N−1 +... + x ′ ₃ × 2 ³ + x ′ ₁ × 2 ¹ ) / 16)
However, x ′ is the result of majority vote.

  Next, the control unit 71 checks whether or not the first remainder and the second remainder are equal (step S123).

  Specifically, it is checked whether the first remainder y ′ and the second remainder y ″ are equal and the first remainder z ′ and the second remainder z ″ are equal.

  The fact that at least one of the above two conditions is not satisfied indicates that at least one erroneous correction has been performed. Therefore, in such a case, an error flag is set and the error ends (NO in step S123).

  If the above two conditions are both satisfied (YES in step S123), ID is detected using the result of majority decision (step S125).

[Embodiment 2]
In the first embodiment, intermediate bits are generated by using the binary bits as they are. On the other hand, in the second embodiment, binary-decimal conversion is performed to generate intermediate bits based on the numerical value of each decimal digit.

That is,
X = x _N-1 × 2 ^N-1 + ... + x ₂ × 2 ² + x ₀ × 2 ⁰
= Q _M-1 × 10 ^M-1 +... + Q ₂ × 10 ² + q ₀ × 10 ⁰
Q _{M−1 to} q ₀ are obtained, and based on these, the numerical value that is the basis of the intermediate bit is obtained by the following equation.

y = MOD ((q _M-2 × 10 ^M-2 +... + q ₂ × 10 ² + q ₀ × 10 ⁰ ) / 16)
z = MOD ((q _M-1 × 10 ^M-1 +... + q ₃ × 10 ³ + q ₁ × 10 ¹ ) / 16)
Next, the numerical values y and z are expressed in binary numbers as follows, and the bits representing the binary numbers are intermediate bits.

y = y ₃ × 2 ³ + y ₂ × 2 ² + y ₁ × 2 ¹ + y ₀ × 2 ⁰
z = z ₃ × 2 ³ + z ₂ × 2 ² + z ₁ × 2 ¹ + z ₀ × 2 ⁰
Therefore, the first Hamming codeword is
(Y ₃ , y ₂ , y ₁ , y ₀ , p ₁ , p ₂ , p ₃ )
And the second Hamming codeword is
(Z ₃ , z ₂ , z ₁ , z ₀ , q ₁ , q ₂ , q ₃ )
It becomes.

The decoded first Hamming codeword is (y ′ ₃ , y ′ ₂ , y ′ ₁ , y ′ ₀ , p ′ ₁ , p ′ ₂ , p ′ ₃ )
As a decoded second Hamming codeword (z ′ ₃ , z ′ ₂ , z ′ ₁ , z ′ ₀ , q ′ ₁ , q ′ ₂ , q ′ ₃ )
In this case, the first remainders y ′ and z ′ are obtained by the following equation.

y ′ = y ′ ₃ × 2 ³ + y ′ ₂ × 2 ² + y ′ ₁ × 2 ¹ + y ′ ₀ × 2 ⁰
z ′ = z ′ ₃ × 2 ³ + z ′ ₂ × 2 ² + z ′ ₁ × 2 ¹ + z ′ ₀ × 2 ⁰
Further, the second remainders y ″ and z ″ are obtained by the following equations.

y ″ = MOD ((q ′ _M−2 × 10 ^M−2 +... + q ′ ₂ × 10 ² + q ′ ₀ × 10 ⁰ ) / 16)
z ″ = MOD ((q ′ _M−1 × 10 ^M−1 +... + q ′ ₃ × 10 ³ + q ′ ₁ × 10 ¹ ) / 16)
[Embodiment 3]
In the first embodiment, the numerical value that is the basis of the intermediate bit is obtained by the following equation.

y = MOD ((x _N-2 × 2 ^N-2 +... + x ₂ × 2 ² + x ₀ × 2 ⁰ ) / 16)
z = MOD ((x _N-1 × 2 ^N-1 +... + x ₃ × 2 ³ + x ₁ × 2 ¹ ) / 16)
In the second embodiment, the numerical value that is the basis of the intermediate bit is obtained by the following equation.

y = MOD ((q _M-2 × 10 ^M-2 +... + q ₂ × 10 ² + q ₀ × 10 ⁰ ) / 16)
z = MOD ((q _M-1 × 10 ^M-1 +... + q ₃ × 10 ³ + q ₁ × 10 ¹ ) / 16)
That is, in the first embodiment and the second embodiment, the numerical values that are the bases of two series of intermediate bits are obtained using the numerical values of the skipped digits while maintaining the weight of each digit.

