JP2003264686A - Image processor, image processing method, and program therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor, an image processing method and a program therefor which realize highly accurate detection of invisibly embedded information without lowering picture quality and without requiring especial arithmetic processing (resulting in high speed and low cost). <P>SOLUTION: The image processor is provided with: a storage means for storing the relationship of correspondence between the parameter information of half tone processing to be utilized for preparing a print image and the attribute information of the print image; a read means for obtaining digital image data by scanning the print image original; and a detection means for detecting the parameter information of half tone processing used for the print image out of the digital image data obtained from the read means, and the image attribute information is taken out of the storage means by utilizing the parameter information of half tone processing obtained from the detection means. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, an image processing method, and a program for detecting additional information from a print image to which invisible information is added.

[0002]

2. Description of the Related Art There is a digital watermark technique as a technique for embedding information in image data in a form that cannot be perceived by humans. A first application of this technique is to embed information specifying an authorized person for the image to track the illegal copying or unauthorized use of the image. A second use is to embed specific pattern information and determine whether or not the image has been tampered with from the detection result of that information.

In the first and second uses, it is necessary to assume alteration (attack) of data. Therefore, an embedding method that retains some hidden regularity is also taken for the modified data. For example, even if the data has been modified,
When this is input to a predetermined function, the output is statistically biased. JP 2001-14877 A
Image data in the frequency space, as in Japanese Patent No. 5,
A method of performing a specific process is often used.

[0004]

The technique of embedding information in image data in a form that cannot be perceived by humans has the following third application in addition to the above. A device for creating image data has a purpose of embedding the attribute information of the image in the image data and transmitting it to the detection device side. In this third use, it is not necessary to assume alteration (attack) of data. This is because the purpose of this use is not originally defense against fraud, but propagation of attribute information. If the created image is a printed matter instead of electronic data, it is considered that the degree of artificial modification is smaller. Since it is not necessary to assume data modification, the conditions for the embedding method are
It will be relaxed, and a simpler method can be applied.

However, since such a simple method has not been considered so far, the conventional digital watermark method has to be adopted for this third application.
That is, the disadvantages such as slowness and high cost due to the complexity of the conventional method and the image quality deterioration due to the improvement of the tamper resistance have to be accepted. By the way, as a simple technology to realize the third application, there is something like a barcode, but this is because the original image data must be added with dedicated object data, so that the original image looks good. However, it is not a very preferable technique in terms of deterioration of printing quality and increase of consumption of printing toner (ink).

The present invention has been made in view of the above-mentioned problems, and an image processing apparatus capable of detecting invisible embedded information with high accuracy without deterioration of image quality and special calculation processing (high speed, low cost), An object is to provide an image processing method and its program.

[0007]

In order to achieve the above object, the invention according to claim 1 provides a correspondence relationship between parameter information of halftone processing used when a print image is created and attribute information of the print image. Storage means for storing, reading means for scanning a print image original to obtain digital image data, and detecting means for detecting parameter information of halftone processing used in the print image from the digital image data obtained by the reading means And using the parameter information of the halftone processing obtained from the detecting means, and extracting the image attribute information from the storing means.

According to a second aspect of the present invention, in the first aspect of the invention, the parameter information of the halftone process is at least one of a phase, a cycle, and a waveform of the halftone process.
It is characterized by being one piece of information.

According to a third aspect of the invention, in the first aspect of the invention, the attribute information of the print image is at least one of the storage location of the print image, the creation date and time, and the creator. It has a feature.

A fourth aspect of the invention is characterized in that, in the first aspect of the invention, a part of the range in which the parameter can be set and a range not used are provided.

The invention according to claim 5 is characterized in that, in the invention according to claim 1, the correspondence of a plurality of attribute information to one certain parameter value is stored in the storage means.

A sixth aspect of the present invention is characterized in that, in the first aspect of the invention, a pattern indicating a reference of a parameter of halftone processing is included in a print image.

A seventh aspect of the invention is characterized in that, in the first aspect of the invention, the detecting means detects only within a certain specific range in the image data.

According to an eighth aspect of the present invention, a storage step of storing a correspondence relationship between parameter information of halftone processing used when creating a print image and attribute information of the print image; A halftone process including a reading process of obtaining image data and a detection process of detecting parameter information of the halftone process used in the print image from the digital image data obtained by the reading process. The image attribute information stored in the storing step is extracted by using the parameter information of 1.

