JP4613807B2 - Document processing apparatus and document processing method - Google Patents

Description

  The present invention relates to a document processing apparatus or the like used for a copying machine, a printer, a facsimile machine, or an image forming apparatus such as a multifunction machine having these functions in combination.

In recent years, so-called “digitization” in which documents are stored as electronic data has become common in offices, and further, copiers, printers, and the like that convert electronic data into paper documents have become widespread. Along with this, leakage of confidential information from inside the company has become a serious problem. For example, highly confidential information such as customer lists and information on products under development has leaked outside the company. In particular, electronic documents (electronic data) can be easily duplicated exactly as the original, and can be taken out to the outside very easily by using a network. It was. However, due to recent advances in encryption technology, authentication technology, access restriction technology, etc., it is relatively difficult to take out electronic documents if appropriate measures are taken.
On the other hand, once an electronic document is printed on paper and converted into a paper document, there is no way to prevent copying or taking it out of the office. Therefore, the current situation is that the progress of countermeasures against the leakage of confidential information of paper documents is more noticeable than that of electronic documents.

As one of countermeasures against confidential leakage of a paper document, there is a technique for adding tracking information to the paper document in advance. In this technology, information such as output person information, output device information, output date and time when an electronic document is printed out and converted into a paper document is recorded on the paper document. With this technology, even if a paper document on which confidential information is printed leaks out of the company, it is possible to specify the outflow source from the tracking information recorded on the paper document.
Such tracking information is desired to be highly invisible and inseparable from the content. For example, if the tracking information is recorded by a highly visible recording method such as a barcode, it is clear where the tracking information is recorded on the paper document, so that there is a high risk of the recorded information being deciphered / tampered. . Further, since the barcode is separable from the content, it is possible to easily prevent the outflow source from being identified by cutting or painting the barcode portion.
It is also desired that the tracking information is highly resistant to repeated copying. This is because the leaked confidential information is not only distributed as it is, but it is also possible that a copy of the confidential information, secondary copies, and tertiary copies may be circulated.

Here, among the methods for recording additional information such as tracking information on a paper document, the following methods have been proposed as having high invisibility.
For example, there is a method of embedding information by shifting the character position and changing the blank length before and after the character (see, for example, Patent Document 1). In this method, when the space lengths before and after the character to be embedded with information bits are P and S, the character position is shifted so that P> S if the information bit is 1, and P <S if the information bit is zero. Embed. Additional information is embedded in the document by performing this operation on a number of characters corresponding to the number of bits of the embedded information. At the time of embedding, if the character positions before and after the punctuation marks are shifted, it is easy to see them.

  There is also a method of embedding information by changing the shape of the character pattern such as the size of the character pattern and the font type (see, for example, Patent Document 2). In this method, characters such as “no” and “ha” that frequently appear in a normal document are set as information embedding target characters. Information is embedded in the target characters in order from the beginning of the document. Only when the information bit is 1, the embedded information is expressed by replacing it with another font or increasing the character width by about 10%, and nothing is done when the information bit is zero. When restoring the embedded information, it is compared with the original document before the information is embedded, and if the character pattern is different, it is interpreted that 1 is embedded, and if it is the same, zero is embedded.

JP 2003-230001 (page 5-7) JP 2001-251490 A (page 4-6)

However, the additional information embedding methods disclosed in Patent Document 1 and Patent Document 2 described above cannot sufficiently function the information tracking effect for paper documents that have been copied many times. This is because in a paper document that has been copied many times, image quality degradation such as thick and thin characters or noise and roughness on characters occurs.
For example, in the method of embedding information in the character position shift amount as in Patent Document 1, the space length between characters changes due to image quality deterioration due to repeated copying, and the embedded information may not be correctly restored. In order to avoid this, it is necessary to increase the shift amount of the character position so that the size relationship of the space length before and after the character is maintained even if the space length changes slightly. However, if the shift amount of the character position is increased, the change made to the document becomes visually apparent, and the invisibility of the embedded information is impaired.
In a so-called kerned document in which the character spacing is adjusted according to the characters before and after the character string so that it looks natural to the eye, the character spacing is not constant. If an attempt is made to change the space length before and after the character so that P <S, the character position must be largely shifted, which also causes a problem of impairing the invisibility.

Similarly, the method disclosed in Patent Document 2 also has a problem of low resistance to image quality degradation due to repeated copying. In other words, in order to determine the difference in shape such as the character pattern size and font type from a paper document whose image quality has deteriorated, it is necessary to change the character size greatly or use fonts with greatly different shapes. . However, if the shape of the character pattern is greatly changed, the change made to the document becomes visually apparent, and the invisibility of the embedded information is impaired.
In addition, there is a problem that information cannot be embedded in a document in which the frequency of appearance of characters to be embedded such as “no” and “ha” is small.

Therefore, the present invention has been made to solve the technical problems as described above, and the object of the present invention is to record additional information that is invisible and highly inseparable from the content on a paper document. It is to do.
Another object is to enable recording of additional information with high robustness against repeated copying.

For this purpose, the document processing apparatus of the present invention is a document processing apparatus capable of embedding additional information in document data consisting of character strings, and is a parameter value relating to document appearance in character strings from input document data. A parameter sequence extraction unit that extracts a sequence, an information input unit that inputs additional information to be embedded in document data, a code sequence generation unit that generates a predetermined code sequence, and additional information input from the information input unit as a shift amount An information encoding unit that generates an encoded information sequence obtained by shifting the predetermined code sequence generated by the code sequence generating unit by the shift amount, and a modified parameter value sequence obtained by synthesizing the encoded information sequence with the parameter value sequence. A correction parameter sequence generation unit for generating, and a document correction unit for correcting the document data using the generated correction parameter value sequence. It is a symptom.
Note that the document data here includes page description language such as PostScript, electronic document data in a word processor output format, raster data of a document photographed by a scanner or a digital camera, and the like. The document format in the character string includes character spacing, character position, word spacing, line spacing, character height, character width, character inclination, and the like. The same applies hereinafter.

  Here, a code sequence group generation unit that generates the same code sequence as the predetermined code sequence generated by the code sequence generation unit and a shifted version of the code sequence, a parameter value sequence extracted by the parameter sequence extraction unit, And an information restoration unit for restoring additional information embedded in the document data based on a correlation value between the code sequence generated by the code sequence group generation unit and a shifted version of the code sequence. be able to.

