JP4155213B2 - Digital watermark embedding device, digital watermark detection device, digital watermark embedding method, and digital watermark detection method - Google Patents

Description

  The present invention relates to an apparatus and method for embedding / detecting a digital watermark in a document image, and in particular, it is possible to embed embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. The present invention relates to a digital watermark embedding apparatus and method, and a digital watermark detection apparatus and method capable of detecting such embedded information.

  2. Description of the Related Art Conventionally, a technique for changing the contents of watermark detection processing in accordance with display / printing resolution is known in order to minimize the load of watermark detection processing for an image / printed material in which a digital watermark is embedded. For example, in Japanese Patent Laid-Open No. 2002-101288 “Image Transmission System and Method and Recording Medium”, when a digital watermark is detected from low-resolution data to be displayed / printed, high-resolution data is stored from the detected watermark information. A technique for detecting and displaying / printing a location is disclosed. Japanese Patent Laid-Open No. 2001-218038 “Image Forming System and Control Method Therefor” executes digital watermark detection processing and forgery prevention processing only when the input print information is image data having a resolution exceeding 100 dpi. Thus, a technique for minimizing the load on the determination process is disclosed.

JP 2002-101288 A JP 2001-218038 A

  By the way, the resolution setting of the image in which watermark is embedded / detected differs depending on the printing quality and printing speed required by the user, the performance of the printer / scanner to be used, and the like. However, when the watermark is embedded / detected by changing the resolution by the above-mentioned conventional method, the density per unit area of the watermark increases in high resolution printing because the size of the signal pattern and filter pattern is a fixed value. As a result, the document appears to have increased in density, making it difficult to read, and in low-resolution printing, the dots can be visually recognized, giving rise to a visual discomfort.

  In addition, as the resolution for embedding / detecting a watermark increases, the amount of information that can be embedded increases as the resolution increases. Therefore, it is desirable to embed with the minimum necessary resolution according to the amount of data to be embedded.

  The present invention has been made in view of the above-mentioned problems of the conventional digital watermark technology, and an object of the present invention is to perform a dynamic conversion process of the size of a signal pattern, thereby embedding a watermark in a printed document. New and improved digital watermark embedding device and digital watermark detection capable of satisfying the required amount of information / detection accuracy with the minimum necessary resolution without causing visual discomfort An apparatus, a digital watermark embedding method, and a digital watermark detection method are provided.

  In order to solve the above problems, a first digital watermark embedding device according to the present invention is a digital watermark embedding device capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. The image processing apparatus is characterized by comprising signal pattern changing means for changing the resolution of the signal pattern of the embedded information in accordance with the printing resolution when the document image is printed.

  A second digital watermark embedding device according to the present invention is a digital watermark embedding device capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. The present invention is characterized by comprising signal pattern changing means for changing the size of the signal pattern according to the amount of embedded information to be embedded (so as to have the minimum necessary resolution).

  A third electronic watermark embedding apparatus according to the present invention is an electronic watermark embedding apparatus capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image, and is printed by a user. Based on the resolution input unit (1006) to which the resolution is input, the signal resolution calculation unit (1007) for calculating the resolution of the signal pattern according to the print resolution, and the resolution of the signal pattern calculated by the signal resolution calculation unit, A watermark image forming unit (1008) for forming a watermark image from the embedded information and a resolution conversion unit (1009) for changing the resolution of the document image to the printing resolution are provided (claim 3).

  According to such a configuration, even if the watermark print resolution is changed by an instruction from the user, the watermark can be embedded with a signal pattern size of the same size as before the change on the paper surface, so that the print resolution can be increased. Regardless, the same information can be embedded. In addition, it is possible to embed a watermark without visual discomfort.

  In the above configuration, the signal resolution calculation unit (1007) uses a signal pattern generated at a specific resolution as a reference signal pattern, and uses the ratio between the print resolution and the specific resolution of the reference signal pattern to determine the resolution of the signal pattern. It may be calculated (claim 4).

  In addition, the watermark image forming unit (1008) changes the resolution of the signal pattern by selecting a signal pattern table that is suitable for the resolution of the signal pattern calculated by the signal resolution calculating unit from the signal pattern table prepared in advance. (Claim 5).

  A fourth digital watermark embedding apparatus according to the present invention is an electronic watermark embedding apparatus capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. An information amount detection unit (2006) that detects the amount of information compares the information amount of the embedded information with the information amount that can be embedded in the document image, and calculates the size of the signal pattern that can embed the embedded information in the document image. A signal size calculation unit (2007); and a watermark image formation unit (2008) that forms a watermark image from embedded information based on the size of the signal pattern calculated by the signal size calculation unit. (Claim 6).

