WO2006027823A1

WO2006027823A1 - Electronic watermark device, authentication processing device, decoding processing device, and re-quantization device

Info

Publication number: WO2006027823A1
Application number: PCT/JP2004/012947
Authority: WO
Inventors: Hiroshi Ito; Mitsuyoshi Suzuki; Ryousuke Fujii; Tomohiro Kimura; Koichi Magai
Original assignee: Mitsubishi Denki Kabushiki Kaisha
Priority date: 2004-09-06
Filing date: 2004-09-06
Publication date: 2006-03-16
Also published as: JP4624359B2; JPWO2006027823A1

Abstract

There is provided a signature circuit (1) for quantizing an image signal, calculating an authenticator from the quantization index of the image signal, an embedding the authenticator in the quantization index. On the other hand, there is provided an encoder (2) for calculating a difference signal between the image signal and the reference signal, quantizing the difference signal according to the quantization index having the authenticator embedded by the signature circuit (1), and outputting the quantization index of the difference signal.

Description

Specification

Digital watermarking device, authentication processing device, decryption processing device, and requantization device

[0001] The present invention relates to, for example, a digital watermark device that embeds electronic watermarks in multimedia data such as image signals and audio signals, an authentication processing device that authenticates multimedia data in which digital watermarks are embedded, and a digital watermark The present invention relates to a decoding processing device that decodes multimedia data in which is embedded, and a requantization device that requantizes multimedia data in which a digital watermark is embedded.

Background art

[0002] As a general method for authenticating digital data that has been properly issued and has not been altered, there is a method such as an electronic signature.

The principle of the electronic signature method is that the issuer creates an authentication code by encrypting the hash value of the digital data, and sends the authentication code together with the digital data.

On the receiving side, the authentication code sent from the issuer is decrypted, the hash value of the digital data is recalculated, the authenticity of the digital data is compared with the authentication value and the authentication code. Confirm.

[0003] When digital data is image data or audio data, a number of electronic permeability devices have been proposed in which the authentication code is embedded in the digital data as a digital watermark so that the authentication code is securely linked to the digital data. (For example, see Non-Patent Document 1).

In Non-Patent Document 1, a hash value is calculated from the DCT (Discrete Cosine Transform) coefficient for moving image data encoded in particular with MPEG (Motion Pictures Experts Group), and the no-shake value is electronically calculated. A method of embedding as a permeability is disclosed. According to this method, if the DCT coefficient value in the code key data changes even a little, it is possible to detect the change on the receiving side.

In the electronic permeability device disclosed in Non-Patent Document 1, the code amount is reduced. For this reason, in a moving image, if temporally adjacent images are similar to each other, it is possible to perform predictive coding that transmits only the difference using the characteristic.

[0004] Non-Patent Document 1: R. Du and J. Fridrich, "Lossless authentication of MPE

G— 2 video, Proceedings of IEEE International Conference on Image Processing, September 2002

[0005] The conventional electronic permeability device is configured as described above. Therefore, when the code amount is reduced by transmitting the differential signal of the moving image data adjacent to each other, the receiving side is required. Differential signal force Once the video data is decoded, the differential signal cannot be reproduced. For this reason, the hash value embedded in the difference signal also disappears simultaneously with the decoding of the moving image data, and the authentication function is lost.

[0006] The present invention has been made to solve the above-described problems, and can provide multimedia data without losing the authentication function even when multimedia data such as images and sounds are decoded. The purpose is to obtain an electronic permeability device.

The present invention also provides an authentication processing device that authenticates multimedia data that is also provided with the above-described electronic transparency and device power, a decryption processing device that decrypts the multimedia data, and requantizes the multimedia data. The object is to obtain a requantizer. Disclosure of the invention

[0007] The digital watermarking apparatus according to the present invention quantizes an input signal, calculates an authenticator from a quantum index cover of the input signal, and embeds the authenticator in the quantized index. While providing the signature means, obtain the difference signal between the input signal and the reference signal, quantize the difference signal according to the quantization index in which the authenticator is embedded by the signature means, and output the quantization index of the difference signal A sign means is provided.

[0008] This makes it possible to provide multimedia data that does not lose the authentication function even if multimedia data such as images and sounds are decrypted.

Brief Description of Drawings

FIG. 1 is a configuration diagram showing an electronic force transmission device according to Embodiment 1 of the present invention.

FIG. 2 is an explanatory diagram showing an example of quantizing a k-th transform coefficient. FIG. 3 is a flowchart showing processing contents of a correction circuit in a signature circuit.

[Fig. 4] Fig. 4 is a configuration diagram showing an electronic permeability device according to Embodiment 2 of the present invention.

FIG. 5 is a block diagram showing an authentication processing device according to Embodiment 3 of the present invention.

FIG. 6 is a block diagram showing the inside of a coefficient acquisition unit.

FIG. 7 is a block diagram showing the inside of a coefficient acquisition unit.

FIG. 8 is a block diagram showing a decoding processing apparatus according to Embodiment 4 of the present invention.

FIG. 9 is a block diagram showing the inside of a decoding circuit.

FIG. 10 is a flowchart showing processing contents of a correction circuit.

FIG. 11 is a block diagram showing a requantization apparatus according to Embodiment 5 of the present invention.

FIG. 12 is a block diagram showing the inside of a coefficient acquisition circuit.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, in order to describe the present invention in more detail, the best mode for carrying out the present invention will be described with reference to the accompanying drawings.

Embodiment 1.

