JP2005269039A - Electronic watermark embedding apparatus, method, and program compatible with printed matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic watermark embedding apparatus, method, and program compatible with printed matters capable of stably detecting electronic watermark information in low gradation printing. <P>SOLUTION: An electronic watermark embedding image generating means generates a printed gradation image by reducing colors of a received digital image in matching with a set print gradation, succeedingly embeds electronic watermark information to the print gradation image to generate an initial electronic watermark embedding image, generates a difference image between the initial electronic watermark embedding image and the print gradation image, reduces colors of the difference image in matching with the print gradation, and composes the resulting difference image with the digital image whose colors are reduced to produce an electronic watermark embedded image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electronic watermark embedding apparatus and method for printed matter, and a program for embedding digital watermark information in a digital image, generating an electronic watermark embedded image, and printing.

  There is a digital watermark technology corresponding to a printed matter in which the “digital watermark” technology is applied to a printed matter. In this method, image information processed in the digital plate making process is changed in a form that cannot be recognized by the naked eye when it becomes a printed matter, and identification information for digital watermark is embedded. There is almost no effect on the finish of the printed matter such as the pattern and color, and the human eye cannot recognize the difference. When this printed matter is digitized again using a scanner or the like and input to dedicated software, the embedded digital watermark information can be detected (see, for example, Patent Literature 1 and Patent Literature 2).

By the way, embedding of digital watermark information in a general image is mainly performed for each color 256 value of the RGB image, and is printed with a resolution that can realize substantially the same gradation or color change. It is assumed that. In this case, the difference between the digital data of the RGB image and the CMYK image corresponding to printing is considered.
As described above, embedding of digital watermark information into a digital image is performed by degrading the image to a level that cannot be recognized by humans. Therefore, when digital watermark information is embedded in a 256-gradation digital image, the color value at each pixel of the finally generated image changes only about ± 5 compared to the original image. However, the pattern may change more than this in the case of a pattern with a sharp color change. By the way, in RGB images such as BMP (Bit MaP), JPEG (Joint Photographic Expert Group), EPS (Encapsulated PostScript file), and CMYK images that are normally used, the values (R, G, B, C, M) of each color are used. , Y, K) are used in 256 gradations.

However, printed materials are often printed at a lower gradation than digital images. In particular, when the print gradation is extremely small, the color value changed by the digital watermark is printed in exactly the same color when printing, and the change cannot be recognized. As a result, the embedded digital watermark information cannot be detected from the printed matter, and the meaning of embedding the digital watermark information is lost.
FIG. 12 shows an example of embedding digital watermark information in a single color image. Here, the state of color change reproduction when a digital image is printed with 256 gradations and when printed with 64 gradations is shown. According to the example shown in FIG. 12, the digital watermark can be detected because the color change is faithfully reproduced in 256 gradations, and the color change cannot be reproduced in the one printed in 64 gradations. For this reason, the digital watermark cannot be detected.
JP 2001-157002 A JP 2002-64700 A

When the resolution is high, even if the number of colors is small, pseudo gradation can be realized by the fineness of halftone dots or the like. However, it is difficult when the resolution is low. Further, by embedding digital watermark information in the image data, a minute change occurs in the image data.
However, as described above, the low gradation printed matter cannot accurately represent the change, and even if the color is slightly different, the same color is printed. For this reason, conventionally, it has not been possible to detect digital watermark information from printed matter with low gradation.

  The present invention has been made in view of the above circumstances, and the digital watermark information embedded in a digital image is adjusted as the amount of change in color in accordance with the gradation to be printed. An object of the present invention is to provide an electronic watermark embedding apparatus, method, and program for printed matter, which can stably detect electronic watermark information by generating an image embedded with an electronic watermark.

  In order to solve the above-described problems, the present invention provides an electronic watermark embedding apparatus for printed matter that embeds digital watermark information in a digital image, generates a digital watermark embedded image, and prints the image. An electronic watermark embedded image generating means for converting the amount of change into a printable change amount according to the key and generating the digital watermark embedded image is provided.