  According to such a configuration, the watermark detection processing time can be shortened by changing the signal pattern size to a minimum required data amount according to the amount of data embedded as a watermark.

  In the above configuration, the watermark image forming unit (2008) calculates the embeddable information amount for each signal pattern size in advance, and compares the signal pattern size with the signal pattern size calculated by the signal size calculating unit. The pattern size may be changed (claim 7).

  A fifth digital watermark embedding apparatus according to the present invention includes a resolution acquisition unit (3006) for acquiring a print resolution from document image printing means or document image format information, and a signal for calculating the resolution of a signal pattern corresponding to the print resolution. A resolution calculation unit (1007), a watermark image formation unit (1008) that forms a watermark image from embedded information based on the resolution of the signal pattern calculated by the signal resolution calculation unit, and changes the resolution of the document image to the print resolution And a resolution conversion unit (1009).

  According to such a configuration, even if the watermark printing resolution is changed according to the printer setting or the document format, the watermark can be embedded with the same signal pattern size on the paper as before the change. Thus, it is possible to embed a watermark without visual discomfort.

  In the above configuration, the signal resolution calculation unit (1007) uses a signal pattern generated at a specific resolution as a reference signal pattern, and uses the ratio between the print resolution and the specific resolution of the reference signal pattern to determine the resolution of the signal pattern. It may be calculated (claim 9).

  In addition, the watermark image forming unit (1008) changes the resolution of the signal pattern by selecting a signal pattern table that is suitable for the resolution of the signal pattern calculated by the signal resolution calculating unit from the signal pattern table prepared in advance. (Claim 10).

  In the digital watermark embedding apparatus of the present invention as described above, the signal pattern may be a dot pattern in which dots are regularly arranged on a document image.

  In order to solve the above problems, the first digital watermark detection apparatus of the present invention can detect embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. An electronic watermark detection apparatus comprising a watermark detection unit (2014) for detecting the size of a signal pattern and determining the size of a signal pattern for watermark detection when the size of the detected signal pattern is plural. (Claim 12).

  According to this configuration, the embedded information can be easily determined by determining the size of the signal pattern when signal patterns of various sizes are arranged, such as the embedded information embedded by the digital watermark embedding apparatus of the present invention. Can be detected.

  In the digital watermark detection apparatus, the watermark detection unit (2014) performs signal detection (for example, pattern matching or filter processing) for each of different signal pattern sizes in at least a part of the area where the signal pattern is embedded in the document image. And the size of the signal pattern for watermark detection may be determined according to the detection result. For example, as a result of calculating a histogram of a detected signal, a case where a histogram of a certain coordinate exceeds a threshold and the number of coordinates exceeding the threshold exceeds a certain number can be determined as a detectable signal pattern.

When signal detection is performed for each of the different signal pattern sizes as described above, for example, the size of the signal pattern for watermark detection can be determined as follows.
Among the detectable signal pattern sizes, the size with the largest number of detections is determined as the size of the signal pattern for watermark detection.
Among the detectable signal pattern sizes, a specific size is determined as a watermark detection signal pattern size.
The smallest size among the detectable signal pattern sizes is determined as the size of the signal pattern for watermark detection.

  A second digital watermark detection apparatus according to the present invention is a digital watermark detection apparatus capable of detecting embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. A watermark detection unit (3014) is provided for detecting the detection resolution from the document image reading means or the format information of the document image, and detecting the signal pattern with a filter having a size corresponding to the detection resolution. Item 17).

  According to such a configuration, when signal patterns with various resolutions are arranged as in the embedded information embedded by the digital watermark embedding apparatus of the present invention, the embedded information can be easily obtained by acquiring the resolution of the signal pattern. Can be detected.

  In the digital watermark detection apparatus, the watermark detection unit (3015) uses a signal pattern generated at a specific resolution as a reference signal pattern, and uses the ratio between the detection resolution and the specific resolution of the reference signal pattern to filter the size of the filter. May be calculated (claim 18). By generating a reference resolution in advance, the detection resolution can be easily acquired.

  Alternatively, the watermark detection unit (3015) may select a filter suitable for the detection resolution from a filter table prepared in advance (claim 19). By preparing a filter table in advance, the detection resolution can be easily acquired.