According to a ninth aspect of the present invention, a storage process for storing a correspondence relationship between the parameter information of the halftone process used when creating the print image and the attribute information of the print image, the print image original is scanned, and digital data is scanned. Intermediate processing obtained by causing a computer to execute a reading process for obtaining image data and a detecting process for detecting parameter information of halftone processing used in a print image from digital image data obtained by the reading process. Using the parameter information of key processing,
The feature is that the image attribute information stored by the storage processing is extracted.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to an embodiment of the present invention. The image processing apparatus of the present invention includes a control unit 1, an image data creation unit 2, an image data storage unit 3, a printer unit 4, a scanner unit 5, a detection unit 6,
And a storage unit 7.

The image data creating unit 2 creates bitmap image data with the halftone processing parameter instructed by the control unit 1. The image data storage unit 3 stores and saves this data. Based on this data, the printer unit 4 forms (prints) an image on a recording medium such as paper with toner or ink.

Then, the scanner unit 5
It is converted into bitmap image data (electronic data) again.
The detection unit 6 extracts the parameters of the halftone processing that would have been used in this image data. The storage unit 7 is composed of a table in which the correspondence between halftone processing parameters and image attributes is recorded. Using this table, the detection unit 6
Image attribute data is obtained from the parameters extracted in.
Hereinafter, each block will be described in order.

(Image Data Creating Unit 2) When outputting an image to a medium having a small number of gradations that can be expressed per pixel, a halftone process called an ordered dither method is often used. For example, a printer that prints with or without dots can usually express only two gradations per pixel. With such an output medium,
When expressing the concentration, the systematic dither method is used.

The systematic dithering method compares the original multi-gradation data (FIG. 2) with the value (threshold value) of the dither matrix (FIG. 3 (b)) and compares the result (FIG. 2 (a)). Is an output halftone processing method. The dither matrix is repeatedly used for the original multi-gradation data as shown by the thick line in FIG.
FIG. 4 shows an example in which only the phase of the dither matrix differs from that of FIG. If the dither matrix has A * B pixels, there are A * B types of phases.

Further, in the case of a color printer which prints with four colors of c, m, y, k (cyan, magenta, yellow, black), different dither matrices are used for each of the four colors. The number is (Ac * Bc) * (Am * B
m) * (Ay * By) * (Ak * Bk). For example, 16 * 16 for all four colors
If the dither matrix is, the number of types of phases is about 4 * 109. This is the life of the printing device (1 * 106
It is a number that is much higher than the page), and it is possible to have different phases for all pages. Furthermore, if the total production number of the printing device is small, it is possible to set the phase unique to the device in addition to the page.

In addition to the phase, the period and the waveform can be used as the parameters of the halftone processing. In contrast to FIG. 3, FIG. 5 shows an example in which the dither matrix period (vertical and horizontal sizes) is
FIG. 6 shows an example in which the waveforms (threshold values) are different. By properly using a plurality of types of dither matrixes having different periods and waveforms, information can be propagated by a printed matter like the phase.

There are parameters, such as dither phase, in the printed image that have little effect on image quality. Paying attention to this redundancy, the halftone processing parameter of the printed matter,
The point of the present invention is to give a role of propagating image attribute information.

The present invention is premised on the fact that a halftone-processed area by the dither method exists in the printed image. However, in the practical use of the present invention, a person who intends to propagate the information by the printed matter creates the image data, so that satisfying the above condition is not a particular obstacle. This is because it is only necessary to intentionally express the bare characters and letterhead with an intermediate density.

Compared to the addition of an originally unnecessary object such as a barcode, the printed document can be made clear. However, in the case of a color printer, there is a contradictory relationship between the number of colors that can be used in the intermediate density area and the total number of parameter values (about 4 * 109 in the case of the above phase example). For example, when trying to make the area yellow, only the toner of y is placed here, so that the parameter information of c, m, k cannot be transmitted. If you try to select an arbitrary color like this, in the case of phase example, (Ac * Bc), (Am * Bm), (Ay * By),
The minimum number of (Ak * Bk) is the total number of representable parameter values.

