JP4096902B2 - Watermark information detection apparatus and watermark information detection method - Google Patents

Description

The present invention relates to a technique for detecting secret information from a printed document containing secret information.

  “Digital watermarking” that embeds information to prevent copying / counterfeiting and confidential information in images and document data in a form that is invisible to the human eye is based on the premise that all storage and data transfer are performed on electronic media. Since the information embedded by the watermark is not deteriorated or lost, the information can be reliably detected. Similarly, documents printed on paper media cannot be easily tampered with in a form that is not visually unsightly other than text to prevent unauthorized tampering and copying. There is a need for a method for embedding confidential information in a printed document.

  In the special table 2002-504272, information is embedded at a thin level that is not unpleasant to human eyes. Also, the digital watermark embedding / detection method described in Japanese Patent Application Laid-Open No. 2003-101762 embeds a background pattern with information in the background portion of an image, and correlates the background pattern read by a scanner with a Gabor filter to obtain information. Extraction is performed. The target of signal extraction by the Gabor filter is mainly a grayscale document image read by a scanner or the like, and a certain gray level difference that allows a wave to be expressed in the signal pattern from which the signal is extracted by the Gabor filter. Demands. Therefore, in these digital watermarks, signal enhancement processing is performed so that the filter output is stabilized and the spectrum in which the information is embedded can be efficiently detected when information is detected from the scanned image.

Special table 2002-504272 JP 2003-101762 A

  As described above, the above-described digital watermark uses a pattern that facilitates signal detection by a Gabor filter. The signal detection method using this digital watermark detection method is not sufficient for correction of differences in density due to toner density, luminance values due to toner color, and changes in density due to toner fading. Depending on the density, color, and toner fading, the output of a filter sufficient to extract information may not be obtained. In addition, there are cases where the pattern becomes dull due to various types of paper having a wide luminance distribution, paper patterns, etc., and sufficient filter output cannot be obtained. For example, in Japanese Patent Application Laid-Open No. 2003-101762, when extracting information, a signal position is determined by scanning a filter output value and searching for a peak position. In some cases, location search may act as noise, and as a result, information cannot be extracted.

The present invention has been made in view of the above problems of the conventional digital watermark technology, and an object of the present invention is a novel and improved technique capable of stabilizing the signal output value and improving the signal detection rate. Provided is a watermark information detecting apparatus and a watermark information detecting method .

In order to solve the above problems, according to a first aspect of the present invention, there is provided a watermark information detecting apparatus for reading information corresponding to a pattern from an image in which patterns having a certain spatial period are regularly arranged. . The watermark information detection apparatus of the present invention includes image correction means for performing image correction in units of small areas on an input image, and the image correction means has a value that is greater than a predetermined threshold value from the pixel values of the pixels that constitute the small area. A representative value of a set of pixel values having a high value and a representative value of a set of pixel values having a value lower than a predetermined threshold are detected, and a character and a distribution of pixel values in an area composed of arbitrary pixels surrounding a small area are detected. A threshold for determining whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the figure is obtained, and the representative value of the set of pixel values having a high value or the representative value of the set of pixel values having a low value For one of the pixel values, based on the comparison between the pixel value and the obtained threshold value, it is determined whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the character and the figure. , determined that the pixel value is lowered The case, the pixel value is a determination target and alternate to the determined pixel value and the pixel value is not decreased, less representative value or values of the set of high pixel values of the pixel value and the value after alternative The dynamic range of the small region is corrected using the other pixel value of the representative value of the set of pixel values .

Another watermark information detection apparatus of the present invention is a watermark information detection apparatus that reads information corresponding to a pattern from an image in which a pattern having a certain spatial period is regularly arranged. Image correction means for performing image correction in units of small areas, and the image correction means includes a representative value of a set of pixel values higher than a predetermined threshold value from the pixel values of the pixels constituting the small area, and a predetermined threshold value. Pixels of pixels that form a pattern by pixels that form characters and figures from the distribution of pixel values in an area consisting of arbitrary pixels surrounding the small area , and a representative value of a set of pixel values having a low value A threshold value for determining whether the value is decreasing is obtained, and for one pixel value of a representative value of a set of pixel values having a high value or a representative value of a set of pixel values having a low value, the pixel value and the above value are obtained. For comparison with the threshold And Zui, it is determined whether or not the pixel values of the pixels constituting the pattern by pixels constituting a character and graphic is reduced, when the pixel value is determined to have decreased is the discrimination object The pixel value is replaced with the average value of the pixel values determined that the pixel values are not deteriorated, and the representative value of the set of pixel values after replacement and the pixel value having a high value or the set of pixel values having a low value The dynamic range of the small area is corrected using the other pixel value of the representative value .

According to this configuration, it is possible to correct the density from the local density change of the pattern for recording the signal, and to stabilize the signal peak value obtained after the filter processing. For example, when the pattern size is configured with a resolution of 600 dpi and a size of 18 × 18 dots, the size of one pattern is about 0.7 mm square, and a portion with a high density of one pattern is included in this minute area. There will be a thin part. Therefore, the luminance correction for one pattern can be performed only with this small area of 0.7 mm square. As described above, according to the present invention, the signal output value can be stabilized and the signal detection rate can be improved by dynamically performing the signal enhancement processing from the local luminance value distribution of the image. Furthermore, the influence of characters and the like can be removed, and luminance correction can be performed effectively.

  In the watermark information detecting apparatus of the present invention, the following applications are possible.

A high pixel value of the values, the maximum value of the values in the small regions, the lower pixel value of the value may be a minimum value of the values in a small area (claim 4).

As the pixel value, for example, a luminance value ( Claim 5 ), chromaticity , saturation , density of a specific color, or the like can be adopted.

The small region is regularly arranged pattern may be a region segmented into the same size (claim 6), at best (according as regions divided in a larger size than the pattern are regularly arranged Item 7 ) may be a region divided into a smaller size than a regularly arranged pattern ( Claim 8 ).

The means for performing image correction in the small area may use a value obtained from a nearby small area for correction. It is possible to remove the influence of characters and the like from the low luminance value in the small area. Specifically, for example, the values obtained from the neighboring small areas may be averaged and used for correction, or a histogram of values obtained from the neighboring small areas is calculated and obtained from the neighboring small areas. The mode value may be used for correction .

The detection of low pixel values of the values carried by a means that performs image compensation in the small area, may be performed only for high pixel value than set threshold (claim 3). The influence of characters and the like can be removed, and brightness correction can be performed effectively.

