JP5338170B2 - Apparatus, method and program for embedding and extracting digital watermark information - Google Patents

Description

  The present invention relates to a technique for embedding and transmitting digital watermark information, and more particularly to a technique for embedding and transmitting digital watermark information in an acoustic signal propagating in the air and extracting the digital watermark information from the acoustic signal or the like on the receiving side.

Various techniques have been proposed in which an audio signal is used as a carrier signal that bears digital watermark information, and the digital watermark information is embedded in a part of the band of the carrier signal for transmission (see, for example, Patent Document 1). According to this embedding technique, for example, an audio signal in which digital watermark information is embedded is reproduced as sound, and the audio signal obtained by collecting the sound with a microphone is recorded and propagated in the process of being recorded and propagated. Digital watermark information can be kept in an audio signal. Therefore, this embedding technique can be used for a wider range of applications than the technique of embedding digital watermark information in compression-encoded data.
Japanese Patent No. 3659321

  By the way, in the above-described conventional technology, when the band of the carrier signal in which the digital watermark information is embedded is known, it becomes possible for a third party who has acquired the carrier signal to extract the digital watermark information from this band. There has been a problem that an act of falsifying digital watermark information embedded in the band becomes possible.

  The present invention has been made in view of the circumstances described above, and technical means that can enhance the confidentiality of digital watermark information embedded in a carrier signal when the digital watermark information is embedded in a carrier signal for transmission. The purpose is to provide.

The present invention provides a band dividing means for performing band division on a carrier signal and outputting a plurality of band carrier signals belonging to different bands, and a modulation signal generating means for generating a modulation signal corresponding to each symbol indicating digital watermark information. And the plurality of band carrier signals are divided into symbol frames having a predetermined time length, and the plurality of band carrier signals in each symbol frame are distributed in a direction crossing between the bands of the plurality of band carrier signals, and time Embedding means for performing modulation processing using a modulation signal for one symbol generated by the modulation signal generating means on a plurality of modulation target elements dispersed in the axial direction, and a plurality of bands after processing by the embedding means Band synthesizing means for synthesizing carrier signals and outputting a carrier signal in which digital watermark information is embedded. Providing embedding apparatus of the electronic watermark information and said.
The present invention also provides band dividing means for performing band division on a carrier signal and outputting a plurality of band carrier signals belonging to mutually different bands, and dividing the plurality of band carrier signals into symbol frames having a predetermined time length, In a plurality of band carrier signals in a frame, a demodulation process is performed on a plurality of modulation target elements dispersed in a direction crossing between the bands of the plurality of band carrier signals and dispersed in a time axis direction. A cross-correlation coefficient between a demodulation means for outputting a signal, a demodulation result signal obtained from the demodulation means and a modulation signal indicating a predetermined symbol, and based on the calculation result of the cross-correlation coefficient, An electronic watermark information extracting device comprising: electronic watermark information extracting means for determining a symbol indicating embedded digital watermark information To provide.
The embedding means of the embedding device according to the present invention is generated by the modulation signal generating means for a plurality of modulation target elements dispersed in a direction crossing between each band of a plurality of band carrier signals and dispersed in a time axis direction. Modulation processing using a modulation signal for one symbol is performed. Therefore, it is extremely difficult for an apparatus other than the extracting apparatus according to the present invention to identify a plurality of modulation target elements in a plurality of band carrier signals constituting a carrier signal and extract symbols embedded in the carrier signal from them. is there. Therefore, according to the present invention, it is possible to improve the confidentiality of the digital watermark information embedded in the carrier signal.
Note that Patent Literature 1 discloses a technique (for example, see FIG. 11 of Patent Literature 1) that changes a band into which digital watermark information is embedded. However, this technique changes the embedding band in symbol frame units, and as in the present invention, a plurality of modulation target elements distributed between a plurality of band carrier signals and distributed in the time axis direction. The column is not subjected to a modulation process using a modulation signal indicating one symbol.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<First Embodiment>
An embedded transmission technique in which digital watermark information is embedded in a carrier signal and transmitted is a blind watermark embedded transmission technique that does not require an original carrier signal in which digital watermark information is not embedded in the extraction of digital watermark information. It is roughly classified into a non-blind watermarking embedded transmission technique that requires a single carrier signal. The first embodiment described below belongs to the former blind watermarking embedded transmission technique.

  FIG. 1 is a block diagram showing a configuration of a digital watermark information embedding device 100 according to the first embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a digital watermark information extracting device 200 according to the first embodiment. Note that each of the embedding device 100 and the extraction device 200 may be realized as dedicated hardware for executing processing for embedding digital watermark information in a carrier signal or processing for extracting digital watermark information from a carrier signal, or embedding processing. Or a computer program that causes a computer to execute extraction processing.

  First, the digital watermark information embedding device 100 shown in FIG. 1 will be described. In FIG. 1, a band dividing unit 110 performs band division on a sample sequence of carrier signals and outputs M band carrier signals belonging to different bands. Here, the carrier signal may be an audio signal, or may be a signal obtained by one-dimensionalizing pixel signals constituting an image in the raster scan order.