  In the digital watermark detection apparatus of the present invention as described above, the signal pattern may be a dot pattern in which dots are regularly arranged on a document image.

  In order to solve the above problems, a first digital watermark embedding method of the present invention is a digital watermark embedding method capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. In this case, the resolution of the signal pattern of the embedded information is changed in accordance with the printing resolution when the document image is printed (claim 21).

  A second digital watermark embedding method according to the present invention is a digital watermark embedding method capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. The size of the signal pattern is changed according to the information amount of the embedded information to be embedded (so that the necessary minimum resolution is obtained) (claim 22).

  A third digital watermark embedding method of the present invention is a digital watermark embedding method capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image, and is printed by a user. Based on the resolution input step for inputting the resolution, the signal resolution calculation step for calculating the resolution of the signal pattern in accordance with the print resolution, and the resolution of the signal pattern calculated in the signal resolution calculation step, the watermark image is obtained from the embedded information. A watermark image forming step for forming, and a resolution converting step for changing the resolution of the document image to the print resolution.

  According to this method, even if the watermark printing resolution is changed by an instruction from the user, the watermark can be embedded with a signal pattern size of the same size as before the change on the paper. A watermark can be embedded without a sense of incongruity.

  In the signal resolution calculation step of the above method, the signal pattern generated at a specific resolution is set as a reference signal pattern, and the resolution of the signal pattern is calculated using the ratio between the print resolution and the specific resolution of the reference signal pattern. (Claim 24).

  In the watermark image forming step, the resolution of the signal pattern is changed by selecting a signal pattern table prepared in advance from the signal pattern table that matches the resolution of the signal pattern calculated in the signal resolution calculating step. (Claim 25).

  A fourth digital watermark embedding method of the present invention is a digital watermark embedding method capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. An information amount detection step for detecting the amount of information, and a signal size calculation for calculating the size of a signal pattern capable of embedding embedded information in a document image by comparing the amount of embedded information and the amount of information that can be embedded in the document image And a watermark image forming step of forming a watermark image from the embedding information based on the size of the signal pattern calculated in the signal size calculating step.

  According to this method, the watermark detection processing time can be shortened by changing the signal pattern size to a minimum required data amount according to the amount of data embedded as a watermark.

  In the watermark image forming process of the above method, the amount of embeddable information is calculated in advance for each signal pattern size, and the signal pattern size is changed by comparing with the signal pattern size calculated in the signal size calculating process. (Claim 27).

  A fourth digital watermark embedding method of the present invention is a digital watermark embedding method capable of embedding embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. A resolution acquisition step of acquiring print resolution from the format information of the printing means or document image, a signal resolution calculation step of calculating the resolution of the signal pattern according to the print resolution, and the resolution of the signal pattern calculated in the signal resolution calculation step Basically, the method includes a watermark image forming step of forming a watermark image from the embedded information, and a resolution conversion step of changing the resolution of the document image to the print resolution.

  According to such a method, even if the watermark printing resolution is changed according to the printer setting or the document format, the watermark can be embedded with the same signal pattern size on the paper as before the change. Thus, it is possible to embed a watermark without visual discomfort.

  In the signal resolution calculation step of the above method, the signal pattern generated at a specific resolution is set as a reference signal pattern, and the resolution of the signal pattern is calculated using the ratio between the print resolution and the specific resolution of the reference signal pattern. (Claim 29).

  In the watermark image forming step, the resolution of the signal pattern is changed by selecting a signal pattern table prepared in advance from the signal pattern table that matches the resolution of the signal pattern calculated in the signal resolution calculating step. (Claim 30).

  In the digital watermark embedding method of the present invention as described above, the signal pattern may be a dot pattern in which dots are regularly arranged on a document image.

  In order to solve the above-described problem, the first digital watermark detection method of the present invention can detect embedded information embedded by regularly arranging a plurality of types of signal patterns in the background of a document image. An electronic watermark detection method comprising a watermark detection step of detecting a signal pattern size and determining the size of a signal pattern for watermark detection when the detected signal pattern size is plural. (Claim 32).

  According to such a method, the embedded information can be easily determined by determining the size of the signal pattern when signal patterns of various sizes are arranged as in the embedded information embedded by the digital watermark embedding apparatus of the present invention. Can be detected.