FIG. 1 is a block diagram showing an electronic power transmission device according to Embodiment 1 of the present invention. In the figure, a signature circuit 1 quantizes an image signal that is an input signal, and a quantization index of the image signal. Calculates the force authenticator and performs processing to embed the authenticator in the quantization index. The signature circuit 1 constitutes a signature means.

The encoder 2 obtains the difference signal between the image signal and the reference signal, quantizes the difference signal according to the quantization index in which the authenticator is embedded by the signature circuit 1, and outputs the quantization index of the difference signal. The encoder 2 constitutes a code key means.

[0011] A change 11 of the encoder 2 converts an image signal X (where X is a vector signal), which is an input signal, into a frequency domain signal T (X) in units of blocks.

The subtracter 12 of the encoder 2 is a reference image signal Χρ previously encoded from the frequency domain signal Τ (Χ), which is the conversion result of the converter 11, where Χρ is a vector of the reference image signal. The frequency domain signal Τ (Χρ) is subtracted to obtain the frequency domain prediction error Τ (X) — Τ (Χρ).

[0012] The quantizer 13 of the signature circuit 1 converts the frequency domain signal Τ (Χ) output from the variable 11 into The signal is quantized and a quantization index Qw (T (X)) of the signal T (X) is output. The correction circuit 14 of the signature circuit 1 has a quantization index Qw (T

(X)) is corrected, and the corrected quantization index Qw (T (X)) is output to the authenticator operation circuit 15 and the modulator 16.

The authenticator computing circuit 15 of the signature circuit 1 computes the quantized index Qw (T (X)) and the authenticator W (where W is a vector of authenticators) after being corrected by the correcting circuit 14. The modulator 16 of the signature circuit 1 modulates a part of the corrected quantization index Qw (T (X)) according to the authenticator W calculated by the authenticator arithmetic circuit 15, and outputs the modulation result Yw. .

[0013] The quantizer 17 of the encoder 2 predicts the frequency domain calculated by the subtractor 12 according to the modulation result Yw of the modulator 16 (quantization index in which the authenticator W is embedded by the modulator 16). Quantizes the error T (X) -T (Xp) and outputs the quantization error Y of the prediction error T (X) -T (Xp) (where Y is a vector of quantum indices).

The inverse quantizer 18 of the encoder 2 performs inverse quantization on the quantization error Y of the prediction error output from the quantizer 17 and decodes the prediction error T (X) —T (Xp).

The adder 19 of the encoder 2 calculates the prediction error T (X)-T (Xp) decoded by the inverse quantizer 18 and the frequency domain signal Τ (Χρ) of the reference image signal Xp output from the switch 23. Addition and output the addition signal Τ (Χ).

[0014] The inverse change of the encoder 2 converts the addition signal Τ (Χ) output from the adder 19 into the time domain, and outputs the signal in the time domain as the reference image signal Xp.

The storage circuit 21 of the encoder 2 stores the reference image signal Xp output from the inverse converter 20 for the moving time and outputs it.

The converter 22 of the encoder 2 converts the reference image signal Xp output from the storage circuit 21 into the frequency domain, and outputs a signal T (Xp) in the frequency domain.

The switch 23 of the encoder 2 supplies the frequency domain signal Τ (Χρ) output from the variable to the subtractor 12 and the adder 19. However, when encoding a moving image, it is necessary to appropriately mix images that can be decoded without referring to other images. In this case, “0” is added to the subtracter 12 and the adder 19. give. In this case, the quantizer 17 It operates to encode as it is.

Next, the operation will be described.

First, the conversion 11 of the encoder 2 receives the image signal X, converts the image signal X into the frequency domain in units of blocks, and converts the signal T (X) in the frequency domain into the subtractor 12 and the signature. Output to the quantizer 13 of the nominal circuit 1.

Here, Τ () is an operator of the converter 11.

[0016] The subtracter 12 of the encoder 2 receives the frequency domain signal T (X) from the converter 11, and the reference image signal に ρ encoded in the past from the converter 22 via the switch 23. When the frequency domain signal Τ (Χρ) is received, the frequency domain signal Χ (Χ) is subtracted from the signal Τ (Χρ) and the frequency domain prediction error Τ (Χ) -Τ (Χρ) is calculated. Ask.

On the other hand, when the quantizer 13 of the signature circuit 1 receives the signal Τ (Χ) in the frequency domain from the converter 11, the quantizer 13 quantizes the signal Τ (Χ) in the frequency domain. Output the generalized index Qw (T (X)).

Here, Qw () is an operator of the quantizer 13.

[0017] The correction circuit 14 of the signature circuit 1 corrects the quantization index Qw (T (X)) output from the quantizer 13, and uses the corrected quantization index Qw (T (X)) as an authenticator. Output to arithmetic circuit 15 and modulator 16.

Specific processing contents of the correction circuit 14 will be described later.

The authenticator calculation circuit 15 of the signature circuit 1 calculates the authenticator W from the quantized index Qw (T (X)) corrected by the correction circuit 14.

For the calculation of this authenticator, for example, the method described in Ito et al., “Method of digital watermark to prove authenticity of JPEG image” (National Conference of the Institute of Electronics, Information and Communication Engineers, March 2003) is used. That's fine.

In this method, N transform blocks are grouped together, the hash value of all the quantization indexes is calculated, and the signature obtained by encrypting the hash value. If the number of bits in the hash value is equal to N, a 1-bit authenticator is calculated for each conversion block.

[0019] The modulator 16 of the signature circuit 1 receives the authentication when the authenticator operation circuit 15 calculates the authenticator W. A part of the corrected quantization index Qw (T (X)) is modulated according to the witness W, and the modulation result Yw is output.

