JP2004023566A - Electronic watermark burying apparatus, electronic watermark extracting apparatuses, and method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for burying an electronic watermark which reduce the image quality deterioration of a document image, if data series of the electronic watermark are buried in the document image, and bury the electronic watermark hardly recognizable by the human's eyes. <P>SOLUTION: The method comprises a step for executing a document analysis of a document image to obtain circumscribed rectangles of characters (S601); obtaining two distances d1, d2 between circumscribed rectangles not adjacent to each other from the head of the document (S603), and executing either change process for changing parameters about the size of the circumscribed rectangle or that about the position of the circumscribed rectangle, or a combination thereof so that d1 > d2, if data to be buried are 1 (S605); or executing either of the two change processes or a combination thereof so that d1 < d2, if the data to be buried are 0 (S606). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital watermark embedding device for embedding a digital watermark in a document image, a digital watermark extracting device for extracting a digital watermark from a document image in which a digital watermark is embedded, and a method thereof.
[0002]
[Prior art]
2. Description of the Related Art Digital watermarks have attracted attention as a method for protecting copyrights when digital data such as images and sounds are distributed on the Internet. Digital watermarking is a technique for embedding watermark information in digital data such as images and sounds so that humans cannot perceive it. For example, as a digital watermarking technique for a multi-valued image, various methods using the redundancy of the density of a multi-valued pixel are known.
[0003]
On the other hand, a binary image such as a document image has a low degree of redundancy, and it is difficult to implement a digital watermarking technique. However, there are some known digital watermarking systems that use features unique to document images. For example, a method of moving the baseline of a line (Japanese Patent No. 3136061), a method of operating the space length between words (US Pat. No. 6,086,706, Japanese Patent Application Laid-Open No. 9-186603), and a method of operating the space length between characters (King Mongcut) "Electronic document data hiding technique using inter-character space" by The University, The 1998 IEEE Asia-Pacific Conf. Digital Watermark by Image ", Transactions of Information Processing Society of Japan, Vol. 38 No. 11 Nov. 1997. And rotating the character to change the inclination.
[0004]
[Problems to be solved by the invention]
However, the document image has a low degree of redundancy, and the conventional methods proposed up to now have noticeable changes to embed information due to changes in one variable such as line baseline, inter-word space, and character rotation. Had the disadvantage of being large.
[0005]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a digital watermark embedding apparatus and method for reducing image quality deterioration of a document image in which a digital watermark data string is embedded.
[0006]
[Means for Solving the Problems]
In order to achieve the object of the present invention, for example, a digital watermark embedding device of the present invention has the following configuration.
[0007]
That is, an electronic watermark embedding device that embeds an electronic watermark data string in a document image,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. Parameter calculation means for obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between both circumscribed rectangles in a second set different from the first set When,
The height of the circumscribed rectangles constituting the set and the distance between the circumscribed rectangles in the set are changed so that the magnitude relationship between the value indicated by the first parameter and the value indicated by the second parameter changes according to the data to be embedded. A control unit that controls a character corresponding to a circumscribed rectangle to be changed by changing at least one of them.
[0008]
In order to achieve the object of the present invention, for example, a digital watermark embedding device of the present invention has the following configuration.
[0009]
That is, an electronic watermark embedding device that embeds an electronic watermark data string in a document image,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Average value calculating means for obtaining the average value of the values indicated by all the parameters.
In accordance with the data to be embedded, the height of the circumscribed rectangle constituting the target set and the distance between the circumscribed rectangles in the target set are changed so that the magnitude relationship between the value indicated by the parameter and the average value for the target set changes. A control unit that controls a character corresponding to a circumscribed rectangle to be changed by changing at least one of the rectangles.
[0010]
In order to achieve the object of the present invention, for example, a digital watermark extracting device of the present invention has the following configuration.
[0011]
That is, a digital watermark extracting device for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding device,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. Parameter calculation means for obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between both circumscribed rectangles in a second set different from the first set When,
An extraction unit that expresses the magnitude relationship between the value indicated by the first parameter and the value indicated by the second parameter by a predetermined value to obtain the value as digital watermark data is provided.
[0012]
In order to achieve the object of the present invention, for example, a digital watermark extracting device of the present invention has the following configuration.
[0013]
That is, a digital watermark extracting device for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding device,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Average value calculating means for obtaining the average value of the values indicated by all the parameters.
An extraction means for expressing the magnitude relationship between the average value and the value indicated by the parameter of the target set by a predetermined value to obtain the value as digital watermark data is provided.
[0014]
In order to achieve the object of the present invention, for example, a digital watermark embedding method of the present invention has the following configuration.
[0015]
That is, a digital watermark embedding method for embedding a digital watermark data string in a document image,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. A parameter calculating step of obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between the two circumscribed rectangles in a second set different from the first set When,
The height of the circumscribed rectangles constituting the set and the distance between the circumscribed rectangles in the set are changed so that the magnitude relationship between the value indicated by the first parameter and the value indicated by the second parameter changes according to the data to be embedded. A control step of controlling a character corresponding to the circumscribed rectangle to be changed by changing at least one of them.
[0016]
In order to achieve the object of the present invention, for example, a digital watermark embedding method of the present invention has the following configuration.