  In the watermark detection step of the above method, signal detection (such as pattern matching and filter processing) is performed for each size of a different signal pattern in at least a part of a region where the signal pattern is embedded in the document image, and the detection result is determined according to the detection result. The size of the signal pattern for watermark detection may be determined (claim 33). For example, as a result of calculating a histogram of a detected signal, a case where a histogram of a certain coordinate exceeds a threshold and the number of coordinates exceeding the threshold exceeds a certain number can be determined as a detectable signal pattern.

When signal detection is performed for each of the different signal pattern sizes as described above, for example, the size of the signal pattern for watermark detection can be determined as follows.
Among the detectable signal pattern sizes, the size with the maximum number of detections is determined as the size of the signal pattern for watermark detection.
A specific size among the detectable signal pattern sizes is determined as the size of the signal pattern for watermark detection.
The smallest size among the detectable signal pattern sizes is determined as the size of the signal pattern for watermark detection.

  The second digital watermark detection method of the present invention is a digital watermark detection method capable of detecting embedded information by regularly arranging a plurality of types of signal patterns in the background of a document image. And a watermark detection step of acquiring a detection resolution from the document image reading means or the format information of the document image, and detecting a signal pattern with a filter having a size corresponding to the detection resolution.

  According to this method, the embedded information can be easily obtained by acquiring the resolution of the signal pattern when signal patterns of various resolutions are arranged, such as the embedded information embedded by the digital watermark embedding apparatus of the present invention. Can be detected.

  In the watermark detection step of the above method, a signal pattern generated at a specific resolution may be used as a reference signal pattern, and a filter size may be calculated using a ratio between the detection resolution and the specific resolution of the reference signal pattern. Good (claim 38). By generating a reference resolution in advance, the detection resolution can be easily acquired.

  Alternatively, in the watermark detection step, a filter suitable for the detection resolution may be selected from a filter table prepared in advance (claim 39). By preparing a filter table in advance, the detection resolution can be easily acquired.

  In the digital watermark detection method of the present invention as described above, the signal pattern may be a dot pattern in which dots are regularly arranged on a document image.

  According to another aspect of the present invention, there are provided a program for causing a computer to function as the digital watermark embedding device or the digital watermark detection device, and a computer-readable recording medium on which the program is recorded. . Here, the program may be described in any programming language. In addition, as a recording medium, for example, a CD-ROM, a DVD-ROM, a floppy disk (FD), a recording medium that is currently used as a recording medium capable of recording a program, or any recording that will be used in the future Media can also be employed.

  In the above description, the reference numerals in parentheses attached to the constituent elements are merely examples of corresponding constituent elements and signals in the embodiments and drawings to be described later for easy understanding. However, it is not limited to this.

  As described above, according to the present invention, since the watermark signal / filter size can be freely set, the minimum necessary amount can be obtained without embedding a visual feeling in the printed document by embedding the watermark. It is possible to satisfy the resolution and the amount of information that can be embedded / detection accuracy. That is, the present invention has the following effects. First, even if the watermark printing resolution is changed, the watermark can be embedded with the same signal pattern size on the paper as before the change, so that the watermark can be embedded without visual discomfort. It becomes possible. Second, the watermark detection processing time can be shortened by changing the signal pattern size to a minimum required amount of data in accordance with the amount of data embedded as a watermark. Third, by changing the size of the signal pattern and filter pattern according to the setting resolution of the printer / scanner, the watermark can be embedded at any resolution setting regardless of the print / scan resolution ratio and the corresponding relationship.・ Detection is possible.

  Exemplary embodiments of a digital watermark embedding device, a digital watermark detection device, a digital watermark embedding method, and a digital watermark detection method according to the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted. In the following embodiments, a dot pattern in which dots are regularly arranged in a predetermined area will be described as an example of a signal pattern. The signal pattern resolution refers to the number of pixels having a width or height constituting one signal pattern (dot pattern). The signal pattern size means the width or height of one signal pattern (dot pattern).

(First embodiment)
As a first embodiment, a print resolution for printing a document image is input by a user, and the resolution of a signal pattern of information to be embedded (hereinafter referred to as “embedded information”) according to the print resolution. The case of changing is described.

FIG. 1 is an explanatory diagram showing the configuration of the first embodiment.
In this embodiment, as shown in FIG. 1, a digital watermark embedding device 1001 and a digital watermark detection device 1002 will be described.

  The digital watermark embedding apparatus 1001 according to the present embodiment is an apparatus that can embed embedding information by regularly arranging a plurality of types of signal patterns in the background of a document image. The digital watermark detection apparatus 1002 according to the present embodiment is an apparatus capable of detecting embedded information by regularly arranging a plurality of types of signal patterns on the background of a document image. Hereinafter, it demonstrates in order.