Further, the information processing unit further includes a partial information generation unit that generates a plurality of partial additional information by dividing the additional information input from the information input unit, and the information encoding unit includes a unit for each partial additional information generated by the partial information generation unit. A partial encoded information sequence is generated, and the partial encoded information sequence is further concatenated to generate an encoded information sequence.
In this case, a code sequence group generation unit that generates the same code sequence as the predetermined code sequence generated by the code sequence generation unit and a shifted version of the code sequence, and a parameter value extracted by the parameter sequence extraction unit A partial parameter value sequence generation unit that generates a plurality of partial parameter value sequences by dividing the sequence, a partial parameter value sequence generated by the partial parameter value sequence generation unit, and a code sequence generated by the code sequence group generation unit Based on the correlation value with the shift version of the code sequence, the additional information embedded for each partial parameter value sequence is restored, and the restored additional information for each partial parameter value sequence is concatenated and embedded in the document data. It is also possible to further include an information restoration unit that restores the information.

Furthermore, it further includes a partial information generation unit that divides the additional information input from the information input unit to generate a plurality of partial additional information, and the code sequence generation unit is provided for each partial additional information generated by the partial information generation unit. A unique code sequence is generated, and the information encoding unit generates a partial encoded information sequence for each partial additional information based on a specific code sequence for each partial additional information, and further multiplexes the partial encoded information sequence to generate a code. Generating a digitized information sequence.
In this case, the code sequence group generation unit that generates the same code sequence as the unique code sequence for each partial additional information generated by the code sequence generation unit and the shift version of the code sequence, and the parameter sequence extraction unit A partial parameter value series generation unit that generates a plurality of partial parameter value series by dividing the extracted parameter value series, a partial parameter value series generated by the partial parameter value series generation unit, and a code sequence group generation unit The additional information embedded for each partial parameter value sequence is restored based on the correlation value between the generated code sequence and the shifted version of the code sequence, and the additional information embedded for each partial parameter value sequence is further connected. An information restoration unit that restores information embedded in the document data can be further provided.

In addition, the information processing unit further includes a partial information generation unit that generates additional partial information by dividing the additional information input from the information input unit, and the information encoding unit includes the partial additional information generated by the partial information sequence generation unit. Generates a partially encoded information sequence periodically and generates a coded information sequence by concatenating such partially coded information sequences, and generates a synchronization code synchronized with the coded information sequence. The correction parameter sequence generation unit may multiplex the synchronization code into the correction parameter value sequence.
In this case, a parameter series extraction unit that extracts a parameter value series related to the document appearance in the character string from the input document data, and a plurality of partial parameter value series by dividing the parameter value series extracted by the parameter series extraction unit The same code sequence as the predetermined code sequence generated by the code sequence generation unit, the shifted version of the code sequence, and the synchronization code synchronized with the encoded information sequence A code sequence group generation unit that generates a code sequence of the code sequence and a shifted version of the code sequence, a partial parameter value sequence generated by the partial parameter value sequence generation unit, a code sequence generated by the code sequence group generation unit, and the code sequence Restore additional information embedded in each partial parameter value series based on the correlation value with the shift version of the code series In addition, the position of the synchronization code sequence embedded for each parameter value sequence is detected based on the correlation value between the parameter value sequence, the synchronization code sequence and the shifted version of the code sequence, and the detected synchronization code sequence is detected. The positional relationship between the position and the partial parameter value series is detected to determine the order of the additional information of the partial parameter value series, and the additional information embedded in the document data is connected by linking the additional information of the partial parameter value series according to the order. An information restoring unit for restoring may be further provided.

Further, the present invention is regarded as a document processing method, and the document processing method of the present invention is a document processing method capable of embedding additional information in document data consisting of character strings, and inputting document data consisting of character strings. Extracting a parameter value series related to the document appearance in the character string from the input document data, and generating an encoded information series obtained by shifting a predetermined code series by the shift amount using the additional information embedded in the document data as a shift amount. A modified parameter value sequence obtained by synthesizing an encoded information sequence with a parameter value sequence is generated, and document data is modified by the modified parameter value sequence.
Here, the additional information is divided to generate a plurality of partial additional information, a partial encoded information sequence for each partial additional information is generated, and further, the partial encoded information sequence is concatenated to generate an encoded information sequence. The document data may be corrected using such an encoded information sequence.

Further, the document processing method of the present invention is a document processing method capable of restoring the additional information from the document data in which the additional information is embedded, the document data consisting of a character string being input, and the input document data The parameter value series related to the document format in the character string is extracted from the code string, the same code series as the code series used when the additional information is embedded and a shifted version of the code series are generated, and the parameter value series and the code The additional information embedded in the document data is restored based on the correlation value between the sequence and the shift version of the code sequence.
Here, the extracted parameter value series is divided to generate a plurality of partial parameter value series, and based on the correlation value between the generated partial parameter value series and the code series and a shifted version of the code series, the partial parameter The additional information for each value series is restored, and the additional information embedded in the document data is restored by connecting the restored additional information for each partial parameter value series.

  According to the present invention, it is possible to make it difficult to decode, falsify, and remove embedded additional information. Further, it is possible to stably restore additional information embedded from a kerning-processed document or a paper document that has been repeatedly copied.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a block diagram illustrating a configuration of a document processing apparatus 1 to which the exemplary embodiment is applied. A document processing apparatus 1 shown in FIG. 1 inputs a first document input unit 10 that inputs document data or the like to be embedded with additional information into the processing unit 30, and inputs raster data or the like with additional information embedded into the processing unit 30. The second document input unit 20, the embedded information input unit 40 that inputs additional information to be embedded in the document data input from the first document input unit 10, the document data input from the first document input unit 10, etc. A processing unit 30 for executing processing for embedding additional information input from the embedding information input unit 40, or for restoring additional information embedded from raster data or the like input from the second document input unit 20, and processing unit 30 The document output unit 50 that outputs the document data and the like subjected to the additional information embedding process in a predetermined format, and the information output unit that outputs the additional information restored by the processing unit 30 It is equipped with a 0.