  On the other hand, the third embodiment is similar to the first embodiment and the second embodiment in that the numerical value that is the basis of two series of intermediate bits is obtained using the numerical value of the skipped digits. Are consecutive. That is, in the third embodiment, a numerical value that is the basis of the intermediate bit is obtained by the following equation.

X = x _N-1 × 2 ^N-1 + ... + x ₂ × 2 ² + x ₀ × 2 ⁰
= Q _2L-1 × 10 ^2L-1 + ... + q ₂ × 10 ² + q ₀ × 10 ⁰
y = MOD ((q _2L−2 × 10 ^L−1 +... + q ₂ × 10 ¹ + q ₀ × 10 ⁰ ) / 16)
z = MOD ((q _2L-1 × 10 ^L-1 +... + q ₃ × 10 ¹ + q ₁ × 10 ¹ ) / 16)
Next, the numerical values y and z are expressed in binary numbers as follows, and the bits representing the binary numbers are intermediate bits.

y = y ₃ × 2 ³ + y ₂ × 2 ² + y ₁ × 2 ¹ + y ₀ × 2 ⁰
z = z ₃ × 2 ³ + z ₂ × 2 ² + z ₁ × 2 ¹ + z ₀ × 2 ⁰
Therefore, the first Hamming codeword is
(Y ₃ , y ₂ , y ₁ , y ₀ , p ₁ , p ₂ , p ₃ )
And the second Hamming codeword is
(Z ₃ , z ₂ , z ₁ , z ₀ , q ₁ , q ₂ , q ₃ )
It becomes.

The decoded first Hamming codeword is (y ′ ₃ , y ′ ₂ , y ′ ₁ , y ′ ₀ , p ′ ₁ , p ′ ₂ , p ′ ₃ )
As a decoded second Hamming codeword (z ′ ₃ , z ′ ₂ , z ′ ₁ , z ′ ₀ , q ′ ₁ , q ′ ₂ , q ′ ₃ )
In this case, the first remainders y ′ and z ′ are obtained by the following equation.

y ′ = y ′ ₃ × 2 ³ + y ′ ₂ × 2 ² + y ′ ₁ × 2 ¹ + y ′ ₀ × 2 ⁰
z ′ = z ′ ₃ × 2 ³ + z ′ ₂ × 2 ² + z ′ ₁ × 2 ¹ + z ′ ₀ × 2 ⁰
Further, the second remainders y ″ and z ″ are obtained by the following equations.

y ″ = MOD ((q ′ _2L−2 × 10 ^L−1 +... + q ′ ₂ × 10 ¹ + q ′ ₀ × 10 ⁰ ) / 16)
z ″ = MOD ((q ′ _2L−1 × 10 ^L−1 +... + q ′ ₃ × 10 ¹ + q ′ ₁ × 10 ¹ ) / 16)
[Embodiment 4]
In the first embodiment, the second embodiment, and the third embodiment, a plurality of circles are provided in the two-dimensional frequency space, and in each circle, a predetermined number n of points where the data value can be 1 is determined, and the data value is actually The number of points to be 1 was also a predetermined number m (<n). A frequency component having a predetermined non-zero amplitude is arranged at a point where the data value is 1. By doing this, after performing Fourier transform, rotation angle, enlargement / reduction ratio correction, and amplitude calculation on the image taken by the camera, a predetermined number of frequency components in a predetermined position on the circle in descending order of amplitude. The points were detected, and the ID could be restored by the pattern formed by those points.

  In the fourth embodiment, a point where the data value can be 1 is set at a predetermined position by a predetermined number n, and the number of points where the data value is actually 1 is also a predetermined number m (<n). Common to the second embodiment and the second embodiment. However, in the fourth embodiment, the position of a point where the data value can be 1 is not a position on the circle. For example, n1 × n2 (= n) positions are defined in a lattice shape, and m (<n1 × n2) points among them are points where the data value is 1. Even in this case, after performing the Fourier transform, the rotation angle, the enlargement / reduction ratio correction, and the amplitude calculation, the predetermined number of points are detected in descending order of the amplitude of the frequency component at the predetermined position on the lattice. An ID can be restored by a pattern formed by dots.