In order to solve the above-mentioned problem, according to a second aspect of the present invention, in a watermark information detection apparatus comprising image correction means for performing image correction in units of small regions on an input image, a pattern having a certain spatial period There is provided a watermark information detection method for reading information corresponding to a pattern from an image arranged regularly. In the watermark information detecting method, the image correction means uses a pixel value of a pixel constituting a small area to represent a representative value of a set of pixel values higher than a predetermined threshold value and a set of pixel values lower than the predetermined threshold value. Pixels of pixels that form a pattern from pixels constituting characters and figures from the distribution of pixel values in an area consisting of arbitrary pixels surrounding the small area by a detection step for detecting a representative value of the image and image correction means A threshold for determining whether or not the value is decreased is obtained, and for one pixel value of a representative value of a set of pixel values having a high value or a representative value of a set of pixel values having a low value, the pixel value and the above based on the comparison of the determined threshold value, a determination step of pixel values of pixels constituting a pattern by pixels constituting a character and graphics it is determined whether or not reduced, the pixel value is lowered in the judgment step and a determination is to If the, the image compensation unit, the pixel value of the discrimination object replaced to the determined pixel value and the pixel value is not decreased, the representative value or values of the set of high pixel values of the pixel value and the value after alternative And a correction step of correcting the dynamic range of the small area using the other pixel value of the representative value of the set of low pixel values .

In another watermark information detection method of the present invention, a pattern having a certain spatial period is regularly arranged in a watermark information detection apparatus including image correction means for performing image correction in units of small areas on an input image. A watermark information detection method for reading information corresponding to a pattern from a recorded image, wherein a representative value of a set of pixel values higher than a predetermined threshold value from pixel values of pixels constituting a small region by image correction means And a detection step of detecting a representative value of a set of pixel values lower than a predetermined threshold value, and by image correction means, from the distribution of pixel values in an area consisting of arbitrary pixels surrounding the small area, characters and A threshold for determining whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the figure is obtained, and the representative value of the set of pixel values having a high value or the value of the set of pixel values having a low value is substituted. For one of the pixel values of values, based on a comparison between the pixel value and the calculated threshold value, the pixel values of the pixels constituting the pattern by pixels constituting a character and graphics it is determined whether or not reduced An average value of pixel values determined by the image correction means as a plurality of pixel values that are not decreased by the image correction means when it is determined that the pixel value is decreased in the determination step And a correction step of correcting the dynamic range of the small area using the pixel value after substitution and the representative value of the set of pixel values having a high value or the other pixel value of the representative value of the set of pixel values having a low value It is characterized by including .

According to such a method, it is possible to correct the density from the local density change of the pattern for recording the signal, and to stabilize the signal peak value obtained after the filter processing. For example, when the pattern size is configured with a resolution of 600 dpi and a size of 18 × 18 dots, the size of one pattern is about 0.7 mm square, and a portion with a high density of one pattern is included in this minute area. There will be a thin part. Therefore, the luminance correction for one pattern can be performed only with this small area of 0.7 mm square. As described above, according to the present invention, the signal output value can be stabilized and the signal detection rate can be improved by dynamically performing the signal enhancement processing from the local luminance value distribution of the image. Furthermore, the influence of characters and the like can be removed, and luminance correction can be performed effectively.

  The watermark information detection method of the present invention can be applied as follows.

A high pixel value of the values, the maximum value of the values in the small regions, the lower pixel value of the value may be a minimum value of the values in a small area (claim 12).

As the value of the pixel value, for example, a luminance value ( Claim 13 ), chromaticity , saturation , density of a specific color, or the like can be adopted.

The small region may be a region divided into the same size as a regularly arranged pattern ( Claim 14 ), or may be a region divided into a larger size than a regularly arranged pattern ( Billing). Item 15 ) may be a region divided into a smaller size than a regularly arranged pattern ( Claim 16 ).

In the step of performing image correction in the small area, a value obtained from a nearby small area may be used for correction. It is possible to remove the influence of characters and the like from the low luminance value in the small area. Specifically, for example, the values obtained from the neighboring small areas may be averaged and used for correction, or a histogram of values obtained from the neighboring small areas is calculated and obtained from the neighboring small areas. The mode value may be used for correction .

Detection of low pixel values of the value performed in the detecting step may also be carried out only for the higher pixel value than set threshold (claim 11). The influence of characters and the like can be removed, and brightness correction can be performed effectively.

According to another aspect of the present invention, there are provided a program for causing a computer to function as the watermark information detecting 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 recording medium that is currently used as a recording medium capable of recording a program, such as a CD-ROM, a DVD-ROM, or a flexible disk, or any recording medium that is used in the future should be adopted. Can do.

  As described above, according to the present invention, the signal output value can be stabilized and the signal detection rate can be improved by performing the signal enhancement process dynamically from the local luminance value distribution of the image.

  Exemplary embodiments of a watermark information embedding device, a watermark information detecting device, a watermark information embedding method, a watermark information detecting method, and a printed material 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.

(First embodiment)
FIG. 1 is an explanatory diagram showing a configuration of a watermark information embedding device and a watermark information detection device according to the present embodiment.

(Watermark information embedding device 10)
The watermark information embedding device 10 is a device that synthesizes a watermarked image based on image data and information embedded in the image and prints it on a paper medium. As shown in FIG. 1, the watermark information embedding device 10 includes an encoding unit 11, a pattern allocation unit 12, a watermarked document synthesis unit 13, and an output device 14. The watermark information embedding device 10 receives image data 15 and embedding information 16 embedded in the image.

  The image data 15 is input from an image input terminal (not shown) of the watermark information embedding device 10. As the image data 15, arbitrary data such as a document, a chart, a picture, a map, and a photograph, or data obtained by arbitrarily combining these data is converted into an image. For imaging, a method of reading with a scanner, or a document output by a word processor, such as a print image, can be used. In this embodiment, the description will be made on the assumption that printing is performed on white paper with black ink (single color). However, the present invention is not limited to this, and printing is performed in color (multicolor). Similarly, the present invention can be applied. On the other hand, the embedded information 16 is information (character string, image, audio data) embedded in a paper medium in a format other than characters.

  The encoding unit 11 performs an encoding process on the data of the embedded information 16. The pattern assigning unit 12 assigns a watermark signal (pattern) to each encoded symbol. That is, the embedded information 16 digitized and converted into a numerical value is subjected to N-element coding (N is 2 or more), and each symbol is assigned to a watermark signal prepared in advance. The watermark signal of this embodiment represents a wave having an arbitrary direction and wavelength by arranging dots in a rectangular area of an arbitrary size, and a symbol is assigned to the direction and wavelength of the wave. . Such a watermark signal is hereinafter referred to as a “signal unit”. Details of the signal unit will be described later.

  The watermarked document synthesizing unit 13 directly draws a pattern expressing embedded information on an image input from an image input terminal. In this way, the watermarked document composition unit 13 of the present embodiment creates a watermarked document image. The output device 14 is an output device such as a printer, and prints a watermarked document image on a paper medium. Therefore, the encoding unit 11, the pattern assignment unit 12, and the watermarked document synthesis unit 13 may be realized as one function in the printer driver.