On the contrary, if the restriction that colors that are always represented by four colors are used, the total number of parameter values is (Ac * Bc) *.
(Am * Bm) * (Ay * By) * (Ak * Bk). The former means that an unused combination is provided among all combinations of four color parameters. However, even if you can choose any color, you cannot choose a color that does not show a dither pattern, such as the maximum density of yellow.

In the former case, the total number of usable parameter values becomes extremely small. In the above example, only 16 * 16 = 256 types of information can be propagated. But even in this case,
A plurality of attribute information may be associated with one parameter value. For example, when the attribute information is the storage location of the image data, one parameter value is not associated with the storage location of the one-page data, but is associated with the storage location of the plurality of pages of data.

(Storage Unit 7) The storage unit 7 stores the correspondence between the above-mentioned parameters of the halftone processing and the image attribute information. Depending on the contents of the image attribute information, various convenient things can be done as follows.

When the attribute information is the storage location information of the print data itself, reprinting can be performed at high speed and with high image quality. Reprinting means that a print original is used, the original bitmap data is read from the image data storage unit 3, and a print original is made again based on this data. Even if the application software file, such as a word processor, that created the print document is lost, the bitmap data of the image remains in the image data storage unit 3, and therefore reprinting can be performed.

Reprinting can be performed much faster than starting application software, transferring a file, and recreating bitmap data. Since the storage location of the image is directly known, the retrieval can be performed at a much higher speed than the comparison with all the bitmap data in the image data storage unit 3.

Further, it is possible to perform high-quality printing as compared with printing (normal copying operation) using data obtained by scanning a print document. Dirt on the printed document due to additional writing,
This is because it is possible to eliminate a factor of image quality deterioration due to noise that is mixed when the document is read. Difference extraction can also be performed in addition to reprinting. Difference extraction is the process of using a print document and converting the original bitmap data into the image data storage unit 3
It means that the non-coincidence portion between this data and the scan data of the print document is extracted, and printing or display is performed based on this. It is used to detect tampering with the printed manuscript and to extract only the added part.

When the attribute information is storage location information other than print data, access can be restricted. For example, as shown in FIG. 7, page (b) contains confidential information, and page (a) contains only the link and non-confidential information.
Both pages will be distributed at meetings, etc., but the page (b) will be collected to prevent leakage of confidential information. On page (a),
By adding the storage location information of the page image of (b), the pages of (a) to (b) can be obtained later using the device of the present invention. If the device of the present invention is provided with a personal authentication means such as a password, it is possible to restrict access to confidential information to only authorized persons.

When the attribute information is the printing date / person information, the creation date / person can be certified. If a clock or a personal authentication means is provided, the date and time when the print data or the printed matter is created and the person information are associated with the halftone processing parameter,
You can prove it. If a print page cumulative counter is provided, the same information as the date and time can be added to some extent.

(Control unit 1) The storage contents of the storage unit 7 are fixed (no rewriting with the initial value) and dynamic (rewriting in the middle). In the case where the attribute information is date / time / person etc., it is the latter. In the former case, the control unit 1 determines the parameters of the halftone processing from the attributes of the image data to be created according to the correspondence relationship of the storage unit 7, and informs the image data creation unit 2 of this.

In the latter case, the control unit 1 determines the correspondence between the attribute of the image data to be created and the parameter of the halftone processing, and stores this in the storage unit 7 and at the same time.
The halftone processing parameter is transmitted to the image data creating unit 2. When the system of the present invention is divided into two devices (dotted line in FIG. 1), rewriting of the storage unit 7 results in data transfer between the devices, but one device (composite of a printer and a scanner combined) Machine), there is no need for that.

(Detection unit 6) An example will be described in which the phase is used as a parameter using the dither matrix of FIG. First,
The bitmap data obtained by the scanner unit 5 is divided into blocks of the same size as the dither matrix ((a) in the figure).
), Take statistics. FIG. 6D shows the result of statistics obtained from the area for eight blocks indicated by the bold line. The numbers represent the number of black pixels. The statistics are obtained individually for each of the 16 positions of the dither matrix. It means that the larger the number, the stronger the tendency toward black pixels. That is, this leads to a low original dither threshold. That is, it can be said that the statistical information thus obtained has a large correlation with the dither threshold.