Yw = Qw (T (X)) + W (1)

Specifically, the modulator 16 embeds the authenticator W in the quantization index Qw (T (X)) using the method described in the above document.

In the method of the above document, in each transform block, the value of the last quantization index of the zigzag scan is set to “1” or “+1” depending on whether the bit of the authenticator W is “0” or “1”. To change.

As a result, the quantum index in which the authenticator W of the input image is embedded from 16 modulators is output.

Here, if the value of force N, which explains how to embed a 1-bit signature in each conversion block, is set to be larger than the number of bits in the hash value, priority will be given to blocks that change rapidly, and the electronic permeability Can be embedded.

[0021] The quantizer 17 of the encoder 2 receives the modulation result Yw from the modulator 16, and receives the frequency domain prediction error T (X) —T (Xp) from the subtractor 12 The frequency domain prediction error T (X) -T (Xp) is quantized according to the modulation result Yw of the modulator 16, and the quantization index Y of the prediction error T (X) -T (Xp) is output.

That is, the quantizer 17 outputs a quantum index Y that minimizes d in the equation (3) under the condition that the following equation (2) is satisfied.

Qw (Qc ^_1 (Y) + Τ (Xp)) = Yw (2)

d = I Qc— ^ Y) — (T (X) — T (Xp)) I (3)

[0022] However, Qc ^_1 () is an operator of inverse quantization for the quantizer 17, II represents the norm of a vector.

In Equation (2), Qc− ¹ (Y) + T (Xp) is obtained by adding a prediction error signal obtained by inverse quantization to the transform coefficient of the reference frame. It represents the conversion coefficient.

Equation (2) gives the condition that the transform coefficient to be decoded becomes Yw when quantized with Qw. Equation (3) is the difference between the reconstruction value of the prediction error and the true value T ( X) — gives T (Xp) It is.

Therefore, the quantizer 17 has a prediction error T (X) — that minimizes the distortion caused by the sign key 匕 under the condition that the modulation result Yw of the signature circuit 1 is stored in the decoded image signal. Outputs the quantization index Υ of Τ (Χρ).

The quantizer 17 may perform the above operation for each transform coefficient.

FIG. 2 is an explanatory diagram showing an example of quantizing the kth transform coefficient.

The upper side shows the quantization characteristics of Qw, and the lower side shows the quantization characteristics of Qc, expressed in terms of the quantization index and its quantization range.

The point on the center number line is the quantized representative value of Qc. Further, the subscript k on the right shoulder of the vector indicates the k-th component of the vector. q ^k and q ^k are the quantization widths of Qc and Qw for this transform coefficient, and are set to be Eq. (4)!

q ^k ≤q ^k (4)

For example, if Yw ^k = i and T (X) ^ T (Xp) ^k is in the position of FIG.

When (X) ^k — T (Xp) ^k is quantized with Qc, its quantum index is Y = 1.

However, the quantization representative value is not in the i-th quantization range of Qw, and Y = 1 does not satisfy the condition of equation (2). Since the quantum index is Y = 2 closest to T (X) ^k belonging to the i-th quantization range of the representative value Qw, this is the output of the quantum device 17.

[0025] Here, in order for the above Υ to always exist, at least one quantized representative value of Qc must exist in all quantization ranges of Qw. As shown in Fig. 2, if Qc is quantized, equation (4) should be established for all coefficients k. However, encoding such as MPEG uses non-uniform quantization characteristics that are coarse near 0. In this case, assuming that the interval of the coarsest part of the quantized representative value of Qc is Tmax ^k , the following equation (5) is satisfied, which is a sufficient condition for Y to exist.

q> = Tmax (5)

w

[0026] For example, in the case of a quantizer according to the H.263 code standard, Qw is set as follows. H. 263 inverse quantization operation is defined by the following equation (6) when Q is an odd number if the quantization parameter that controls the amount of code is Q (= l, ..., 31). If Q is an even number, it is defined by equation (7). y = (2Y + sign (Y)) Q (6)

y = (2Y + sign (Y)) Q— sign (Y) (7)

Where y is the representative quantized value to be restored, and sign (Y) is a function that becomes 1 when Y is 0, 0 when Y = 0, and 1 when Υ> 0.

In this quantizer, Tmax = 3Q (Q is an odd number) or Tmax = 3Q−1 (Q is an even number), so Qw may be set as follows. That is, when Q is an odd number, the following equation (8) is set. When Q is an even number, the following equation (9) is set.

q ^k = 3Q (8)

w

q ^k = 3Q-l (9)

w

[0028] The inverse quantizer 18 of the encoder 2 is used for the next electronic permeability embedding process when the quantizer 17 outputs the prediction error quantum index Y as described above. In order to generate a reference image, the quantization index Y of the prediction error is inversely quantized to decode the prediction error T (X) −Τ (Χρ).

When the inverse quantizer 18 decodes the prediction error Τ (Χ) -Τ (Χρ), the adder 19 of the encoder 2 sets the switch 23 from the prediction error — (Χ) -Τ (変 ρ) and the variable 22. The signal 参照 (Χρ) in the frequency domain of the reference image signal Xp output via the signal is added, and the added signal Τ (Χ) is output.

[0029] The inverse change of encoder 2 is that when the addition signal T (X) is received from the adder 19, the addition signal Τ (Χ) is converted into the time domain, and the signal in the time domain is converted to the reference image signal Xp. Is stored in the memory circuit 21.

The converter 22 of the encoder 2 reads the reference image signal Xp shifted by the moving time from the storage circuit 21, converts the reference image signal Xp into the frequency domain, and converts the reference image signal Xp into the frequency domain via the switch 23. The signal T (Xp) is supplied to the subtracter 12 and the adder 19.

