JP2010044147A - Device, method and program, for embedding and extracting electronic watermark information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promptly extract electronic watermark information from a carrier signal. <P>SOLUTION: In an embedding device 100, a band splitting section 110 splits a carrier signal into bands, and outputs a plurality of sub-band signals. Embedding sections 120-1 and 120-2 apply amplitude modulation by two phase modulation signals m1 and m0 for indicating symbols, on an amplitude envelope of two sub-band signals. A band synthesizing section 130 outputs the carrier signal by synthesizing the sub-band signal after the amplitude modulation, with other sub-band signal. A set of the modulation signals m1 and m0 includes a synchronous signal component for indicating a start point of a symbol frame. In an extraction device side, an embedding zone of a symbol string is determined by using the synchronous signal component as a key, and timing control of a band splitting section 230 for suitably extracting the watermark information from the embedding zone. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus, a method, and a program for embedding digital watermark information in a carrier signal such as an acoustic signal and extracting digital watermark information from the carrier signal.

Various techniques have been proposed in which an acoustic signal is used as a carrier signal and various digital watermark information is embedded in a part of the band of the carrier signal and transmitted. For example, in the technique disclosed in Patent Document 1, the embedding apparatus divides the carrier signal into a plurality of subband signals, and uses two-phase modulation signals corresponding to the symbols to be embedded in the subband signals of two bands among them. Modulation is performed, and a carrier signal in which digital watermark information is embedded is generated by synthesizing the subband signal subjected to this modulation and a subband signal of another band. In the extraction device, the carrier signal generated in the embedding device is band-divided into a plurality of subband signals, and modulation is performed from the subband signals of two bands to which symbol sequences are embedded among these subband signals. The modulation signal used in the above is demodulated to obtain a symbol string corresponding to the modulation signal.
JP 2006-251676 A

  By the way, in order for the extraction device that has received the carrier signal to extract a symbol string indicating digital watermark information from the carrier signal, the symbol string embedding interval in the carrier signal must be specified. In order to appropriately extract a symbol string from the subband signal obtained by dividing the carrier signal in the extraction device, the content of the band division performed on the carrier signal on the extraction device side is In other words, the relationship between the carrier signal and subband signal on the extraction device side is the same as the carrier signal and subband on the embedding device side. It is necessary to match the relationship with the signal. For example, in the band division processing on the embedding device side, for example, the carrier signal is divided into blocks each having a predetermined number of samples, and FFT (Fast Fourier Transform) of the sample sequence of the carrier signal is performed on a block basis. When generating a subband signal (in this case, a spectral coefficient), in the band division processing on the extraction device side, the carrier signal is ideally located at the same position as the division position where the carrier signal is divided into a plurality of blocks on the embedding device side. It is necessary to divide into a plurality of blocks and perform FFT. Therefore, under the prior art, an extraction device that has received a carrier signal performs band division of the carrier signal within the analysis range while sequentially shifting the analysis range from the beginning of the carrier signal, and subbands obtained by band division. The operation of demodulating the band signal and obtaining the correlation between the demodulation result and the modulation signal indicating bit “0” or “1” was repeated. The symbol string embedding interval is obtained based on the peak correlation. Since such an operation requires a large amount of calculation, there is a problem that it takes a long time from the reception of the carrier signal to the start of the extraction of the symbol string.

  The present invention has been made in view of the circumstances described above, and it is an object of the present invention to provide a technical means that makes it possible to quickly extract a symbol string of digital watermark information from a carrier signal with a small amount of calculation. And

The present invention includes a band dividing unit that performs band division on a carrier signal and outputs a plurality of subband signals belonging to different bands, and a two-phase modulation signal indicating each symbol constituting a symbol string indicating digital watermark information. A modulation signal generating means for outputting a two-phase modulation signal including a synchronization signal component indicating a start point of each symbol, and two subband signals forming part of the plurality of subband signals. An embedding unit that performs amplitude modulation using a modulation signal; and a band synthesizing unit that synthesizes a subband signal processed by the embedding unit with another subband signal and outputs a carrier signal in which digital watermark information is embedded. An electronic watermark information embedding device is provided.
The present invention also provides band dividing means for performing band division on a carrier signal and outputting a plurality of subband signals belonging to different bands, and an embedding destination of a symbol string indicating digital watermark information among the plurality of subband signals Are obtained in the generation process of the two embedding subband signals or the two embedding subband signals in the band dividing means, and the synchronization indicating the embedding interval of the symbol string is obtained from the acquired signals. A synchronization signal component extraction process for extracting a signal component is executed, and based on a result of the synchronization signal component extraction process, the two subband signals in the embedding section are output from the carrier signal to the band dividing unit. Synchronization control means for performing timing control, and demodulation processing on the two embedded subband signals. And demodulating means for outputting a demodulated result signal, and symbol determining means for dividing the demodulated result signal into an embedding section for one symbol and determining a symbol indicated by the demodulated result signal for each section. An apparatus for extracting digital watermark information is provided.
According to this invention, in the embedding device, a two-phase modulation signal indicating a symbol string of digital watermark information, and a two-phase modulation signal including a synchronization signal component indicating the start point of each symbol, Amplitude modulation of the two subband signals is performed. In the extraction device, a synchronization signal component that extracts a synchronization signal component from two embedding destination subband signals among a plurality of subband signals obtained by dividing a carrier signal or signals generated in the generation process thereof Extraction processing is executed, and based on the result of the synchronization signal component extraction processing, timing control is performed to output two embedding destination subband signals synchronized with the symbol string embedding interval to the band dividing means. As described above, in the present invention, since the modulation signal itself indicating the symbol sequence to be embedded includes the synchronization signal component, the extraction device side quickly executes the process of extracting the symbol sequence from the symbol sequence embedding interval in the carrier signal. can do.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a digital watermark information embedding device 100 according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a digital watermark information extracting device 200 according to the embodiment. Note that each of the embedding device 100 and the extracting device 200 may be realized as dedicated hardware for executing a process of embedding a symbol string indicating digital watermark information in a carrier signal or a process of extracting the symbol string from the carrier signal. In addition, the computer program may be implemented as a computer program that causes a computer to execute symbol string embedding processing and extraction processing.