FIG. 6E is a normalized version of FIG. Specifically, the number of individual black pixels is divided by the maximum number of black pixels that can be generated (here, 8) to obtain a normalized value of 0 to 1. The threshold of the dither matrix is also normalized as shown in Fig. 6 (c) (the polarities are reversed for the sake of meaning).

The phase at which the least square error of these two normalized values is the minimum is the detection result. That is, the squared error of all 16 types of dithers having different phases is calculated from the statistical value of FIG. 3 (e), and the dither phase showing the minimum value is used as the detection result. For example, the squared error for the statistical values in Figure 3 (e) is
1.29 in correct phase diagram 3 (c), incorrect phase diagram 4
The value is smaller than 2.17 in (c). This processing is expressed in C language as follows. However, dither matrix size = n * m, statistical normalization value = a [j] [i], dither threshold normalization value = b [j] [i], detection result phase value = ii,
jj.

[0040]         float min, sum, temp, a [m] [n], b [m] [n];         int i, j, x, y, n, m, ii, jj;         min = 1.0;         for (y = 0; y <m; y ++) {for (x = 0; x <n; x ++) {                 sum = 0;                 for (j = 0; j <m; j ++) {for (i = 0; i <n; i ++) {                         temp = a [j] [i]-b [(j + y)% m] [(i + x)% n];                         sum + = temp * temp;                 }}                 if (sum <= min) {                         min = sum;                         ii = i; jj = j;                 }         }}

Next, an example in which the cycle is used as a parameter will be described. The distance at which the autocorrelation of the bitmap data obtained by the scanner unit 5 is maximized is the detection result. When expressed in C language, it becomes as follows. However, in the detection example of the cycle in the horizontal direction (x direction), the search range of the bitmap data = 0 to X, the search range of the cycle = 1 to F, and the cycle value of the detection result = ii.

[0042]

Next, an example using a waveform as a parameter will be described. The detection result is the dither matrix in which the least squared error between the normalized statistical values of the bitmap data obtained by the scanner unit 5 and the normalized values of the plurality of defined dither matrices is the minimum. That is, the squared error of all the defined dithers is calculated for the statistical value of FIG. 3 (e), and the dither showing the minimum value is set as the detection result.

For example, the squared error for the statistical value of FIG. 3 (e) is smaller than 1.29 in the correct waveform of FIG. 3 (c) and smaller than 3.79 in the incorrect waveform of FIG. 6 (c). When expressed in C language, it becomes as follows. However, dither matrix size = n * m, number of dither matrix types = K, statistical normalization value = a [j] [i], dither threshold normalization value = d [k]
[j] [i], detection result = kk.

[0045]         float min, sum, temp, a [m] [n], d [K] [m] [n];         int i, j, k, n, m, kk;         min = 1.0;         for (k = 0; k <K; k ++) {                 sum = 0;                 for (j = 0; j <m; j ++) {for (i = 0; i <n; i ++) {                         temp = a [j] [i]-d [k] [j] [i];                         sum + = temp * temp;                 }}                 if (sum <= min) {                         min = sum;                         kk = k;                 }         }

The above is the basic detection method, but a method for further improving the detection accuracy will be described below.

When the above-mentioned phase is used as a parameter, a phase reference is necessary. The edge of the printing paper may be used as a reference, but in order to improve the accuracy, a method of adding a pattern indicating a phase reference to the print image is used. For example, a cross pattern such as "dragonfly" is added to the corner of the printed image. Based on this pattern position,
It is possible to reduce the influence of vertical and horizontal deviations.

The reference pattern is essentially an unnecessary object, but it does not cause much trouble in clearing the printed document. Further, as another reference pattern, a relative relationship with another phase can be used. For example, if the dither phases of the y and c plates of the color image are detected with respect to an arbitrary reference, the relative phase of the c plate phase with respect to the y plate phase can be detected without the influence of printing misalignment. Even if the phase of the same plate is different, the relative phase can be similarly detected by using the dither of different phase in different regions.

However, if the distance between the reference and the halftone processing area is large, the halftone processing area is liable to be affected by the deviation of the magnification and the deviation of the rotation direction.
Place it within a predetermined range.

If the print and scan resolutions are the same, the detection process can be facilitated. Even if the printer is 1200dpi and the scanner is 600dpi, 600dpi, that is,
The dither matrix may be constructed with 2 * 2 as the smallest unit.