[Embodiment 5]
In the first to fourth embodiments, a remainder is obtained by dividing a numerical value represented by an information symbol, this is represented by a plurality of intermediate symbols, and a check symbol is added to the intermediate symbol to generate a Hamming codeword. Was.

  In contrast, in the fifth embodiment, a numerical value represented by an information symbol is input to a hash function, a hash value obtained thereby is represented by an intermediate symbol, and a check symbol is added to the intermediate symbol to obtain a Hamming codeword. Generate.

  A plurality of information bits may be divided into two groups, and information symbols of each group may be input to the same or different hash functions to obtain a hash value for each group. Alternatively, the entire plurality of information symbols may be input to a plurality of mutually different hash functions, and the respective hash values obtained from the respective hash functions may be used as intermediate symbols of the respective groups.

[Embodiment 6]
In the first to fifth embodiments, a Hamming codeword generator polynomial is used when adding a check symbol to an intermediate symbol. However, an error correction codeword other than a Hamming codeword may be generated using other generator polynomials.

It is a figure which shows the pattern in the frequency space of the digital watermark by embodiment of this invention. It is a block diagram which shows the structure of the digital watermark insertion apparatus by embodiment of this invention. It is a block diagram which shows the structure of the digital watermark detection apparatus by embodiment of this invention. It is a flowchart (1/2) which shows the digital watermark detection method by Embodiment 1 of this invention. It is a flowchart (2/2) which shows the digital watermark detection method by Embodiment 1 of this invention.

Explanation of symbols

11 ID input unit 13 Information point generation unit 15 Duplicate point generation unit 17 Intermediate bit generation unit 19 Check bit generation unit 21 Complementary point generation unit 23 Correction point generation unit 25 Composition unit 27 Inverse Fourier transform unit 29 Image input unit 31 Addition unit 51 Fourier transform unit 53 Absolute value calculation unit 55 Correction unit 57 Point detection unit 59 Majority determination unit 61 Error correction unit 63 Score check unit 65 First residue calculation unit 67 Second residue calculation unit 69 ID detection unit 71 Control unit

Claims (23)