(Printed matter 20)
The printed matter 20 is paper or a card printed with the embedded information 16 embedded in the original image data 15, and is physically stored and managed.

(Watermark information detection device 30)
The watermark information detection device 30 is a device that takes in a document printed on a paper medium as an image and restores the embedded information 16 embedded therein. As shown in FIG. 1, the watermark information detection apparatus 30 includes an input device 31 and a watermark detection unit 32.

  The input device 31 is an input device such as a scanner, and captures the printed matter 20 as a multi-value gray image in a computer. The input image may be the image itself output from the digital watermark embedding device 10, an image deteriorated by irreversible compression such as JPEG, an image reduced by a digital filter, printed, photographed / scanned It may be an image.

  The watermark detection unit 32 performs filtering processing on all or part of the image captured by the input device 31 to detect a signal unit drawn on the image and extract the embedded information 16.

  The watermark information embedding device 10 and the watermark information detection device 30 according to the present embodiment are configured as described above. Next, operations of the watermark information embedding device 10 and the watermark information detection device 30 will be described. First, the operation of the watermark information embedding device 10 will be described with reference to the flowchart of FIG.

(Step S101)
First, the image data 15 and the embedding information 16 are input to the watermark image embedding device 10 (step S101). As described above, the document data 15 is data including font information and layout information, and is created by word processing software or the like. The document data 15 is, for example, monochrome binary data. On the image, white pixels (pixels having a value of 1) are backgrounds, and black pixels (pixels having a value of 0) are character regions (regions to which ink is applied). ). On the other hand, the confidential information 16 is various data such as characters, sounds and images.

(Step S102)
Next, the embedded information 16 is converted into an N-element code (step S102). N is arbitrary, but in the present embodiment, N = 2 for ease of explanation. Therefore, the code generated in step S102 is a binary code, and is expressed by a bit string of 0 and 1. In this step S102, the embedded information 16 may be encoded as it is, or an encoded version of the embedded information 16 may be encoded.

(Step S103)
Next, a signal unit is assigned to each encoded symbol (step S103). The watermark signal of this embodiment represents a wave having an arbitrary wavelength and direction by the arrangement of dots (black pixels).

  The signal unit assigned to each symbol in step S103 will be described. FIG. 3 is an explanatory diagram showing an example of a signal unit.

  Let the width and height of the signal unit be Sw and Sh, respectively. Sw and Sh may be different, but in the present embodiment, Sw = Sh is set for ease of explanation. The unit of length is the number of pixels. In the example of FIG. 3, Sw = Sh = 12. The size when these signals are printed on the paper surface depends on the resolution of the watermark image. For example, the watermark image is an image of 600 dpi (dot per inch: unit of resolution, number of dots per inch). 3, the width and height of the signal unit in FIG. 3 is 12/600 = 0.02 (inch) on the printed matter.

  Hereinafter, a rectangle having a width and a height of Sw and Sh is referred to as a “signal unit” as one signal unit. In FIG. 3 (1), the distance between dots is dense in the direction of arctan (3) (arctan is an inverse function of tan) with respect to the horizontal axis, and the wave propagation direction is arctan (−1/3). . Hereinafter, this signal unit is referred to as unit A. In FIG. 3B, the distance between dots is dense in the direction of arctan (−3) with respect to the horizontal axis, and the wave propagation direction is arctan (1/3). Hereinafter, this signal unit is referred to as unit B.

  FIG. 4 is a cross-sectional view of the change in the pixel value in FIG. 3A as viewed from the direction of arctan (1/3). In FIG. 4, the portion where the dots are arranged is the antinode of the minimum value of the wave (the point where the amplitude is maximum), and the portion where the dots are not arranged is the antinode of the maximum value of the wave.

  In addition, since there are two regions in each unit where dots are densely arranged, the frequency per unit is 2 in this example. Since the wave propagation direction is perpendicular to the direction in which the dots are densely arranged, the wave of unit A is arctan (-1/3) with respect to the horizontal direction, and the wave of unit B is arctan (1/3). Become. Note that a × b = −1 when the direction of arctan (a) and the direction of actan (b) are perpendicular.

  In this embodiment, symbol 0 is assigned to the signal unit represented by unit A, and symbol 1 is assigned to the signal unit represented by unit B. These are called symbol units.

In addition to the signal units shown in FIGS. 3 (1) and (2), for example, dot arrangements as shown in FIGS. 5 (3) to (5) are conceivable.
In FIG. 5 (3), the distance between dots is dense in the direction of arctan (1/3) with respect to the horizontal axis, and the wave propagation direction is arctan (-3). Hereinafter, this signal unit is referred to as unit C.
In FIG. 5 (4), the distance between dots is dense in the direction of arctan (−1/3) with respect to the horizontal axis, and the wave propagation direction is arctan (3). Hereinafter, this signal unit is referred to as unit D.
In FIG. 5 (5), the distance between dots is dense in the direction of arctan (1) with respect to the horizontal axis, and the wave propagation direction is arctan (−1). In FIG. 5 (5), it can be considered that the distance between the dots is dense in the direction of arctan (−1) with respect to the horizontal axis, and the wave propagation direction is arctan (1). Hereinafter, this signal unit is referred to as unit E.

  In this way, in addition to the previously assigned combinations, there can be a plurality of combinations of units to which symbol 0 and symbol 1 are assigned. Therefore, it is a third party to keep secret which signal unit is assigned to which symbol. It is also possible to make it impossible to easily decipher the embedded signal.

  Further, when the embedded information 16 is encoded by a quaternary code in step S103 shown in FIG. 2, for example, symbol 0 is assigned to unit A, symbol 1 is assigned to unit B, symbol 2 is assigned to unit C, unit It is also possible to assign symbol 3 to D.

  In the example of the signal unit shown in FIG. 3 and FIG. 5, since the number of dots in one unit is all equal, the apparent density of the watermark image becomes uniform by arranging these units without gaps. . Therefore, it appears that a gray image having a single density is embedded as a background on the printed paper.

  In order to produce such an effect, for example, unit E is defined as a background unit (signal unit to which no symbol is assigned), and this is arranged without any gap as a background of the watermark image, and symbol unit (unit A, unit B) Is embedded in the watermark image, the background unit (unit E) and the symbol unit (unit A, unit B) at the position to be embedded are exchanged.

  FIG. 6 (1) is an explanatory diagram showing a case where the unit E is defined as a background unit and arranged as a background of a watermark image without gaps. 6 (2) shows an example in which the unit A is embedded in the background image of FIG. 6 (1), and FIG. 6 (3) shows an example in which the unit B is embedded in the background image of FIG. 6 (1). Show. In the present embodiment, a method for setting a background unit as the background of a watermark image will be described. However, a watermark image may be generated by arranging only symbol units.

  Next, a method for embedding a signal unit in a watermark image will be described with reference to FIG.