  First, the electronic watermark information embedding device 100 will be described. As shown in FIG. 1, the embedding device 100 includes a band dividing unit 110, a band synthesizing unit 130, two embedding units 120-0 and 120-1 interposed therebetween, and an encoder 140. And a modulation signal generation unit 150.

  In the present embodiment, the carrier signal that plays a role in digital watermark information is an audio sample sequence obtained by sampling an audio waveform at a constant sampling rate. The band dividing unit 110 receives the audio sample sequence which is the carrier signal, performs band division, and outputs subband signals belonging to different M (M is an integer of 2 or more) bands. The band dividing unit 110 is, for example, an analysis filter bank. As illustrated in FIG. 3A, the analysis filter bank includes M analysis filters 111 and M downsamplers 112. Here, the M analysis filters 111 have different passbands and pass signals in the respective passbands in the carrier signal. Each of the M down-samplers 112 performs down-sampling in which the sample of the signal output from the analysis filter 111 in the previous stage is selected at a ratio of 1 to M, and outputs the selected sample as a subband signal.

  In the present embodiment, two embedding destination subband signals having adjacent bands among the M band subband signals obtained from the band dividing unit 110 are embedding destinations of symbol strings indicating digital watermark information. It is only necessary that the embedding device 100 and the extracting device 200 agree on which of the M band subband signals obtained by the band division is to be used as the embedding destination subband signal. The signal selection method is arbitrary.

  The encoder 140 is a device that performs an encoding process on the digital watermark information and outputs a symbol string indicating the digital watermark information. The modulation signal generation unit 150 is a means for generating a two-phase modulation signal indicating a symbol string to be embedded and having an opposite phase relationship to each other. In the example illustrated in FIG. 1, the modulation signal generation unit 150 includes a waveform memory 151 and a waveform reading unit 152. The waveform memory 151 stores each sample sequence of the positive and reverse two-phase modulation signals m1 and m0 corresponding to the bit “0” and each sample sequence of the normal and reverse two-phase modulation signals m1 and m0 corresponding to the bit “1”. I remember it. When the encoder 140 outputs the bit “0” as the symbol to be embedded, the waveform reading unit 152 reads each sample sequence of the modulation signals m1 and m0 corresponding to the bit “0” from the waveform memory 151, The sample sequence of the modulation signal m1 is supplied to the embedding unit 120-1, and the sample sequence of the modulation signal m0 is supplied to the embedding unit 120-0. When the symbol to be embedded is bit “1”, each sample sequence of modulation signals m1 and m0 corresponding to bit “1” is read from the waveform memory 151 and supplied to the embedding units 120-1 and 120-0. To do.

  The embedding units 120-1 and 120-0 are specifically multipliers, and amplitude modulation using two-phase modulation signals m 1 and m 0 indicating a symbol sequence to be embedded for two embedding destination subband signals. By performing each processing, each subband signal having an amplitude envelope modulated by the modulation signal of each phase is output.

  The band synthesizing unit 130 synthesizes the subband signals obtained from the embedding units 120-0 and 120-1 and the subband signals of other bands output from the band dividing unit 110, and embeds digital watermark information. Output as a carrier signal. The band synthesis unit 130 is, for example, a synthesis filter bank. As illustrated in FIG. 3B, the synthesis filter bank includes an upsampler 131 that inserts M−1 zero samples between each sample of the subband signals for each of the subband signals having M bands. The M synthesis filters 132 that perform filter processing corresponding to the inverse transformation of the analysis filter 111 corresponding to each of the output signals of each upsampler 131 and the output signals of the respective synthesis filters 111 are added together to obtain a digital watermark. The adder 133 outputs a carrier signal in which information is embedded.

