JP2007036833A - Method and apparatus for embedding digital watermark, and method and apparatus for detecting digital watermark - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To display an image in which digital watermark is embedded in a display so that the digital watermark cannot be viewed easily with human eyes, but can be detected easily when detecting digital watermarks. <P>SOLUTION: An image input part 21 reads out original moving image data 25a, decodes an image for one frame and stores the decoded image in a frame buffer 15. Then the image input part 21 notifies a watermark pattern embedding part 11 of the frame number of the image stored in the frame buffer 15 for image input. A watermark pattern generation part 3 generates an image by specific image generation algorithm, on the basis of added information 1, such as a URL and stores the generated image in a frame buffer 5 for watermark patterns. The image generation algorithm simply requires that the generated watermark pattern be detected by a watermark detection algorithm of a watermark detection part; and not only watermark algorithm for still images but also two-dimensional symbol algorithm and algorithm that utilizes OCR technology may be adopted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital watermark technique. Digital watermarking is a technology that uses the redundancy of digital data such as images and sound to embed additional information with little effect on image quality and sound quality, and detect this embedded information. is there. The present invention relates to a technique for detecting information by printing an image with information embedded therein or displaying it on a display, taking a picture with a camera-equipped mobile phone, among digital watermarks.

  Digital watermarking is a technique for detecting additional information by embedding additional information with respect to digital data such as an image and sound by using redundancy thereof and hardly affecting image quality and sound quality. It can be used for purposes such as embedding the author's name and the number of copies, and claiming copyright for illegal copies.

  Hereinafter, a digital watermark in an image related to the present invention will be described. Specific algorithms for performing digital watermarking on images include a method of embedding in a bit plane and a method of embedding in a frequency.

  The method of embedding in a bit plane is a method of replacing a part of a specific bit plane of an image with another pattern. It is used that the low-order bits of the image are mostly noise, and the image quality is hardly affected even if they are replaced with other patterns.

  As a method of embedding in a frequency, there is a method of changing a value to be quantized to an odd number or an even number depending on whether the bit of information to be embedded is 0 or 1 when quantizing a specific frequency. There are various other algorithms, which are described in the following patent documents and non-patent documents. (Patent Documents 1 and 2, Non-Patent Document 1).

  In the image distribution process, image compression, enlargement / reduction, partial cropping, and the like are performed. Therefore, in practical use, it is required that the watermark information is not erased even if these processes are performed, that is, the process is highly resistant. Even if a digital watermark is embedded to claim copyright, if the watermark information is rewritten or erased by a duplicator, the purpose of the digital watermark cannot be achieved. Accordingly, resistance to these treatments is also required.

  However, it is important to have resistance, but in order to have resistance, the same information must be embedded in duplicate. That is, the strength of tolerance and the amount of information to be embedded are in a trade-off relationship.

  By the way, there is a digital watermark for printed matter. Digital watermarks for printed materials are not distributed as digital data, but images that have been embedded with digital watermarks are printed or displayed on a display, and the printed or displayed images are captured by a scanner or camera. This technology detects watermarks from images, and services using camera-equipped mobile phones have been put into practical use.

  Therefore, digital watermarks for printed materials need to be stronger than digital distribution because watermarks are embedded due to color irregularities and stains due to printing and display, lens distortion, and image shooting conditions, resulting in severe deterioration of images. .

In addition to copyright claims, the use of digital watermarks for printed materials includes services such as scanning images with a camera-equipped mobile phone, detecting the address of an Internet site from the images, and downloading content such as videos. .
JP 2005-028797 JP 2004-015396 A Kojio Matsui, “Basics of Digital Watermarking”, Morikita Publishing Co., Ltd., Published: August 21, 1998.

  Several algorithms have also been proposed for digital watermarks for printed materials, such as the technology of embedding in the gradation difference of adjacent blocks, the frequency domain, and the technology of embedding wavelet transform coefficients in the patchwork method for luminance and yellow components. Has been proposed. However, even in digital watermarks for printed materials, the strength of tolerance and the amount of information to be embedded are a trade-off. Although it is desirable that image quality degradation is small even when information is embedded, image quality degradation is conspicuous only by embedding information of about several tens of bits in an image of the size of about QVGA because it is required to have strong resistance against image input / output degradation. There is a problem.

  An object of the present invention is to provide a digital watermark embedding technique capable of suppressing deterioration in image quality when an image with a digital watermark embedded is displayed on a display.