[0017]
That is, a digital watermark embedding method for embedding a digital watermark data string in a document image,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Calculating, an average value calculating step of calculating an average value of values indicated by all the parameters,
In accordance with the data to be embedded, the height of the circumscribed rectangle constituting the target set and the distance between the circumscribed rectangles in the target set are changed so that the magnitude relationship between the value indicated by the parameter and the average value for the target set changes. A control step of controlling a character corresponding to a circumscribed rectangle to be changed by changing at least one of the rectangles.
[0018]
In order to achieve the object of the present invention, for example, a digital watermark extracting method of the present invention has the following configuration.
[0019]
That is, a digital watermark extraction method for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding method,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. A parameter calculating step of obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between the two circumscribed rectangles in a second set different from the first set When,
An extraction step of expressing the magnitude relationship between the value indicated by the first parameter and the value indicated by the second parameter as a predetermined value to obtain the value as digital watermark data.
[0020]
In order to achieve the object of the present invention, for example, a digital watermark extracting method of the present invention has the following configuration.
[0021]
That is, a digital watermark extraction method for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding method,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Calculating, an average value calculating step of calculating an average value of values indicated by all the parameters,
An extraction step of expressing a magnitude relationship between the average value and a value indicated by the parameter of the target group by a predetermined value to obtain the value as digital watermark data.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to the accompanying drawings.
[0023]
[First Embodiment]
A method for embedding a data string of a digital watermark according to the present embodiment will be described with reference to FIG. FIG. 2 is a view for explaining a method of embedding a data string of a digital watermark according to the present embodiment using a distance between circumscribed rectangles that are not adjacent to each other in a document image.
[0024]
The rectangles A to G indicate circumscribed rectangles of each character in the document image, and are extracted using a document analysis technique. The circumscribed rectangle of each character is a rectangle circumscribing the character, and is information indicating an area for character recognition. As a method of obtaining a circumscribed rectangle of each character, first, each pixel value of the document image is projected on a vertical coordinate axis, a blank portion (a portion without a black character) is determined, a line is determined, and line division is performed. Do. Thereafter, the document image is projected line by line on the horizontal coordinate axis, a blank portion is searched, and the document image is divided into characters. This makes it possible to cut out each character as a circumscribed rectangle. As this method, for example, a method disclosed in JP-A-6-68301 can be mentioned.
[0025]
In the same figure, 201 indicates the distance between circumscribed rectangles A and C, 202 indicates the distance between circumscribed rectangles B and D, 203 indicates the distance between circumscribed rectangles D and F, and 204 indicates the circumscribed rectangles E and G. Indicates the distance between them. As described above, in the method of embedding the data string of the digital watermark according to the present embodiment, these distances are changed according to the data to be embedded.
[0026]
Hereinafter, a method of embedding the above-described digital watermark data string will be described. FIG. 3 shows a basic configuration of a computer as a digital watermark embedding device according to the present embodiment and a digital watermark extracting device for extracting a digital watermark data sequence from a document image in which the digital watermark data sequence is embedded. It is not essential to use all the units shown in FIG. 3 in order to realize the above-described embedding method and extraction method.
[0027]
In the figure, a computer 301 is a personal computer, a workstation, or the like, which is widely used, and is capable of inputting an image read by a scanner 317 and editing or storing the image. Further, the image obtained from the scanner 317 can be printed from the printer 316 on a recording medium such as paper or OHP. Various instructions and the like from the user can be input using the mouse 313 and the keyboard 314.
[0028]
Inside the computer 301, blocks described later are connected by a bus 307, and various data can be transferred between the respective blocks. The MPU 302 controls the operation of each block in the computer 301 and executes a program stored in the main storage device 303 as a RAM to execute a series of processes related to embedding of a digital watermark data sequence, which will be described later, and this embedding. A series of processing for extracting a data string of a digital watermark embedded in a document image by the processing is executed.
[0029]
The main storage device 303 includes an area for temporarily storing programs and data loaded from the HDD 304, the CD-ROM drive device 309, the DVD-ROM drive device 310, the FD drive device 311 and the like. And a work area for temporarily storing data to be processed in order to execute the processing.
[0030]
A hard disk drive (HDD) device 304 can store a program and document image data loaded in the main storage device 303 in advance, or can store processed document image data. An interface (I / F) 315 is connected to a scanner 317 that reads information recorded on a document or a film and generates image data, and is an I / F for inputting image data obtained by the scanner 317. is there. The I / F 308 is connected to the printer 316 that prints image data, and is an I / F for transmitting the image data to be printed to the printer 316.
[0031]
The CD-ROM drive device 309 is a device that can read or write data stored in a CD-ROM (CD-R / CD-RW), which is one of the external storage media. An FD (floppy (registered trademark) disk) drive device 311 is a device capable of reading data from the FD and writing data to the FD, similarly to the CD-ROM drive device 309. The DVD-ROM drive device 310 is a device that can read data from a DVD and write data to a DVD, like the FD drive device 311. If a program or a printer driver is stored in the CD-ROM, FD, DVD-ROM, or the like, install the program in the HDD 304 and load the program into the main storage device 303 as necessary. Has become.
[0032]
The I / F 312 is an I / F connected to a mouse 313 or a keyboard 314 in order to receive an input instruction therefrom. The monitor 306 is a display device that can display the result of processing for extracting a data string of a digital watermark and the process of processing. Further, the video controller 305 is a device for transmitting display data to the monitor 306.
[0033]
The digital watermark embedding process performed by the computer having the above configuration will be described with reference to FIG. 6 showing a flowchart of the process. In the following description, the distance between alternate circumscribed rectangles (201 and 202, 203 and 204 in FIG. 2 as an example) is used. The progress of the following processing may be displayed on the monitor 306 as appropriate.