  A feature of the present embodiment is that the two-phase modulation signals m1 and m0 supplied to the embedding units 120-1 and 120-0 by the modulation signal generation unit 150 include a synchronization signal component indicating a symbol start point. FIG. 4 illustrates the waveforms of the modulation signals m1 and m0 in the present embodiment. In the example shown in FIG. 4, the modulation signals m1 and m0 are rectangular wave signals with one symbol frame as one cycle. As shown in FIG. 4, a set of modulation signals m1 and m0 corresponding to bit “0” and a set of modulation signals m1 and m0 corresponding to bit “1” are common at a common relative time in one symbol frame. It has the characteristics. That is, it is a set of a rising edge of the modulation signal m1 and a falling edge of the modulation signal m0 that appear at the start point of the symbol frame. Therefore, when the modulation signal generation unit 150 continuously outputs the modulation signals m1 and m0 corresponding to each symbol in response to the symbols sequentially supplied from the encoder 140, the modulation signals m1 and m0 At the common relative time of the symbol frame (in this example, the start timing of the symbol frame), a common feature of a set of a rising edge of the modulation signal m1 and a falling edge of the modulation signal m0 appears. In the present embodiment, a common feature between the symbols of the modulation signals m1 and m0 appearing at the common relative time of each symbol frame plays a role as a synchronization signal component.

In the present embodiment, the levels of the modulation signals m1 and m0 are inverted at a common timing in the middle of one symbol frame. The position of the level inversion timing in one symbol frame represents the symbol type. More specifically, in the example shown in FIG. 4, the levels of the modulation signals m1 and m0 corresponding to the bit “0” are inverted at the timing when 25% of the symbol frame length has elapsed from the start timing of the symbol frame. On the other hand, the levels of the modulation signals m1 and m0 corresponding to the bit “1” are inverted at the timing when 75% of the symbol frame length has elapsed from the start timing of the symbol frame.
The above is the details of the embedding device 100 shown in FIG.

  Next, the digital watermark information extraction apparatus 200 will be described with reference to FIG. As illustrated in FIG. 2, the extraction device 200 includes a buffer 210, a read control unit 220, a band division unit 230, a demodulation unit 240, a synchronization control unit 250, a symbol determination unit 260, and a decoder 270. Have The operation of the extraction device 200 can be roughly divided into a synchronization phase and a symbol extraction phase. Here, the synchronization phase detects an embedded section in which a symbol string indicating digital watermark information is embedded in a carrier signal, and causes the band dividing unit 220 to output two embedded subband signals synchronized with the embedded section. This is the phase for timing control. The symbol extraction phase is a phase in which a symbol string is extracted from the embedded section detected by the synchronization phase in the carrier signal. Each part of the extraction device 200 may operate differently in the synchronization phase and the symbol extraction phase.

  The buffer 210 plays a role of storing a carrier signal in which digital watermark information is embedded for a predetermined period of time. A carrier signal (audio signal) in which digital watermark information is embedded by the embedding device 100 described above is emitted into the air as, for example, sound, collected by a sound collecting device (not shown), and a carrier that is a time-series sample of a speech waveform. A signal is written into the buffer 210. The read control unit 220 is a device that reads the carrier signal stored in the buffer 210.

  The band dividing unit 230 has the same configuration as the band dividing unit 110 of the embedding device 100, performs band division on the sample sequence of the carrier signal read from the buffer 210 by the read control unit 220, and subbands for M bands. Output a sample sequence of signals.

  The demodulator 240 selects two embedding destination subband signals, which are embedding destinations of symbol strings indicating digital watermark information, from the M band subband signals, and performs demodulation processing on the two embedding destination subband signals. It is a device to apply. In this demodulator 240, the envelope detectors 241 and 242 are, for example, low-pass filters, detect the amplitude envelope components of the two embedding destination subband signals, and output sample sequences of the respective amplitude envelope components. The division unit 243 divides each sample of the amplitude envelope component output from the envelope detection unit 241 by each sample of the amplitude envelope component output from the envelope detection unit 242 and outputs each sample indicating the division result. The logarithmic conversion unit 244 calculates the logarithm of the sample of the division result output from the division unit 243 and outputs it as a demodulation result signal.

  Here, since the two embedding destination subband signals given from the band dividing unit 230 to the demodulating unit 240 are in adjacent bands, the sample sequences of the amplitude envelope components output from the envelope detection units 241 and 242 are as follows: If there is no modulation by the modulation signals m1 and m0, the contents are approximate to each other. Therefore, when the operation of the extraction device 100 is synchronized with the operation of the embedding device 100, the demodulation result signal obtained from the demodulation unit 240 is ideally a modulation signal generated for embedding symbols in the embedding device 100. The signal has the same waveform as one of m1 or m0 (modulated signal m1 in this example). Here, “the operation of the extraction device 100 is synchronized with the operation of the embedding device 100” means that the following two conditions are satisfied. The first condition is that the embedding destination subband signal output from the band dividing unit 230 is in a section modulated by the modulation signal m1 or m0 indicating the symbol string. For example, when the band dividing unit 110 of the embedding device 100 and the band dividing unit 230 of the extracting device 200 are analysis filter banks as shown in FIG. The sampling timing of the downsampler 112 in the extraction device 200 is controlled so that the downsampler 112 in the extraction device 200 outputs a sample at the same timing as the sample output as the embedding destination subband signal. It is a condition.