  The first document input unit 10 is for inputting document data to be embedded with additional information to the processing unit 30. Document data includes page description language such as PostScript, electronic document data in a word processor output format, or raster data of a document photographed by a scanner or a digital camera. The first document input unit 10 receives data via, for example, a hard disk drive (HDD) in which document data is stored, a mass storage device such as a DVD (Digital Video Disc) -RAM / ± RW / ± R drive, a network, or the like. It can be realized by a data transfer device that exchanges images, a scanner device and its control device, a memory reader device that takes out images stored in a memory (card) of a digital camera, and its control device.

  The second document input unit 20 inputs raster data of a document in which additional information is embedded. As raster data of a document, there is image data of a paper document photographed by a scanner or a digital camera. Note that the second document input unit 20 can have the same configuration as the information embedding processing unit 300 described later.

  The embedded information input unit 40 is used to input additional information to be embedded in the document data input from the first document input unit 10 to the processing unit 30. As the additional information to be input, any digital data such as numbers, characters, URLs, multimedia data such as sounds and images, and the like can be used. The embedded information input unit 40 includes, for example, a keyboard for inputting characters and the like, a hard disk drive (HDD) for inputting multimedia data, a DVD (Digital Video Disc) -RAM / ± RW / ± R drive, and the like. It can be realized by a large-capacity storage device, a data transfer device that transmits and receives information via a network, and the like.

  The document output unit 50 outputs document data or the like whose document format has been corrected by the processing unit 30 in a predetermined format. From the document output unit 50, for example, a document printed on paper, a page description language such as PostScript, electronic document data in a word processor output format, or a file in a raster data format of a document is output as an output result. Therefore, the document output unit 50 is realized by, for example, a printer device and its control device, a read / write device such as a magnetic disk or a memory card and its control device, or a data transfer device that exchanges data via a network or the like. Is done.

  The information output unit 60 is for outputting the restored additional information. The information output unit 60 includes, for example, a display device such as a CRT (Cathode Ray Tube) or a liquid crystal display and its control device, a printer device and its control device, a read / write device such as a magnetic disk or memory card, and its control device, or This is realized by a data transfer device that exchanges data via a network or the like.

  The processing unit 30 includes a CPU (Central Processing Unit) 31, a first document input unit 10, a second document input unit 20, an embedded information input unit 40, a document output unit 50, and the like. Processed by an I / O circuit 32 that manages input / output with peripheral devices such as the information output unit 60, a ROM 33 that stores processing programs, a RAM 34 as a primary storage device including a DRAM (Dynamic Random Access Memory), and the CPU 31 A hard disk drive (HDD) 35 for storing document data is included.

Next, an information embedding process executed in the document processing apparatus 1 according to the present embodiment will be described.
The information embedding process in the document processing apparatus 1 is executed by the information embedding processing unit 300 built in the processing unit 30. FIG. 2 is a block diagram illustrating a functional configuration of the information embedding processing unit 300. As shown in FIG. 2, the information embedding processing unit 300 includes a parameter value sequence extraction unit 301, a code sequence generation unit 302, an information encoding unit 303, a correction parameter value sequence generation unit 304, and a document correction unit 305. Has been.

The parameter value series extraction unit 301 analyzes the electronic document data input from the first document input unit 10 or the raster data of the document, and obtains a character interval, a character position, a word interval, a line interval obtained from a character string on the document, A series of parameter values related to the document appearance such as character height, character width, and character inclination is obtained.
The code sequence generation unit 302 is for generating encoded information obtained by encoding the additional information input from the embedded information input unit 40, and generates a single code sequence.
The information encoding unit 303 generates an encoded information sequence obtained by encoding the additional information input from the embedded information input unit 40 with the code sequence generated by the code sequence generating unit 302. Here, an encoded information sequence is obtained by changing the shift amount of the code sequence in accordance with the input information.

The corrected parameter value series generation unit 304 corrects the parameter value series related to the input document obtained by the parameter value series extraction unit 301. The corrected parameter value series is obtained by correcting each symbol value of the parameter value series in accordance with the corresponding symbol value of the encoded information sequence obtained by the information encoding unit 303.
The document correction unit 305 corrects the appearance of the document input from the first document input unit 10 according to each symbol value of the correction parameter value series obtained by the correction parameter value series generation unit 304. And here, the parameter values related to the document format, such as the character spacing, character position, word spacing, line spacing, character height, character width, character inclination, etc. obtained from the character string on the revised document are the correction parameters. Modified to be equal to each symbol value in the value series.

  Next, an information embedding processing method used in the document processing apparatus 1 according to this embodiment will be described. FIG. 3 is a flowchart showing an example of the procedure of the information embedding process executed by the document processing apparatus 1. In the example shown below, a case will be described in which additional information to be embedded is n-bit binary data, and character spacing is used as a parameter relating to a document format for embedding information.

First, in the document input step (S101), electronic document data to be embedded with additional information is input from the first document input unit 10 to the parameter value series extraction unit 301.
In the next parameter value series extraction step (S102), the parameter value series extraction unit 301 analyzes the electronic document data input from the first document input unit 10 or the raster data of the document, and forms a character string on the document. An interval between characters is obtained, and this is used as a series of parameter values relating to the document style.
Specifically, as shown in FIG. 4, a series in which the intervals between the characters constituting the character string on the document input from the first document input unit 10 are arranged is a parameter value series a ( k), (k = 0, 1, 2,..., L−1). The character spacing at any position on the document may be used as the character spacing, but in this embodiment, L character spacings from the beginning of the document (L ≧ 2 ⁿ ) are used. When the number of character intervals obtained from one line on the document is less than L, a character value parameter having a sequence length L is obtained by concatenating character interval parameters obtained from a plurality of subsequent lines.

Here, in the parameter value series extraction step (S102), if the input electronic document data is in a page description language such as PostScript or a word processor output format, the character spacing can be directly obtained by analyzing the electronic document data. it can. The method of analyzing the electronic document data is not limited to a specific method, and an appropriate method can be used according to the format of the electronic document data.
In addition, when the electronic document data is raster data of a document taken by a scanner or a digital camera, a character segmenting process generally performed as a character recognition pre-process is performed, and the distance between the extracted character rectangles. Can be the character spacing. The character cut-out processing is not limited to a specific method, and any generally used appropriate method can be used.
In this embodiment, the character spacing is used as a parameter relating to the document format for embedding information. The parameter values include character position, word spacing, line spacing, character height, character width, character inclination, and A combination of some of these can also be used.