  In a preferable aspect, the band dividing unit 110 includes a windowing unit and a band dividing filter bank (not shown). Here, the windowing unit divides the band by multiplying the sample sequence of the carrier signal into half blocks of N samples per half block, and multiplying the sample sequence of the latest 1 block = 2 half blocks up to the present by a window function The process of supplying to the filter bank is repeated. Each of the band division filter banks includes M complex coefficients BPF (Band Pass Filter) having different passband center angular frequencies. Each time the complex coefficient BPF receives a sequence of samples for one block multiplied by a window function from the windowing unit, a complex coefficient corresponding to each passband center angular frequency is used for the received sample sequence. By performing the BPF process, a complex spectrum coefficient indicating a component of the passband center angular frequency included in the sample sequence is calculated and output as a band carrier signal.

  In another preferred embodiment, the band dividing unit 110 performs an FFT (Fast Fourier Transform) on a windowing unit similar to the above and a sample sequence for one block obtained by multiplying the window function by the windowing unit. The FFT unit calculates M complex spectrum coefficients corresponding to different frequencies.

  In each of the above modes, a complex spectrum coefficient (band carrier signal) obtained from carrier signals for L blocks (L is an integer of 2 or more) is an embedding destination of one symbol in a symbol string indicating digital watermark information.

In still another preferred embodiment, the band dividing unit 110 is a complex wavelet transform unit or a complex wavelet packet decomposition unit. In this aspect, the band division unit 110 divides the sample sequence of the carrier signal into blocks that do not overlap on the time axis, performs complex wavelet transform or complex wavelet packet decomposition on the divided blocks, and performs complex wavelet for M bands. Coefficients are output as band carrier signals. In this aspect, a complex wavelet coefficient obtained from complex wavelet transform or complex wavelet packet decomposition for L blocks is an embedding destination of one symbol in a symbol string indicating digital watermark information.
In the following, it is assumed that band division section 110 outputs (N / M) * L band carrier signal samples per L block (one symbol frame) for each band.

  The absolute value detection unit 121 calculates an absolute value component of each band carrier signal from the real part and imaginary part of each of the M band carrier signals output from the band division unit 110. Further, the declination detection unit 122 calculates the declination component of each band carrier signal from the real part and imaginary part of each of the M band carrier signals output from the band division unit 110.

  Modulation signal generation units 131 and 132 are means for generating a modulation signal corresponding to a symbol indicating digital watermark information. The embedding device 100 according to the present embodiment includes a first embedding unit 140 that embeds symbols in the absolute value components of M band carrier signals obtained from the absolute value detection unit 121 as means for embedding symbols indicating digital watermark information. And a second embedding unit 150 that embeds symbols in the declination components of the M band carrier signals obtained from the declination detection unit 122. The modulation signal generation unit 131 is a unit that supplies a modulation signal indicating a symbol to be embedded to the first embedding unit 140. The modulation signal generation unit 132 is a unit that supplies a modulation signal indicating a symbol to be embedded to the second second embedding unit 150. The modulation signal generation units 131 and 132 may generate modulation signals corresponding to different symbols in the symbol string indicating the digital watermark information, or generate the modulation signals corresponding to the same symbol in duplicate. It may be a thing.

  Each of the modulation signal generation units 131 and 132 generates a two-phase modulation signal having an opposite phase relationship as a modulation signal indicating one symbol. These modulation signals are composed of Lm samples (Lm ≦ M × (N / M) * L) per symbol. In the example illustrated in FIG. 1, the modulation signal generation unit 131 generates a forward / reverse two-phase triangular wave signal as a modulation signal indicating one symbol b. Here, when the symbol b to be expressed is a bit “0”, the positive phase modulation signal has a peak in the first half and a waveform in the valley in the second half. When the symbol to be expressed is a bit “1”, the first half is The valley and the latter half have a mountain waveform. The modulated signal having the opposite phase is a signal having the opposite phase.

  The first embedding unit 140 includes a spectrogram storage unit 141, a multiplier 142, and an adder 143. The spectrogram storage unit 141 is a matrix in which the absolute values of M × (N / M) * L band carrier signals obtained from the absolute value detection unit 121 for each symbol frame are M rows (N / M) * L columns. Written as

  In the example shown in FIG. 1, in the box indicating the spectrogram storage unit 141, a matrix of M rows (N / M) * L columns whose elements are absolute values of band carrier signals is illustrated. Among the elements, there are elements written with numbers 1 ′ to 12 ′ and elements written with numbers 1 to 12. Here, each element in which the numbers 1 ′ to 12 ′ are entered is an example of an element (hereinafter referred to as a positive phase modulation target element) that is a target of modulation processing using a positive phase modulation signal provided from the modulation signal generation unit 131. To do. Also, each element with the numbers 1 to 12 is an example of an element (hereinafter referred to as an anti-phase modulation target element) that is a target of modulation processing using the anti-phase modulation signal given from the modulation signal generation unit 131. is there.