[0034]
First, in response to an instruction input from the user using the mouse 313 or the keyboard 314, a document image to be embedded with a digital watermark is loaded into the main storage device 303 (step S600). This document image is obtained by reading a recording medium such as paper on which a document is recorded by the scanner 317 and converting the read result into a bitmap.
[0035]
However, the method of obtaining a document image is not limited to this. For example, a document created by a general document editor, or the above-described CD-ROM drive 309, DVD-ROM drive 310, or FD A document image may be created by bitmapping using the data of the document loaded from the drive device 311 into the main storage device 303. Further, a network I / F that can be connected to a network such as a LAN or the Internet may be provided in the device, and a document image may be received and obtained from outside via the network. However, in any of the above cases, the document image is bit-mapped.
[0036]
Next, the above-described document analysis is performed on the bit-mapped document image to obtain a circumscribed rectangle of each character (step S601). Next, when the user inputs a digital watermark data string consisting of 1 or 0 using the keyboard 314 or the mouse 313, this data string is output to the main storage device 303 via the I / F 312, and 303 (step S602).
[0037]
Next, the distance between two non-adjacent circumscribed rectangles from the head of the document is obtained, and these are set as d1 and d2, respectively (step S603). In the example of FIG. 2, the distance of 201 is obtained, and the distance is d1, and the distance of 202 is obtained, which is d2 (step S603). If the data to be embedded is 1, the process proceeds to step S605, and a process of changing one of the following two parameters or a combination thereof is performed so that d1> d2 (step S605).
[0038]
-Increase the size of the circumscribed rectangle B in the column direction or reduce the size of the circumscribed rectangle C in the column direction (change the parameter related to the size)
-Move the position of the circumscribed rectangle C to the circumscribed rectangle D, or move the position of the circumscribed rectangle B to the circumscribed rectangle D (change the parameter related to the position)
An instruction to perform either of these two parameter change processes or a process based on a combination thereof may be predetermined or may be input by the user.
[0039]
On the other hand, if the data to be embedded is 0, the process proceeds to step S606, and a process based on one of the following two parameter changing processes or a combination thereof is performed so that d1 <d2 (step S606).
[0040]
-Decrease the size of the circumscribed rectangle B in the column direction, or increase the size of the circumscribed rectangle C in the column direction (change the size parameter)
Move the position of the circumscribed rectangle C to the side of the circumscribed rectangle A, or move the position of the circumscribed rectangle B to the side of the circumscribed rectangle A (change the parameter related to the position)
An instruction to perform either of these two parameter change processes or a process based on a combination thereof may be predetermined or may be input by the user. Also, with the control processing for changing the position and size of the circumscribed rectangle, the position and size of the character surrounded by the circumscribed rectangle are also changed in the same manner.
[0041]
In the processing in steps S605 and S606, the above-described parameters are adjusted in advance so that the changed portion is the least noticeable, that is, the image quality deterioration is reduced.
[0042]
In particular, in the example of FIG. 2, the position of every third circumscribed rectangle (in FIG. 2, the circumscribed rectangles A, D, and G) does not change. Then, a data embedding process is performed. As a result, embedding that does not cause a sense of strangeness to human eyes can be realized when the space “only” between the circumscribed rectangles is changed.
[0043]
Returning to FIG. 6, if there is more data to be embedded, the process returns to step S603, and the above process is repeated. For example, if there is still data to be embedded, in the example of FIG. 2, the distance between the circumscribed rectangles D and F is obtained, this is set to d1, the distance between the circumscribed rectangles E and G is further obtained, and this is set to d2. In the above description, the circumscribed rectangles A, B, C, and D are replaced with circumscribed rectangles D, E, F, and G, respectively, and the above processing is repeated.
[0044]
With the above processing, the data string of the digital watermark can be embedded in the document image.
[0045]
Next, a method of extracting a data string of a digital watermark embedded by the above processing will be described. As described above, the process of extracting the data string of the digital watermark is also performed by the computer shown in FIG. FIG. 7 shows a flowchart of a process performed by the computer to extract a data string of a digital watermark embedded by the above process.
[0046]
First, in response to an instruction input from a user using the mouse 313 or the keyboard 314, a document image in which a digital watermark data string is embedded (hereinafter, an embedded image) is loaded into the main storage device 303 (step S700). This embedded image is obtained by reading a recording medium, such as paper or OHP, on which the embedded image obtained by the above-described embedding processing is printed by the printer 316 by the scanner 317, and converting the read result into a bitmap. However, the method of obtaining the embedded image is not limited to this, and the embedded image is loaded into the main storage device 303 from the HDD 304, the CD-ROM drive device 309, the DVD-ROM drive device 310, or the FD drive device 311. It may be something. Further, a network I / F connectable to a network such as a LAN or the Internet may be provided in the above-described device, and may be received and obtained from the outside via the network.
[0047]
Next, the above-described document analysis is performed on the embedded image to obtain a circumscribed rectangle of each character (step S701). The processing in this step is the same as the processing in step S601.
[0048]
Next, the distance d1 of 201 and the distance d2 of 202 are obtained (step S702). If d1> d2 (step S703), the process proceeds to step S704, and the embedded data is recorded as 1 in the main storage device 303 (step S704). On the other hand, if d1 <d2, the process proceeds to step S705, and the embedded data is recorded as 0 in the main storage device 303 (step S705).