  In the next embedded information encoding step (S103), n-bit binary data input from the embedded information input unit 40 is encoded by the code sequence generated by the code sequence generation unit 302 in the information encoding unit 303. To obtain an encoded information sequence. Here, n-bit binary data input from the embedded information input unit 40 is represented by b.

Details of the process for obtaining the encoded information sequence in the embedded information encoding step (S103) will be described below.
As the code sequence generated by the code sequence generation unit 302, a code sequence having a small average value and having randomness is used. The generated code sequence has a sharp autocorrelation characteristic as shown in FIG. Known code sequences having such properties include m sequences, but the code sequences generated by the code sequence generation unit 302 are not limited to these, and any code sequences having the above properties may be used.
Here, an example in which an m-sequence having a one-sequence length L is used as the code sequence generated by the code sequence generation unit 302 will be described. However, the sequence length L is 2 ⁿ or more. Also, the code sequence is represented by pn (k), and the symbol value thereof takes any of ± 1. That is, the code sequence pn (k) is expressed by the following equation (1). In the following description, Equations (1) to (26) correspond to [Equation 1] to [Equation 26].

The information encoding unit 303 encodes the n-bit embedded information b using the code sequence pn (k). In the present embodiment, as shown in FIG. 6, information is expressed by a shift amount of a code sequence pn (k) as an information encoding method. The code of the sequence length L can express L states from the shift zero to the shift L−1. Therefore, log ₂ L-bit information can be encoded using the code sequence pn (k) having the sequence length L. Using this principle, a coded information sequence c (k) obtained by coding the embedded information b is obtained. That is, the encoded information sequence c (k) is expressed by the following equation (2). However, in the following equation (2), the code sequence pn (k) is regarded as a periodic code sequence of period L (pn (k + L) = pn (k)).

  In the next modified parameter value sequence generation step (S104), the modified parameter value sequence generation unit 304 embeds the character spacing sequence a (k) obtained in the parameter value sequence extraction step (S102) into embedded information encoding. A modified parameter value sequence d (k) modified according to the encoded information sequence c (k) obtained in step (S103) is obtained. That is, the correction parameter value series generation unit 304 performs the calculation of the following equation (3).

In Expression (3), δ is a constant indicating the embedding strength of information, and the invisibility of embedded information increases as the value decreases. As will be described later, in the present embodiment, when a code sequence having a sequence length L of several hundred to several thousand is used, δ in Expression (3) is a much smaller value than each symbol value of a (k). It can be. That is, if a code sequence having a long alignment length is used, the invisibility can be increased to such an extent that embedded information can hardly be discriminated visually.
It should also be noted here that in the present embodiment, when embedding n-bit information, the variation range of the character spacing series a (k) can be stored in [−δ, δ]. That is, when embedding n-bit information, in the conventional method of multiplexing n encoded information sequences corresponding thereto, it is necessary to vary the character spacing sequence a (k) in the range of [−nδ, nδ]. was there. On the other hand, in the present embodiment, the variation range of the character spacing series a (k) can be reduced to 1 / n of the conventional one, so that the invisibility of embedded information can be greatly improved.

  In the next document correction step (S105), the document correction unit 305 uses the correction parameter value series d (k) obtained in the correction parameter value series generation step (S104) from the first document input unit 10. Correct the appearance of the input document data. Here, as shown in FIG. 7, the character spacing obtained from the character string on the corrected document is corrected so as to be equal to each symbol value of the correction parameter value series d (k).

In the document correction step (S105), when the original document data is electronic document data in a page description language such as PostScript or a word processor output format, the character spacing is equal to each symbol value of the correction parameter value series d (k). The description of the electronic document data is corrected so that
On the other hand, when the document data is raster data of a document photographed by a scanner or a digital camera, the result of the character segmentation process performed in the parameter value series extraction step (S102) is used, and the character rectangles between the segmented character rectangles are used. Each character image is rearranged so that the distance of becomes equal to each symbol value of the correction parameter value series d (k).

  In the next document output step (S106), the document output unit 50 outputs the document data in which the character spacing is corrected using the correction parameter value series d (k) in the form of a paper document or electronic document data.

In this way, a document in which additional information is embedded is obtained. In the document processing method according to the present embodiment, information is embedded in a form that is inseparable from the document content as the character spacing of the character string, unlike information that is written in the document with a barcode or the like. Therefore, when the tracking information of a confidential document or the like is embedded as embedded information in the document, the document content itself is lost when the embedded information is removed in order to prevent the identification of the leakage source, and high security can be obtained.
Further, as described above, the code sequence used in the present embodiment has a small average value of symbol values and has randomness. Looking at equation (3) on the premise of this, the spacing a (k) between characters is randomly expanded or narrowed, and if a certain range (for example, one line) is seen, the correction amount It can be seen that the sum is small. That is, since the length of each corrected line is almost the same as the line length of the original document, the invisibility of the information embedding process can be increased.
Furthermore, the information embedding processing method of the present embodiment embeds information in the character image itself. Therefore, even when repeated copies are made, the embedded information is preserved as long as the characters themselves do not disappear, and it has the feature of being robust against image quality deterioration due to repeated copies (high robustness).

Here, the information embedding process in the document processing apparatus 1 of the present embodiment described above will be described based on a specific example. Note that the information embedding process of the present embodiment is not limited to such a specific example.
This specific example shows a simple example in which the information b to be embedded is 3-bit information, its value is (b = 5), and the sequence length L of the code sequence is 15. Originally, in order to increase the invisibility of embedded information, it is necessary to set the sequence length L of the code sequence from several hundred to several thousand, but here L = 15 for easy understanding. . That is, in this specific example, the following equation (4) is used.

  From this code sequence pn (k) and embedded information b, the encoded information sequence c (k) is expressed by the following equation (5) according to equation (2).

  Using the obtained encoded information sequence c (k), the character spacing a (k), which is a parameter value sequence for the input document, is corrected according to the equation (3). The character spacing a (k) is assumed to be, for example, the following equation (6).