  In the present invention, the digital watermark embedded image generating means generates a print gradation image by reducing the color of an input digital image in accordance with a set print gradation, and the printing An electronic watermark embedding unit that embeds digital watermark information in a gradation image to generate an initial digital watermark embedded image, a difference image generation unit that generates a difference image between the initial electronic watermark embedded image and the print gradation image, and the difference An image generation unit configured to reduce an image in accordance with the print gradation and combine the image with the reduced difference image to generate the digital watermark embedded image.

  In the present invention, the difference image generation unit performs color difference conversion to the print gradation using a maximum or average absolute value of the difference image as a color difference threshold, and reproduces a color change based on the conversion result. It is characterized by.

  Further, the present invention is a digital watermark embedding method for printed matter that embeds digital watermark information in a digital image, generates a digital watermark-embedded image, and performs printing, and the input digital image is set to a set print gradation. A step of generating a print gradation image by color reduction, a step of embedding digital watermark information in the print gradation image to generate an initial digital watermark embedded image, the initial digital watermark embedded image, and the print gradation image; Generating the difference image, reducing the color of the difference image in accordance with the print gradation, and combining the reduced difference image and the generated print gradation image to form the digital watermark embedded image. And generating.

  Further, the present invention is a program used in a digital watermark embedding apparatus for printed matter that embeds digital watermark information in a digital image, generates a digital watermark-embedded image, and performs printing, and sets the input digital image A process for generating a print gradation image by performing color reduction according to a print gradation; a process for embedding digital watermark information in the print gradation image to generate an initial digital watermark embedded image; and the initial digital watermark embedded image and the print A process of generating a difference image with a gradation image; and color-reducing the difference image in accordance with the print gradation; combining the reduced difference image and the generated print gradation image; A process for generating an embedded image is executed by a computer.

  According to the present invention, the digital watermark-embedded image generating means adjusts the color change amount according to the gradation to be printed with respect to the digital watermark information added to the digital image, and the change amount that can be printed even in low gradation printing Since the digital watermark embedded image is generated, the detection accuracy of the digital watermark information can be made higher than that when the color image is directly printed at low gradation.

According to the present invention, the input digital image is reduced in color according to the set print gradation to generate a print gradation image, and then the digital watermark information is embedded in the print gradation image and the initial digital watermark is embedded. An image is generated, a difference image between the initial digital watermark embedded image and the print gradation image is generated, the color of the difference image is reduced in accordance with the print gradation, and the digital image reduced here is combined with the digital watermark. Generate an embedded image. This makes it possible to embed digital watermark information in a low-tone printed material such as flexographic printing (corrugated cardboard box) or a low-quality printed material. In addition, unlike barcodes, part of a product can have identification information as digital watermark information without wasting part of the design, and the contents can be kept secret.
Further, the difference image generation unit performs color difference conversion to a print gradation using the maximum or average absolute value of the difference image as a color difference threshold, and reproduces a color change based on the conversion result, whereby a low gradation printed matter The digital watermark information is embedded in the digital watermark information, and the digital watermark information can be detected stably.

FIG. 1 is a diagram cited for explaining a digital watermark embedding method for printed matter according to an embodiment of the present invention.
As shown in FIG. 1, according to the digital watermark embedding method for printed matter of the present invention, first, a print gradation image is generated by reducing the color of an input digital image (a) according to a set print gradation. (B). Then, in parallel with the process (c) for decomposing the print gradation image into CMYK, digital watermark information is embedded in the print gradation image to generate an initial digital watermark embedded image (d).
Subsequently, a difference image between the initial digital watermark embedded image and the print gradation image is generated (e). Next, the difference image is decomposed into CMYK (f), the difference image is subtracted in color according to the print gradation (g), and the digital image that has been reduced in color is combined with the previously generated print gradation image. (H) to generate a digital watermark embedded image (i).