  FIG. 7 is an explanatory diagram illustrating an example of a method for embedding a signal unit in a watermark image. Here, a case where a bit string “0101” is embedded will be described as an example.

  As shown in FIGS. 7A and 7B, the same symbol unit is repeatedly embedded. This is to prevent the character unit in the document from being detected when a signal is detected when it is superimposed on the embedded symbol unit. The symbol unit repetition number and arrangement pattern (hereinafter referred to as a unit pattern) are used. Is optional.

  That is, as an example of the unit pattern, the repetition number is set to 4 (four symbol units exist in one unit pattern) as shown in FIG. 7 (1), or the repetition number is set to 2 as shown in FIG. 7 (2). (There are two symbol units in one unit pattern) or the number of repetitions may be one (only one symbol unit exists in one unit pattern).

  7 (1) and 7 (2), one symbol is given to one symbol unit. However, even if symbols are given to the symbol unit arrangement pattern as shown in FIG. 7 (3). good.

  The number of bits of information that can be embedded in a watermark image for one page depends on the size of the signal unit, the size of the unit pattern, and the size of the document image. The number of signals embedded in the horizontal and vertical directions of the document image may be detected as a known signal, or may be calculated backward from the size of the image input from the input device and the size of the signal unit.

  If Pw unit patterns in the horizontal direction and Ph units in the vertical direction can be embedded in a watermark image for one page, unit patterns at arbitrary positions in the image are represented by U (x, y), x = 1 to Pw, y = 1 to Ph, and U (x, y) is referred to as a “unit pattern matrix”. In addition, the number of bits that can be embedded in one page is referred to as the “number of embedded bits”. The number of embedded bits is Pw × Ph.

FIG. 8 is a flowchart showing a method of embedding the embedded information 16 in the watermark image.
Here, a case where the same information is repeatedly embedded in one (one page) watermark image will be described. By repeatedly embedding the same information, it is possible to extract the embedded information even if the embedded information disappears due to, for example, the entire unit pattern being filled when the watermark image and the document image are overlaid. Because.

  First, the embedded information 16 is converted into an N-element code (step S201). This is the same as step S102 in FIG. Hereinafter, the encoded data is referred to as a data code, and the data code expressed by a combination of unit patterns is referred to as a data code unit Du.

  Next, based on the code length of the data code (here, the number of bits) and the number of embedded bits, how many times the data code unit can be embedded in one image is calculated (step S202). In this embodiment, it is assumed that the code length data of the data code is inserted into the first row of the unit pattern matrix. The code length of the data code may be fixed, and the code length data may not be embedded in the watermark image.

  The number Dn of embedding the data code unit is calculated by the following equation with the data code length as Cn.

  Here, assuming that the remainder is Rn (Rn = Cn− (Pw × (Ph−1))), the unit pattern matrix is embedded with a data pattern unit of Dn times and a unit pattern corresponding to the first Rn bits of the data code. become. However, the Rn bit of the remainder part does not necessarily have to be embedded.

  In the description of FIG. 9, the size of the unit pattern matrix is 9 × 11 (11 rows and 9 columns), and the data code length is 12 (numbers 0 to 11 in the figure represent each symbol of the data code). To do.

  Next, the code length data is embedded in the first row of the unit pattern matrix (step S203). In the example of FIG. 9, the code length is expressed by 9-bit data and has been embedded only once. However, if the unit pattern matrix width Pw is sufficiently large, It can be embedded repeatedly.

  Further, the data code unit is repeatedly embedded in the second and subsequent rows of the unit pattern matrix (step S204). As shown in FIG. 9, the MSB (most significant bit) or LSB (least significant bit) of the data code is sequentially embedded in the row direction. The example of FIG. 9 shows an example in which the data code unit is embedded seven times and the first 6 bits of the data code are embedded.

  The data embedding method may be embedded so as to be continuous in the row direction as shown in FIG. 9, or may be embedded so as to be continuous in the column direction.

  The watermark signal allocation (step S103) in the pattern allocation unit 12 has been described above. Next, step S104 and subsequent steps will be described with reference to FIG. 2 again.

(Step S104)
The watermarked document image composition unit 13 superimposes the image data 15 and the watermark signal assigned by the pattern assignment unit 12 (step S104). When the image data 15 is a binary image, the value of each pixel of the watermarked document image is calculated by a logical product operation (AND) of the corresponding pixel values of the document image and the watermark image. That is, if either the document image or the watermark image is 0 (black), the pixel value of the watermarked document image is 0 (black), otherwise 1 (white).

  On the other hand, when the image data 15 is multi-value data having three or more values, processing is performed as follows.

(Color pattern drawing method)
The input image has a background color that constitutes the background of a document or a figure, and a foreground color that constitutes a text child, a line, or a figure. The signal unit also has a foreground color representing a signal and a background color as a background. When drawing on an image by the watermarked image compositing unit 13, as shown in FIG. 10, the background color of the signal unit is treated as a transparent color, and the background color portion of the signal unit outputs the color of the image itself. May be left on the image. In addition, a portion where the foreground color on the input image and the foreground color of the signal unit overlap may be left on the output image with priority given to the foreground color of the input image. Further, when the background color on the input image and the foreground color of the signal unit overlap, the foreground color of the signal unit may be left on the output image. Further, only luminance components may be synthesized, or other color components may be superimposed and expressed.

  By the above method, a watermarked image in which the input image and the signal unit are superimposed can be generated. FIG. 11 is an explanatory diagram showing an example of a watermarked document image. FIG. 12 is an explanatory view showing a part of FIG. 11 in an enlarged manner. Here, the unit pattern shown in FIG. 7A is used.

(Step S105)
The watermarked document image generated as described above is output by the output device 14 (step S105).

The operation of the watermark information embedding device 10 has been described above.
Next, the operation of the watermark information detection apparatus 30 will be described with reference to FIGS. 1 and 12 to 20.

(Watermark detection unit 32)
FIG. 13 is a flowchart showing the processing flow of the watermark detection unit 32.
First, the printed material 20 is input to the memory of the computer or the like by the input device 31 such as a scanner (step S301). An image read by the input device 31 is referred to as an input image. The input image is a multi-valued image, and will be described below as a gray image with 256 gradations. Further, the resolution of the input image (resolution when read by the input device 31) may be different from that of the watermark information embedding apparatus 10, but here it is assumed that the resolution is the same. Also, it is assumed that the input image has been corrected for rotation, expansion and contraction.

  Next, the number of unit patterns embedded is calculated from the size of the input image and the size of the signal unit (step S302). For example, assuming that the size of the input image is W (width) × H (height), the size of the signal unit is Sw × Sh, and the unit pattern is composed of Uw × Uh units. The number of unit patterns embedded in (N = Pw × Ph) is calculated as follows.