  According to one aspect of the present invention, there is provided a digital watermark embedding method for embedding a digital watermark in an image, an image input step for inputting a moving image, a digital watermark pattern storing step for storing a digital watermark pattern, A digital watermark pattern embedding step for embedding a digital watermark pattern in a frame; and an image output step for outputting a video image in which the digital watermark pattern is embedded, wherein in the step of embedding the digital watermark pattern in the video image, the video image There is provided a digital watermark embedding method characterized by embedding a frame of a digital watermark pattern and a frame of an inverted pattern of the watermark pattern therein.

  Preferably, the digital watermark pattern is embedded in a first frame, and the inverted pattern is embedded in a second frame adjacent to the first frame.

  According to the above method, since the component in which the watermark is embedded in the moving image is temporally averaged, it becomes difficult for the human eye to perceive the watermark pattern.

  An electronic watermark embedding method for embedding an electronic watermark in an image, comprising the step of converting a range of a watermark pattern to be embedded in the step of embedding a watermark pattern in a moving image. A method is provided.

  It is preferable to make it smaller than the original range in the range conversion of the range conversion step. According to the above method, it becomes difficult for the human eye to perceive the watermark pattern by making the range of the embedded pattern sufficiently small with respect to the fluctuation of the input image. The digital watermark is additional information for an image.

According to another aspect of the present invention, there is provided an electronic watermark embedding apparatus for embedding an electronic watermark in an image, an image input means for inputting a moving image, an electronic watermark pattern storage means for storing an electronic watermark pattern, and a moving image There is provided an electronic watermark embedding apparatus comprising: an electronic watermark pattern embedding means for embedding an electronic watermark pattern in the frame; and an image output means for outputting a moving image in which the electronic watermark pattern is embedded.

  It is preferable to have range conversion means for converting the range of the watermark pattern stored in the digital watermark pattern storage unit. Further, it is preferable that the digital watermark pattern embedding means has means for inverting a part of the frame. Further, it is preferable that the digital watermark pattern embedding unit includes a unit that leaves one of a pair of frames of the digital watermark pattern as it is and reverses the other.

  According to another aspect of the present invention, there is provided a digital watermark detection method for detecting additional information embedded in an image, an image input step for inputting a moving image in which a digital watermark pattern is embedded, and electronic processing of the moving image. There is provided a digital watermark detection method comprising a frame difference extraction step of extracting a frame difference in which a watermark pattern is embedded. A digital watermark can be detected based on the difference between frames.

  According to still another aspect of the present invention, there is provided an electronic watermark detection method for detecting additional information embedded in an image, an image input step for inputting a moving image in which an electronic watermark pattern is embedded, There is provided a digital watermark detection method comprising: a frame difference extraction step for extracting a frame difference in which a digital watermark pattern is embedded; and a histogram conversion step for converting a histogram of the extracted frame difference.

  An electronic watermark detection apparatus for detecting additional information embedded in an image, the image input means for inputting a moving image in which the digital watermark pattern is embedded, and a frame difference in which the digital watermark pattern of the moving image is embedded There is provided a digital watermark detection apparatus characterized by comprising a frame difference extraction means for extracting.

  According to the digital watermark embedding apparatus of the present invention, it is difficult for the human eye to perceive the watermark pattern by setting the range of the embedding pattern sufficiently small with respect to the fluctuation of the input image.

  Further, according to the digital watermark embedding apparatus of the present invention, since the embedded pattern is inverted with respect to one of the pair of frames and embedded, the components with embedded watermark are temporally averaged. It becomes difficult for human eyes to perceive. According to the digital watermark detection apparatus of the present invention, it is easy to detect a digital watermark pattern by taking a frame difference.

  According to the digital watermark embedding device and the digital watermark detection device of the present invention, the above-described device makes it possible to use not only a generally known digital watermark algorithm for still images but also a two-dimensional symbol algorithm and OCR. it can.

  The first embodiment of the present invention will be described below with reference to the drawings. First, the digital watermark technique according to the first embodiment of the present invention will be described. The present embodiment is characterized in that a digital watermark is embedded in the moving image data on the memory, and the moving image data in which the watermark is embedded is stored in the memory.

  As shown in FIG. 1, the digital watermark embedding apparatus A according to the present embodiment includes an image input unit 21, a watermark pattern embedding unit 11, a watermark pattern generation unit 3, a range conversion unit 7, an image output unit 23, and an image. An input frame buffer 16, a watermark pattern frame buffer 5, and an image output frame buffer 17 are provided. The image input unit 21 reads the original moving image data 25 a stored in the memory 25 and stores an image for one frame in the frame buffer 15. Here, since the original moving image data 25 a is generally a compressed file, the image input unit 21 includes a decoder, decodes the original moving image data 25 a, and outputs an image of one frame to the frame buffer 15. The image input unit 21 notifies the watermark pattern embedding unit 11 of the decoded image, that is, the frame number of the image stored in the image input frame buffer 15.