FIG. 2 is a block diagram showing an example of the internal configuration of the digital watermark embedding apparatus corresponding to a printed matter according to the embodiment of the present invention.
The digital watermark embedding apparatus for printed matter according to the present invention relates to digital watermark information to be added to a digital image, adjusts the amount of color change in accordance with the gradation to be printed, and uses the digital watermark as the amount of change that can be printed even in low gradation printing. An electronic watermark embedded image generating unit that generates an embedded image is provided. The electronic watermark embedded image generating unit includes an image data storage unit 21, a print gradation setting unit 22, a print gradation image generation unit 23, and an electronic watermark. An embedding setting unit 24, a digital watermark embedding unit 25, a difference image generation unit 26, a print resolution difference image conversion unit 27, a print resolution image conversion unit 28, an image composition unit 29, and a digital watermark embedded image storage unit 30 And the low gradation image printing unit 31.

The image data storage unit 21 stores input digital images. The print gradation image generation unit 23 converts the input digital image (I in FIG. 1) read from the image data storage unit 21 based on the print gradation set by the print gradation setting unit 22 (see FIG. 1). II) is generated and supplied to the digital watermark embedding unit 25 and the print resolution image converting unit 28.
The digital watermark embedding unit 25 embeds the digital watermark information by using the digital watermark embedding amount parameter set by the digital watermark setting unit 24 and the digital watermark information, and the initial digital watermark embedded information (the image in FIG. 1). III) is supplied to the difference image generation unit 26. In addition, the difference image generation unit 26 is supplied with a print gradation image generated by the print open book image generation unit 23. Here, the difference from the image embedded with the initial digital watermark is calculated to obtain a print resolution difference image. It supplies to the conversion part 27 (image IV of FIG. 1).

  The image further decomposed into CMYK by the print resolution difference image conversion unit 27 and reduced in color according to the print gradation is supplied to the image composition unit 29 together with the image obtained by decomposing the print gradation image into CMYK by the print resolution image conversion unit 28. Then, the image synthesizing unit 29 synthesizes and generates a low gradation printing digital watermark embedded image, which is supplied to the low gradation image printing unit 31 via the digital watermark embedded image storage unit 30 to cause printing to occur.

FIG. 3 and FIG. 4 are flowcharts cited for explaining each of the digital watermark information embedding operation and the detection operation by the digital watermark embedding apparatus for printed matter according to the embodiment of the present invention shown in FIG. 3 and 4 also show the processing procedure of the program of the present invention.
The operation of the embodiment of the present invention shown in FIG. 2 will be described in detail below with reference to the flowcharts shown in FIGS.

In the flowchart shown in FIG. 3, first, the print gradation image generating unit 23 captures image data and digital watermark information (S31). The former is acquired from the image data storage unit 21 and the latter is acquired from the digital watermark embedding setting unit 24. At this time, the print gradation is set by the print gradation setting unit 22 and is also taken in (S32). As a result, the print gradation image generating unit 23 performs a color reduction process on the image data in accordance with the set print gradation (S33). The print gradation image generated here is assumed to be α.
Subsequently, a digital watermark embedding process by the digital watermark embedding unit 25 is executed. At this time, a parameter (digital watermark embedding amount) is set by the digital watermark embedding setting unit 24 (S36). The digital watermark embedding unit 25 generates an initial embedded image β of digital watermark information for the print gradation image based on the digital watermark embedding amount (S37). The generation of the initial embedded image by the digital watermark embedding unit 25 and the CMYK decomposition process (S34) of the print gradation image by the print resolution image converting unit 28 are performed in parallel.

Next, the difference image generation unit 26 performs a difference calculation between the initial embedded image β and the print gradation image α, and a difference value is obtained for each pixel (S38). Subsequently, the printing gradation difference image obtained by the printing resolution difference image converting unit 27 is decomposed into CMYK (S39), and further color reduction processing according to the printing gradation is executed (S40), and the printing gradation degree image conversion is performed. After waiting for the result of the CMYK decomposition of the print gradation image by the unit 28 (S41), the images are synthesized by the image synthesis unit 29 (S42).
Then, a low gradation, digital watermark embedded image for printing is generated by the image synthesis unit 29 and stored in the digital watermark embedded image storage unit 30. The digital watermark embedded image stored here is printed on a printed matter by the low gradation image printing unit 31.