(Digital watermark embedding apparatus 1001)
As shown in FIG. 1, the digital watermark embedding device 1001 is a device that performs processing based on document data 1003 and embedding information 1004, and includes a document image forming unit 1005, a resolution input unit 1006, and signal resolution calculation. A section 1007, a watermark image forming section 1008, a resolution conversion section 1009, a watermarked document image composition section 1010, and a printing section 1011 are provided.

  The document data 1003 is a document or table composed of text or a specific format. The embedded information 1004 is information that is embedded in a print document in a format other than characters, and is, for example, confidential information that allows only a specific person to browse.

  The document image forming unit 1005 is a functional unit that converts the document data 1003 into an image. The resolution input unit 1006 is a functional unit that acquires the print resolution input and set by the user. The signal resolution calculation unit 1007 is a functional unit that calculates the signal resolution of the signal pattern according to the print resolution input and set by the user. The watermark image forming unit 1008 is a functional unit that generates a watermark image with the calculated signal resolution based on the embedded information. The resolution conversion unit 1009 is a functional unit that changes the resolution of the document image to the resolution input and set by the user. The watermarked document image synthesis unit 1010 is a functional unit that synthesizes a document image and a watermark image. The printing unit 1011 is a functional unit that prints a watermarked document on a print medium such as paper.

  The print document 1012 is a printed matter such as paper on which a watermarked document is printed.

(Digital watermark detection apparatus 1002)
As shown in FIG. 1, the electronic watermark detection apparatus 1002 includes an input unit 1013 and a watermark detection unit 1014.

  An input unit 1013 is a functional unit that reads a watermarked print document and converts it into an image. The watermark detection unit 1014 is a functional unit that detects a watermark from a watermarked print document image.

The digital watermark embedding device and the digital watermark detection device according to the present embodiment are configured as described above. Next, the operation of this embodiment will be described. FIG. 2 is an explanatory diagram showing a processing flow of the present embodiment.
First, the operation on the digital watermark embedding apparatus 1001 side will be described.

(1) Document image formation (S1001 to S1002, document image forming unit 1005)
First, document data 1003 is input to the document image forming unit 1005 (step S1001). The document image forming unit 1005 forms a document image based on the document data 1003 (step S1002). Specifically, the document image can be formed by acquiring a print image of document data, a hard copy of a display screen, or the like.

(2) Resolution information input (S1003, resolution input unit 1006)
In this embodiment, the resolution information used is input by the user through the resolution input unit 1006. The print resolution can be freely set by the user.

(3) Calculation of signal pattern size (S1004, signal resolution calculation unit 1007)
Next, the size of the signal pattern is calculated in order to change the resolution of the signal pattern.
FIG. 3A shows a signal pattern in which the width and height are a ₀ × a ₀ pixels at the resolution A ₀ as the reference signal pattern. On the other hand, in the case of resolution p, as shown in FIG.

The resolution of the signal pattern is calculated so as to be a pixel (A ₀ , a ₀ , p is a natural number, p <A ₀ ). here,

Is called a floor function and represents the largest integer not exceeding X. The same applies to the resolution q (q is a natural number, q> A ₀ ), as shown in FIG.

  When the resolution is changed in this way, a watermarked document is printed at the resolution of the signal pattern calculated by the signal resolution calculation unit 1007, so that a signal pattern having the same size as the reference signal pattern is printed on the print document 1012. It becomes like this.

(4) Resolution conversion of signal pattern (S1005 to S1006, watermark image forming unit 1008)
Next, embedded information 1004 is input (step S1005). The signal pattern resolution conversion when embedding information is embedded will be described with reference to FIG.

First, let the upper left coordinates of the area of the reference signal pattern resolution A ₀ , width and height a ₀ × a ₀ pixels be (x, y). The signal pattern in that case is

Is a black pixel and all the remaining white pixels are expressed as one signal.

  In contrast, resolution p, width and height

  If pixel,

  Is converted to be expressed as one signal with black pixels and all remaining white pixels.

  By using these signal patterns, even when the resolution is changed, a signal pattern having the same size as the reference signal pattern is printed on the paper. At this time, since the dot size (black pixel size) varies depending on the resolution, a process for bringing the dot size closer to the reference signal pattern, such as a dot expansion process or a luminance value increase / decrease process, may be performed.