Note that when the moving image is encoded, the switch 23 needs to appropriately mix images that can be decoded without referring to other images. In this case, “0” is subtracted from the subtractor 12. Give to adder 19. At this time, the quantizer 17 operates so as to code the current input image as it is.

[0030] In the description of the signature circuit 1 above, all the conversion blocks are grouped together. The hash value of the quantum index is shown as above, but when the number of bits M of the hash value is smaller than the number N of blocks that calculate the hash value (M <N holds) If so, the modulator 16 can select M blocks out of N and apply modulation only to those blocks!

Since there is a degree of freedom in selecting this block, image quality degradation due to embedding of the authenticator W can be achieved by selecting a block that has as little obscure interference as possible (the part with the least influence of modulation) and applying modulation. Can be reduced. However, it must be possible to detect which block is modulated at the time of decoding.

[0031] There are several such methods. When the above method for modulating the value of the last quantum index of a zigzag scan is used, for example, the number of non-zero quantization indexes (significant coefficients) is obtained. It is sufficient to select a block having a significant coefficient greater than a predetermined number. At this time, the embedding of electronic permeability increases the number of significant coefficients by 1. The order of the significant coefficients of each block does not change, so that the embedding block can be uniquely identified during decoding. Any block with the same number of significant coefficients may be selected. In a flat part of an image where deterioration is conspicuous, since the number of significant coefficients is generally small, the probability of embedding a digital watermark is low. Accordingly, it is possible to generate a code image that is difficult to perceive interference due to embedding of an electronic watermark.

Finally, the processing content of the correction circuit 14 will be specifically described.

As described above, the authenticator calculation circuit 15 calculates the authenticator W based on the currently input image signal X related to the reference image, and the quantizer 17 embeds this authenticator W. Since the prediction error T (X) -T (Xp) is quantized so as to preserve the quantization index Yw, the signal output from the encoder 2 is a complete signature for authenticating the image signal in units of frames. Holds information. As will be described later, this signature information is extracted when a part of a frame is extracted from a moving image and its transform coefficient is re-encoded (for example, a moving image encoded by MPEG). In the case where a part is re-encoded with JPEG), it can be inherited without loss in the re-encoded signal.

However, when decoding an image into a signal in the time domain, signature information may disappear due to an error introduced in the process of decoding. Such an error is generally a conversion factor. Occurs when a number is converted to a real force integer and when that integer value is clipped to a further fixed dynamic range. Therefore, unless sufficient measures are taken, signature information cannot be inherited by time domain images.

The correction circuit 14 of the signature circuit 1 corrects the quantum index Qw (T (X)) so that the decoded signal V does not greatly exceed the dynamic range.

This correction can be performed, for example, according to the procedure shown in FIG.

[0034] When the correction circuit 14 of the signature circuit 1 receives the quantization index Qw (T (X)) from the quantizer 13, the correction circuit 14 embeds 0 in the quantization index Qw (T (X)). (Step ST1).

Next, the correction circuit 14 determines that the embedded result of 0 does not greatly exceed the dynamic range (step ST2).

That is, the correction circuit 14 inversely quantizes the quantization index Yw embedded with electronic permeability corresponding to Qw and inversely transforms it to obtain a vector X in the time domain.

x = T ^_1 (Qw " ¹ (Qw (T (X)) + W)) (10)

The correction circuit 14 calculates a shortest distance d (x, A) between the vector X and the set A, where A is a set of vectors in which all components fall within the dynamic range, and the shortest distance d (x, Judge whether or not A) is within a certain value D.

d (x, A) ≤ D (11)

If the shortest distance d (x, A) is within a certain value D, the correction circuit 14 certifies that the result of zero embedding does not greatly exceed the dynamic range.

When D = 0, the judgment condition is satisfied only when X is included in A.

Next, when the correction circuit 14 determines that the embedded result of 0 does not greatly exceed the dynamic range, the correction circuit 14 performs a process of embedding 1 in the quantization index Qw (T (X)) (step S T3) .

Next, the correction circuit 14 determines that the result of embedding 1 does not greatly exceed the dynamic range (step ST4). Since this determination method is the same as the determination method in step ST2, description thereof is omitted. If the correction circuit 14 certifies that the embedding result of 1 does not greatly exceed the dynamic range, the quantization index Qw (T (X)) is embedded in the authentication index W, which is electronic permeability, Since it is guaranteed that Qw (T (X)) is close to the set A, the quantized index value Qw (T (X)) is output to the authenticator operation circuit 15 and the modulator 16.

[0037] However, if it is determined that the embedding result of 0 greatly exceeds the dynamic range, or if it is determined that the embedding result of 1 greatly exceeds the dynamic range, the quantization index Qw (T (X)) After embedding the authenticator W, which is the electronic permeability, it is not guaranteed that the quantized index Qw (T (X)) is close to the set A, so the quantized index Qw (T (X) ) Is corrected (step ST5).

That is, the correction circuit 14 calculates a target vector t given by the following equation, and stores the target vector t.

t = T (P (T '' ¹ (Qw ^-1 (Qw (T (X))))))) (12)

Where P () is an operator representing the orthogonal projection for set A, and t is the vector obtained by inverse quantization and inverse transformation of Qw (T (X)), and s is the vector of all vectors belonging to set A. It is the closest to s, and the vector is transformed by T.

[0039] Next, the correction circuit 14 inversely quantizes the current quantum index Qw (T (X)) to calculate Qw— ^ wO ^ X)), and compares this with the target vector t. Then, the quantization index of Qw (T (X)) corresponding to the component farthest from the target vector t is corrected by 1 in the direction of the target vector t.