The above-mentioned embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited to this, and various modifications can be made without departing from the scope of the invention. Is possible.

The present invention can be realized by causing a computer to execute a program. The program is provided by being recorded in an optical recording medium, a magnetic recording medium, a magneto-optical recording medium or a semiconductor IC recording medium. Alternatively, it is provided by being downloaded from a server via a network using a protocol such as FTP or HTTP.

[0053]

As is apparent from the above description, according to the present invention, since the image attribute information is associated with the parameter on the printed image which hardly affects the image quality, no special calculation is required. Information can be embedded invisible at high speed (low cost) without adding a special object such as a barcode.

Further, according to the image processing apparatus of the third aspect, since the storage location of the image data and the date / time / person information can be read from the print original, reprinting, difference extraction, access restriction of confidential information, The date and time of printing / certification of a person can be provided.

Further, according to the image processing apparatus of the fourth aspect, since information is embedded in all toners equally,
The restriction on the number of colors of the information embedding area can be relaxed.

According to the image processing device of the fifth aspect, since a plurality of image attribute information is associated with one parameter, a large amount of image attribute information is propagated even if there are few expressible parameters. be able to.

Further, according to the image processing apparatus of the sixth aspect, since the pattern serving as the reference of the phase is printed, highly accurate information which is hardly affected by the vertical and horizontal misalignment between the print image and the print paper. Can be embedded.

Further, according to the image processing apparatus of the seventh aspect, since the information embedding area is provided in the vicinity of the reference pattern, it is unlikely to be affected by the magnification deviation or the rotation direction deviation between the print image and the printing paper. Highly accurate information can be embedded.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of multi-tone data before halftone processing.

FIG. 3 is a diagram illustrating an example of data, a dither, and a statistical value after halftone processing.

FIG. 4 is a diagram showing an example of data and dither after halftone processing when a phase is used as a parameter.

FIG. 5 is a diagram showing an example of data and dither after halftone processing when phase is used as a parameter.

FIG. 6 is a diagram showing an example of data and dither after halftone processing when a waveform is used as a parameter.

FIG. 7 is a diagram showing an example in which the present invention is applied to an application of access restriction.

[Explanation of symbols]

1 control unit 2 Image data creation section 3 Image data storage 4 Printer section 5 Scanner section 6 detector 7 memory

Claims (9)

[Claims] 1. A storage unit for storing a correspondence relationship between parameter information of halftone processing used when a print image is created and attribute information of the print image; and scanning the print image document to obtain digital image data. A reading unit; and a detecting unit that detects parameter information of the halftone processing used in the print image from the digital image data obtained from the reading unit, and the halftone processing obtained from the detecting unit. An image processing apparatus, wherein image attribute information is extracted from the storage means using parameter information. 2. The halftone processing parameter information includes:
The image processing apparatus according to claim 1, wherein the information is at least one of a phase, a cycle, and a waveform of the halftone processing. 3. The image processing apparatus according to claim 1, wherein the attribute information of the print image is at least one of a storage location of the print image, a creation date and time, and a creator. 4. A part of the possible range of the parameter and a non-use range are provided.
The image processing device described. 5. The image processing apparatus according to claim 1, wherein a correspondence of a plurality of the attribute information to a certain one parameter value is stored in the storage means. 6. The image processing apparatus according to claim 1, wherein a pattern indicating a reference of a parameter of the halftone processing is included in the print image. 7. The detection means performs detection only within a certain specific range in image data.
The image processing device described. 8. A storage step of storing a correspondence relationship between parameter information of halftone processing used when creating a print image and attribute information of the print image; and scanning the print image document to obtain digital image data. A reading step; and a detecting step of detecting parameter information of the halftone processing used in the print image from the digital image data obtained by the reading step, the halftone processing of the halftone processing being obtained by the detecting step. An image processing method characterized in that the image attribute information stored in the storing step is retrieved using parameter information. 9. A storage process of storing a correspondence relationship between parameter information of halftone processing used when creating a print image and attribute information of the print image, and scanning the print image document to obtain digital image data. The reading process and the detection process of detecting the parameter information of the halftone process used in the print image from the digital image data obtained by the reading process are executed by the computer, and the halftone obtained by the detection process is executed. An image processing program, wherein the image attribute information stored by the storage processing is extracted by using processing parameter information.