(7) Watermark image formation (S1006, watermark image forming unit 1008)
The watermark image formation will be described with reference to FIG. By defining bits 0 and 1 from signal patterns having different shapes and regularly arranging the signal patterns indicating the respective bits, the input embedded information can be expressed by the signal pattern.

  A watermark image is formed through the above steps. FIG. 6 is an explanatory diagram showing a synthesis process of a watermark image and a document image. The combined watermarked document image is printed as a print document 1012 from the printing unit 1011 of the digital watermark embedding apparatus 1001.

  Next, the operation of the digital watermark detection apparatus 1002 will be described.

(8) Watermark detection (S1011, watermark detection unit 1014)
Regarding the watermark detection in the first embodiment, even when the resolution is changed, a signal pattern having the same size as the reference signal pattern is printed on the paper surface. The filter processing corresponding to is performed, and the watermark is detected.

(Effects of the first embodiment)
As described above, according to the present embodiment, even when the print resolution is changed by changing the resolution of the watermark signal pattern in accordance with the print resolution input and set by the user, it is visually uncomfortable. It is possible to print a watermarked document that does not give

(Second Embodiment)
As a second embodiment, a case where the signal pattern size is changed according to the amount of embedded information will be described. As a result, the minimum amount of embeddable information can be set, so that the surplus portion of the embeddable information amount can be omitted, and the processing accuracy and processing speed can be improved.

FIG. 7 is an explanatory diagram showing the configuration of the second embodiment.
In the present embodiment, as shown in FIG. 7, a digital watermark embedding apparatus 2001 and a digital watermark detection apparatus 2002 will be described.

  As shown in FIG. 7, the digital watermark embedding apparatus 2001 replaces the resolution input unit 1006 and the signal resolution calculation unit 1007 of the digital watermark embedding apparatus 1001 (FIG. 1) according to the first embodiment with an information amount. A feature is that a detection unit 2006 and a signal size calculation unit 2007 are provided, and the resolution conversion unit 1009 is not a component.

  An information amount detection unit 2006 is a functional unit that acquires the information amount of embedded information and the size of a document image. The signal size calculation unit 2007 is a functional unit that compares the information amount of the embedded information 1004 with the information amount that can be embedded in the document image, and calculates the size of the signal pattern in which the embedded information can be embedded. The other components are substantially the same as those in the first embodiment, and a duplicate description is omitted.

  As shown in FIG. 7, the digital watermark detection apparatus 2002 includes a watermark detection unit 2014 instead of the watermark detection unit 1014 of the digital watermark detection apparatus 1002 (FIG. 1) according to the first embodiment. It is characterized by.

  The watermark detection unit 2014 performs signal detection such as pattern matching and filter processing for each size of a different signal pattern for at least a part of a region in which a signal pattern is embedded in a document image, and performs watermark detection according to the detection result. It is a functional unit that determines the size of a signal pattern. Details of the operation of the watermark detection unit 2014 will be described later.

The digital watermark embedding device and the digital watermark detection device according to the present embodiment are configured as described above. Next, the operation of this embodiment will be described. FIG. 8 is an explanatory diagram showing a processing flow of the present embodiment. Note that redundant description of operations substantially similar to those of the first embodiment is omitted, and only operations different from those of the first embodiment are described.
First, the operation on the digital watermark embedding apparatus 2001 side will be described.

  (1) Image data input to (3) Resolution information acquisition is substantially the same as in the first embodiment.

(4) Calculation of signal pattern size (S1004, signal size calculation unit 1007)
The calculation of the size of the signal pattern will be described with reference to FIGS. Parameters required for calculating the signal pattern size are defined as follows.
Amount of embedded data: x (bit)
Document image width: w (pixels)
Document image height: h (pixels)
Document image area: w × h (pixels)
Signal pattern area: m (pixel) (x, w, h, m are natural numbers)
Signal pattern size (width / height) (pixels):

  Amount of data that can be embedded:

  Here, the conditional expression for enabling embedding data amount: x is:

  It is.

  Signal pattern area satisfying this conditional expression: m is

And is represented as a line segment parallel to the x-axis in FIG. 9 (the curve in FIG. 9 is m = w × h / x).

  This makes the signal pattern size (number of pixels in width / height):

Is obtained.

Further, the size-converted signal pattern is expressed as shown in FIG. In Figure 10 shows the case of a resolution A _0, by changing the signal size even with the same resolution, be possible to increase or decrease the amount of embedded information can be seen.