  The synchronization control unit 250 is a device that detects a symbol string embedding interval in a carrier signal in a synchronization phase. In this embodiment, when the carrier signal is received and the writing of the carrier signal to the buffer 210 is started, the extraction device 200 starts the operation of the synchronization phase. In this synchronization phase, the carrier signal written in the buffer 210 is immediately read out by the read control unit 220 and is processed by the band dividing unit 230. During this time, the synchronization control unit 250 generates a signal generated in the process of generating two embedding destination subband signals, which are embedding destinations of symbol sequences indicating digital watermark information, from the M subband signals. And executing a synchronization signal component extraction process for extracting a synchronization signal component indicating a symbol string embedding interval from the acquired signal, and based on the result of the synchronization signal component extraction process, two embedding destinations of the embedding interval Timing control for outputting the subband signal to the band dividing unit 230 is performed. In the aspect in which the band dividing unit 110 in the embedding device 100 and the band dividing unit 230 in the extracting device 200 are both analysis filter banks as shown in FIG. 3A, the processing content of the synchronization control unit 250 is as follows. It will be like that. That is, in the analysis filter bank that is the band dividing unit 230, the synchronization control unit 250 generates a synchronization signal from the output signals of the two analysis filters 111 in the previous stage of the two downsamplers 112 that output the two embedding destination subband signals, respectively. By extracting the components, the start point of the symbol string embedding interval in the output signals of the two analysis filters 111 is obtained, and the two downsamplers 112 subsequent to the two analysis filters 111 are used in the output signals of the two analysis filters 111. The sampling timing of the two downsamplers 112 is controlled so that the sample at the start point of the embedding interval is selected and output.

  Here, the meaning of the processing performed by the synchronization control unit 250 will be described with reference to FIG. 5A shows a sample sequence of a carrier signal given to the embedding device 100, FIG. 5B shows a sample sequence output by the analysis filter 111 in the band dividing unit 110 of the embedding device 100, and FIG. ) Shows a sample sequence of the embedding destination subband signal output from the band dividing unit 110 of the embedding device 100. In this example, M = 8, and the down sampler 112 selects the samples output from the analysis filter 111 at a rate of 1 out of 8 samples, and outputs it as an embedding destination subband signal. FIG. 5D shows an embedding subband signal that has undergone amplitude modulation processing. The white circle is a sample modulated by an L level modulation signal, and the black circle is a sample modulated by an H level modulation signal. Show. FIG. 5E shows the output of the synthesis filter 132 that receives the embedded subband signal that has undergone the amplitude modulation processing through the upsampler 131 in the synthesis filter bank of FIG. A sample sequence of signals is shown. 5B to 5E, one of the two embedding destination subband signals (for example, supplied to the embedding unit 120-1) is used in the embedding device 100 in order to prevent the drawing from becoming complicated. Only the waveform of the signal related to the embedded subband signal) is shown. FIG. 5 (f) shows a carrier signal given to the extraction device 200, and FIG. 5 (g) shows a sample string output by the analysis filter 111 in the band dividing unit 230 of the extraction device 200. 5 (h) and 5 (i) show a sample string of the embedding destination subband signal output from the band dividing unit 230, and FIG. 5 (h) shows before the processing of the synchronization control unit 250 is performed. FIG. 5 (i) shows the sample sequence of the embedding destination subband signal that has been synchronized with the embedding interval through the processing of the synchronization control unit 250, respectively. In FIGS. 5G to 5I, one of the two embedding destination subband signals (for example, the embedding destination subband signal supplied to the envelope detection unit 241) is used to prevent the drawing from becoming complicated. Only the waveform of the signal related to) is illustrated.

  In the present embodiment, the extraction device 200 operates completely asynchronously with the embedding device 100. Therefore, the downsampler 112 in the band dividing unit 230 of the extraction apparatus 200 selects and outputs as a sample of the embedding destination subband signal from the sample sequence output from the analysis filter 111, and the band division of the embedding apparatus 100. There is no guarantee that the sample output by the downsampler 112 in the unit 110 as the sample of the subband signal to be embedded matches, and in general, the two samples are different as shown in FIG. . Therefore, in the present embodiment, the synchronization control unit 250 outputs a sample string of output signals of the two analysis filters 111 in the preceding stage of the two downsamplers 112 that output the two embedded subband signals (one of which is shown in FIG. g)) is monitored and a rising edge is generated in the signal corresponding to the embedded subband signal sent to the envelope detector 241 and the signal corresponding to the embedded subband signal sent to the envelope detector 242 is detected at the same time. When the occurrence of a falling edge is first detected (the change point from a white circle to a black circle in FIG. 5G), the generation point of the rising edge and the falling edge is set as the start point of the symbol string embedding interval, and the band Two downsamplers 112 in the dividing unit 230 select and output a sample at the start point of the embedding interval. Controlling the sampling timing of the sampler 112. Also, the synchronization control unit 250 obtains the start point of the symbol string embedding interval from among the carrier signal samples in the buffer 210 based on the rising edge and falling edge occurrence points. When the above processing is completed, the operation of the extraction apparatus 200 is the symbol extraction phase.

  In the symbol extraction phase, the synchronization control unit 250 causes the read control unit 220 to read the sample sequence of the carrier signal starting from the sample at the start point of the embedding interval obtained in the synchronization phase from the buffer 210, and the carrier in this embedding interval. The signal is processed by the band division unit 230, the demodulation unit 240, and the symbol determination unit 260. At this time, the downsampler 112 in the band dividing unit 230 includes the embedding destination subband signal out of the sample sequence output from the analysis filter 111 in the band dividing unit 230. A sample having the same timing as the selected sample is selected as a sample of the sub-band signal to be embedded (see FIGS. 5C, 5D, and 5I).