In this way, the character spacing does not need to be equal, and the character spacing may be so-called kerning in which the character spacing is adjusted according to the characters before and after the character string so that it looks natural.
The information embedding strength is δ = 2. When the sequence length L of the code sequence is several hundred to several thousand, a small value can be set as the information embedding strength, and the invisibility of the embedded information can be increased. However, since the sequence length L is as small as 15 in this example, the information embedding strength needs to be a certain large value.
Under these assumptions, the corrected parameter value series d (k) is obtained according to the equation (3) as shown in the following equation (7).

  Finally, the arrangement of the corresponding characters is corrected so that the character spacing of the document becomes d (k) in the above formula (7), and the document is output in the form of a paper document or electronic document data. A specific example of processing for restoring original 3-bit information from a document in which additional information is embedded will be described later.

Next, an embedded information restoration process executed in the document processing apparatus 1 according to the present embodiment will be described.
The embedded information restoration processing in the document processing apparatus 1 is executed by the embedded information restoration processing unit 350 built in the processing unit 30. FIG. 8 is a block diagram illustrating a functional configuration of the embedded information restoration processing unit 350. As illustrated in FIG. 8, the embedded information restoration processing unit 350 includes a parameter value sequence extraction unit 301, a code sequence group generation unit 307, and an embedded information restoration unit 306.

The parameter value series extraction unit 301 analyzes raster data and electronic document data of a document in which additional information is embedded, which is input from the second document input unit 20 (see also FIG. 1), and obtains it from a character string on the document. A series of parameter values relating to a document style such as a character interval, a character position, a word interval, a line interval, a character height, a character width, and a character inclination is obtained.
The code sequence group generation unit 307 is for generating the same code sequence as that generated by the information embedding processing unit 300 and a shift version thereof. The code sequence generation unit is the information embedding processing unit 300. The same configuration can be taken.
The embedded information restoration unit 306 is for restoring the embedded information from the parameter value series related to the document format of the document embedded with the additional information extracted by the parameter value series extraction unit 301. The parameter value series is decoded with each code series generated by the code series group generation unit 307 to restore the embedded additional information.

  Here, the embedding information restoration processing unit 350 according to the present embodiment aims to restore the embedding information from the image of the document embedded in the additional information and output to the paper. Embedded information can also be restored from page description languages such as PostScript and electronic document data in a word processor output format. Therefore, the document data input from the second document input unit 20 is not limited to raster data, and may be electronic document data in a page description language or a word processor output format.

  Next, an embedded information restoration processing method used in the document processing apparatus 1 according to this embodiment will be described. FIG. 9 is a flowchart showing an example of the procedure of the embedded information restoration process executed by the document processing apparatus 1. In the following, a case will be described as an example where the n-bit embedded information b embedded in a paper document by the above-described information embedding processing procedure is restored. Assume that the input paper document includes image quality degradation due to repeated copying.

First, in the document input step (S201), a paper document in which information is embedded is input from the second document input unit 20 such as a scanner or a digital camera.
In the next parameter value series extraction step (S202), the raster data of the document obtained from the second document input unit 20 is analyzed, the interval between the characters constituting the character string on the document is obtained, and this is converted into the document format. Parameter value series.
In the present embodiment, a case where embedding information is restored from an image of a document output on a paper in which additional information is embedded will be described. However, a page description language such as PostScript before output on paper or a word processor output format electronic Document data may be used as input data. In any case, the method for extracting the character interval series is the same as that in the above-described information embedding, and thus the description thereof is omitted.

  The character spacing series a ′ (k) obtained in the parameter value series extraction step (S202) can be written as the following expression (8) using the above expression (3).

  In equation (8), e (k) represents an error component due to character thickening or thinning due to repetitive copying, or noise or roughness on the character, and a detection error component in the character interval detection processing.

  In the next code sequence group generation step (S203), the code sequence group generation unit 307 generates the same code sequence as that used at the time of information embedding and its shifted version. Since the generated code sequence is the same as that shown in the above equation (1), description thereof is omitted.

In the next embedded information restoring step (S204), the n-bit embedded information b embedded from the character spacing series a ′ (k) is restored. Details of the embedding information restoring process here will be described with reference to FIG. 10 (a flowchart showing an example of a processing procedure in the embedding information restoring step (S204)).
As shown in the flowchart of FIG. 10, in the code sequence group generation unit 307, after the initial setting (S301), the same code sequence as that generated by the information embedding processing unit 300 described above and its shift A version is generated, and a correlation value between each version and the character spacing series a ′ (k) is obtained (S302). The correlation value R (i) between the character spacing sequence a ′ (k) and the code sequence pn (k + i) having the shift amount i can be written as the following equation (9).

If the shift amount imax that maximizes the correlation value R (i) is obtained (S303 to S306), the shift amount imax corresponds to the embedded information b.
In order to explain this, Equation (9) is rewritten as Equation (10) below using Equation (2) and Equation (8).

  Here, attention is focused on the second term in the last row of the above-described formula (10). The second term is the autocorrelation value of the code sequence pn (k). As described above, the code sequence having a sharp autocorrelation characteristic as shown in FIG. 5 is used. In other words, the second term in the last row of Equation (10) takes a large value only when i = b, and in other cases it means a very small value. In fact, it is known that the cross-correlation value between the m-sequence used as the code sequence group and its shifted version in this embodiment has the following properties. That is, the second term in the last row of Expression (10) is expressed as the following Expression (11).

Since the sequence length L of the code sequence is several hundred to thousands, if the value of the information embedding strength δ is appropriately set, the second term in the last row of the equation (11) is only when i = b. It takes a very large value (see FIG. 11).
On the other hand, the first term and the third term in the last line of the expression (11) represent the cross-correlation value between the character spacing series and the error component and the code series, respectively. Its absolute value is much smaller. This is because, as already described, the code sequence has a small average symbol value and has randomness, and therefore has a low correlation with any signal other than itself.
Further, the first term is so-called kerning in which the character spacing of the original document to be information-embedded does not have to be equal, and the character spacing is adjusted according to the preceding and following characters so that the character string looks natural. It is shown that it may be given. Although a (k) in the first term represents a character spacing sequence of the original document, even if this takes various values depending on k, it is because of low correlation due to the above properties of the code sequence. is there.