An intermediate inspection value calculation step for obtaining an intermediate inspection value by performing a predetermined operation on a numerical value represented by a plurality of information symbols;
An intermediate symbol generation step of representing the intermediate inspection value with a plurality of intermediate symbols;
An error codeword generation step of generating an error correction codeword by adding a check symbol to the plurality of intermediate symbols;
An output step of outputting the plurality of information symbols and the error correction codeword;
An encoding method comprising: The encoding method according to claim 1,
In the intermediate check value calculation step, each of the plurality of information symbols is treated as a weighted bit representing a numerical value represented by an N-ary number, and the numerical value is obtained to obtain a plurality of intermediate symbols constituting the error correction codeword The encoding method is characterized in that the remainder obtained by the division is used as the intermediate check value. The encoding method according to claim 1,
In the intermediate check value calculating step, a hash function is applied to the plurality of information symbols, and a hash value obtained thereby is used as the intermediate check value. The encoding method according to claim 1,
In the output step, an odd number of three or more information symbols are output in an overlapping manner. The encoding method according to claim 1,
The information symbol, the intermediate symbol and the check symbol are binary symbols;
The number of information symbols whose value is 1 is a predetermined number,
In the output step, each of a predetermined number of information symbols with a value of 1 is output as one data so that the number of data with a value of 1 is a constant number, and each intermediate code included in the error correction codeword An encoding method comprising: outputting a symbol and each check symbol as a pair of data having complementary data values. The plurality of information symbols that are output by the encoding method according to claim 1 and that may have been added with errors in the transmission path, and that are output by the encoding method according to claim 1 and that have errors in the transmission path. An input step of inputting the error correction codeword that may have been added;
An error correction step of obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
A first intermediate check value calculating step for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols;
A second intermediate check value calculating step of obtaining a second decoded intermediate check value by performing the predetermined operation on a numerical value represented by the plurality of information symbols;
Comparing the first decoded intermediate check value and the second decoded intermediate check value, and if both do not match, determining that an error remains;
A decoding method comprising: The plurality of information symbols that are output by the encoding method according to claim 2 and that may have been added with errors in the transmission path, and are output by the encoding method according to claim 2, and errors are transmitted in the transmission path. An input step of inputting the error correction codeword that may have been added;
An error correction step of obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
A first intermediate check value calculating step for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols;
A second intermediate check value calculating step of obtaining a second decoded intermediate check value by performing the predetermined operation on a numerical value represented by the plurality of information symbols;
Comparing the first decoded intermediate check value and the second decoded intermediate check value, and if both do not match, determining that an error remains;
With
In the second intermediate check value calculation step, each of the plurality of information symbols is treated as a weighted bit representing a numerical value represented by an N-ary number, and the numerical symbol is converted into a plurality of intermediate symbols constituting the error correction codeword. A decoding method, comprising: dividing by a numerical value to obtain, and using the remainder obtained by the division as the second decoding intermediate check value. The plurality of information symbols that are output by the encoding method according to claim 3 and that may have been added with errors in the transmission path, and that are output by the encoding method according to claim 3, and errors are transmitted in the transmission path. An input step of inputting the error correction codeword that may have been added;
An error correction step of obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
A first intermediate check value calculating step for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols;
A second intermediate check value calculating step of obtaining a second decoded intermediate check value by performing the predetermined operation on a numerical value represented by the plurality of information symbols;
Comparing the first decoded intermediate check value and the second decoded intermediate check value, and if both do not match, determining that an error remains;
With
In the second intermediate check value calculating step, a hash function is applied to the plurality of information symbols, and a hash value obtained thereby is used as the intermediate check value. The plurality of information symbols output by the encoding method according to claim 4 and possibly having errors added in the transmission path, and output by the encoding method according to claim 4, and errors in the transmission path are An input step of inputting the error correction codeword that may have been added;
An error correction step of obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
A first residue calculating step for obtaining a first decoded residue based on the plurality of decoded intermediate symbols;
A majority step for performing error correction on the information symbol by majority;
A second residue calculating step of obtaining a second decoded residue by dividing a numerical value represented by the plurality of information symbols that has been error-corrected by the majority vote;
Comparing the first decoded residue with the second decoded residue and determining that there is an error if they do not match;
A decoding method comprising: The plurality of information symbols that are output by the encoding method according to claim 5 and that may have been added with errors in the transmission path, and are output by the encoding method according to claim 5, and errors are transmitted in the transmission path. An input step of inputting data representing the error correction codeword that may have been added;
If the number of data having a single value among the input data is not the predetermined number, an error end step for terminating the process with an error;
An error correction step of obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
A first residue calculating step for obtaining a first decoded residue based on the plurality of decoded intermediate symbols;
A second residue calculating step of obtaining a second decoded residue by dividing the numerical value represented by the plurality of information symbols;
Comparing the first decoded residue with the second decoded residue and determining that there is an error if they do not match;
A decoding method comprising: The decoding method according to any one of claims 6 to 10,
The decoding method according to claim 1, further comprising an error ending step of ending the process with an error if the error correction cannot be corrected. Intermediate test value calculation means for obtaining an intermediate test value by performing a predetermined operation on a numerical value represented by a plurality of information symbols;