This modification brings the quantization index Qw (T (X)) closer to the set A. If the quantization index Qw (T (X)) is already close enough to the target vector t, set the target vector t to the center vector of the set A (a vector with all components at intermediate gray levels). Switch to the one converted to, and repeat the modification of the quantization index Qw (T (X)).

As described above, the correction circuit 14 corrects the quantum index Qw (T (X)) so that the modulation result Yw of the modulator 16 does not greatly exceed the dynamic range. In particular, when D = 0, the quantization index Qw (T (X)) is corrected so that the modulation result Yw of the modulator 16 is always within the dynamic range. [0041] It should be noted that the problem of rounding errors due to integers can be avoided by setting Qw sufficiently coarse.

That is, the following equation (13) is a sufficient condition that the electronic permeability is not lost due to rounding error.

q ^k ≥R (13)

w

In the case of 8 001, it is proved that the effect of rounding error can be eliminated by setting R = 8 and making the quantization width of all coefficients 8 or more.

[0042] As described above, in order to save the signature information in the image signal decoded in the time domain, the restriction of Equation (13) is set in Qw to eliminate the influence of rounding error, and the correction circuit 14 is installed in the signature circuit 1. Then, you need to take measures against clipping. For example, when using the quantization of H. 263, the equation (8), equation (9) and equation (13) force Qw should be set as follows:

That is, when Q is an odd number, it can be set according to equation (14), and when Q is an even number, it can be set according to equation (15).

Qw = max (8, 3Q) (14)

Qw = max (8, 3Q— 1) (15)

As apparent from the above, according to the first embodiment, an image signal is quantized, an authentication code is calculated from the quantization index of the image signal, and the authentication code is quantized. While the signature circuit 1 to be embedded in the index is provided, the difference signal between the image signal and the reference signal is obtained, and the difference signal is quantized according to the quantization index in which the authenticator is embedded by the signature circuit 1, Since the encoder 2 that outputs the quantization index of the difference signal is provided, it is possible to provide multimedia data without losing the authentication function even if multimedia data such as images and sounds are decoded. There is an effect that can be done.

Further, according to the first embodiment, since the quantization index Qw (T (X)) output from the quantizer 13 is corrected, an image embedded with a digital watermark is converted into a dice. It is possible not to greatly exceed the dynamic range. Therefore, even when an image is decoded in the time domain, the authenticity of the image can be confirmed.

Embodiment 2.

FIG. 4 is a block diagram showing an electronic permeability device according to Embodiment 2 of the present invention. The same reference numerals as those in FIG. 1 denote the same or corresponding parts, and the description thereof will be omitted.

The quantizer 31 of the encoder 2 quantizes the frequency domain prediction error T (X) —Τ (Χρ) calculated by the subtractor 12, and quantizes the prediction error Τ (X) —Τ (Χρ). Outputs index Υ.

The inverse quantizer 32 of the signature circuit 1 decodes the quantization index Υ output from the quantizer 31 and outputs a frequency domain prediction error Τ (Χ) − Τ (の ρ).

[0046] The adder 33 of the signature circuit 1 includes the prediction error Τ (Χ) —Τ (Χρ) output from the inverse quantizer 32 and the frequency domain signal Τ (Χρ) of the reference image signal Χρ output from the switch 23. ) Is added and the added signal Τ (Χ) is output.

The correction circuit 34 of the encoder 2 corrects the quantization index Y output from the quantizer 31 according to the modulation result Yw of the modulator 16 (quantization index in which the authenticator W is embedded by the modulator 16). To do.

[0047] In the first embodiment, the case where the authenticator W is directly calculated from the input image has been described. However, the authenticator W is calculated on the basis of the prediction error signal cover and the decoded image. Please do it.

Specifically, it is as follows.

[0048] The quantizer 31 of the encoder 2 performs the prediction error T when the subtractor 12 outputs the prediction error T (X) — T (Xp) in the frequency domain in the same manner as in the first embodiment. (X) —T (Xp) is quantized and the quantization index Υ of the prediction error T (X) —T (Xp) is output to the inverse quantizer 32 and the correction circuit 34.

When receiving the quantization index の from the quantizer 31, the inverse quantizer 32 of the signature circuit 1 decodes the quantization index して and adds a frequency domain prediction error Τ (X) -X (Xp) Output to 33.

The adder 33 of the signature circuit 1 uses the prediction error T (X)-T (Xp) output from the inverse quantizer 32 and the frequency domain signal Τ (Χρ) of the reference image signal Xp output from the switch 23. Addition is performed, and the addition signal Τ (Χ) is output to the quantizer 13.

Since the processing contents from the quantizer 13 to the modulator 16 are the same as those in the first embodiment, description thereof is omitted. [0049] When the correction circuit 34 of the encoder 2 receives the quantization index Y from the quantizer 31 and receives the modulation result Yw from the modulator 16, the correction circuit 34 is the same as the quantizer 17 of the first embodiment. Then, the quantization index Y output from the quantizer 31 is corrected according to the modulation result Yw.

That is, the correction circuit 34 outputs a quantization index Y that minimizes d in the equation (17) under the condition that the following equation (16) is satisfied.

Qw (Qc ^_1 (Y) + Τ (Χρ)) = Yw (16)

d = I Qc— ^ Y) — (T (X) — T (Xp)) I (17)

[0050] In order to suppress the noise in the moving image code する, the prediction error signal having a small value is roughly quantized. In the second embodiment, the authenticator W is generated from the decoded image signal. Thus, there is an effect that it is possible to obtain a coded image with little noise, without impairing the noise suppression function in the code i.