From the above, if the sequence length L of the code sequence is sufficiently large and the embedding strength δ of information is appropriately set, the correlation value R (i) in equation (9) is the code sequence of the shift amount b (= imax). It turns out that it becomes a big value only with respect to. As a result, the restoration value of the embedded information is b = imax.
The embedded information restored by the embedded information restoration unit 306 in this way is output from the information output unit 60 (S205).

Here, the embedded information restoration process in the document processing apparatus 1 according to the present embodiment will be described based on a specific example. The embedded information restoration process according to the present embodiment is not limited to such a specific example.
In this specific example, a procedure is described in which the information-embedded document obtained in the above-described specific example of the information embedding process is repeatedly copied, and the original 3-bit information is restored from the document in which the image quality has deteriorated.

In the specific example of the information embedding process described above, the character interval series d (k) of the document in which the information is embedded is represented by the above-described equation (7). In the series a ′ (k) in which the character spacing is detected from the repeated copies of this document, error components due to thickening and thinning of the characters due to repeated copying, noise on the characters and roughness, and detection errors of the character spacing detection processing The fact that the component e (k) representing the component is included has been described in the equation (8).
Therefore, it is assumed that the error component e (k) is as follows.

  Then, the character spacing series a ′ (k) detected from the repeatedly copied document is expressed by the following equation (13) by substituting equations (7) and (12) into equation (8).

When the cross-correlation value between the detected character spacing sequence a ′ (k) and the code sequence having various shift amounts is obtained by Equation (9), the shift amount imax of the code sequence having the maximum correlation value is embedded. Information b. FIG. 12 shows the cross-correlation values between the character spacing sequence a ′ (k) in equation (13), the code sequence in equation (5), and the shifted version thereof.
From the results shown in FIG. 12, the maximum correlation value was obtained when the shift amount was 5, and the 3-bit embedded information b = 5 was restored.

As described above, in the document processing apparatus 1 according to the present embodiment, electronic document data or a document image to be information-embedded is input, and a series of parameter values related to the document appearance from the input character string. Ask for. Next, a code sequence is generated by shifting a predetermined code sequence using the embedded information as a shift amount, and this is used as an encoded information sequence. Then, a correction parameter value series obtained by combining the encoded information series and the parameter value series is obtained, and the document format of the electronic document data or the document image is changed according to the correction parameter value series, so that information is added to the document. Embedded.
In addition, a document image or electronic document data in which information is embedded is input, and a parameter value series related to the document appearance is obtained from a character string on the input document. Next, a correlation value between the parameter value series and a predetermined code series and its shifted version is obtained. Then, the information is reconstructed using information in which the shift amount of the code sequence from which the maximum correlation value is obtained is embedded.

As a result, the document processing apparatus 1 according to the present embodiment can embed additional information such as tracking information not only in the digital data of the document but also in a text document printed on paper.
In addition, since the additional information is directly embedded in the parameter values of the document content itself relating to the document format such as character spacing, character position, word spacing, line spacing, character height, character width, etc. obtained from the character string on the document, the document content It is inseparable, making it difficult to tamper and remove information.

In particular, the document processing apparatus 1 according to the present embodiment uses only one encoded information sequence when embedding n-bit additional information in a character string. Thereby, the amplitude of the additional information after encoding can be made extremely small. Therefore, the invisible information is highly invisible, and it is possible to make it difficult to decode, falsify, and remove the information.
Furthermore, as a result of the decoding process using the code sequence, components other than the additional information such as parameter values relating to the document format and image degradation components caused by repeated copying are greatly reduced. Therefore, it is possible to stably restore the embedded information from a document that has been subjected to kerning processing or a paper document that has been repeatedly copied.

[Embodiment 2]
In the first embodiment, the information embedding processing unit 300 generates an encoded information sequence c (k) obtained by encoding n-bit embedded information b with one code sequence pn (k), and this is generated as a modified parameter value sequence. The case where the generation unit 304 performs the process of embedding in the parameter value series a (k) relating to the document format has been described. In Embodiment 2, when embedding more bits of information, the embedded information b is divided into a plurality of partial embedded information sequences, each partial embedded information sequence is encoded, and the concatenated one is encoded. A case where information embedding processing is performed as the information series c (k) will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

The information embedding process of this embodiment will be described with reference to FIG. In the present embodiment, when the information to be embedded to be input is m × n bits long, the embedded information input unit 40 divides this into n-bit partial embedded information sequences b _q , and the information encoding unit It outputs to 303. That is, the partially embedded information series b _q is expressed by the following equation (14). Here, the embedded information input unit 40 also functions as a partial information generation unit.

The partial embedded information sequence b _q obtained in this way is encoded by the information encoding unit 303 by the code sequence generated by the code sequence generating unit 302 by the same method as the above equation (2). An encoded information sequence c _q (k) is obtained. That is, the partial encoded information sequence c _q (k) is expressed as the following equation (15).

L in the above equation (15) is the sequence length of the code sequence pn (k). Therefore, the sequence length of the partial encoded information sequence c _q (k) is also L, respectively. The thus obtained partial encoded information sequence c _q (k) is connected to form an encoded information sequence c (k) having a sequence length m × L. That is, the encoded information sequence c (k) is expressed as the following equation (16).

  Then, the modified parameter value sequence generation unit 304 embeds the encoded information sequence c (k) of the above equation (16) in the parameter value sequence a (k) related to the document length of sequence length m × L (expression (Refer to (3)), and obtain a correction parameter value series d (k). Further, the document correction unit 305 corrects the appearance of the document data input from the first document input unit 10 using the correction parameter value series d (k). Thereafter, the corrected document data is output from the document output unit 50.

On the other hand, in order to restore the embedded information in the present embodiment, a parameter value series a ′ (k) relating to the document format is obtained from the information-embedded document, and this is obtained as a partial parameter value series a ′ of length L. Divide into _q (k). That is, the partial parameter value series a ′ _q (k) is expressed as in the following equation (17). Here, the parameter value series extraction unit 301 functions as a partial parameter value series extraction unit.