Intermediate symbol generating means for representing the intermediate inspection value by a plurality of intermediate symbols;
Error codeword generation means for generating an error correction codeword by adding a check symbol to the plurality of intermediate symbols;
Output means for outputting the plurality of information symbols and the error correction codeword;
An encoding device comprising: The encoding device according to claim 12,
The intermediate check value calculation means treats each of the plurality of information symbols as a weighted bit representing a numerical value represented by an N-ary number, and obtains the plurality of intermediate symbols constituting the error correction codeword. The encoding apparatus is characterized in that the remainder obtained by the division is used as the intermediate check value. The encoding device according to claim 12,
The intermediate check value calculating means applies a hash function to the plurality of information symbols, and uses a hash value obtained thereby as the intermediate check value. The encoding device according to claim 12,
3. The encoding apparatus according to claim 1, wherein the output means outputs three or more odd numbers of information symbols. The encoding device according to claim 12,
The information symbol, the intermediate symbol and the check symbol are binary symbols;
The number of information symbols whose value is 1 is a predetermined number,
The output means outputs each of a predetermined number of information symbols with a value of 1 as one data so that the number of data with a value of 1 is a constant number, and each intermediate part included in the error correction codeword An encoding apparatus that outputs a symbol and each check symbol as a pair of data having complementary data values. The plurality of information symbols output by the encoding device according to claim 12 and possibly having errors added in the transmission path, and output by the encoding device according to claim 12, and errors in the transmission path are Input means for inputting the error correction codeword that may have been added;
Error correcting means for obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
First intermediate check value calculating means for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols;
Second intermediate check value calculating means for obtaining a second decoded intermediate check value by performing the predetermined operation on the numerical values represented by the plurality of information symbols;
Means for comparing the first decoded intermediate check value with the second decoded intermediate check value and determining that an error remains if they do not match;
A decoding device comprising: The plurality of information symbols that are output by the encoding device according to claim 13 and that may have been added with errors in the transmission path, and that are output by the encoding device according to claim 13 and that have errors in the transmission path. Input means for inputting the error correction codeword that may have been added;
Error correcting means for obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
First intermediate check value calculating means for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols;
Second intermediate check value calculating means for obtaining a second decoded intermediate check value by performing the predetermined operation on the numerical values represented by the plurality of information symbols;
Means for comparing the first decoded intermediate check value with the second decoded intermediate check value and determining that an error remains if they do not match;
With
In the second intermediate check value calculation means, each of the plurality of information symbols is treated as a weighted bit representing a numerical value represented by an N-ary number, and the numerical value is converted into a plurality of intermediate symbols constituting the error correction codeword. A decoding apparatus, characterized by dividing by a numerical value to be obtained and using the remainder obtained by the division as the second decoding intermediate check value. The plurality of information symbols output by the encoding device according to claim 14 and possibly having an error added in the transmission path, and output by the encoding device according to claim 14, wherein an error occurs in the transmission path. Input means for inputting the error correction codeword that may have been added;
Error correcting means for obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
First intermediate check value calculating means for obtaining a first decoded intermediate check value based on the plurality of decoded intermediate symbols;
Second intermediate check value calculating means for obtaining a second decoded intermediate check value by performing the predetermined operation on the numerical values represented by the plurality of information symbols;
Means for comparing the first decoded intermediate check value with the second decoded intermediate check value and determining that an error remains if they do not match;
With
The decoding apparatus characterized in that the second intermediate check value calculating means applies a hash function to the plurality of information symbols and uses the hash value obtained thereby as the intermediate check value. The plurality of information symbols output by the encoding device according to claim 15 and possibly having errors added in the transmission path, and output by the encoding device according to claim 15, wherein errors are transmitted in the transmission path. Input means for inputting the error correction codeword that may have been added;
Error correcting means for obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
First residue calculating means for obtaining a first decoded residue based on the plurality of decoded intermediate symbols;
A majority means for performing error correction on the information symbol by majority;
Second residue calculating means for obtaining a second decoded residue by dividing a numerical value represented by the plurality of information symbols that has been error-corrected by the majority vote;
Means for comparing the first decoding residue and the second decoding residue and determining that an error remains if they do not match;
A decoding device comprising: The plurality of information symbols output by the encoding device according to claim 16 and possibly having errors added in the transmission path, and output by the encoding device according to claim 16, wherein errors are transmitted in the transmission path. Input means for inputting data representing the error correction codeword that may have been added;
An error ending means for ending the process with an error when the number of data having one value among the input data is not the predetermined number;
Error correcting means for obtaining a plurality of decoded intermediate symbols by performing error correction processing on the error correction codeword;
First residue calculating means for obtaining a first decoded residue based on the plurality of decoded intermediate symbols;
Second residue calculating means for obtaining a second decoded residue by dividing the numerical value represented by the plurality of information symbols;
Means for comparing the first decoding residue and the second decoding residue and determining that an error remains if they do not match;
A decoding device comprising: The decoding device according to any one of claims 17 to 21,
The decoding apparatus according to claim 1, further comprising error ending means for ending the process with an error when the error correction means cannot correct the error.   The program for making a computer perform the method of any one of Claims 1 thru | or 11.

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