[0051] Embodiment 3.

FIG. 5 is a block diagram showing an authentication processing apparatus according to Embodiment 3 of the present invention. In the figure, the coefficient acquisition unit 41 is an encoding in which an authenticator is embedded by, for example, the electronic permeability device of FIG. 1 or FIG. When the signal is received, the conversion coefficient of the sign signal is acquired.

The quantizer 42 quantizes the transform coefficient acquired by the coefficient acquisition unit 41 and outputs the quantization index to the authenticator operation circuit 43 and the authenticator detector 44. The coefficient acquisition unit 41 and the quantizer 42 constitute a quantization means.

The authenticator operation circuit 43 calculates an authenticator from the quantization index output from the quantizer 42. The authenticator operation circuit 43 constitutes an authenticator operation means.

The authenticator detector 44 detects the authenticator embedded in the quantization index output from the quantizer 42. The authenticator detector 44 constitutes an authenticator detecting means. The comparator 45 compares the authenticator detected by the authenticator detector 44 with the authenticator calculated by the authenticator calculation circuit 43. If the two match, it is recognized that the authenticity of the image is maintained. If they do not match, it is determined that the authenticity of the image is lost. The comparator 45 constitutes a comparison means.

FIG. 6 is a block diagram showing the inside of the coefficient acquisition unit 41. In the figure, the inverse quantizer 51 The adder 52 restores the prediction error conversion coefficient by decoding the quantization index, which is a sign signal, and the prediction error conversion coefficient restored by the coefficient acquisition unit 41 and the reference image transformed by the change. The conversion coefficient is added, and the addition result is output as the conversion coefficient of the encoded signal.

The inverse change 53 decodes the time domain image signal output from the adder 52 and stores the image signal in the storage circuit 54.

The conversion converts the image signal stored in the storage circuit 54 into the conversion coefficient of the reference image and outputs the conversion coefficient to the adder 52.

Next, the operation will be described.

For example, when the coefficient acquisition unit 41 receives an encoded signal in which an authenticator is embedded by the electronic permeability device of FIGS. 1 and 4, the coefficient acquisition unit 41 acquires a conversion coefficient of the code signal.

If the input signal is a signal sequence in which transform coefficients are encoded, the portion corresponding to the signal sequence power may be extracted. However, the input signal is decoded into the time domain. If the image is a converted image, the coefficient acquisition unit 41 may acquire the conversion coefficient using the conversion 56 (see FIG. 7) for converting the input image into the frequency domain.

[0055] When the coefficient acquisition unit 41 acquires the transform coefficient, the quantizer 42 quantizes the transform coefficient and outputs the quantization index to the authenticator calculation circuit 43 and the authenticator detector 44. When receiving the quantization index from the quantizer 42, the authenticator operation circuit 43 calculates an authenticator from the quantum index.

However, there are cases where the electronic permeability is embedded in the quantization index, so the portion where the electronic permeability is embedded is not used for the calculation of the authenticator. For example, when a digital watermark is embedded by the method described in the first embodiment, the last quantized index of the block in which the electronic watermark is embedded is 0, and the authenticator is calculated.

[0056] Upon receiving the quantization index from the quantizer 42, the authenticator detector 44 detects an authenticator embedded in the quantization index.

For example, the electronic permeability is embedded by the method described in the first embodiment. In the case, the authenticator is restored from the value of the last quantization index of the block in which the electronic permeability is embedded.

[0057] When the authenticator detector 44 detects the authenticator and the authenticator calculation circuit 43 calculates the authenticator, the comparator 45 compares both authenticators, and if the two match, the authenticity of the image is detected. It is recognized that the sexuality is maintained. On the other hand, if they do not match, it is determined that the authenticity of the image has been lost.

As apparent from the above, according to the third embodiment, since the authentication code is calculated depending on the input image, it is decoded not only by the encoded signal sequence power but also by decoding. Even from the image, there is an effect that the authenticity can be proved.

[0059] Embodiment 4.

FIG. 8 is a block diagram showing a decryption processing apparatus according to Embodiment 4 of the present invention. In the figure, the decryption circuit 61 uses, for example, a signal sequence in which an authenticator is embedded by the electronic permeability device of FIG. 1 or FIG. When received, the signal sequence is decoded into a time domain signal. Note that the decryption circuit 61 constitutes decryption means!

When the coefficient acquisition circuit 62 receives the signal sequence in which the authenticator is embedded, the coefficient acquisition circuit 62 restores the conversion coefficient used for calculating the authenticator from the signal sequence.

The quantizer 63 quantizes the transform coefficient restored by the coefficient acquisition circuit 62 with the same characteristics as those used for calculating the authenticator. The coefficient acquisition circuit 62 and the quantizer 63 constitute a quantization means.

The correction circuit 64 corrects the decoding result of the decoding circuit 61 in accordance with the transform coefficient quantized by the quantizer 63. The correction circuit 64 constitutes correction means.

FIG. 9 is a block diagram showing the inside of the decoding circuit 61. In FIG. 9, when the inverse quantizer 71 receives a quantization index of a prediction error that is a signal sequence in which an authenticator is embedded, Index force Restores the signal value of the prediction error.

The adder 72 adds the signal value of the prediction error restored by the inverse quantizer 71 and the signal value of the reference image, and outputs a transform coefficient of the decoded image.