[0049]
Then, it is determined whether the circumscribed rectangle to be processed still remains (step S706). In the example of FIG. 2, since E, F, and G still remain after the circumscribed rectangles A, B, C, and D, the process returns to step S702, and the distance between the circumscribed rectangles D and F is obtained. Further, the distance between the circumscribed rectangles E and G is obtained, and this is set as d2. In the above description of the extraction processing, the circumscribed rectangles A, B, C, and D are replaced with the circumscribed rectangles D, E, F, and G, respectively. Is repeated. If the number of pieces of digital watermark data is known in advance, it may be determined whether the number of pieces of data has been recorded in the main storage device 303 or not.
[0050]
If it is determined in step S706 that there is no circumscribed rectangle to be processed, the data sequence recorded in the main storage device 303 in steps S704 and S705 can be obtained as a digital watermark data sequence. With the above processing, this data string can be extracted from the document image in which the digital watermark data string is embedded by the above method.
[0051]
In the above description, after embedding the digital watermark data according to the magnitude relationship between the distance between the circumscribed rectangles A and C and the distance between the circumscribed rectangles B and D, the distance between the circumscribed rectangles D and F is then determined. Although the digital watermark data is embedded according to the magnitude relationship with the distance between the circumscribed rectangles E and G, the comparison target of the magnitude relationship is not limited to this. That is, for example, after embedding digital watermark data in accordance with the magnitude relation between the distance between the circumscribed rectangles A and C and the distance between the circumscribed rectangles D and F, the distance between the circumscribed rectangles B and D and the circumscribed rectangle are then embedded. Digital watermark data may be embedded according to the magnitude relationship with the distance between E and G.
[0052]
Alternatively, a pseudo random number may be generated with a certain value as an initial value, and a comparison target having a magnitude relation may be selected according to the value of the random number. For example, if the value of the random number is 1, after embedding the digital watermark data according to the magnitude relationship between the distance between the circumscribed rectangles A and C and the distance between the circumscribed rectangles B and D, then, Is performed according to the magnitude relationship between the distance between the circumscribed rectangles E and G, and if the value of the random number is 2, the distance between the circumscribed rectangles A and C and the circumscribed rectangles D and F After embedding the digital watermark data in accordance with the magnitude relationship with the distance between them, the digital watermark data is then embedded in accordance with the magnitude relationship between the distance between the circumscribed rectangles B and D and the distance between the circumscribed rectangles E and G. An embedding process may be performed.
[0053]
Although the method of embedding a data string of a digital watermark using an example of a combination of four distances has been described here, when the number of circumscribed rectangles further increases, a combination of which circumscribed rectangles use the magnitude relationship between the distances is used. Since the number is enormous, if the method for selecting the comparison target of the magnitude relation using the random numbers is used, if the initial value is shared between the embedding side and the extracting side as a key, a third party who does not know the key Even if the algorithm is made public, the embedded information cannot be extracted, and the confidentiality is improved.
[0054]
In the above description, every other circumscribed rectangle is described as a non-adjacent circumscribed rectangle for simplicity. However, the method of embedding and extracting the digital watermark is not limited to every other circumscribed rectangle. it is obvious.
[0055]
In the above description, the parameter processing is performed so that d1> d2 when the data to be embedded is 1, and d1 <d2 when the data to be embedded is 0. However, the present invention is not limited to this. The direction may be reversed. That is, the parameter processing may be performed such that d1 <d2 when the data to be embedded is 1, and d1> d2 when the data to be embedded is 0. In this case, the extraction process must also correspond to this. When d1> d2, the embedded data is recorded as 0 in the main storage device 303, and when d1 <d2, the embedded data is set as 1 The information is recorded in the storage device 303.
[0056]
[Second embodiment]
In this embodiment, a digital watermark data string is embedded in a document image by a method different from the digital watermark data string embedding method according to the first embodiment. Hereinafter, a method of embedding a digital watermark data string in a document image and a method of extracting a digital watermark data string from the document image according to the present embodiment will be described. The basic configuration of a computer that executes the embedding method and the extracting method, and the functions of each unit are the same as those in the first embodiment.
[0057]
A method for embedding a digital watermark data string according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram for explaining a method for embedding a data string of a digital watermark according to the present embodiment using a distance between circumscribed rectangles that are not adjacent to each other in a document image.
[0058]
The rectangles A to G indicate circumscribed rectangles of each character constituting one line in the document image, and are obtained by the processing described in the first embodiment. In the same figure, 101 indicates the distance between circumscribed rectangles A and C, 102 indicates the distance between circumscribed rectangles B and D, 103 indicates the distance between circumscribed rectangles C and E, and 104 indicates the circumscribed rectangles D and F. 105 indicates the distance between the circumscribed rectangles E and G. As described above, in the method of embedding the data string of the digital watermark according to the present embodiment, these distances are changed according to the data to be embedded.
[0059]
Next, a process of embedding a data string of a digital watermark according to the present embodiment performed by a computer will be described with reference to FIG. 4 showing a flowchart of the process. In the following description, the distance between alternate circumscribed rectangles (101 to 105 in FIG. 1) is used. The progress of the following processing may be displayed on the monitor 306 as appropriate.
[0060]
Note that the processing in each step from step S400 to step S402 is the same as the processing in each step from step S600 to step S602, and a description thereof will be omitted.