  On the other hand, in the detection flowchart shown in FIG. 4, the printed matter is A / D converted by a scanner, a digital camera or the like to extract a digital image (S51, S52), and a normal digital watermark information detection process is executed (S53).

Here, a supplementary description will be given of a procedure for embedding digital watermark information and a procedure for detecting digital watermark information.
FIG. 5 shows a detailed procedure for embedding digital watermark information by the digital watermark embedding apparatus for printed matter according to the present invention.
In FIG. 5, reference numeral 254 denotes original image data. By performing Fourier transform (255) on the original image data 254, amplitude data 258 and phase information 259 can be obtained through block division (256) and color space conversion (2557). Reference numeral 251 denotes digital watermark information embedded in the original image data 254. Spreading digital watermark information is obtained by performing spectrum spreading (263) on the digital watermark information 251. Next, the spread digital watermark information is combined with the amplitude data 258 (265). Furthermore, inverse Fourier transform (264) is executed using the phase information 359, and thereby image data obtained by synthesizing the digital watermark information is obtained.

On the other hand, the original image data 354 is wavelet transformed (260) in order to reduce the noise by combining the noise caused by the combination of the digital watermark information with the local features of the image, and the original image data 254 is decomposed into subband images. Are represented by partial images orthogonal to each other. Then, energy map data having the same size as that of the original image 254 is obtained based on this partial image (261: high frequency energy calculation).
Next, a difference between the image obtained by combining the digital watermark information obtained by the inverse Fourier transform (264) and the original image data 254 is obtained (267). Further, the above-described energy map data weight mask creation (262) is performed, and the digital watermark information is again synthesized with the original image data 354 (268, 269). In this way, digital watermark embedded image data is obtained and stored in the digital watermark embedded image storage unit 30.

  Note that the following procedure is followed when detecting the digital watermark information embedded as described above. That is, the digital watermark embedded image data to be detected by the digital watermark is, for example, digital data obtained by scanning a printed matter with a scanner or the like. By performing discrete Fourier transform (not shown) on the digital watermark embedded image data, amplitude data of the image data can be obtained. On the other hand, a symbol value detection sequence is obtained based on the pseudo-random number sequence. Next, based on the amplitude data and the symbol value detection series, a process of calculating a symbol response value is performed to detect a symbol value. Radix conversion is performed on the symbol value thus obtained to obtain detected digital watermark information.

  FIG. 6 shows an example of a printing gradation setting method set by the printing gradation setting unit 22. Here, as shown in (a), an image having a value from 0 to 255 is taken as an example, and color difference 4 (64 gradations), 8 (32 gradations), 128 (2 gradations), etc. This corresponds to the case where the print gradation is uniform. (B) shows the case of four equal gradations, and (c) shows the case of three gradations.

  7 and 8 conceptually show the color reduction method by the print gradation image generation unit 23. FIG. The example shown in FIG. 7 illustrates a case where the color difference is smaller than twice the color difference threshold, and the example shown in FIG. 8 is a case of a ternary image, where the color difference is larger than twice the color difference threshold. Here, the “color difference threshold” refers to the maximum or average absolute value of the difference image generated by the difference image generation unit 26.

In FIG. 7, a difference value with 256 values is shown in the dotted line frame, 0 is assigned to the center, and +/− difference values are assigned to the left and right, respectively. Here, a case where the print gradation is expressed by 32 gradations is shown, and the range of color differences 1 to 7 is converted to color difference 8 and the range of 9 to 15 is converted to 16 color differences.
FIG. 9 shows a case where the value of all pixels is 128, and when the color difference between the original image and the digital watermark embedded image at 256 gradations shown in (a) is printed as it is, as shown in (b). , There is almost no color change due to the color difference between the original image and the printed material during 32 gradation printing. On the other hand, when printing is performed together with the print gradation, the original image at the time of 32 gradation printing is displayed as shown in (d) via color difference conversion to 32 gradations as shown in (c). The color change is reproduced by the color difference of the printed matter.