  The first embedding unit 140 determines where each of these positive phase modulation target elements and each of the negative phase modulation target elements is located in a matrix of M rows (N / M) * L columns stored in the spectrogram storage unit 141, that is, A two-dimensional embedding pattern indicating the location of the symbol embedding destination is stored in advance. Then, according to this two-dimensional embedding pattern, the first embedding unit 140 out of matrix elements (samples of absolute values of band carrier signals) of M rows (N / M) * L columns stored in the spectrogram storage unit 141 Amplitude modulation processing according to the positive-phase modulation signal for the series of normal-phase modulation target element sequences and amplitude-modulation processing according to the negative-phase modulation signal for the series of reverse-phase modulation target element sequences are executed.

  More specifically, the first embedding unit 140 selects a plurality of positive phase modulation target elements (numbers 1 ′ to 12 ′ in the example of FIG. 1) from among the matrix elements of M rows and L columns stored in the spectrogram storage unit 141. Read each element), and multiply each positive phase modulation target element by each sample (each of 12 samples in this example) of the positive phase modulation signal provided from the modulation signal generator 131. Each of the containers 142 is made to perform. Then, the adder 143 is caused to add each multiplication result and each positive phase modulation target element (each element in which numerals 1 ′ to 12 ′ are entered in the example of FIG. 1), and each addition result is stored in a spectrogram. Each original positive phase modulation target element in the unit 141 is overwritten. In addition, the first embedding unit 140 includes a plurality of anti-phase modulation target elements (elements numbered 1 to 12 in the example of FIG. 1) among the matrix elements of M rows and L columns stored in the spectrogram storage unit 141. ) And each of the anti-phase modulation target elements and the respective samples (in this example, each of 12 samples) of the anti-phase modulation signal provided from the modulation signal generation unit 131 are multiplied by the multiplier 142. Make it. Then, the adder 143 performs addition of each multiplication result and each anti-phase modulation target element (elements with numerals 1 to 12 in the example of FIG. 1), and the addition result is stored in the spectrogram storage unit 141. In other words, each element of the original anti-phase modulation is overwritten.

  The second embedding unit 150 includes a spectrogram storage unit 151 and an adder 152. In the spectrogram storage unit 151, the deviation components of M × (N / M) * L band carrier signals obtained from the deviation detection unit 122 for each symbol frame are M rows (N / M) * L columns. Written as a matrix. The second embedding unit 150 is a two-dimensional unit that indicates where each normal phase modulation target element and each negative phase modulation target element are located in a matrix of M rows (N / M) * L columns stored in the spectrogram storage unit 151. The embedding pattern is stored in advance. The two-dimensional embedding pattern may have the same contents as those stored in the first embedding unit 140 or may have different contents. Then, in accordance with this two-dimensional embedding pattern, the second embedding unit 150 performs a series of normal phase modulation among the matrix elements (samples of the declination component of the band carrier signal) of M rows and L columns stored in the spectrogram storage unit 151. A phase modulation process corresponding to the normal phase modulation signal for the target element sequence and a phase modulation process corresponding to the reverse phase modulation signal for the series of reverse phase modulation target element sequences are executed.

  More specifically, the second embedding unit 150 includes a plurality of positive phase modulation target elements (numerical numbers in the example of FIG. 1) among the matrix elements of M rows (N / M) * L columns stored in the spectrogram storage unit 151. 1 ′ to 12 ′ written elements), and each positive phase modulation target element and each sample of the positive phase modulation signal given from the modulation signal generation unit 132 (in this example, 12 samples) And adder 152 to each adder 152. Then, each addition result is overwritten on each original positive phase modulation target element in the spectrogram storage unit 151. In addition, the second embedding unit 150 includes a plurality of anti-phase modulation target elements (numbers 1 to 12 in the example of FIG. 1) among the matrix elements of M rows (N / M) * L columns stored in the spectrogram storage unit 151. Are added to each of the anti-phase modulation target elements and each sample of the anti-phase modulation signal given from the modulation signal generating unit 132 (each of the twelve samples in this example). Are added to each of the adders 152. Then, each addition result is overwritten on each original anti-phase modulation target element in the spectrogram storage unit 151.

  As illustrated in FIG. 1, in the present embodiment, a normal phase modulation target element and an antiphase modulation target element, which are embedding destinations of each part of one symbol (each sample of a modulation signal representing one symbol), are M band bands. It is distributed in the direction crossing between each band of the carrier signal and distributed in the time axis direction. Therefore, it is extremely difficult for a third party to read out each part of the modulation signal indicating one symbol from the band carrier signal in the M band to form a modulation signal for one symbol, and high confidentiality can be realized.

  The recombination unit 160 receives a sample of the absolute value of the band carrier signal composed of M rows (N / M) * L columns that has undergone the amplitude modulation process of the first embedding unit 140 and the phase modulation process of the second embedding unit 150. The sample of the declination component of the band carrier signal consisting of M rows (N / M) * L columns after passing through is combined, and each absolute value component and each declination component of the same band and the same time are combined with each other in a complex format Band carrier signals for M bands are generated. The band synthesizing unit 170 is a means for performing an inverse transform process on the process of the band dividing unit 110, and combines the band carrier signals for M bands back to a time domain signal, and synthesizes the carrier signal in which digital watermark information is embedded. Output.