[0061]
Next, the distance between the circumscribed rectangles of one line sentence, that is, the sum of the distances 101 to 105 is calculated, and the average value p is obtained (step S403). Specifically, assuming that the distances of 101 to 105 are x1, x2, x3, x4, and x5, the average value p is p = (x1 + x2 + x3 + x4 + x5) / 5
Asking. If the data to be embedded is 1, the parameter related to the size of the circumscribed rectangle and / or the parameter related to the position is changed so that the distance between the circumscribed rectangles is longer than the average value (step S405). For example, if the distance of 101 is to be controlled, and the data to be embedded is 1,
-Decrease the size of the circumscribed rectangle C in the column direction (change the size parameter)
・ Move the position of the circumscribed rectangle C to the circumscribed rectangle D (change the parameter related to the position)
, Or a combination thereof. Note that the instruction to perform either may be determined in advance, or may be input by the user.
[0062]
On the other hand, when the data to be embedded is 0, the parameters related to the size of the circumscribed rectangle and / or the parameters related to the position are changed so that the distance between the circumscribed rectangles is shorter than the average value (step S406). For example, if the distance of 101 is to be controlled, and if the data to be embedded is 0,
・ Increase the size of the circumscribed rectangle C in the column direction (change the size parameter)
・ Move the position of the circumscribed rectangle C to the circumscribed rectangle B (change the parameter related to the position)
, Or a combination thereof. Note that the instruction to perform either may be determined in advance, or may be input by the user. Also, with the control processing for changing the position and size of the circumscribed rectangle, the position and size of the character surrounded by the circumscribed rectangle are also changed in the same manner. In the processing in steps S405 and S406, the above-described parameters are adjusted in advance so that the changed portion is the least noticeable, that is, the image quality deterioration is reduced.
[0063]
If there is more data to be embedded, the process returns to step S404, and the above process is repeated. For example, when there is data to be embedded, the above processing is performed with the distance 102 as a control target in the example of FIG.
[0064]
With the above processing, the data string of the digital watermark can be embedded in the document image. If the data string to be embedded does not fit in one row, the same processing is repeated in the next row.
[0065]
Finally, the average value is stored in the HDD 304 as a key (step S408). However, if the embedding process extends over multiple lines, if the average value of the length between non-adjacent circumscribed rectangles for multiple lines, such as all the lines to be embedded or for each paragraph, is used as the key, the number to be stored as a key is reduced. Can be reduced.
[0066]
Next, a method of extracting a data string of a digital watermark embedded by the above processing will be described. As described above, the process of extracting the data string of the digital watermark is also performed by the computer shown in FIG. FIG. 5 shows a flowchart of a process performed by the computer for extracting a data string of a digital watermark embedded by the process.
[0067]
Since the processing in each of the steps S500 and S501 is the same as the processing in each of the steps S700 and S701, the description thereof is omitted. Then, in step S502, the average value D stored in the HDD 304 as a key in step S408 is loaded into the main storage device 303 (step S502). Then, a distance d between circumscribed rectangles that are not adjacent to each other is obtained (step S503). In the example of FIG. 1, initially, the distance d is a distance of d = 101.
[0068]
If d> D, the process proceeds to step S505, and the embedded data is recorded as 1 in the main storage device 303 (step S505). On the other hand, if d <D, the process proceeds to step S506, and the embedded data is recorded as 0 in the main storage device 303 (step S506).
[0069]
Then, it is determined whether or not the circumscribed rectangles to be processed still remain (step S507). In the example of FIG. 1, since the distance of 102, the distance of 103, the distance of 104, and the distance of 105 still remain after the distance of 101, the process returns to step S503, and the distance is set to d = 102. repeat. If the number of pieces of digital watermark data is known in advance, it may be determined whether the number of pieces of data has been recorded in the main storage device 303 or not.
[0070]
If it is determined in step S507 that there is no circumscribed rectangle to be processed, the data sequence recorded in the main storage device 303 in steps S506 and S507 can be obtained as a data sequence of a digital watermark. With the above processing, this data string can be extracted from the document image in which the digital watermark data string is embedded by the above method.
[0071]
The method of embedding a data string of a digital watermark according to the present embodiment is different from the method of embedding a data string of a digital watermark according to the first embodiment in that a data string of a digital watermark is added to a document image containing the same number of characters. When embedding, more information can be embedded. This is because the method according to the first embodiment embeds one piece of information (one-bit information in the above description) using four circumscribed rectangles, while the method according to the second embodiment uses two circumscribed rectangles. This is because one piece of information can be embedded.
[0072]
However, when the entire document image is enlarged or reduced, the embedding method according to the present embodiment is not a relative comparison of lengths as in the embedding method according to the first embodiment, but a fixed value called an average value. Therefore, it may be difficult to extract information. However, when the information sequence at the time of embedding is random, that is, when the appearance probabilities of 1 and 0 are equal, the average value at the time of embedding and the average value at the time of extraction are the same. In step S502, the same processing as step S403 may be performed again to calculate the average again without storing the used average as a key.
[0073]
Randomization of the information sequence can be easily realized by encryption processing of the information to be embedded. Also, in order to absorb the deviation of the appearance probabilities of 1 and 0 of the information sequence to be embedded, all the circumscribed rectangles in one line are not used, and several lines at the end of the line can be used for correcting the deviation. This is because, for example, when data indicating 1 is extremely large in a data string to be embedded in one row, the length of this row is significantly longer than the average value of the lengths of all rows, and is clearly conspicuous. .