In FIG. 8, as in FIG. 7, a difference value with 256 values is shown in the dotted line frame, 0 is assigned to the center, and + − difference values are assigned to the left and right. Here, a case where the print gradation is expressed by three gradations is shown, and-indicates that the color difference is converted to -1, + is +1, and 0.
FIG. 10 shows a case where the color value of all pixels is 128. When the color difference between the original image and the digital watermark embedded image at 256 gradations shown in (a) is printed as it is, three gradation printing is performed in (b). There is almost no color change as shown by the color difference between the original image and the printed material. On the other hand, when printing is performed together with the print gradation, the color difference between the original image and the printed material at the time of three gradation printing is shown in (d) via the color difference flag corresponding to printing shown in (c). The color change is reproduced.

FIG. 11 shows an operation concept of an image composition method (color difference flag and original image composition) by the image composition unit 29. Here, a case where the print gradation is 3 is shown, (a) is an original image, (b) is a ternary image, (c) is a color difference flag, (d) is a third floor which is a combination of the color difference flag and the original image. The digital watermark embedded image at the time of adjustment is shown.
In the case of three gradations, when the color difference is 1, the next largest color value (for example, 128 → 255) after the designated color, and when the designated color is the maximum value (for example, 255 → 255), the color difference is −1. When the specified color is the smallest value (example: 0 → 0), the specified color is the minimum value (example: 0 → 0), and when the color difference is 0, the specified color value (example: 0 → 0) : 128 → 128).

  As described above, the present invention relates to digital watermark information to be embedded in a digital image. The amount of color change is adjusted in accordance with the gradation to be printed, and the digital watermark embedded image is used as the changeable amount of printing even in low gradation printing. As a result, the detection accuracy of the digital watermark information is higher than that of printing a color image as it is in low gradation.

Note that printing on corrugated cardboard can be considered as an application example to low gradation printed matter. Corrugated cardboard mainly uses flexographic printing, and printing with fine gradation like offset printing cannot be performed. Therefore, conventionally, the color change caused by the normal digital watermark embedding process could not be reproduced at the time of printing, but can be easily reproduced by the present invention. Thus, for example, the product can be handled in a secret manner that can give the product unique information. Specifically, identification information can be acquired from a product by setting identification information as digital watermark information. Unlike barcodes, you can keep hidden information while maintaining the design.
According to the present invention, it is difficult to understand that information is written, and even if it is known that information is written, the contents are not known. Conventionally, the use of barcodes (one-dimensional and two-dimensional) as management of identification information has become widespread, but because the specifications of the barcode are open to the public, the description content is decoded by some people. Since a barcode area is required, it is necessary to allocate a part of the design for affixing the barcode. However, according to the digital watermark embedding device realized by the present invention, all these disadvantages are eliminated. The

  Note that the image data storage unit 21, the print gradation setting unit 22, the print gradation image generation unit 23, the digital watermark embedding setting unit 24, the digital watermark embedding unit 25, the difference image generation unit 26, and the print resolution difference image shown in FIG. The procedure executed by each of the conversion unit 27, the print resolution image conversion unit 28, the image composition unit 29, the digital watermark embedded image storage unit 30, and the low gradation image printing unit 31 is recorded on a computer-readable recording medium. The present invention can also be realized by causing a computer system to read and execute a program recorded on a recording medium. The computer system here includes an OS and hardware such as peripheral devices.

Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.
The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within the scope not departing from the gist of the present invention.