  Next, the extraction device 200 shown in FIG. 2 will be described. The band dividing unit 210, the absolute value detecting unit 221 and the declination detecting unit 222 have the same configuration as the band dividing unit 110, absolute value detecting unit 121 and declination detecting unit 122 of the embedding device 100. For example, when an audio signal is used as a carrier signal, the carrier signal (audio signal) in which digital watermark information is embedded by the embedding device 100 described above is emitted into the air as sound, for example, and collected by a sound collecting device (not shown). The carrier signal, which is a time-series sample of the speech waveform, is accumulated in the temporary storage means. Then, it is read from this storage means and supplied to the band dividing unit 210. The band dividing unit 210 divides this carrier signal into sections of one symbol frame, and outputs band carrier signals for M bands composed of (N / M) * L samples per band for each symbol frame. . The absolute value detection unit 221 outputs the absolute value of the sample of the band carrier signal in the M band, and the deviation angle detection unit 222 outputs the deviation component of the sample of the band carrier signal in the M band.

  The first demodulator 240 performs a demodulation process which is an inverse process of the amplitude modulation process described above on the absolute value of the M band carrier signal obtained from the absolute value detector 221 and outputs a demodulation result signal It is. Also, the second demodulator 250 performs a demodulation process, which is the reverse process of the above-described phase modulation process, on the declination component of the M-band carrier signal obtained from the declination detector 222, and outputs a demodulation result signal. It is a means to output.

  As shown in FIG. 2, the first demodulation unit 240 includes a spectrogram storage unit 241, a divider 242, and a post-processing unit 243. The spectrogram storage unit 141 is a matrix in which the absolute values of M × (N / M) * L band carrier signals obtained from the absolute value detection unit 221 for each symbol frame are M rows (N / M) * L columns. Written as The first demodulation unit 240 stores a two-dimensional embedding pattern similar to that stored in the first embedding unit 140 of the embedding device 100. In accordance with this two-dimensional embedding pattern, the first demodulator 240 selects the positive phase modulation target element from the matrix elements (samples of absolute values of the band carrier signals) of M rows and L columns stored in the spectrogram storage unit 241. A sequence of possible components and a sequence of components that are considered to be antiphase-modulated elements are read out, and the processing of dividing the former by the latter is performed by the divider 242, and the demodulation result signal is output from the divider 242.

  The post-processing unit 243 is means for performing an offset removal process and a normalization process on the demodulation result signal. More specifically, in the offset removal process, an average value (that is, a moving average value) of the demodulation result signal samples output within a predetermined period in the past is obtained, and is used as an offset to be subtracted from the demodulation result signal samples. . As a result, the offset component (DC component) is removed from the demodulation result signal. In the normalization process, the maximum value of the demodulation result signal from which the offset component has been removed in this way is obtained in a past fixed period, and the sample of the demodulation result signal from which the offset has been removed is divided by this maximum value. Normalize and output the normalized demodulation result signal.

  As illustrated in FIG. 1 and FIG. 2, in the M band carrier signal, the positive phase modulation target elements (elements with numbers 1 ′ to 12 ′) are reversed phase modulation target elements (numbers 1 to 12 are written). Is an element of an adjacent band of the band to which the element belongs. Therefore, it is considered that the normal phase modulation target element and the negative phase modulation target element have approximate contents before amplitude modulation. Therefore, in the first demodulator 240, if the normal phase modulation target element sequence and the reverse phase modulation target element sequence are normally read and supplied to the divider 242, the demodulation result signal obtained by the division is The first embedding unit 140 becomes a signal having a waveform close to the modulation signal used for amplitude modulation of the column of the normal phase modulation target element and the column of the negative phase modulation target element.

  The second demodulation unit 250 includes a spectrogram storage unit 251, a subtracter 252, and a post-processing unit 253. The spectrogram storage unit 251 stores M × (N / M) * L declination components of the band carrier signals obtained from the declination detection unit 222 for each symbol frame in M rows (N / M) * L columns. Written as a matrix. The second demodulator 250 stores a two-dimensional embedding pattern similar to that stored by the second embedding unit 150 of the embedding device 100. In accordance with this two-dimensional embedding pattern, the second demodulator 250 selects from the matrix elements (samples of the declination component of the band carrier signal) of M rows (N / M) * L columns stored in the spectrogram storage unit 251. Read out the sequence of elements considered to be the positive phase modulation target and the sequence of the elements considered to be the reverse phase modulation, cause the subtractor 252 to perform the process of subtracting the latter from the former, and output the demodulation result signal from the subtractor 252 . The post-processing unit 253 is means for performing the same offset removal processing and normalization processing as the post-processing unit 243 on the demodulation result signal.

  In the second demodulator 250, if the normal-phase modulation target element sequence and the reverse-phase modulation target element sequence are normally read and supplied to the subtractor 252, the demodulation result obtained from the second demodulation unit 250 The signal is a signal having a waveform close to the modulation signal used in the second embedding unit 150 for phase modulation of the sequence of the normal phase modulation target elements and the sequence of the negative phase modulation target elements.

  The first digital watermark information extraction unit 260 is a means for extracting a symbol indicating the digital watermark information from the demodulation result signal output from the first demodulation unit 240. The second digital watermark information extraction unit 270 is means for extracting a symbol indicating the digital watermark information from the demodulation result signal output from the second demodulation unit 250.