[0061] Inverse transformation 73 converts the transform coefficient of the decoded image output from adder 72 into an image signal in the time domain. Therefore, the output of the inverse converter 73 is the image signal expressed in the time domain. Since the output of the inverse change is generally a real number, an integer such as rounding is applied. If the result exceeds the specified numerical range, clipping is performed to correct it to the specified range. The inverse change output is corrected by the correction circuit 64 as necessary, and becomes an image signal having an authenticator.

The storage circuit 74 stores the time-domain image signal converted by the inverse converter 73. The converter 75 converts the time domain image signal stored by the storage circuit 74 into a reference image signal value.

Next, the operation will be described.

When receiving the signal sequence in which the authenticator is embedded by, for example, the electronic permeability device of FIGS. 1 and 4, the decoding circuit 61 decodes the signal sequence into a time domain signal according to a certain rule.

On the other hand, when the coefficient acquisition circuit 62 receives the signal sequence in which the authenticator is embedded, the coefficient acquisition circuit 62 restores the conversion coefficient used for calculating the authenticator from the signal sequence. However, as shown in FIG. 9, when the adder 72 of the decoding circuit 61 restores the transform coefficient and outputs it to the quantizer 63, the coefficient acquisition circuit 62 is unnecessary.

[0063] The quantizer 63 quantizes the transform coefficient restored by the coefficient acquisition circuit 62 with the same characteristics as those used for calculating the authenticator in the digital watermark device.

The transform coefficient Yw quantized by the quantizer 63 is given to the correction circuit 64 as a target for correcting the decoding result of the decoding circuit 61.

[0064] When receiving the quantized transform coefficient Yw from the quantizer 63, the correction circuit 64 corrects the decoding result of the decoding circuit 61 according to the conversion coefficient Yw.

That is, when the correction circuit 64 receives the integer vector X (decoding result) of the image signal output from the decoding circuit 61, when the image signal is converted and quantized, the image signal is converted into a conversion coefficient Yw. Modify the integer vector X of the image signal to match The reason for this modification is that if integer processing or clipping processing is included in the decryption process, the authenticator information embedded as a digital watermark may be lost due to errors in the processing. That's it.

FIG. 10 is a flowchart showing the processing contents of the correction circuit 64. Hereinafter, the processing contents of the correction circuit 64 will be specifically described with reference to FIG.

The correction circuit 64 determines whether or not the integer vector X of the image signal satisfies the condition of the following equation (18) (step ST11).

Qw (T (X)) = Yw (18)

Here, T () is an operator representing transformation, and Qw () is an operator that performs quantization with the same characteristics as those used in the computation of the authenticator.

[0066] When equation (18) is satisfied (step ST11), correction circuit 64 ends the correction process because vector X holds the authenticator information.

However, if equation (18) does not hold (step ST11), the vector X is corrected (step ST12).

Correction of the vector X is performed by bringing the component of the solid X that is farthest from the real vector Xw by 1 closer to the real vector Xw, where Xw is the real vector from which the transformation coefficient Yw is restored. Here, the real vector Xw is given by the following equation.

Xw = T— ¹ (Qw— ¹ (Yw)) (19)

For quantization Qw, when equation (12) holds, it can be proved that the integer vector closest to the real vector Xw always has the authenticator information, so by repeating the modification of vector X, equation (18) An integer vector X that satisfies) can always be found.

As apparent from the above, according to the fourth embodiment, since the authentication code is calculated depending on the input image, the authentication code can be inherited to the decrypted image signal. There is an effect. In addition, since the decryption vector is corrected so as to have the authenticator, the effect of being able to inherit the authenticator in the image decoded into the time domain signal is obtained.

[0068] Embodiment 5.

FIG. 11 is a block diagram showing a requantization apparatus according to Embodiment 5 of the present invention. In the figure, the coefficient acquisition circuit 81 is embedded with an authenticator, for example, by the electronic permeability device of FIG. 1 or FIG. When the received image signal is received, the conversion coefficient used to calculate the authenticator is restored from the image signal. The coefficient acquisition circuit 81 constitutes conversion coefficient acquisition means.

The quantizer 82 quantizes the transform coefficient acquired by the coefficient acquisition circuit 81 with the same characteristics as those used for calculating the authenticator. The quantizer 82 constitutes the first quantization means. It is made.

The quantizer 83 quantizes the transform coefficient acquired by the coefficient acquisition circuit 81 according to the quantization result of the quantizer 82. The quantizer 83 constitutes the second quantizing means.

FIG. 12 is a block diagram showing the inside of the coefficient acquisition circuit 81. In FIG. 12, when the inverse quantizer 91 receives a quantization index of a prediction error that is a signal sequence in which an authenticator is embedded.

The signal value of the prediction error is restored from the quantization index.

The adder 92 adds the signal value of the prediction error restored by the inverse quantizer 91 and the signal value of the reference image, and outputs a transform coefficient of the decoded image.

The inverse transformer 93 converts the transform coefficient of the decoded image output from the adder 92 into a time domain image signal.

The storage circuit 94 stores the time domain image signal converted by the inverse converter 93. The converter 95 converts the time domain image signal stored by the storage circuit 94 into a reference image signal value.

Next, the operation will be described.

For example, when the coefficient acquisition circuit 81 receives an image signal in which an authenticator is embedded by the electronic permeability device shown in FIGS. 1 and 4, the coefficient acquisition circuit 81 restores the conversion coefficient used for calculating the authenticator from the image signal.

However, the input image signal may be a coded signal sequence or a decoded time domain signal.

[0072] When the quantizer 82 receives the transform coefficient from the coefficient acquisition circuit 81, the quantizer 82 converts the conversion coefficient acquired by the coefficient acquisition circuit 81 with the same characteristics as those used for calculating the authenticator by the digital watermarking device. Quantize.