It is the figure quoted in order to demonstrate the electronic watermark embedding method corresponding to printed matter of this invention. It is a figure which shows an example of the internal structure of the digital watermark embedding apparatus corresponding to printing concerning embodiment of this invention. It is the flowchart quoted in order to demonstrate the operation | movement concerning embodiment of this invention. It is the flowchart quoted in order to demonstrate the operation | movement concerning embodiment of this invention. It is the figure quoted in order to demonstrate the procedure of the digital watermark information embedding concerning embodiment of this invention. It is the figure quoted in order to demonstrate the operation | movement concept of the printing gradation setting process concerning embodiment of this invention. It is the figure quoted in order to demonstrate the operation | movement concept of an example of the color reduction process concerning embodiment of this invention. It is the figure quoted in order to demonstrate the operation | movement concept of the other example of the color reduction process in connection with this invention embodiment. FIG. 8 is a diagram comparing the case where printing is performed on a printed material in the same manner as in the past and the case where printing is performed according to the present invention, according to FIG. FIG. 9 is a diagram comparing a case where printing is performed on a printed material in the same manner as in the past and a case where printing is performed according to the present invention, according to FIG. It is the figure which showed the operation | movement concept about the synthesis | combination of the color difference flag and original image concerning embodiment of this invention. It is a figure quoted in order to explain how color changes are reproduced when digital data is printed with 256 gradations and with 64 gradations.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 ... Image data storage part, 22 ... Print gradation setting part, 23 ... Print gradation image generation part, 24 ... Digital watermark embedding setting part, 25 ... Digital watermark embedding part, 26 ... Difference image generation part, 27 ... Print resolution Difference image conversion unit, 28... Print resolution image conversion unit, 29... Image synthesis unit, 30... Digital watermark embedded image storage unit, 31.

Claims (5)

A digital watermark embedding device corresponding to a printed matter that embeds digital watermark information in a digital image, generates a digital watermark embedded image, and performs printing.
A digital watermark embedded image generating means for converting the digital watermark information into a printable change amount according to a print gradation and generating the digital watermark embedded image;
A digital watermark embedding apparatus corresponding to printed matter. The digital watermark embedded image generation means includes:
A print gradation image generating unit that generates a print gradation image by reducing the color of an input digital image in accordance with a set print gradation;
A digital watermark embedding unit that embeds digital watermark information in the print gradation image and generates an initial digital watermark embedded image;
A difference image generation unit for generating a difference image between the initial digital watermark embedded image and the print gradation image;
An image generation unit that reduces the color of the difference image in accordance with the print gradation, combines the reduced color difference image with the generated print gradation image, and generates the digital watermark embedded image;
The electronic watermark embedding apparatus for printed matter according to claim 1, further comprising: The difference image generation unit
3. The printed matter-compatible electronic device according to claim 2, wherein color difference conversion to the print gradation is performed using a maximum or average absolute value of the difference image as a color difference threshold value, and color change is reproduced based on the conversion result. Watermark embedding device. A digital watermark embedding method for printed matter that embeds digital watermark information in a digital image, generates a digital watermark embedded image, and performs printing.
Reducing the color of the input digital image in accordance with the set print gradation to generate a print gradation image;
Embedding digital watermark information in the print gradation image to generate an initial digital watermark embedded image;
Generating a difference image between the initial digital watermark embedded image and the print gradation image;
Reducing the color of the difference image in accordance with the print gradation, and combining the reduced color difference image and the generated print gradation image to generate the digital watermark embedded image;
A digital watermark embedding method for printed matter, comprising: A program used in a digital watermark embedding apparatus for printed matter that embeds digital watermark information in a digital image, generates a digital watermark-embedded image, and performs printing.
A process of generating a print gradation image by reducing the color of the input digital image in accordance with the set print gradation;
Processing for embedding digital watermark information in the print gradation image and generating an initial digital watermark embedded image;
Processing to generate a difference image between the initial digital watermark embedded image and the print gradation image;
Processing to reduce the color of the difference image in accordance with the print gradation, and to generate the digital watermark embedded image by combining the reduced difference image and the generated print gradation image;
A program that causes a computer to execute.

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