  As illustrated in FIG. 2, the first digital watermark information extraction unit 260 includes a buffer 261, a modulation signal generation unit 262, a correlation calculation unit 263, and a correlation determination unit 264. The buffer 261 is a buffer that temporarily stores a sample of the demodulation result signal for one symbol frame output from the first demodulator 240. The modulation signal generation unit 262 is means for alternately generating a modulation signal sample string indicating bit “0” and a modulation signal sample string indicating bit “1”. The correlation calculation unit 263 includes a cross-correlation coefficient (hereinafter referred to as a first cross-correlation coefficient) between the sample sequence of the demodulation result signal stored in the buffer 261 and the sample sequence of the modulation signal indicating bit “0”, and the demodulation result. A cross-correlation coefficient (hereinafter referred to as a second cross-correlation coefficient) between the sample sequence of the signal and the sample sequence of the modulation signal indicating bit “1” is calculated.

  The correlation determining unit 264 has two roles. The first role is based on the history of the first cross-correlation coefficient and the second cross-correlation coefficient obtained from the correlation calculation unit 263, and the operations of the band division unit 210 and the first demodulation unit 240 are symbols in the carrier signal. It is a role to determine whether or not it is synchronized with the frame delimiter.

  When a band carrier signal in a section other than a section in which symbols are embedded in the carrier signal is processed by the band dividing section 210, the absolute value detecting section 221 and the first demodulating section 240, a matrix is generated from the spectrogram storage section 241 according to a two-dimensional embedding pattern. Even if the element is read, the normal phase modulation corresponding element and the negative phase modulation target element are not read. Therefore, the demodulation result signal obtained from the first demodulator 240 is neither a modulation signal indicating bit “0” nor a modulation signal indicating bit “1”, and is a signal uncorrelated with such a modulation signal. . Accordingly, the first and second cross-correlation coefficients obtained by the correlation calculation unit 263 are both close to 0.

  Further, the band carrier signal in the section that substantially matches the section in which the symbol is embedded in the carrier signal has been processed by the band dividing section 210, the absolute value detecting section 221 and the first demodulating section 240. The same result is obtained when the dividing position when dividing is shifted from the dividing position when the band dividing unit 110 of the embedding apparatus 100 divides the carrier signal into symbol frames.

  Therefore, the correlation determination unit 264 monitors the history of the first and second cross-correlation coefficients obtained from the correlation calculation unit 263, and the period in which both of these cross-correlation coefficients are values close to 0 is The read start position (symbol frame start position) is shifted by a predetermined amount to cause the band division unit 210 to perform band division processing for one symbol frame, and the absolute value detection unit 221 and the first demodulation unit 240 perform band division processing. The operation of causing the band carrier signal obtained from 110 to be processed is repeated. The first and second cross-correlation coefficients obtained from the correlation calculation unit 263 are monitored while repeating such operations, and one of the cross-correlation coefficients is remarkably close to “1”. It is determined that the operations of the band dividing unit 210, the absolute value detecting unit 221 and the first demodulating unit 240 are synchronized with the symbol frame delimiter in the carrier signal.

  The second role of the correlation determining unit 264 is to determine a symbol indicating the digital watermark information embedded in the carrier signal. In the state where the operations of the band dividing unit 210, the absolute value detecting unit 221 and the first demodulating unit 240 are synchronized with the symbol frame delimiter in the carrier signal as described above, the correlation determining unit 264 maintains this synchronized state. Each of the symbol frames is processed by the band dividing unit 210, the absolute value detecting unit 221 and the first demodulating unit 240. Then, the first cross-correlation coefficient and the second cross-correlation coefficient obtained from the correlation calculation unit 263 are compared for each symbol frame. If the first cross-correlation coefficient is larger, the first cross-correlation coefficient is embedded. The symbol is determined to be bit “0”, and if the second cross-correlation coefficient is larger, it is determined that the embedded symbol is bit “1”.

The second digital watermark information extraction unit 270 also has the same configuration as the first digital watermark information extraction unit 260. When the first digital watermark information extraction unit 260 is provided with a synchronization control function (a control function for synchronizing the operations of the band division unit 210 and the subsequent stage at the symbol frame delimiter positions in the carrier signal), the synchronization is performed. The second digital watermark information extraction unit 270 may not be provided with the digitization control function.
The above is the details of the present embodiment.

According to this embodiment, the following effects can be obtained.
(1) In the embedding device 100, among a plurality of band carrier signals obtained by dividing a carrier signal into a plurality of bands, a plurality of band carrier signals distributed in a direction crossing between bands of the plurality of band carrier signals and distributed in a time axis direction The modulation target element is modulated by a modulation signal indicating one symbol of the digital watermark information. Accordingly, it is extremely difficult for a device other than the extraction device 200 to find a place where the digital watermark information is embedded in the carrier signal, and it is possible to prevent a third party from falsifying the digital watermark information embedded in the carrier signal. it can.