[0074]
Therefore, in this case, instead of embedding ones between all the circumscribed rectangles in this one row, it is recognized that a predetermined number (one embeddings in one row becomes considerably longer than the above average value). 1 is embedded for the number of data of 1 up to a difficult level), and 0 is embedded between the remaining circumscribed rectangles. The reason why 0 is embedded is to correct the length of one line longer than the average value by embedding many 1s.
[0075]
For example, when embedding a data string composed of eight 1s between six circumscribed rectangles, 1 is embedded between the four circumscribed rectangles from the beginning, and 0 is embedded between the last two circumscribed rectangles. Then, the remaining two 1s are embedded in the next line. In this way, when embedding a large number of data strings, one row does not become extremely long.
[0076]
Conversely, when data indicating 0 is remarkable in a data string to be embedded in one row, the length of this row becomes significantly shorter than the above average value, which is clearly noticeable. Therefore, in the description of the above process, when a process in which 1 is read as 0 and 0 is read as 1 to embed a data string having many 0s, one row is not significantly shortened.
[0077]
In this case, the number of circumscribed rectangles for correction needs to be shared between the embedding side and the extracting side, and the extracting side does not extract information from the last few circumscribed rectangles.
[0078]
In the above description, every other circumscribed rectangle is described as a non-adjacent circumscribed rectangle for simplicity. However, the method of embedding and extracting the digital watermark is not limited to every other circumscribed rectangle. it is obvious.
[0079]
In the above description, the parameter processing is performed such that d> D when the data to be embedded is 1 and d <D when the data to be embedded is 0. However, the present invention is not limited to this. The direction may be reversed. That is, the parameter processing may be performed such that d <D when the data to be embedded is 1, and d> D when the data to be embedded is 0. In this case, the extraction process must also correspond to this. When d> D, the embedded data is recorded as 0 in the main storage device 303, and when d <D, the embedded data is set as 1 The information is recorded in the storage device 303.
[0080]
[Third Embodiment]
In the present embodiment, a data string of a digital watermark is embedded in a document image by a method different from the method of embedding a data string of a digital watermark according to the above embodiment. Hereinafter, a method of embedding a digital watermark data string in a document image and a method of extracting a digital watermark data string from the document image according to the present embodiment will be described. The basic configuration of a computer that executes the embedding method and the extracting method, and the functions of each unit are the same as those in the first embodiment.
[0081]
A method for embedding a data string of a digital watermark according to the present embodiment will be described with reference to FIG. FIG. 8 shows a data string of a digital watermark according to the present embodiment using an area defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles in two adjacent circumscribed rectangles in the document image. FIG. 6 is a diagram for explaining a method of embedding.
[0082]
In the figure, 801 is the distance between the left end of the circumscribed rectangle A and the right end of the circumscribed rectangle B, 802 is the distance between the left end of the circumscribed rectangle B and the right end of the circumscribed rectangle C, and 803 is the distance between the left end of the circumscribed rectangle C and the circumscribed rectangle D. 804 is the distance between the left end of circumscribed rectangle D and the right end of circumscribed rectangle E, 805 is the distance between the left end of circumscribed rectangle E and the right end of circumscribed rectangle F, 806 is the left end of circumscribed rectangle F and circumscribed rectangle G Indicates the distance to the right end of In the same figure, b is the height of the circumscribed rectangle B, c is the height of the circumscribed rectangle C, d is the height of the circumscribed rectangle D, e is the height of the circumscribed rectangle E, f is the height of the circumscribed rectangle F, g Indicates the height of the circumscribed rectangle G.
[0083]
The method of embedding the data string of the digital watermark according to the present embodiment is performed by using a set of circumscribed rectangles (in the example of FIG. 8, a set of circumscribed rectangles A and B, a set of circumscribed rectangles B and C, and a set of circumscribed rectangles C and D). Set, a set of circumscribed rectangles D and E, a set of circumscribed rectangles E and F, a set of circumscribed rectangles F and G), a rectangle defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles In the example of FIG. 8, the area represented by distance 801 × b, the area represented by distance 802 × c, the area represented by distance 803 × d, the area represented by distance 804 × e, the area represented by distance 804 (Area indicated by distance × f, area indicated by distance × g of 806) is changed according to the data to be embedded. The height used for calculating the area of each set may be the height of any circumscribed rectangle included in the set. Further, in the present embodiment, the number of circumscribed rectangles included in one set is not limited to two.
[0084]
Next, a process of embedding a data string of a digital watermark according to the present embodiment performed by a computer will be described with reference to FIG. 9 showing a flowchart of the process. The progress of the following processing may be displayed on the monitor 306 as appropriate.
[0085]
Note that the processing in each step from step S900 to step S902 is the same as the processing in each step from step S600 to step S602, and a description thereof will be omitted.
[0086]
Next, the area of the two sets from the head of the document is obtained, and these areas are set as S1 and S2 (step S903). In the example of FIG. 8, a distance × b of 801 is obtained, this is S1, a distance 802 × c is obtained, and this is S2. If the data to be embedded is 1, the process proceeds to step S905, and the four parameters of the width and height defining the area S1 and the width and height defining the area S2 are changed so that S1 <S2. (Step S905). In the example of FIG. 8, one or more of the four parameters of height b, distance 801, height c, and distance 802 are changed so that S1 <S2.