  The subsequent (5) embedded information input to (7) watermark image formation are substantially the same as those in the first embodiment.

  Through the above steps, a print document 1012 is printed from the printing unit 1011 of the digital watermark embedding apparatus 1001.

  Next, the operation of the digital watermark detection apparatus 1002 will be described.

(8) Watermark detection (S1011, watermark detection unit 1014)
The watermark detection will be described with reference to FIGS. First, as shown in FIG. 11, a signal is detected by performing pattern matching or filter processing corresponding to the signal pattern in order from the maximum size signal pattern to a part of the watermark area such as the center of the scanned image. . FIG. 11A shows small filters F2 and F3 in order from the maximum size filter F1. FIG. 11B shows a case where the filter processing is performed in the order of the filters F1 and F2. FIG. 11C shows a case where the filter processing is performed in the order of the filters F1, F2, and F3.

  As shown in FIG. 12, the determination of whether or not the signal has been detected is performed by calculating a signal detection histogram for a part of the watermark area in the scanned image. When the histogram of a certain coordinate exceeds a threshold and the number of coordinates exceeding the threshold exceeds a certain number, it is determined that a signal pattern can be detected. Further, among the detectable signal patterns, the signal pattern having the smallest signal size is determined as the signal pattern used for watermark detection, and the watermark is detected by performing pattern matching on the entire watermark region or filter processing corresponding to the signal pattern.

(Effect of the second embodiment)
As the watermark embedding / detection resolution increases, the amount of information that can be embedded increases as the resolution increases. However, the amount of data of a printed / scanned image is large at the time of printing / scanning, and a long time is required for processing. Therefore, the watermark signal / filter size is converted in accordance with the embedding / detection resolution so as to be embedded at the minimum necessary resolution in accordance with the amount of data to be embedded. As a result, the surplus of information to be embedded can be eliminated, and the processing time can be shortened and the detection accuracy can be improved.

(Third embodiment)
As a third embodiment, a case will be described in which information such as the resolution of a document image and the setting resolution of a printer / scanner is acquired and the resolution of a signal pattern of embedded information is changed according to the resolution.

FIG. 13 is an explanatory diagram showing the configuration of the third embodiment.
In this embodiment, as shown in FIG. 13, a digital watermark embedding device 3001 and a digital watermark detection device 3002 will be described.

  As shown in FIG. 13, the digital watermark embedding apparatus 3001 includes a resolution acquisition unit 3006 instead of the resolution input unit 1006 of the digital watermark embedding apparatus 1001 (FIG. 1) according to the first embodiment. The resolution acquisition unit 3006 is a functional unit that acquires resolution information from the print resolution set in the printing unit 1011 and image file format information of the document image. The other components are substantially the same as those in the first embodiment, and a duplicate description is omitted.

  As shown in FIG. 13, the digital watermark detection device 3002 includes a watermark detection unit 3014 instead of the watermark detection unit 1014 of the digital watermark detection device 1002 (FIG. 1) according to the first embodiment. It is characterized by.

  The watermark detection unit 3014 is a functional unit that acquires resolution information used for watermark detection from the reading resolution set in the input unit 1013, image file format information of a document image, and the like. Details of the operation of the watermark detection unit 3014 will be described later.

The digital watermark embedding device and the digital watermark detection device according to the present embodiment are configured as described above. Next, the operation of this embodiment will be described. FIG. 14 is an explanatory diagram showing a processing flow of the present embodiment. Note that redundant description of operations substantially similar to those of the first embodiment is omitted, and only operations different from those of the first embodiment are described.
First, the operation on the digital watermark embedding apparatus 3001 side will be described.

  (1) Image data input to (2) Document image formation is substantially the same as in the first embodiment.

(3) Resolution information acquisition (S1003, resolution acquisition unit 3006)
The resolution information is acquired from the print resolution set in the printing unit 3011, the image file format information of the document image, or the like. FIG. 15A shows a signal pattern having a width and height of a ₀ × a ₀ pixels at the resolution A ₀ as the reference signal pattern. On the other hand, in the case of the resolution p, as shown in FIG.

The resolution of the signal pattern is calculated so as to be a pixel (A ₀ , a ₀ , p is a natural number, p <A ₀ ). The same applies to the case of resolution q (q is a natural number, q> A ₀ ), as shown in FIG.

  Subsequent (4) signal pattern size calculation to (7) watermark image formation are substantially the same as those in the first embodiment.