(2) In the embedding device 100, the modulation processing using each sample of the modulation signal corresponding to the symbol is distributed in a direction across the bands of the plurality of band carrier signals in the plurality of band carrier signals, and the time axis This is applied to a plurality of modulation target elements dispersed in the direction. Therefore, even if the symbol frame length for embedding one symbol is shortened, a sufficient number of samples as modulation signal samples corresponding to one symbol can be used for modulation of the band carrier signal in the symbol frame. Therefore, the symbol frame length can be shortened without sacrificing the ease of symbol extraction on the extraction apparatus 200 side.

(3) When the complex wavelet transform or the complex wavelet packet decomposition is used as the band dividing means in the band dividing unit 110 of the embedding device 100, the following effects can be obtained. First, when a carrier signal is divided into blocks and band-divided into band carrier signals by FFT, artifacts (discontinuity in amplitude and phase) occur at the block boundary when digital watermark information is extracted. For this reason, when using FFT as a means for clipping, it is necessary to divide the carrier signal into overlapping blocks on the time axis. However, if a carrier signal is divided into such overlapping blocks and a symbol of digital watermark information is embedded in each block, interference between adjacent symbols may occur when the symbol is extracted. On the other hand, when using complex wavelet transform or complex wavelet packet decomposition that performs temporal and frequency division as a means of band division, carrier signals can be placed on the time axis without generating artifacts during extraction. By dividing the block into non-overlapping blocks, the carrier signal can be divided into band carrier signals, and interference of adjacent symbols during extraction can be avoided.

(4) In the present embodiment, the embedding device 100 generates waveforms corresponding to the symbols of the digital watermark information for the adjacent two-phase normal phase modulation target elements and reverse phase modulation target elements scattered in the M band carrier signal. The digital watermark information symbol was embedded in the carrier signal by performing modulation using the normal / reverse two-phase modulation signal. Therefore, the extraction apparatus 200 can extract the modulation signal used for modulation with a large amplitude, and can stably extract digital watermark information from the carrier signal.

Second Embodiment
In this embodiment, the first embodiment belonging to the blind watermarking embedded transmission technique is changed to a non-blind watermarking method. Although not shown, the digital watermark information embedding device according to the present embodiment is the absolute value and the declination component of each band carrier signal stored in, for example, the spectrogram storage units 141 and 151 in the embedding device 100 according to the first embodiment. In each of the matrix elements, for example, only the positive phase modulation target element (the element in which the numbers 1 ′ to 12 ′ are entered) is subjected to modulation processing using the positive phase modulation signal, and the negative phase modulation target elements (numbers 1 to 12) The element is not subjected to modulation processing.

  FIG. 3 is a block diagram showing the configuration of the extraction apparatus 200A according to the present embodiment. Note that FIG. 3 shows only a device configuration for extracting a symbol embedded by amplitude modulation in order to prevent the drawing from becoming complicated, and a device configuration for extracting a symbol embedded by phase modulation. Is omitted.

  As shown in FIG. 3, in the extraction device 200A, a band dividing unit 210a is added to the extraction device 200 in the first embodiment, and the first demodulation unit 240 of the extraction device 200 is replaced with the first demodulation unit 240a. Has been replaced.

  In the present embodiment, in synchronization with the supply of the carrier signal embedded with the digital watermark information to the band dividing unit 210, the original carrier signal without the embedded digital watermark information is supplied to the band dividing unit 210a. The band dividing unit 210a performs band division on the original carrier signal, and outputs a band carrier signal in the same band as the M band carrier signal output from the band dividing unit 210. The absolute value detector 221a calculates the absolute value of the M band carrier signal output from the band divider 210a, and outputs a sample string of absolute values for the M band.

  In addition to the spectrogram storage unit 241, the first demodulation unit 240a includes a spectrogram storage unit 241a. As in the first embodiment, the spectrogram storage unit 241 stores a matrix of absolute values of M × (N / M) * L band carrier signals per symbol frame output from the absolute value detection unit 221. . In addition, a matrix of absolute values of M × (N / M) * L band carrier signals per symbol frame output from the absolute value detection unit 221a is written in the spectrogram storage unit 241a.

  The first demodulator 240a is a modulation target element in the matrix of M rows and L columns stored in the spectrogram storage unit 241 (in the example of FIG. 3, in the matrix of M rows and L columns in the spectrogram storage unit 241, the numbers 1 ′ to A two-dimensional embedding pattern indicating the location of the element 12) is stored. In accordance with the two-dimensional embedding pattern, the first demodulator 240a reads a column of the matrix elements stored in the spectrogram storage unit 241 that is considered to be a modulation target element, and among the matrix elements stored in the spectrogram storage unit 241a. A sequence of elements that are at the same position as the modulation target element is read, the former is divided by the latter, the divider 242 is processed, and the divider 242 outputs a demodulation result signal. The processing content of the post-processing unit 242 is the same as that in the first embodiment.

  Also in the present embodiment, in the first demodulator 240a, if the modulation target element column is normally read out and supplied to the divider 242, the demodulation result signal obtained by the division is modulated on the embedding device side. The signal has a waveform close to the modulation signal used for amplitude modulation of the element row. Therefore, as in the first embodiment, the digital watermark information extraction unit 260 can determine the symbol of the digital watermark information embedded in the carrier signal by amplitude modulation.