The symbol determination unit 260 is a device that extracts a symbol string indicating digital watermark information from the demodulation result signal in the extraction phase. More specifically, the symbol determination unit 260 divides the demodulation result signal output from the demodulation unit 240 into symbol frame length sections in the extraction phase, and determines the type of symbol indicated by the demodulation result signal for each section. To do. As a determination method of the symbol type, the position in the symbol frame of the level inversion timing appearing in the demodulation result signal is obtained, and the symbol is bit “0” depending on whether the position is in the first half or the second half of the symbol frame. A method of determining whether the bit is “1” or not is also conceivable. However, since the demodulation result signal includes noise, it is difficult to accurately determine a symbol by this method. Therefore, in this embodiment, the time integration value of the demodulation result signal in one symbol frame is obtained, and this time integration value is used as the demodulation result signal in one symbol frame when the demodulation result signal always maintains a predetermined maximum value. The duty ratio is calculated by dividing by the time integral value of, and whether the symbol indicated by the demodulation result signal is bit “0” or bit “1” depending on whether this duty ratio is lower or higher than 50% Determine. Then, the decoder 270 converts the series of symbols determined by the symbol determination unit 260 into digital watermark information.
The above is the details of the present embodiment.

  According to the present embodiment, since the modulation signal itself indicating the symbol includes the synchronization signal component indicating the start point of the symbol, the extraction device 200 side generates the synchronization signal from the signal generated in the generation process of the embedding destination subband signal. By detecting the component corresponding to the component, the process of identifying the symbol string embedding interval in the carrier signal, synchronizing the operation of the band dividing unit 230 with the symbol string embedding interval, and immediately extracting the symbol string from the carrier signal. Can start. Therefore, according to the present embodiment, there is an effect that it is possible to shorten the time from the reception of the carrier signal on the extraction apparatus 200 side to the extraction of the symbol string. In addition, since the amount of calculation for obtaining the symbol string embedding interval is small, the extraction device 200 can be made small. Further, according to the present embodiment, a two-phase rectangular wave is employed as a modulation signal for symbol embedding instead of a sine wave as disclosed in Patent Document 1. The two-phase rectangular wave employed as the two-phase modulation signal in this embodiment has a pair of rising edge and falling edge at the timing indicating the start of the symbol, and this is a sync signal component. Play a role. Therefore, according to the present embodiment, it is possible to improve the time accuracy of detection of the embedded section on the extraction device 200 side as compared with the case where the modulation signal waveform is a sine wave or the like.

<Other embodiments>
Although one embodiment of the present invention has been described above, various other embodiments are conceivable for the present invention. For example:

(1) Various modes can be considered for the modulation signals m1 and m0 generated by the modulation signal generation unit 150, as illustrated in FIGS. 6A shows the modulation signals m1 and m0 generated by the modulation signal generation unit 150 in the above embodiment. This is listed for comparison with others.

  The modulation signals m1 and m0 shown in FIG. 6B are almost in reverse phase, but there is a slight phase shift between them, and a delay of a very short time from the rising edge (falling edge) of the modulation signal m1. As a result, the modulation signal m0 falls (rises). Also in this aspect, the same effect as the above embodiment can be obtained. Further, according to this aspect, since the edges of the modulation signals m1 and m0 are not aligned on the time axis, it is possible to reduce the influence on the audibility when the carrier signal in which the symbol string is embedded is emitted as sound. Be expected.

  The modulation signals m1 and m0 shown in FIG. 6 (c) have a sharp rising edge and a sharp falling edge at the start point of the symbol frame, but the level is inverted by drawing a gentle slope in the middle of the symbol frame. ing. Since the edge at the start point of the symbol frame plays a role as a synchronization signal component, it is required to be local on the time axis in order to improve the detection accuracy of the embedded section. Therefore, the edge at the start point of the symbol frame is a sharp edge. On the other hand, the level reversal position in the middle of the symbol frame only needs to be accurate enough to express bit “1” and bit “0” in one symbol frame. Therefore, in this aspect, level inversion in the middle of the symbol frame is performed by drawing a gentle slope so as to mitigate the effect on hearing when the carrier signal in which the symbol string is embedded is emitted as sound. It is.

  In the aspect shown in FIG. 6D, the rising edge of the modulation signal m1 and the falling edge of the modulation signal m0 that play the role of the synchronization signal component are generated after a predetermined delay time from the start timing of the symbol frame. In this aspect, when a rising edge (a component corresponding to the synchronization signal component) appears in the signal acquired from the band dividing unit 230 in the synchronization phase, the synchronization control unit 250 performs the delay from the detection point of the rising edge. The point in time that is back by the amount equivalent to the time is set as the start point of the embedded section, and the process proceeds to the extraction phase.

(2) In order to make the detection of the symbol string embedding interval more accurate, the synchronization signal component is detected over a plurality of times from the signal generated in the generation process of the embedding destination subband signal, and When it is confirmed that the interval has a length corresponding to the symbol frame, the detection position of the first synchronization signal component may be determined as the start point of the symbol string embedding interval.