  However, when the resolution is different between the watermark information embedding device 10 and the watermark information detection device 30, the above calculation is performed after normalizing the size of the signal unit in the input image based on the ratio of the resolutions.

  Next, a unit pattern separation position is set for the input image based on the number of unit patterns calculated in step S302 (step S303). FIG. 14 shows an example of the input image (FIG. 14 (1)) and the input image (FIG. 14 (2)) after setting the unit pattern separation positions.

  Next, a symbol unit is detected for each unit pattern delimiter, and a unit pattern matrix is restored (step S304). Details of signal detection will be described below.

  FIG. 15 is an explanatory diagram showing an example of an area corresponding to the unit A shown in FIG. 3A in the input image. In FIG. 3, the signal unit is a binary image, but here it is a multi-valued image. When a binary image is printed, since the density changes continuously due to ink bleeding or the like, the periphery of the dot becomes an intermediate color between white and black as shown in FIG. Therefore, a cross-sectional view of FIG. 15 viewed from a direction parallel to the wave propagation direction is as shown in FIG. While FIG. 4 is a rectangular wave, FIG. 16 is a smooth wave.

  Also, in reality, many noise components are added to the input image due to factors such as local changes in paper thickness, dirt on the printed document, and instability of the output device and image input device. However, the case where there is no noise component will be described here. However, if the method described here is used, stable signal detection can be performed even for an image to which a noise component is added.

  In the following, in order to detect the signal unit from the input image, a two-dimensional wavelet filter that can simultaneously define the frequency and direction of the wave and the influence range is used. In the following, an example using a Gabor filter, which is one of the two-dimensional wavelet filters, is shown. However, if it is a filter having the same properties as the Gabor filter, it is not necessarily a Gabor filter, and moreover, the same dot as the signal unit. A method of defining a template having a pattern and performing pattern matching may be used.

  The Gabor filter G (x, y), x = 0 to gw−1, and y = 0 to gh−1 are shown below. gw and gh are filter sizes, which are the same size as the signal unit embedded by the watermark information embedding apparatus 10 here.

  For signal detection, the same number of Gabor filters as the frequency of the symbol unit embedded in the watermark image, the frequency, the direction of the wave, and the size are prepared as many as the type of the embedded signal unit. Here, the Gabor filters corresponding to the units A and B in FIG.

  The filter output value at an arbitrary position in the input image is calculated by convolution between the filter and the image. In the case of a Gabor filter, there are a real number filter and an imaginary number filter (an imaginary number filter is a filter whose phase is shifted by a half wavelength from the real number filter), and the mean square value thereof is used as a filter output value. For example, if the convolution between the real filter and the image of the filter A is Rc and the convolution between the imaginary filter is Ic, the output value F (A) is calculated by the following equation.

  FIG. 17 is an explanatory diagram for explaining a method for determining whether the symbol unit embedded in the unit pattern U (x, y) delimited in step S303 is the unit A or the unit B.

The symbol determination step for the unit pattern U (x, y) is performed as follows.
(1) While moving the position of the filter A, the maximum value of the result of calculating F (A) for all the positions in the unit pattern U (x, y) is the value of the filter A for the unit pattern U (x, y). The output value is set to Fu (A, x, y).
(2) The output value of the filter B for the unit pattern U (x, y) is calculated in the same manner as (1), and this is assumed to be Fu (B, x, y).
(3) Fu (A, x, y) and Fu (B, x, y) are compared, and if Fu (A, x, y) ≧ Fu (B, x, y), unit pattern U (x, y) The symbol unit embedded in y) is determined to be unit A, and if Fu (A, x, y) <Fu (B, x, y), it is embedded in the unit pattern U (x, y). It is determined that the existing symbol unit is unit B.

  In (1) and (2), the step width for moving the filter is arbitrary, and only the output value at a representative position on the unit pattern may be calculated. Further, when the absolute value of the difference between Fu (A, x, y) and Fu (B, x, y) is equal to or smaller than a predetermined threshold in (3), the determination may be impossible.

  In (1), when the convolution is calculated while shifting the filter, if the maximum value of F (A) exceeds a predetermined threshold value, the symbol unit immediately embedded in U (x, y) May be determined to be unit A and the process may be stopped. Similarly, in (2), if the maximum value of F (B) exceeds a predetermined threshold value, the symbol unit embedded in U (x, y) is immediately determined to be unit B. good.

  The details of the signal detection (step S304) have been described above. Returning to the flowchart of FIG. 13 again, the following step S305 will be described. In step S305, the symbols of the unit pattern matrix are concatenated to reconstruct the data code, and the original information is restored.

FIG. 18 is an explanatory diagram showing an example of information restoration. The steps of information restoration are as follows.
(1) Detect symbols embedded in each unit pattern.
(2) The symbols are connected to restore the data code.
(3) Decode the data code and take out the embedded information.

  19 to 21 are explanatory diagrams illustrating an example of a data code restoration method. The restoration method is basically the reverse process of FIG.

  First, the code length data portion is extracted from the first row of the unit pattern matrix to obtain the code length of the embedded data code (step S401).

  Next, based on the size of the unit pattern matrix and the code length of the data code obtained in S401, the number Dn of data code units embedded and the remainder Rn are calculated (step S402).

  Next, data code units are extracted from the second and subsequent rows of the unit pattern matrix by the reverse method of step S203 (step S403). In the example of FIG. 20, 12 pattern units are sequentially decomposed from U (1, 2) (2 rows and 1 column) (U (1, 2) to U (3, 3), U (4, 3) to U (6, 4), ...). Since Dn = 7 and Rn = 6, 12 pattern units (data code units) are extracted 7 times, and 6 unit patterns (corresponding to the upper 6 data code units) (U (4 , 11) to U (9, 11)) are taken out.

  Next, the embedded data code is reconstructed by performing bit certainty calculation on the data code unit extracted in step S403 (step S404). Hereinafter, the bit certainty calculation will be described.

  As shown in FIG. 21, the first outer code units extracted from the second row and the first column of the unit pattern matrix are Du (1,1) to Du (12,1), and Du (1,2) to Du are sequentially added. (12, 2),. Further, the surplus portion is assumed to be Du (1, 8) to Du (6, 8). The bit certainty calculation is to determine the value of each symbol of the data code by, for example, taking a majority vote for each element of each data code unit. As a result, even if signal detection cannot be performed correctly from any unit in any data encoding unit (such as a bit reversal error) due to overlap with the character area or dirt on the paper, the data encoding will eventually be performed correctly. Can be restored.

  Specifically, for example, the first bit of the data code is more often when the signal detection result of Du (1, 1), Du (1, 2),..., Du (1, 8) is 1. Is determined to be 1 and when there are more 0s, it is determined to be 0. Similarly, the second bit of the data code is determined by majority decision based on the signal detection result of Du (2, 1), Du (2, 2),..., Du (2, 8), and the 12th bit of the data code is Du (12,1), Du (12,2),..., Du (12,7) (Du (12,8) is not present, so it is up to Du (12,7)). Judgment by majority vote.