  Although not shown, the configuration and operation of an apparatus for extracting digital watermark information embedded in a carrier signal by phase modulation is basically the same as described above.

<Other embodiments>
While the first and second embodiments of the present invention have been described above, various other embodiments are conceivable for the present invention. For example:

(1) In each of the above embodiments, a symbol indicating digital watermark information is embedded in a carrier signal using both amplitude modulation and phase modulation. However, only one of amplitude modulation and phase modulation is used to perform digital watermarking. A symbol indicating information may be embedded in the carrier signal.

(2) When a symbol indicating digital watermark information is embedded in a carrier signal using both amplitude modulation and phase modulation, the same symbol may be embedded by amplitude modulation and phase modulation. In this case, on the extraction device side, for each symbol frame, a process of extracting a symbol embedded by amplitude modulation and a process of extracting a symbol embedded by phase modulation are executed, and the same symbol is extracted in both processes. Whether or not the reliability of the extracted symbol is determined may be determined based on whether or not the extracted symbol is determined.

(3) When embedding a symbol string composed of a plurality of symbols indicating digital watermark information in a carrier signal, for example, the first symbol is a two-dimensional embedding pattern P1, the second symbol is a two-dimensional embedding pattern P2, and so on. The two-dimensional embedding pattern designating the modulation target element may be changed according to a rule agreed in advance between the embedding device and the extracting device. According to this aspect, the confidentiality of the digital watermark information embedded in the carrier signal can be further enhanced.

(4) In each of the above embodiments, one symbol is a bit representing a binary value, but three or more types of modulation waveforms representing one symbol are prepared, and a symbol representing a ternary value or more per symbol is provided in a band. It may be embedded in the carrier signal.

(5) In the first embodiment, a normal phase modulation target element and a negative phase modulation target element corresponding to the same time and belonging to mutually adjacent bands are selected from a plurality of band carrier signals in each symbol frame. Then, the modulation process by the normal phase modulation signal is performed on the column of the normal phase modulation target elements, and the modulation process by the negative phase modulation signal is performed on the column of the negative phase modulation target elements. However, the positive-phase modulation target element and the negative-phase modulation target element do not necessarily belong to adjacent bands, and may be elements belonging to different bands close in frequency.

(6) In each of the above embodiments, the modulation signal has a predetermined range (for example, a range from −1 to +1 in the case of amplitude modulation. In the case of phase modulation, the difference between the two-phase modulation signals having a negative phase relationship is −π. May be generated by multiplying a basic modulation signal having an amplitude of from + to + π by a modulation intensity A. In this case, the modulation intensity A is selected from a range from 0 to 1. When A = 1, maximum modulation is performed, and when A = 0, no modulation is performed. The modulation intensity A may be determined according to the effect of suppressing sound quality deterioration due to symbol embedding required for each band, the tolerance to disturbance of symbols, and the like.

(7) The number of absolute value or declination samples of the band carrier signal for one symbol frame to be written in the spectrogram storage unit 141 or the like may be appropriately determined according to the band division method performed by the band division unit 110 or the like. . Further, when performing band division that is not equal division by complex wavelet transform or complex wavelet packet decomposition, the number of band carrier signal samples per symbol frame may differ between bands. In such a case, for example, a band carrier signal sample of a band with a large number of samples is processed into a matrix element across multiple rows, and the band carrier signal samples of all bands are stored in one matrix. Just do it. Alternatively, the absolute value or declination sample of the band carrier signal for one symbol frame is stored in the memory without being in the form of a matrix, and the absolute value or declination sample of the band carrier signal for one symbol frame is May be selected according to a predetermined rule and modulated according to the symbol to be embedded.

1 is a block diagram showing a configuration of a digital watermark information embedding device 100 according to a first embodiment of the present invention. FIG. It is a block diagram which shows the structure of the electronic watermark information extraction apparatus 200 by the embodiment. It is a block diagram which shows the structure of 200 A of electronic watermark information extraction apparatuses by 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Embedded device, 200, 200A ... Extraction device, 110, 210, 210a ... Band division part, 121, 221, 221a ... Absolute value detection part, 122, 222 ... Declination angle detection part, 140 ... First embedding unit, 150 ... second embedding unit, 160 ... recombination unit, 170 ... band synthesis unit, 131, 132 ... modulation signal generation unit, 141, 151, 241, 251, 241a ... spectrogram storage , 142... Multiplier, 143, 152... Adder, 242... Divider, 252... Subtracter, 243, 253 .. Post-processing unit, 260, 270. ... Buffer, 262... Modulation signal generator, 263... Correlation calculator, 264.