Next, the embedded information restoration process similar to that of the first embodiment is performed on each partial parameter value series a ′ _q (k) to restore the n-bit partial embedded information series b _q . By connecting these, embedded information b (equation (18)) having a sequence length of m × n can be restored.

In the information embedding processing method of the present embodiment, m code sequences having a sequence length L are used, and information is embedded in a parameter value sequence relating to a document format having a sequence length m × L. Since a code sequence of sequence length L can express information of maximum log ₂ L bits, when information is embedded in a parameter value sequence of sequence length m × L using m code sequences of sequence length L, maximum log ₂ L Bit information can be embedded.
On the other hand, when a single code sequence is used as in Embodiment 1, the length of the code sequence that can be used for a parameter value sequence of sequence length m × L is m × L. The information that can be expressed by this code sequence is maximum log ₂ m × L = log ₂ m + log ₂ L bits.
Since mlog ₂ L ≧ (log ₂ m + log ₂ L) is always satisfied for m ≧ 2, by decomposing the embedded information into partial series as in the present embodiment, the parameter value series of the same length is obtained. It becomes possible to embed more information.

[Embodiment 3]
In Embodiment 2, the information embedding processing unit 300 divides the embedded information b into a plurality of partial embedded information sequences, obtains respective partial encoded information sequences c _q (k), and obtains them by concatenating them. The case where the process of embedding the encoded information sequence c (k) of sequence length m × L in the parameter value sequence a (k) has been described. In Embodiment 3, instead of concatenating partial encoded information sequences, an encoded information sequence c (k) having a sequence length L is generated by multiplexing partial encoded information sequences, and information embedding processing is performed. The case will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

In the information embedding process according to the present embodiment, the information encoding unit 303 multiplexes the generated partially encoded information sequence, so that different code sequences pn _q (k) are used for encoding the partially embedded information sequence b _q. Is used. Thereby, the partial encoded information sequence c _q (k) is expressed as in the following equation (19).

As the code sequence pn _q (k) in the above equation (19), one having a small average symbol value and having randomness is used. The generated code sequence has a sharp autocorrelation characteristic as shown in FIG. Furthermore, the code sequence groups used are orthogonal to each other. The information encoding unit 303 multiplexes the partial encoded information system c _q (k) obtained in this way to configure an encoded information sequence c (k) having a sequence length L. That is, the encoded information sequence c (k) is expressed as in the following equation (20).

  Then, the encoded information sequence c (k) of the above equation (20) is embedded in the parameter value sequence a (k) relating to the document format of the sequence length L (see equation (3)), and the corrected parameter value sequence d ( k). Further, the document correction unit 305 corrects the appearance of the document data input from the first document input unit 10 using the correction parameter value series d (k). Thereafter, the corrected document data is output from the document output unit 50.

  On the other hand, in order to restore the embedded information, a parameter value series a ′ (k) relating to the document format is obtained from the information-embedded document, and a correlation value with each code series is obtained while changing the shift amount. If the correlation value with the q-th code sequence having the shift amount i in the parameter value sequence a ′ (k) is expressed as R (q, i), the following equation (21) is obtained.

  The above equation (21) is further rewritten as the following equation (22).

Here, attention is focused on the second term in the last row of the above equation (22). As described above, the code sequences are orthogonal to each other, and each code sequence has a sharp autocorrelation characteristic as shown in FIG. In other words, the second term of the above equation (23) takes a large value only when j = q and b _j = i, and in other cases it means a very small value.
Therefore, if the correlation value between the parameter value sequence a ′ (k) and each code sequence in the code sequence group is obtained while changing the shift amount, and the shift amount imax for obtaining the maximum correlation is obtained, b _q = imax. The partially embedded information sequence _bq can be restored. By concatenating them, it is possible to restore the embedded information b (equation (23)) having a sequence length of m × n.

In the information embedding processing method according to the present embodiment in which information is embedded as the shift amount of the code sequence, the amplitude of the generated partial encoded information sequence c _q (k) is small. Even if k) is configured, high invisibility can be maintained. Compared to the case of the above-described second embodiment, the sequence length of the encoded information system can be shortened by multiplexing, so that a larger amount of information in a short character string is greatly impaired invisibility. Can be embedded without any problem.

[Embodiment 4]
In Embodiment 2, the information embedding processing unit 300 divides the embedded information b into a plurality of partial embedded information sequences, obtains respective partial encoded information sequences c _q (k), and obtains them by concatenating them. The case where the process of embedding the encoded information sequence c (k) of sequence length m × L in the parameter value sequence a (k) has been described. In the present embodiment, the encoded information sequence c (k) having the sequence length m × L obtained as in the second embodiment is further periodically repeated, and the parameter value sequence a (k) relating to the document format is obtained. A case where the process of embedding is performed will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

In the present embodiment, an information encoding unit 303 concatenates a plurality of partial encoded information sequences to generate an encoded information sequence c (k), and a modified parameter value sequence generation unit 304 generates an encoded information sequence c. (K) is periodically repeated and embedded in the parameter value series a (k) relating to the document appearance. Here, as an example, three partial encoded information sequences c ₀ , c ₁ , and c ₂ are concatenated to generate an encoded information sequence c (k), which is periodically repeated to obtain parameter values relating to the document format. A case of embedding in the sequence a (k) will be described. That is, the encoded information sequence c (k) is formed by the information encoding unit 303 as shown in the following equation (24).

On the other hand, in order to restore the information embedded from the partial parameter value series, it is only necessary to obtain a partial parameter value series having a length of at least 3L. In the present embodiment, a case will be described in which a partial parameter value sequence having a sequence length of 6L is obtained. In this case, encoded information sequences c (k) for two periods are embedded in this partial parameter value sequence as shown in FIG.
If the procedure in the second embodiment is followed, three types of partial embedded information sequences b _a , b _b , and b _c can be restored from here, and these are partially embedded information sequences b ₀ , b ₁ , b _2. It is not possible to determine which of the two corresponds. Therefore, the embedded information b has three possibilities as shown in the following equation (25).