  The bit certainty calculation can also be performed by adding the output values of the signal detection filter of FIG. This is because, for example, a symbol of 0 is assigned to unit A in FIG. 3 (1), a symbol of 1 is assigned to unit B in FIG. 3 (2), and filter A for Du (m, n) is used. When the maximum value of the output value is Df (A, m, n) and the maximum value of the output value by the filter B for Du (m, n) is Df (B, m, n), the M bit of the data code is

  In the case of, it is determined as 1, and in other cases it is determined as 0. However, when N <Rn, the addition of Df is n = 1 to Rn + 1.

  Although the case where data codes are repeatedly embedded has been described here, a method that does not repeat data code units can be realized by using an error correction code or the like when encoding data.

As described above, according to the present embodiment, the following excellent effects can be obtained.
(1-1) Since the embedded information is expressed by the difference in dot arrangement, the original document font, character spacing, and line spacing are not changed.
(1-2) Since the dot pattern to which symbols are assigned and the dot pattern to which symbols are not assigned have the same density (the number of dots in a certain interval), the human eye has a uniform density on the background of the document. It appears to be shaded and the presence of information is inconspicuous.
(1-3) Keeping the dot pattern to which symbols are assigned and the dot pattern to which symbols are not assigned in secret makes it difficult to decipher the embedded information.
(1-4) A pattern representing information is a collection of fine dots that are embedded as a background of a document, so that even if an embedding algorithm is disclosed, it is difficult to falsify embedded information in a printed document. .
(1-5) Since the embedded signal is detected based on the difference in the direction of the wave (change in shading) (because detailed detection is not performed in units of one pixel), the printed document is stable even if there is some dirt, etc. Information detection can be performed.
(1-6) Since the same information is repeatedly embedded and information is restored using all of the repeatedly embedded information at the time of detection, the signal portion is hidden by large font characters or the paper is dirty. Even if partial information loss occurs, the embedded information can be taken out stably.
(1-7) In Japanese Patent Application Laid-Open No. 2003-101762, a configuration in which a document image and a watermark image are separately generated is employed. However, in this embodiment, a pattern can be directly rendered on an image. And the watermark image need not be generated separately.

(Second Embodiment)
In this embodiment, an application example (1) of the signal pattern luminance correction method will be described.

  On the watermark information detection device 30 side, luminance correction is performed before signal detection filtering is performed on all or part of the input image. This luminance correction may be performed before the filtering process for signal detection or may be performed simultaneously with the filtering process for signal detection. Other operations are substantially the same as those in the first embodiment.

  The input image may be an image output from the watermark information embedding device 10 or a printed matter (paper, card, etc.) 20 itself, an image deteriorated by irreversible compression such as JPEG, or reduced by a digital filter or the like. It may be a printed image or an image printed, photographed or scanned.

  The signal pattern luminance correction method will be described below.

  FIG. 22 is an explanatory diagram showing an example of a signal unit composed of 18 × 18 pixels by the method described in the first embodiment. FIG. 22A shows an example of a pattern for recording information “1”, and FIG. 22B shows an example of a pattern for recording information “0”. When the information to be embedded is information of 3 rows × 4 columns = 12 bits, the pattern shown in FIG. 22C is formed. For example, when this pattern is printed at 600 dpi and scanned at 400 dpi, the pattern of the signal unit of 18 × 18 pixels becomes a blurred pattern of 12 × 12 pixels on the scanned image at the time of printing.

  FIG. 23A is an example of a blurred pattern of 12 × 12 pixels on the scanned image. Since the high-luminance pixels and low-luminance pixels representing one pattern exist within the range of 12 × 12 pixels, the entire image is divided into small areas divided into a 12 × 12 pixel mesh, Thus, by searching for the maximum value and the minimum value of the luminance, it is possible to enhance the wave expressing the signal in units of 12 × 12 pixels.

  The size from which the maximum and minimum pixel values can be obtained within one 12 × 12 pixel pattern may be less than 12 × 12 pixels. For example, as shown in FIG. 23B, the maximum value and the minimum value of luminance can be obtained even when scanning is performed with a size of 6 × 6 pixels. Further, as shown in FIG. 23 (c), a small area is divided into a size larger than the size of one pattern (for example, 21 × 21 pixels), and the maximum and minimum pixel values of the luminance are determined. You may search. Increasing the range weakens the local change, but can reduce the influence of a collection of black pixels such as characters.

  The pixel values to be detected need not be the minimum value and the minimum value of luminance. For example, as shown in FIG. 24, an average value of all pixels is obtained, and (a) an average value of pixel values higher than the average value , (B) An average value of pixel values lower than the average value may be used.

  Alternatively, the threshold for dividing the brightness into bright and dark brightness is not the average value of all pixels, but a set of higher pixel values for all pixel values from the lowest pixel value to the highest pixel value. Are divided into a set of low pixel values, the variance is measured in each set, and the pixel value from which the set with the lowest variance is obtained is used as a threshold value, and is divided into a pixel having a high luminance value and a pixel having a low luminance value. A value may be used.

  In the above example, an 18 × 18 pixel pattern is printed at 600 dpi and scanned at 400 dpi. However, the resolution at the time of printing, the resolution at the time of scanning, the size of the pattern, etc. are not important for luminance detection. Any range may be used as long as the pattern includes high and low pixel values in the pattern when scanned.

  Through the above processing, as shown in FIG. 25, the luminance distribution constituting the signal pattern is obtained. FIG. 25A shows the pixel distribution of high luminance values in the small area, and FIG. 25B shows the pixel distribution of low pixel values in the small area. With this luminance distribution, luminance correction is performed as follows.

  If a high luminance value of a small area is H and a low luminance value is L, the luminance correction in the small area can be performed as follows, for example.

  The above processing is performed for all the pixels in the small area. Moreover, it implements using H and L for each small area with respect to all the small areas.

  Thus, by performing luminance correction in units of small areas, the dynamic range of the signal portion is expanded and signal detection is facilitated. FIG. 26A is an explanatory diagram showing luminance correction in units of small areas. In the figure, (a1) shows the pattern of the dark part of the input image, and (a2) shows the pattern of the bright part of the input image. (B1) shows a pattern of a region corresponding to (a1) in the corrected image obtained by performing luminance correction in units of small regions, and (b2) after correction in which luminance correction is performed in units of small regions. The pattern of the area | region corresponding to (a2) is shown among the images.

  FIG. 26B shows changes in pixel values corresponding to (a1), (a2), (b1), and (b2) in FIG. 26A. For the bright part of the input image, the pixel value is corrected as (a1) → (b1), and for the dark part of the input image, the pixel value is corrected as (a2) → (b2). . In this way, shadows on the image, the influence of illumination during scanning, and uneven brightness can be corrected.