(3) In the above embodiment, in the extraction apparatus 200, the sample sequence output from the analysis filter 111 in the preceding stage of the downsampler 112 is subjected to edge detection. However, when the requirements regarding the time accuracy of edge detection are not strict, The downsampler 112 performs downsampling at a downsampling ratio M smaller than the normal downsampling ratio M (downsampling ratio in the extraction phase), and the subband signal obtained as a result (output from the band dividing unit 230 in the extraction phase) The subband signal having a lower sample rate than the subband signal to be detected) may be the object of edge detection.

(4) In the above-described embodiment, the synchronization control unit 250 outputs each output of each analysis filter 111 in the previous stage of each downsampler 112 that outputs a two-phase embedded subband signal in the analysis filter bank that is the band dividing unit 230. It was detected that a pair of rising and falling edges appeared in the signal. However, instead of doing this, the synchronization control unit 250 may perform the following processing. First, the synchronization control unit 250 monitors the envelope component of the two-phase embedding subband signal output from the band dividing unit 230 or the two-phase embedding subband signal output from the envelope detection units 241 and 242. , A pair of rising and falling edges is detected. Then, when a pair of rising edge and falling edge is detected, a sample of the carrier signal corresponding to the detected position is obtained, and a reading start position is set a predetermined number of samples before this sample, Reading of the sample and supply of the sample to the band dividing unit 230 are started. At this stage, the synchronization control unit 250, in the band dividing unit 230, outputs each of the analysis filters 111 in the preceding stage of each downsampler 112 that outputs a two-phase embedded subband signal, as in the above embodiment. It is detected that a pair of rising and falling edges appears in the output signal, and that detection point is specified as the start point of the symbol string embedding interval. In this aspect, the sum of the number of samples of the embedding destination subband signal and the number of samples of the output signal of the analysis filter 111 monitored by the synchronization control unit 250 to obtain the start point of the embedding interval is synchronized in the above embodiment. This is smaller than the number of samples of the output signal of the analysis filter 111 monitored by the control unit 250 to obtain the start point of the embedding interval. Therefore, the calculation amount of the synchronization control unit 250 can be reduced.

(5) In the above embodiment, the band dividing units 110 and 230 are configured by the analysis filter bank, and the band synthesis unit 130 is configured by the synthesis filter bank. However, the band dividing units 110 and 230 may be those that perform band division by FFT, and the band synthesizing unit 130 may be one that performs band synthesis by inverse FFT. Hereinafter, an operation example of this aspect will be described with reference to FIG.

  In this aspect, the band dividing unit 110 of the embedding device 100 performs band division of the carrier signal, for example, as follows. First, the band dividing unit 110 divides the sample sequence of the carrier signal into a plurality of blocks including a predetermined number of samples. Here, when the number of samples per block is N, for example, it is preferable to divide the blocks into blocks that are out of phase by N / 2 samples and overlap each other on the time axis. Next, the band dividing unit 110 multiplies each divided block by a predetermined window function, performs FFT on the sample sequence of the block after the window function multiplication, and obtains a plurality of spectral coefficients respectively corresponding to a plurality of bands. calculate. Each of these spectral coefficients becomes a subband signal. In the embedding device 100, subband signals in two bands among these subband signals are subjected to amplitude modulation using a modulation signal indicating a symbol string. In the sample row of subband signals shown in the upper part of FIG. 7, the last two rows of subband signals are embedding destination subband signals, white circles are samples modulated by L level modulation signals, and black circles are H level modulations. A sample modulated by the signal. The modulated subband signal and other subband signals are combined after being subjected to inverse FFT, and supplied to the extraction apparatus 200 as a carrier signal in which digital watermark information is embedded.

  Here, in order to correctly extract the modulation signal indicating the symbol sequence from the carrier signal on the extraction device 200 side, in addition to specifying the start point of the symbol string embedding interval in the carrier signal, Timing control of the band dividing unit 230 must be performed so that the band dividing unit 110 divides the carrier signal into a plurality of blocks at a dividing position that is the same as or very close to the dividing position where the carrier signal is divided into a plurality of blocks. . Therefore, in the synchronization phase, the band dividing unit 230 is controlled by the control by the synchronization control unit 250, rather than the phase difference between the blocks when the band dividing unit 110 of the embedding device 100 divides the carrier signal into a plurality of blocks. The carrier signal is divided into a plurality of blocks by reducing the phase difference between them, and division into subband signals is performed for each block by performing multiplication of the window function and FFT. In the example illustrated in FIG. 7, when the block size is N samples, the band dividing unit 220 divides the carrier signal into blocks whose phases are shifted by N / 8 samples, and performs multiplication of the window function and FFT for each block. To generate subband signals.

  During this time, the synchronization control unit 250 monitors the amplitude envelope components of the embedding subband signals of the two bands among the subband signals output from the band dividing unit 230, and a pair of rising and falling edges appears. Is detected. Then, the synchronization control unit 250 specifies the symbol string embedding interval in the carrier signal based on the detection timing of the pair of rising edge and falling edge, and obtains an appropriate block delimiter position in the carrier signal. For example, when a pair of rising edge and falling edge indicates the starting point of a symbol, a sample of subband signals (shown in FIG. 7) located in the pair of rising edge and falling edge in FFT for each block of the carrier signal. In the example, the starting point of the block used to calculate the two samples corresponding to the black circle and the white circle after the transition in the section where the transition from the white circle to the black circle and the transition from the black circle to the white circle occurs is embedded. Determined as the start point of the section. Then, the delimiter positions arranged at N / 2 sample intervals after the start point of the embedding interval are set as appropriate block delimiter positions.