In order to know the correct order of the embedded information b, an error detection code or the like can be applied to the embedded information b, but in that case, it is necessary to allocate several bits as error detection bits, so that it can be embedded. The number of information bits is reduced.
Therefore, in the present embodiment, a synchronization code as shown in FIG. 14 is periodically multiplexed into the encoded information sequence c (k) and embedded in the parameter value sequence. The synchronization code has a small average symbol value, is random, and has a sharp autocorrelation characteristic as shown in FIG.

When restoring the embedded information b, first, the partial embedded information series b _a , b _b , and b _c are restored by the embedded information restoration processing method according to the second embodiment.
Next, the position where the maximum correlation is obtained is detected while changing the shift amount of the synchronization code. Since the synchronization code has a sharp autocorrelation characteristic as shown in FIG. 5, a large correlation value is generated only at the zero shift position. Therefore, since it can be seen from this position that the partial encoded information sequences are arranged in the order of c ₀ , c ₁ , and c ₂ , the embedded information b (formula (26)) can be restored as follows. .

According to the information embedding processing method of the present embodiment, even if the entire document cannot be obtained and only a part of the document can be obtained, the parameter value is long enough to detect one cycle of the encoded information sequence c (k). If the series is obtained, it is possible to restore the embedded information.
Further, since the correct order of the detected partial embedded information sequence can be known without adding error detection bits or the like, more information can be embedded.

1 is a block diagram showing a configuration of a document processing apparatus to which the present invention is applied. It is a block diagram explaining the function structure of an information embedding process part. It is the flowchart which showed an example of the procedure of the information embedding process performed with a document processing apparatus. It is a figure explaining the parameter value series a (k) of a document using the space | interval between each character which comprises the character string on a document. It is the figure which showed the autocorrelation characteristic of the code sequence produced | generated by the code sequence group production | generation part. It is a figure explaining expressing embedding information with a shift amount in the code sequence pn (k) encoded by the information encoding unit. It is a figure which shows the state corrected so that the character space | interval obtained from the character string on the document after correction | amendment might become equal to each symbol value of the correction parameter value series d (k). It is a block diagram explaining the function structure of an embedded information restoration process part. It is the flowchart which showed an example of the procedure of the embedded information restoration process performed with a document processing apparatus. It is the flowchart which showed an example of the procedure of the process in an embedded information restoration step. Expression (11) is a diagram for explaining that the second term in the last row takes a very large value only when i = b. It is the figure which showed the cross-correlation value between the character spacing series a '(k) of Formula (13), the code sequence of Formula (5), and its shifted version. FIG. 10 is a diagram for explaining information embedding processing in the second embodiment. In Embodiment 4, it is a figure explaining the state which embeds the coding information series c (k) by which the code | symbol for a synchronization was periodically multiplexed in the parameter value series.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Document processing apparatus, 10 ... 1st document input part, 20 ... 2nd document input part, 30 ... Processing part, 31 ... CPU (central processing unit), 32 ... I / O circuit, 33 ... ROM, 34 ... RAM 35 ... Hard disk drive (HDD), 40 ... Embedded information input unit, 50 ... Document output unit, 60 ... Information output unit, 300 ... Information embedding processing unit, 301 ... Parameter value sequence extraction unit, 302 ... Code sequence generation unit , 303 ... Information encoding unit, 304 ... Correction parameter value sequence generation unit, 305 ... Document correction unit, 306 ... Embedded information restoration unit, 307 ... Code sequence group generation unit, 350 ... Embedded information restoration processing unit

Claims (3)

A document processing apparatus capable of embedding additional information in document data consisting of character strings,
A parameter value series extraction unit that extracts a parameter value series related to the document appearance in the character string from the input document data;
An information input unit for inputting additional information to be embedded in the document data;
A partial information generation unit that divides the additional information input from the information input unit to generate a plurality of partial additional information;
A code sequence generator for generating a predetermined code sequence;
Using the partial additional information generated by the partial information generation unit as a shift amount, adding the partial encoded information sequence obtained by shifting the predetermined code sequence generated by the code sequence generation unit by the shift amount Information coding that generates for each information, and further generates a coded information sequence in which the partial coded information sequence is periodically repeated and connected, and generates a synchronization code synchronized with the coded information sequence And
Generating a modified parameter value sequence obtained by synthesizing the encoded information sequence with the parameter value sequence, and a modified parameter sequence generating unit that multiplexes and embeds the synchronization code in the modified parameter value sequence ;
A document processing apparatus comprising: a document correction unit that corrects the document data based on the generated correction parameter value series. The parameter value series extraction unit extracts a parameter value series related to a document appearance in the character string from the document data in which the additional information is embedded,
A partial parameter value series generation unit that divides the parameter value series extracted by the parameter value series extraction unit to generate a plurality of partial parameter value series;
The code sequences shifted version of said generated by the generating unit a predetermined code sequence and the same code sequence and the code sequence, and the encoded information sequence in synchronized so said synchronizing code with the same code sequence and the code sequence A code sequence group generation unit for generating a shifted version of
Based on the correlation value between the partial parameter value sequence generated by the partial parameter value sequence generation unit, the code sequence generated by the code sequence group generation unit and a shifted version of the code sequence, the partial parameter value sequence The additional information embedded every time is restored, and based on the correlation value between the parameter value series and the synchronization code and the shifted version of the code series, the synchronization code embedded for each parameter value series Detecting the position, detecting the positional relationship between the detected position of the synchronization code and the partial parameter value series, determining the order of the additional information of the partial parameter value series, the additional information further comprising an information restoring unit for restoring the additional information linked to embedded in the document data in accordance with the order The document processing apparatus according to claim 1, wherein the door. A document processing method capable of embedding additional information in document data consisting of character strings,
Enter document data consisting of character strings,
Extracting a parameter value series related to the document appearance in the character string from the input document data,
Dividing the additional information embedded in the document data to generate a plurality of partial additional information,
Using the plurality of partial additional information as shift amounts, a partial encoded information sequence obtained by shifting a predetermined code sequence by the shift amount is generated for each partial additional information, and the partial encoded information sequence is periodically repeated. And generating a concatenated encoded information sequence, generating a synchronization code synchronized with the encoded information sequence,
Generating a modified parameter value sequence in which the encoded information sequence is combined with the parameter value sequence, and multiplexing and embedding the synchronization code in the modified parameter value sequence ;
A document processing method, wherein the document data is corrected by the correction parameter value series.

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