  Through the above steps, the print document 1012 is printed from the printing unit 1011 of the digital watermark embedding apparatus 3001.

  Next, the operation of the digital watermark detection apparatus 3002 will be described.

(8) Watermark detection (S1011, watermark detection unit 1014)
For watermark detection, first, the resolution information is acquired by acquiring the reading resolution set in the input unit 1013 or by acquiring the resolution from the image file format information of the read image. With respect to the acquired resolution, the signal size is calculated / reduced in the same manner as in the first embodiment on the basis of the resolution A _{0 of the} preset reference signal pattern and the width and height of α ₀ × α ₀ pixels. The signal pattern is converted, and the signal pattern at the time of embedding is acquired. Further, the watermark is detected by performing template matching or filtering corresponding to the acquired signal pattern at the time of embedding.

(Effect of the third embodiment)
As described above, according to the present embodiment, when printing a document image with a different resolution, or when using a printer / scanner with a different resolution setting, the signal size is calculated / signaled according to the resolution. By performing pattern conversion, watermark embedding / detection can be performed at each set resolution without changing the resolution setting.

  The preferred embodiments of the digital watermark embedding device, the digital watermark detection device, the digital watermark embedding method, and the digital watermark detection method according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. . It will be obvious to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  For example, in the above embodiment, the dot pattern has been described as an example of the signal pattern, but the present invention is not limited to this, and a signal pattern other than the dot pattern may be adopted. Further, for example, a symbol may be given to a dot pattern regularly arranged (pattern unit), and this may be used as a signal pattern.

  The present invention can be used for an apparatus and method for embedding / detecting a digital watermark in a document image. For example, by embedding a plurality of types of signal patterns regularly in the background of a document image, embedding information can be embedded. The present invention can be applied to a possible digital watermark embedding apparatus and method, and a digital watermark detection apparatus and method capable of detecting such embedded information.

It is explanatory drawing which shows the structure of 1st Embodiment. It is a flowchart which shows operation | movement of 1st Embodiment. It is explanatory drawing which shows the resolution calculation of a signal pattern. It is explanatory drawing which shows the resolution change of a signal pattern. It is explanatory drawing which shows watermark image formation. It is explanatory drawing which shows the synthetic | combination process of a watermark image and a document image. It is explanatory drawing which shows the structure of 2nd Embodiment. It is a flowchart which shows operation | movement of 2nd Embodiment. It is explanatory drawing which shows the graph which calculates | requires the area of a signal pattern. It is explanatory drawing which shows the size change of a signal pattern. It is explanatory drawing which shows the detection method of a signal pattern. It is explanatory drawing which shows the detection method of a signal pattern. It is explanatory drawing which shows the structure of 3rd Embodiment. It is a flowchart which shows operation | movement of 3rd Embodiment. It is explanatory drawing which shows the resolution calculation of a signal pattern.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1001 Digital watermark embedding apparatus 1002 Digital watermark detection apparatus 1003 Document data 1004 Embedding information 1005 Document image forming part 1006 Resolution input part 1007 Signal size calculation part 1008 Watermark image forming part 1009 Resolution conversion part 1010 Watermarked document image composition part 1011 Printing part 1012 Print document 1013 Input unit 1014 Watermark detection unit 2006 Information amount detection unit 3006 Resolution acquisition unit

Claims (2)

An electronic watermark embedding device capable of embedding embedded information by regularly arranging a plurality of signal patterns in the background of a document image,
An information amount detection unit for acquiring the information amount of the embedded information and the size of the document image ;
Dividing the size of the document image by the amount of information of the embedded information, and embedding the embedded information in the document image with a maximum integer not exceeding the positive square root of the maximum integer not exceeding the numerical value obtained by the division A signal size calculator that calculates the size of the possible signal pattern;
A watermark image forming unit that forms a watermark image from the embedded information based on the size of the signal pattern calculated by the signal size calculating unit;
An electronic watermark embedding device comprising: An electronic watermark detection apparatus capable of detecting embedded information embedded by regularly arranging a plurality of types of signal patterns in the background of a document image,
When the size of the signal pattern is detected and the detected signal pattern has a plurality of sizes, signal detection is performed for each size of the different signal pattern for at least a part of the area where the signal pattern is embedded in the document image. The watermark is determined such that the size of the signal pattern in which the number of coordinates exceeding the threshold exceeds a certain number is a signal detectable size, and the smallest one is the size of the signal pattern used for watermark detection. An electronic watermark detection apparatus comprising a detection unit.

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