When the quantizer 83 receives the transform coefficient Yw quantized by the quantizer 82, the quantizer 83 quantizes the transform coefficient so that the transform coefficient Yw is stored in the transform coefficient acquired by the coefficient acquisition circuit 81. Turn into.

That is, for example, the quantum device 83 outputs the vector Y that minimizes d in the equation (21) under the condition of the following equation (20). Quantize coefficient Turn into.

Qw (Qc— ¹ (Y)) = Yw (20)

d = I Qc- T (X) I (21)

As apparent from the above, according to the fifth embodiment, since the authentication code is calculated depending on the input image, the authentication code is inherited by the re-encoded signal sequence. The effect that can be done. This is useful, for example, when a part of a frame of a moving image encoded by MPEG or the like is re-encoded by JPEG or the like as a still image.

[0074] In Embodiment 1-15, the input signal is an image signal. However, the present invention can be widely applied to multimedia data such as an audio signal.

Industrial applicability

As described above, the electronic force transmitting apparatus according to the present invention converts the electronic force to multimedia data so that the authentication function is not lost even if the multimedia data is decrypted. Suitable for things that need to be embedded.

Claims

The scope of the claims

[1] Quantizes the input signal, calculates an authenticator from the quantization index of the input signal, embeds the authenticator in the quantization index, and a differential signal between the input signal and the reference signal An electronic watermarking apparatus comprising: an encoding means for quantizing the difference signal according to a quantization index in which an authenticator is embedded by the signing means and outputting a quantization index of the difference signal.

[2] The encoding means is authenticated by a converter that converts an input signal into a frequency domain signal, a subtractor that obtains a difference signal between the frequency domain signal output from the converter and a reference signal, and a signature means. And a quantizer that quantizes the difference signal obtained by the subtractor according to a quantization index in which a child is embedded and outputs a quantization index of the difference signal. Item 1. The electronic permeability device according to Item 1.

[3] The signature means quantizes the frequency domain signal output from the converter of the encoding means, outputs a quantization index of the frequency domain signal, and is output from the quantizer. Quantization index power An authenticator operation circuit for calculating an authenticator, and a modulator for modulating a part of the quantum index output from the quantizer according to the authenticator calculated by the authenticator operation circuit. The digital watermarking device according to claim 2, comprising:

[4] The signature means includes a correction circuit that corrects the quantization index output from the quantizer and outputs the corrected quantum index to the authenticator operation circuit and the modulator. The electronic watermarking device according to claim 3.

5. The electronic permeability device according to claim 3, wherein the quantizer of the signature unit has a quantization characteristic set depending on the quantization characteristic of the quantizer of the encoding unit.

6. The electronic permeability device according to claim 3, wherein the modulator modulates a portion of the quantization index from which the quantizer force is also output, which is less affected by the modulation.

[7] The encoding means includes a converter that converts an input signal into a frequency domain signal, a subtractor that obtains a difference signal between the frequency domain signal output from the converter and a reference signal, and the subtractor. A quantizer that quantizes the obtained difference signal and outputs a quantization index of the difference signal, and a quantization index in which an authenticator is embedded by a signature means. 2. The electronic permeability device according to claim 1, further comprising a correction circuit that corrects the quantization index output from the quantizer.

[8] The signature unit includes an inverse quantizer that decodes the quantization index output from the quantizer of the encoding unit and outputs a difference signal, a difference signal output from the inverse quantizer, and a reference signal An adder that adds the power of the adder, a quantizer that quantizes the added signal output from the adder and outputs a quantization index of the added signal, and an authentication from the quantization index output from the quantizer An authenticator arithmetic circuit for calculating a child, and a modulator for modulating a part of the quantization index output from the quantizer according to the authenticator calculated by the authenticator arithmetic circuit. The digital watermarking device according to claim 7, wherein:

[9] The signature means includes a correction circuit that corrects the quantization index output from the quantizer and outputs the corrected quantum index to the authenticator operation circuit and the modulator. The electronic watermarking device according to claim 8.

10. The electronic permeability device according to claim 8, wherein the quantizer of the signature unit has a quantization characteristic set depending on the quantization characteristic of the quantizer of the encoding unit.

[11] The electronic permeability device according to [8], wherein the modulator modulates a portion of the quantization index from which the quantizer force is also output that is less affected by the modulation.

[12] When receiving a signal in which the authenticator is embedded by the electronic permeability device, the conversion unit of the signal is acquired, the conversion coefficient is quantized, and a quantization index is output. An authenticator calculating means for calculating an authenticator from the quantized index output from the means, an authenticator detecting means for detecting an authenticator embedded in the quantized index output from the quantizing means, and the authenticator An authentication processing apparatus comprising: an authenticator detected by the detecting means; and a comparing means for comparing the authenticator calculated by the authenticator calculating means.

[13] Upon receiving a signal in which the authenticator is embedded by the electronic permeability device, a decoding means for decoding the signal, a quantization means for obtaining the conversion coefficient of the signal, and quantizing the conversion coefficient; A decoding processing apparatus comprising: a correcting unit that corrects a decoding result of the decoding unit according to the transform coefficient quantized by the quantizing unit. [14] Upon receiving a signal in which the authenticator is embedded by the electronic permeability device, the conversion coefficient acquisition means for acquiring the conversion coefficient of the signal, and the conversion coefficient acquired by the conversion coefficient acquisition means are quantized. Requantization comprising: 1 quantization means; and a second quantization means for quantizing the transform coefficient acquired by the transform coefficient acquisition means according to the quantization result of the first quantization means apparatus.