  Further, even when a watermark image is formed by changing the color for each signal pattern using various colors with different luminance values, the signal can be detected because the luminance can be corrected for each pattern.

  The signal detection method is substantially the same as that in the first embodiment.

(Effect of 2nd Embodiment)
As described above, according to the present embodiment, the following excellent effects can be obtained.
(2-1) It is possible to reduce the influence of shadows during scanning and uneven illumination, and improve the signal detection rate.
(2-2) The color of the pattern can be freely changed, and design restrictions can be reduced.

(Third embodiment)
In the present embodiment, an application example (2) of the signal pattern luminance correction method will be described. The description will focus on the differences from the second embodiment.

  In the second embodiment, luminance correction is not effectively performed when there are dark (low luminance) portions such as characters and graphics on the image. That is, as shown in FIG. 27, when (a) a pixel value having a low luminance and (b) a pixel value having a high luminance are detected from a small region including a portion having a high density (low luminance), a pixel having a low luminance is detected. The value is affected by the low-luminance part and becomes lower than the low-luminance pixel of the actual signal pattern, and the luminance correction is not effectively performed.

  Normally, the signal unit size is smaller than the character, line spacing, and character spacing, and there are more signal units that do not contain characters. Therefore, the influence of characters can be canceled by examining the low pixel values in the surrounding small areas. it can. Therefore, in the present embodiment, correction is performed by examining the distribution of low-brightness pixel values in the small areas existing in the vicinity of the small areas with respect to the low-luminance pixel values in the small areas.

  As shown in FIG. 28, in a small area M, an appearance histogram of pixel values with low luminance in 24 surrounding small areas is calculated. Separation is performed on the assumption that there are pixel values that are affected by characters or the like (the luminance is lowered) and pixel values that are not affected by characters or the like (the luminance is increased) in the histogram.

  The separation method is performed, for example, by determining a threshold value for dividing a histogram of pixel values having low luminance into two groups (pixel values that are affected by characters and the like and pixel values that are not affected by characters and the like). be able to. The threshold is moved from the lowest value to the highest value, the variance of the appearance frequency is measured for each of the two groups, and the threshold with the smallest variance is set as the threshold to be used.

  When the small area M is determined to be a pixel value that is influenced by characters or the like, the pixel value is changed to an average value of pixel values that are not determined to be pixel values that are influenced by characters or the like. If the small area M is not determined to be a pixel value influenced by characters or the like, it is not changed.

  By the above processing, the influence of characters can be removed from the low luminance value in the small area. FIG. 29 is an explanatory diagram showing correction of a low luminance value in a small area. By correcting a pattern affected by characters as shown in (a), the influence of characters can be removed as shown in (b).

  Processing other than that described above is performed in the same manner as in the second embodiment.

(Effect of the third embodiment)
As described above, according to the present embodiment, the following excellent effects can be obtained.
(3-1) The influence of characters and the like can be reduced.

(Fourth embodiment)
In the present embodiment, an application example (3) of the signal pattern luminance correction method will be described. The description will focus on the differences from the second and third embodiments.

  In the second embodiment, luminance correction is not effectively performed when there are dark (low luminance) portions such as characters and graphics on the image. That is, as shown in FIG. 27, when (a) a pixel value having a low luminance and (b) a pixel value having a high luminance are detected from a small region including a portion having a high density (low luminance), a pixel having a low luminance is detected. The value is affected by the low-luminance part and becomes lower than the low-luminance pixel of the actual signal pattern, and the luminance correction is not effectively performed.

  Therefore, in this embodiment, when a luminance value having a luminance value higher than the luminance value of a character is set and a pixel value having a low luminance is detected in a small area, only the pixel value equal to or higher than the threshold value is detected. , Detect low pixel values.

  Processing other than that described above is performed in the same manner as in the second and third embodiments.

(Effect of the fourth embodiment)
As described above, according to the present embodiment, the following excellent effects can be obtained.
(4-1) The influence of characters and the like can be reduced.

  The preferred embodiments of the watermark information embedding device, the watermark information detecting device, the watermark information embedding method, the watermark information detecting method, and the printed material according to the present invention have been described above with reference to the accompanying drawings. It is not limited. 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, it can be used for texture amplification in texture detection processing used not only for information extraction but also for image recognition and region segmentation.

  It can be used for general texture amplification of minute amplitude.

  The present invention can be used for a method of adding secret information to a document image in a format other than characters and a technique for detecting secret information from a printed document containing secret information. The present invention can be used for information detection devices, watermark information embedding methods, watermark information detection methods, and printed materials.

It is explanatory drawing which shows the structure of the watermark information embedding apparatus and watermark information detection apparatus concerning 1st Embodiment. It is a flowchart which shows the flow of a process of the watermark information embedding method. It is explanatory drawing which shows an example of a signal unit, (1) shows the unit A and (2) shows the unit B. It is sectional drawing which looked at the change of the pixel value of Fig.3 (1) from the direction of arctan (1/3). It is explanatory drawing which shows an example of a signal unit, (3) shows the unit C, (4) shows the unit D, (5) shows the unit E. It is explanatory drawing of a background image, (1) shows the case where unit E is defined as a background unit and this is used as the background of a watermark image arranged without gaps, and (2) is in the background image of (1) An example in which the unit A is embedded is shown, and (3) shows an example in which the unit B is embedded in the background image of (1). It is explanatory drawing which shows an example of the symbol embedding method to a watermark image. 5 is a flowchart illustrating a method of embedding embedded information 16 in a watermark image. 4 is a flowchart showing a processing flow of a watermark detection unit 32. It is explanatory drawing which shows the synthetic | combination method of a watermarked document image. It is explanatory drawing which shows an example of a watermarked document image. It is explanatory drawing which expanded and showed a part of FIG. 4 is a flowchart showing a processing flow of a watermark detection unit 32. It is explanatory drawing which shows an example of the input image after setting the (1) input image and the division position of (2) unit pattern. It is explanatory drawing which showed an example of the area | region corresponding to the unit A in an input image. It is sectional drawing which looked at FIG. 15 from the direction parallel to the propagation direction of a wave. It is explanatory drawing explaining the method to determine whether the symbol unit embedded in the unit pattern U (x, y) is the unit A or the unit B. FIG. It is explanatory drawing which shows an example of information restoration. It is explanatory drawing which shows an example of the decompression | restoration method of a data code. It is explanatory drawing which shows an example of the decompression | restoration method of a data code. It is explanatory drawing which shows an example of the decompression | restoration method of a data code. It is explanatory drawing which shows an example of the signal unit comprised by 18x18 pixel. It is explanatory drawing which shows the local part in an image. It is explanatory drawing which shows distribution of the luminance value within a small range. It is explanatory drawing which shows a pixel distribution with a high brightness | luminance and a low pixel distribution. It is explanatory drawing which shows the brightness correction in a small area unit. It is explanatory drawing which shows the brightness correction in a small area unit. It is explanatory drawing which shows the noise by a character etc. It is explanatory drawing which shows the surrounding small area | region used when correcting the luminance value of a certain small area | region. It is explanatory drawing which shows correction | amendment of a low luminance value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Watermark information embedding apparatus 11 Encoding part 12 Pattern allocation part 13 Watermarked document synthetic | combination part 14 Output device 15 Image data 16 Embedding information 20 Printed material 30 Watermark information detection apparatus 31 Input device 32 Watermark detection part