[0087]
On the other hand, if the data to be embedded is 0, the process proceeds to step S906, and the four parameters of the width and height defining the area S1 and the width and height defining the area S2 are changed so that S1> S2. (Step S906). In the example of FIG. 8, one or more of the four parameters of height b, distance 801, height c, and distance 802 are changed so that S1 <S2. Also, with the control processing for changing the position and size of the circumscribed rectangle, the position and size of the character surrounded by the circumscribed rectangle are also changed in the same manner.
[0088]
In the processing in steps S905 and S906, the above-described parameters are adjusted in advance so that the changed portion is the least noticeable, that is, the image quality deterioration is reduced.
[0089]
If there is more data to be embedded, the process returns to step S903, and the above process is repeated. For example, if there is data to be embedded, a distance 803 × d is obtained in the example of FIG. 8, this is set as an area S1, a distance 804 × e is obtained, and this is set as S2, and the above processing is repeated.
[0090]
With the above processing, the data string of the digital watermark can be embedded in the document image.
[0091]
Next, a method of extracting a data string of a digital watermark embedded by the above processing will be described. As described above, the process of extracting the data string of the digital watermark is also performed by the computer shown in FIG. FIG. 10 shows a flowchart of a process performed by the computer for extracting a data string of a digital watermark embedded by the above process.
[0092]
The processing of each step of steps S1000, S1001, and S1002 is the same as the processing of each step of steps S700, S701, and S903, and thus description thereof is omitted.
[0093]
Then, first, S1 is obtained as the distance 801 × b and S2 is obtained as the distance 802 × c. If S1 <S2 (step S1003), the process proceeds to step S1004, and the embedded data is recorded as 1 in the main storage device 303. (Step S1004). On the other hand, if S1> S2, the process proceeds to step S1005, and the embedded data is recorded as 0 in the main storage device 303 (step S1005).
[0094]
Then, it is determined whether the circumscribed rectangle to be processed still remains (step S1006). In the example of FIG. 8, next, S1 is set to the distance 803 × d and S2 is set to the distance 804 × e, and the above processing is repeated. If the number of pieces of digital watermark data is known in advance, it may be determined whether the number of pieces of data has been recorded in the main storage device 303 or not.
[0095]
If it is determined in step S1006 that there is no circumscribed rectangle to be processed, the data sequence recorded in the main storage device 303 in steps S1004 and S1005 can be obtained as a data sequence of a digital watermark. With the above processing, this data string can be extracted from the document image in which the digital watermark data string is embedded by the above method.
[0096]
In the present embodiment, S1 and S2 use the area of a rectangle formed by two circumscribed rectangles. However, other than that, a formula formulated using a plurality of independent parameters that define the circumscribed rectangle may be used. .
[0097]
For example, the distance 801 + b may be S1 and the distance 802 + c may be S2, or the distance 801+ (b × 0.1) may be S1 and the distance 802+ (c × 0.1) may be S2. Further, instead of using 801 to 806 as the distance from the left end of the left circumscribed rectangle to the right end of the right circumscribed rectangle, similarly to the first embodiment, the distance from the right end of the left circumscribed rectangle to the left end of the right circumscribed rectangle It may be. The comparison target of the area may be designated by a key. As another method of embedding information in each area, similarly to the second embodiment, an average value of all areas is obtained, and when the information to be embedded is 1, the area to be embedded is increased. When the information to be embedded is 0, the area to be embedded may be reduced.
[0098]
In the above description, the parameter processing is performed such that S1 <S2 when the data to be embedded is 1 and S1> S2 when the data to be embedded is 0. However, the present invention is not limited to this. The direction may be reversed. That is, the parameter processing may be performed such that S1> S2 when the data to be embedded is 1, and S1 <S2 when the data to be embedded is 0. In this case, the extraction process must also correspond to this. When S1 <S2, the embedded data is recorded in the main storage device 303 as 0, and when S1> S2, the embedded data is set as 1 The information is recorded in the storage device 303.
[0099]
[Fourth embodiment]
Further, a program for executing the method for embedding and extracting the data sequence of the digital watermark according to each of the above embodiments may be applied to the printer driver.
[0100]
[Other Embodiments]
An object of the present invention is to supply a recording medium (or a storage medium) on which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and to provide a computer (or CPU or MPU) of the system or the apparatus. Can be achieved by reading and executing the program code stored in the recording medium. In this case, the program code itself read from the recording medium implements the functions of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present invention.
[0101]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0102]
Further, after the program code read from the recording medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is executed based on the instruction of the program code. It goes without saying that the CPU included in the expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0103]
When the present invention is applied to the recording medium, the recording medium stores program codes corresponding to the flowcharts described above.
[0104]
【The invention's effect】
As described above, according to the present invention, even when a data string of a digital watermark is embedded in a document image, deterioration of the image quality of the document image can be reduced, and the digital watermark is hardly recognized by human eyes. it can.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a method for embedding a data string of a digital watermark according to a second embodiment of the present invention using a distance between circumscribed rectangles that are not adjacent to each other in a document image.
FIG. 2 is a diagram for explaining a method for embedding a data string of a digital watermark according to the first embodiment of the present invention using a distance between circumscribed rectangles that are not adjacent to each other in a document image.
FIG. 3 is a block diagram showing a basic configuration of a computer as a digital watermark embedding device and a digital watermark extracting device according to an embodiment of the present invention.
FIG. 4 is a diagram showing a flowchart of a process of embedding a data string of a digital watermark according to a second embodiment of the present invention.
FIG. 5 is a diagram illustrating a flowchart of a process of extracting a data string of a digital watermark according to a second embodiment of the present invention.