Claims (7)

Band division means for performing band division on a carrier signal for each block of a predetermined time length and outputting a plurality of band carrier signals belonging to different bands,
Modulation signal generating means for generating a sample string of a modulation signal waveform for one symbol corresponding to each symbol indicating electronic watermark information;
The plurality of band carrier signals are divided into symbol frames composed of a plurality of temporally continuous blocks, and a plurality of band carrier signals in each symbol frame are crossed between the bands of the plurality of band carrier signals. And a modulation signal waveform for one symbol generated by the modulation signal generating means for a plurality of modulation target elements distributed in the time axis direction over L blocks (L is an integer of 2 or more) . An embedding means for performing modulation processing using each sample of the sample sequence;
An apparatus for embedding digital watermark information, comprising: band synthesizing means for synthesizing a plurality of band carrier signals that have been processed by the embedding means and outputting a carrier signal in which digital watermark information is embedded. The modulation signal generating means outputs a sample sequence of the modulation signal waveform of the normal / reverse two phases as the sample sequence of the modulation signal waveform corresponding to one symbol,
The embedding means includes, as each modulation target element of the plurality of modulation target elements, a normal phase modulation target element and a negative phase modulation target element that correspond to the same time and belong to different bands from each other. A band carrier signal is selected, and a modulation process is performed on each of the samples of the sample sequence of the positive phase modulation signal waveform on the sequence of the positive phase modulation target elements, and the sequence of the negative phase modulation target elements is applied. 2. The digital watermark information embedding apparatus according to claim 1, wherein modulation processing is performed on each sample of the sample sequence of the modulation signal waveform having the opposite phase. Band division means for performing band division on a carrier signal for each block of a predetermined time length and outputting a plurality of band carrier signals belonging to different bands,
The plurality of band carrier signals are divided into symbol frames composed of a plurality of temporally continuous blocks, and a plurality of band carrier signals in each symbol frame are crossed between the bands of the plurality of band carrier signals. Demodulating means for performing demodulation processing on a plurality of modulation target elements distributed in the time axis direction over L blocks (L is an integer of 2 or more) and outputting a demodulation result signal;
A cross-correlation coefficient between a demodulation result signal obtained from the demodulation means and a modulation signal indicating a predetermined symbol is calculated, and digital watermark information embedded in the carrier signal is indicated based on the calculation result of the cross-correlation coefficient An electronic watermark information extracting device comprising: electronic watermark information extracting means for determining a symbol. A band division process for performing band division on a carrier signal for each block having a predetermined time length and outputting a plurality of band carrier signals belonging to different bands;
A modulated signal generating process for generating a sample sequence of a modulated signal waveform for one symbol corresponding to each symbol indicating digital watermark information;
The plurality of band carrier signals are divided into symbol frames composed of a plurality of temporally continuous blocks, and a plurality of band carrier signals in each symbol frame are crossed between the bands of the plurality of band carrier signals. And a modulation signal waveform for one symbol generated by the modulation signal generating means for a plurality of modulation target elements distributed in the time axis direction over L blocks (L is an integer of 2 or more) . An embedding process for performing modulation processing using each sample of the sample sequence;
A method of embedding digital watermark information, comprising: synthesizing a plurality of band carrier signals that have undergone processing in the embedding process, and outputting a carrier signal in which digital watermark information is embedded. A band division process for performing band division on a carrier signal for each block having a predetermined time length and outputting a plurality of band carrier signals belonging to different bands;
The plurality of band carrier signals are divided into symbol frames composed of a plurality of temporally continuous blocks, and a plurality of band carrier signals in each symbol frame are crossed between the bands of the plurality of band carrier signals. A demodulation process of performing demodulation processing on a plurality of modulation target elements distributed in the time axis direction over L blocks (L is an integer of 2 or more) and outputting a demodulation result signal;
A cross-correlation coefficient between a demodulation result signal obtained in the demodulation process and a modulation signal indicating a predetermined symbol is calculated, and digital watermark information embedded in the carrier signal is indicated based on the calculation result of the cross-correlation coefficient A method for extracting digital watermark information, comprising: a digital watermark information extracting step for determining a symbol. On the computer,
A band division process for performing band division on a carrier signal for each block having a predetermined time length and outputting a plurality of band carrier signals belonging to different bands;
A modulated signal generating process for generating a sample sequence of a modulated signal waveform for one symbol corresponding to each symbol indicating digital watermark information;
The plurality of band carrier signals are divided into symbol frames composed of a plurality of temporally continuous blocks, and a plurality of band carrier signals in each symbol frame are crossed between the bands of the plurality of band carrier signals. And a modulation signal waveform for one symbol generated by the modulation signal generating means for a plurality of modulation target elements distributed in the time axis direction over L blocks (L is an integer of 2 or more) . An embedding process for performing modulation processing using each sample of the sample sequence;
A computer program, comprising: combining a plurality of band carrier signals that have undergone the processing in the embedding process, and outputting a carrier signal in which digital watermark information is embedded. On the computer,
A band division process for performing band division on a carrier signal for each block having a predetermined time length and outputting a plurality of band carrier signals belonging to different bands;
The plurality of band carrier signals are divided into symbol frames composed of a plurality of temporally continuous blocks, and a plurality of band carrier signals in each symbol frame are crossed between the bands of the plurality of band carrier signals. A demodulation process of performing demodulation processing on a plurality of modulation target elements distributed in the time axis direction over L blocks (L is an integer of 2 or more) and outputting a demodulation result signal;
A cross-correlation coefficient between a demodulation result signal obtained in the demodulation process and a modulation signal indicating a predetermined symbol is calculated, and digital watermark information embedded in the carrier signal is indicated based on the calculation result of the cross-correlation coefficient A computer program for executing a digital watermark information extracting process for determining a symbol.

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