  Then, in the extraction phase, the synchronization control unit 250 supplies the carrier signal in the embedded section of the symbol sequence obtained in the synchronization phase from the buffer 210 to the band dividing unit 230, and at the appropriate delimiter position obtained in the synchronization phase. Then, the timing of the band dividing unit 230 is controlled so that the carrier signal is divided into blocks, and a symbol string is extracted from the subband signal. In this extraction phase, the band dividing unit 230, like the band dividing unit 110 of the embedding device 100, is divided into a plurality of blocks each consisting of N samples, with phases shifted by N / 2 samples and overlapping on the time axis. Then, division into subband signals is performed for each block. This is to reduce the sample rate of the subband signal output from the band dividing unit 230 and reduce the calculation amount of the demodulation unit 240 and the symbol determination unit 260.

  This embodiment may be modified as in the above embodiment (4). That is, in the extraction phase, the band dividing unit 230 divides the carrier signal into a plurality of blocks whose phases are shifted by N / 2 samples and overlap on the time axis until the rough position of the embedded section is known. Dividing into band signals, the synchronization control unit 250 waits for a pair of rising and falling edges to appear in the two embedding destination subband signals. Then, when a pair of rising edge and falling edge is detected, a sample of the carrier signal corresponding to the detected location is obtained, and a reading start position is set a predetermined number of samples before this sample, and the buffer 210 The reading of the samples and the supply of the samples to the band dividing unit 230 are started. At this stage, the synchronization control unit 250 causes the band dividing unit 230 to divide the carrier signal into a plurality of blocks having a phase difference of N / 8 samples, for example, and divide the carrier signal into subband signals. Then, it is detected that a pair of rising edge and falling edge appears in the two-phase embedding destination subband signal output from the band dividing unit 230, and the detection point is set as the start point of the symbol string embedding interval and an appropriate block. It is specified as the delimiter position.

(6) In the embodiment described above, two types of modulation signal level inversion position candidates in the middle of a symbol frame are provided, and a binary symbol is represented by the modulation signal by selecting a level inversion position from these. However, three or more types of level inversion position candidates of the modulation signal may be provided, and a symbol having three or more values may be represented by the modulation signal by selecting a level inversion position from these.

(7) In the above embodiment, the digital watermark information is embedded in the carrier signal and the digital watermark information is extracted from the carrier signal. However, all or part of the embedding process and the extraction process may be replaced with analog signal processing.

1 is a block diagram showing a configuration of a digital watermark information embedding device 100 according to an 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. 3 is a block diagram illustrating the configuration of an analysis filter bank that is an example of a band dividing unit 110 and a synthesis filter bank that is an example of a band synthesis unit 130 in the embodiment. FIG. It is a figure which illustrates the waveform of the modulation signals m1 and m0 which the modulation signal generation part 150 produces | generates in the same embodiment. It is a figure explaining the processing content of the synchronization control part 250 in the embodiment. It is a figure which shows the various examples of the modulation signals m1 and m0. It is a figure which shows the operation example of the embedding apparatus 100 and the extraction apparatus 200 which are other Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Embedding device, 200 ... Extraction device, 110, 230 ... Band division unit, 120-1, 120-2 ... Embedding unit, 130 ... Band synthesis unit, 140 ... Encoder, 150 ... Modulation signal generation unit 151... Waveform memory 152... Waveform readout unit 210... Buffer, 220... Read control unit 240 .. demodulation unit 241 242. 244... Logarithmic conversion unit 111... Analysis filter 112. Down sampler 131. Up sampler 132. Synthesis filter 133. Adder 250. Synchronization control unit 260 Symbol Determination unit, 270... Decoder.

Claims (10)