FIG. 6 is a diagram showing a flowchart of a process of embedding a data string of a digital watermark according to the first embodiment of the present invention.
FIG. 7 is a diagram showing a flowchart of a digital watermark data string extraction process according to the first embodiment of the present invention.
FIG. 8 shows a third embodiment of the present invention using an area defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles in two adjacent circumscribed rectangles in a document image. FIG. 3 is a diagram for explaining a method of embedding such a digital watermark data sequence.
FIG. 9 is a diagram illustrating a flowchart of a process of embedding a data string of a digital watermark according to a third embodiment of the present invention.
FIG. 10 is a diagram showing a flowchart of a digital watermark data string extraction process according to a third embodiment of the present invention.

Claims (15)

An electronic watermark embedding device that embeds an electronic watermark data sequence in a document image,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. Parameter calculation means for obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between both circumscribed rectangles in a second set different from the first set When,
The height of the circumscribed rectangles constituting the set and the distance between the circumscribed rectangles in the set are changed so that the magnitude relationship between the value indicated by the first parameter and the value indicated by the second parameter changes according to the data to be embedded. A digital watermark embedding device, comprising: control means for controlling a character corresponding to a circumscribed rectangle to be changed by changing at least one of them. The electronic device according to claim 1, wherein the first parameter and the second parameter indicate an area of a rectangle defined by a height of one circumscribed rectangle and a distance between both circumscribed rectangles. Watermark embedding device. An electronic watermark embedding device that embeds an electronic watermark data sequence in a document image,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Average value calculating means for obtaining the average value of the values indicated by all the parameters.
In accordance with the data to be embedded, the height of the circumscribed rectangles constituting the target set and the distance between the circumscribed rectangles in the target set are changed so that the magnitude relationship between the value indicated by the parameter and the average value for the target set changes. Control means for controlling a character corresponding to a circumscribed rectangle to be changed by changing at least one of them. A digital watermark extracting device for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding device according to claim 1 or 2,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. Parameter calculation means for obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between both circumscribed rectangles in a second set different from the first set When,
An electronic device comprising: an extracting unit that expresses a magnitude relationship between a value indicated by the first parameter and a value indicated by the second parameter by a predetermined value to obtain the value as digital watermark data. Watermark extraction device. 5. The electronic device according to claim 4, wherein the first parameter and the second parameter indicate a rectangular area defined by a height of one circumscribed rectangle and a distance between the two circumscribed rectangles. 6. Watermark extraction device. A digital watermark extracting device for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding device according to claim 3,
Circumscribed rectangle calculation means for finding a circumscribed rectangle of each character constituting the document image,
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Average value calculating means for obtaining the average value of the values indicated by all the parameters.
An electronic watermark extracting apparatus, comprising: an extracting unit that expresses a magnitude relationship between the average value and a value indicated by the parameter of the set of interest with a predetermined value to obtain the value as electronic watermark data. . A digital watermark embedding method for embedding a digital watermark data string in a document image,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. A parameter calculating step of obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between the two circumscribed rectangles in a second set different from the first set When,
The height of the circumscribed rectangles constituting the set and the distance between the circumscribed rectangles in the set are changed so that the magnitude relationship between the value indicated by the first parameter and the value indicated by the second parameter changes according to the data to be embedded. Controlling a character corresponding to a circumscribing rectangle to be changed by changing at least one of them. A digital watermark embedding method for embedding a digital watermark data string in a document image,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Calculating, an average value calculating step of calculating an average value of values indicated by all the parameters,
In accordance with the data to be embedded, the height of the circumscribed rectangles constituting the target set and the distance between the circumscribed rectangles in the target set are changed so that the magnitude relationship between the value indicated by the parameter and the average value for the target set changes. Controlling a character corresponding to a circumscribing rectangle to be changed by changing at least one of them. A digital watermark extraction method for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding method according to claim 7,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a first set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the first set is defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles. A parameter calculating step of obtaining a first parameter and a second parameter defined by a height of one circumscribed rectangle and a distance between the two circumscribed rectangles in a second set different from the first set When,
An extraction step of expressing a magnitude relationship between a value indicated by the first parameter and a value indicated by the second parameter by a predetermined value to obtain the value as digital watermark data. Watermark extraction method. A digital watermark extracting method for extracting a digital watermark data sequence from a document image in which a digital watermark data sequence is embedded by the digital watermark embedding method according to claim 8,
A circumscribed rectangle calculating step of finding a circumscribed rectangle of each character constituting the document image;
In a set of a circumscribed rectangle of interest and a circumscribed rectangle located a predetermined number of positions away from the circumscribed rectangle of interest, the parameters defined by the height of one circumscribed rectangle and the distance between both circumscribed rectangles are set for all sets. Calculating, an average value calculating step of calculating an average value of values indicated by all the parameters,
A digital watermark extraction method, comprising: expressing a magnitude relationship between the average value and a value indicated by the parameter of the set of interest by a predetermined value to obtain the value as digital watermark data. . A program for causing a computer to function as the digital watermark embedding device according to any one of claims 1 to 3. A program for causing a computer to function as the digital watermark extraction device according to any one of claims 4 to 6. A program for causing a computer to execute the digital watermark embedding method according to claim 7. A program for causing a computer to execute the digital watermark extraction method according to claim 9. A computer-readable storage medium storing the program according to any one of claims 11 to 14.

Images