Claims (16)

A watermark information detection device that reads information corresponding to a pattern from an image in which patterns having a certain spatial period are regularly arranged,
Image correction means for performing image correction in units of small areas on the input image;
The image correction means includes a representative value of a set of pixel values having a value higher than a predetermined threshold value from a pixel value of a pixel constituting the small area, and a representative value of a set of pixel values having a value lower than the predetermined threshold value. And determining whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the character and the figure from the distribution of the pixel value in the region consisting of arbitrary pixels surrounding the small region A threshold value for calculating the threshold value, and comparing one pixel value of the representative value of the set of pixel values having a high value or the representative value of the set of pixel values having a low value with the obtained threshold value. Based on this, it is determined whether or not the pixel value of the pixel constituting the pattern is lowered by the pixels constituting the character and the figure, and if it is determined that the pixel value is lowered , pixel value does not decrease a certain pixel value Replaced to the determined pixel value, the small region using the other pixel value of the representative values of the set of representative values or low pixel value of the values of a set of high pixel values of the value and the pixel value after the alternative A watermark information detecting apparatus for correcting the dynamic range of a watermark. A watermark information detection device that reads information corresponding to a pattern from an image in which patterns having a certain spatial period are regularly arranged,
Image correction means for performing image correction in units of small areas on the input image;
The image correction means includes a representative value of a set of pixel values having a value higher than a predetermined threshold value from a pixel value of a pixel constituting the small area, and a representative value of a set of pixel values having a value lower than the predetermined threshold value. And determining whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the character and the figure from the distribution of the pixel value in the region consisting of arbitrary pixels surrounding the small region A threshold value for calculating the threshold value, and comparing one pixel value of the representative value of the set of pixel values having a high value or the representative value of the set of pixel values having a low value with the obtained threshold value. Based on this, it is determined whether or not the pixel value of the pixel constituting the pattern is lowered by the pixels constituting the character and the figure, and if it is determined that the pixel value is lowered , It decreases a certain pixel value a plurality of pixel values And without it substitutes the average value of the determined pixel values and the other pixel values of the representative values of the set of representative values or low pixel value of the values of a set of high pixel values of the value and the pixel value after the alternative A watermark information detecting apparatus using the dynamic range of the small area for correction.   3. The watermark information detection according to claim 1, wherein detection of a pixel value having a low value performed by the image correction means is performed only for a pixel value higher than a set threshold value. apparatus. The pixel value having a high value is a maximum value in a small region, and the pixel value having a low value is a minimum value in a small region. The watermark information detection apparatus according to any one of the above.   The watermark information detecting apparatus according to claim 1, wherein the pixel value is a luminance value.   The watermark information detecting apparatus according to claim 1, wherein the small area is an area divided into the same size as a regularly arranged pattern.   The watermark information detecting apparatus according to claim 1, wherein the small area is an area divided into a size larger than a regularly arranged pattern.   6. The watermark information detecting apparatus according to claim 1, wherein the small area is an area divided into a size smaller than a regularly arranged pattern. A watermark for detecting information corresponding to a pattern from an image in which a pattern having a certain spatial period is regularly arranged in a watermark information detecting apparatus including an image correcting means for correcting an image in units of small areas on an input image An information detection method,
A representative value of a set of pixel values having a value higher than a predetermined threshold value from a pixel value of a pixel constituting the small region and a representative value of a set of pixel values having a value lower than the predetermined threshold value by the image correction means. A detection process for detecting
Whether the pixel value of the pixels constituting the pattern is lowered by the pixels constituting the character and the figure from the distribution of the pixel values in the area consisting of arbitrary pixels surrounding the small area by the image correction means A threshold value for determining the pixel value, and for one pixel value of the representative value of the set of pixel values having a high value or the representative value of the set of pixel values having a low value, the pixel value and the obtained threshold value A discriminating step for discriminating whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the character and the figure based on the comparison ;
When it is determined in the determination step that the pixel value has decreased , the image correction means replaces the pixel value to be determined with the pixel value determined that the pixel value has not decreased. A correction step of correcting the dynamic range of the small region using the pixel value of the pixel and the representative value of the set of pixel values having a high value or the other pixel value of the representative value of the set of pixel values having a low value;
A method for detecting watermark information, comprising: A watermark for detecting information corresponding to a pattern from an image in which a pattern having a certain spatial period is regularly arranged in a watermark information detecting apparatus having an image correction means for performing image correction in units of small areas on an input image An information detection method,
A representative value of a set of pixel values having a value higher than a predetermined threshold value from a pixel value of a pixel constituting the small region and a representative value of a set of pixel values having a value lower than the predetermined threshold value by the image correction means. A detection process for detecting
Whether the pixel value of the pixels constituting the pattern is lowered by the pixels constituting the character and the figure from the distribution of the pixel values in the area consisting of arbitrary pixels surrounding the small area by the image correction means A threshold value for determining the pixel value, and for one pixel value of the representative value of the set of pixel values having a high value or the representative value of the set of pixel values having a low value, the pixel value and the obtained threshold value A discriminating step for discriminating whether or not the pixel value of the pixel constituting the pattern is lowered by the pixel constituting the character and the figure based on the comparison ;
When it is determined in the determination step that the pixel value is decreased , the image correction means changes the pixel value to be determined to the average value of the pixel values determined that the plurality of pixel values are not decreased. Instead, the dynamic range of the small region is corrected using the pixel value after replacement and the representative value of the set of pixel values having the higher value or the other pixel value of the set of pixel values having the lower value. A correction process;
A method for detecting watermark information, comprising:   11. The watermark information according to claim 9, wherein detection of a pixel value having a low value in the detection step is performed only for a pixel value higher than a set threshold value. Detection method. 12. The pixel value having a high value is a maximum value in a small region, and the pixel value having a low value is a minimum value in a small region. The watermark information detection method according to any one of the above.   The watermark information detection method according to claim 9, wherein the pixel value is a luminance value.   The watermark information detection method according to claim 9, wherein the small area is an area divided into the same size as a regularly arranged pattern.   The watermark information detection method according to claim 9, wherein the small area is an area divided into a size larger than a regularly arranged pattern. 14. The watermark information detection method according to claim 9, wherein the small area is an area divided into a size smaller than a regularly arranged pattern.

Images