Band dividing means for performing band division on the carrier signal and outputting a plurality of subband signals belonging to different bands;
Modulation signal generating means for outputting a two-phase modulation signal including a synchronization signal component indicating a starting point of each symbol, which is a two-phase modulation signal indicating each symbol constituting a symbol string indicating electronic watermark information;
Embedding means for performing amplitude modulation by the two-phase modulation signal on two subband signals forming part of the plurality of subband signals;
Embedded in digital watermark information, comprising: band combining means for combining a subband signal processed by the embedding means with other subband signals and outputting a carrier signal in which the digital watermark information is embedded. apparatus.   The modulation signal generating means outputs a two-phase modulation signal that is reverse between the phases of the two-phase modulation signal and that has a combination of level transitions common between the symbols as the synchronization signal component. The digital watermark information embedding device according to claim 1.   The modulation signal generating means outputs a two-phase modulation signal whose level is inverted at a position determined by the type of the symbol in a section corresponding to one symbol, as a two-phase modulation signal indicating various symbols. The electronic watermark information embedding device according to claim 1 or 2. Band dividing means for performing band division on the carrier signal and outputting a plurality of subband signals belonging to different bands;
Of the plurality of subband signals, two embedding destination subband signals which are embedding destinations of symbol strings indicating digital watermark information or signals generated in the generation process of the two embedding destination subband signals in the band dividing means And executing a synchronization signal component extraction process for extracting a synchronization signal component indicating an embedding interval of the symbol sequence from the acquired signal, and based on a result of the synchronization signal component extraction process, the embedding from the carrier signal Synchronization control means for performing timing control for causing the band dividing means to output the two embedding destination subband signals in the section;
Demodulation means for performing demodulation processing on the two embedded subband signals and outputting a demodulation result signal;
An apparatus for extracting digital watermark information, comprising: a symbol determination unit that divides the demodulation result signal into embedded sections of one symbol and determines a symbol indicated by the demodulation result signal for each section. The band dividing means includes a plurality of analysis filters that separate the carrier signal into components belonging to different bands, and a plurality of subband signals that are output by down-sampling the output signals of the plurality of analysis filters, respectively. An analysis filter bank with a downsampler,
The synchronization control means outputs the output signals of the two analysis filters preceding the two downsamplers that respectively output the two embedded subband signals in the analysis filter bank or the output signals of the two analysis filters. By extracting the synchronization signal component from the signal down-sampled at a down-sampling ratio lower than the down-sampling normally performed by two down-samplers, the start point of the symbol string embedding interval in the output signals of the two analysis filters is obtained. The sampling timing of the two down samplers is controlled so that the two down samplers at the subsequent stage of the two analysis filters select and output the sample at the start point of the embedding interval in the output signals of the two analysis filters. In claim 4, characterized in that Extractor of the watermark information of the placement. The band dividing unit is a unit that divides the carrier signal into a plurality of blocks arranged on the time axis with a phase difference from a preceding block, and performs band division into subband signals for each block. Yes,
The synchronization control unit causes the band dividing unit to reduce the phase difference between blocks to perform band division, and extracts the synchronization signal component from two embedding destination subband signals obtained from the band dividing unit. When the band dividing unit divides the carrier signal into a plurality of blocks so that the embedded section of the symbol sequence in the carrier signal is obtained, and the band dividing means outputs the subband signal sample of the embedded section. 5. The digital watermark information extracting apparatus according to claim 4, wherein the separation position is controlled. A band division process of performing band division on the carrier signal and outputting a plurality of subband signals belonging to different bands;
A modulation signal generation process for outputting a two-phase modulation signal including a synchronization signal component indicating a start point of each symbol, which is a two-phase modulation signal indicating each symbol constituting a symbol string indicating digital watermark information;
An embedding process in which two subband signals forming part of the plurality of subband signals are subjected to amplitude modulation by the two-phase modulation signal;
A subband signal that has undergone the processing of the embedding process is combined with another subband signal, and a band synthesizing process that outputs a carrier signal in which the digital watermark information is embedded is provided. Method. A band division process of performing band division on the carrier signal and outputting a plurality of subband signals belonging to different bands;
Of the plurality of subband signals, two embedding destination subband signals which are embedding destinations of symbol strings indicating digital watermark information or signals generated in the generation process of the two embedding destination subband signals in the band division process And executing a synchronization signal component extraction process for extracting a synchronization signal component indicating an embedding interval of the symbol sequence from the acquired signal, and based on a result of the synchronization signal component extraction process, the embedding from the carrier signal A synchronization control process for performing timing control to output the two embedded subband signals of the section in the band division process;
A demodulation process of performing demodulation processing on the two embedded subband signals and outputting a demodulation result signal;
A method of extracting digital watermark information, comprising: a symbol determination step of dividing the demodulation result signal into embedded sections of one symbol and determining a symbol indicated by the demodulation result signal for each section. On the computer,
A band division process of performing band division on the carrier signal and outputting a plurality of subband signals belonging to different bands;
A modulation signal generation process for outputting a two-phase modulation signal including a synchronization signal component indicating a start point of each symbol, which is a two-phase modulation signal indicating each symbol constituting a symbol string indicating digital watermark information;
An embedding process in which two subband signals forming part of the plurality of subband signals are subjected to amplitude modulation by the two-phase modulation signal;
A computer program for performing a band synthesis process for synthesizing a subband signal that has undergone the process of the embedding process with other subband signals and outputting a carrier signal in which digital watermark information is embedded. On the computer,
A band division process of performing band division on the carrier signal and outputting a plurality of subband signals belonging to different bands;
Of the plurality of subband signals, two embedding destination subband signals which are embedding destinations of symbol strings indicating digital watermark information or signals generated in the generation process of the two embedding destination subband signals in the band division process And executing a synchronization signal component extraction process for extracting a synchronization signal component indicating an embedding interval of the symbol sequence from the acquired signal, and based on a result of the synchronization signal component extraction process, the embedding from the carrier signal A synchronization control process for performing timing control to output the two embedded subband signals of the section in the band division process;
A demodulation process of performing demodulation processing on the two embedded subband signals and outputting a demodulation result signal;
A computer program that executes a symbol determination step of dividing the demodulation result signal into embedded sections of one symbol and determining a symbol indicated by the demodulation result signal for each section.

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