  The watermark pattern generation unit 3 generates an image with a specific image generation algorithm based on the additional information 1 such as a URL, and stores the generated image in the watermark pattern frame buffer 5. The image generation algorithm only needs to be able to detect the watermark pattern to be generated by the watermark detection algorithm of the watermark detection unit, which will be described later. In addition to the generally known digital watermark algorithm for still images, two-dimensional symbol algorithms and OCR (optical It is also possible to use a formula character reader) technology.

  Further, the watermark pattern generation unit 3 generates the same watermark pattern for a group based on the frame number of the input image.

  FIG. 2 illustrates a situation in which the same watermark pattern is assigned to the above three consecutive input images. This will be described with reference to FIG. As shown in FIG. 2, the watermark pattern embedding unit 11 synthesizes the image stored in the image input frame buffer 15 and the image stored in the watermark pattern frame buffer 5 to generate an image output frame buffer 17. Output to. Further, as shown in FIG. 3, the watermark pattern embedding unit 11 assigns a watermark pattern to a plurality of frames of the input image sequence output from the image input unit 21 and stored in the image input frame buffer 15. Of these, half embed the watermark pattern as it is, and the other half is inverted and embedded. Hereinafter, the processing results by the watermark pattern embedding unit 11 and the range conversion unit 7 will be described using mathematical expressions. In FIG. 2, an input image 31 and an output image 35 are composed of three YUV components. The watermark pattern 33 is composed of three components of YUV or two or one of them. The component in which the watermark is embedded may be any of YUV and any of RGB components. The component of embedding the watermark of the input image 31 and the output image 35 and the value of the pixel of interest on the watermark component are Fi, Gi, and Wk. The subscript i of Fi and Gi corresponds to the frame number i. The subscript k of Wk corresponds to the type of watermark pattern. Also, the range of Fi, Gi, Wk is set to 0 to R-1.

  The range converter 7 converts the range of the watermark pattern components. The value Wk before conversion is converted into wk by the range conversion unit 7 based on the following equation.

  Next, the operation of the watermark embedding unit 11 will be described. The nth frame and the mth frame are paired, the watermark is embedded in the nth frame as it is, and the watermark is inverted and embedded in the mth frame. The target pixels Gn and Gm of the component in which the watermarks of the nth frame and the mth frame are embedded are as follows.

  Here, the reason why Wk is multiplied by (r-1) / (R-1) is to make the Wk range sufficiently smaller than the Fi and Gi ranges. r is smaller than R and smaller than the local variation of the input image Fi. Also, the two frames may be continuous, that is, m = n + 1 or n = m + 1, but may not be continuous. Limit R is a function that allows converted pixels to fall within the range and is defined as follows.

Finally, the image output unit 23 incorporates an encoder, inputs an image for 11 frames embedded with the watermark stored in the image output frame buffer 17, encodes the moving image data in which the watermark is embedded in the memory. 27a is output to the memory 27.
Through the above processing, a watermark can be embedded in the moving image.

Next, an apparatus according to the second embodiment of the present invention will be described.
The apparatus according to the present embodiment is a digital watermark detection apparatus that detects a watermark from moving image data in which a watermark is embedded in a memory. The digital watermark detection apparatus according to the present embodiment includes a memory 27 for storing moving image data 27a in which a watermark is embedded, an image input unit 63, a previous frame frame buffer 61, and a frame delay unit 57 as shown in FIG. A frame buffer 55 for a subsequent frame, a frame difference extraction unit 53, a frame buffer 51 for a frame difference, a histogram conversion unit 47, a frame buffer 45 for a detected image, and a watermark pattern detection unit 43. Yes.

  The image input unit 63 incorporates a decoder, decodes the moving image data 27 a embedded with the watermark on the memory 27, and stores it in the image input frame buffer 61. The frame delay unit 57 has an internal buffer, acquires a frame number from the image input unit 63, stores several frames of the image stored in the frame buffer 61 for the previous frame, and outputs them to the frame buffer 55 for the subsequent frame To do.

  The frame difference extraction unit 55 is stored in the frame buffer 61 for the previous frame and the frame buffer 55 for the subsequent frame, and an image in which the same pattern is embedded as it is, and a pair of images embedded in an inverted manner, , And the difference between the two images is calculated and output to the frame difference buffer 53.

  Here, it is assumed that the watermark pattern is embedded in the nth frame as it is, the mth frame is a pair of the nth frame, and the same watermark is inverted and embedded. If the target pixel of the component in which the watermark of the nth frame and the mth frame is embedded is Gn and Gm, the target pixel ΔG of the output difference image is as follows.

This function LimitR is also defined by equation (3).
The addition of R / 2 takes into account that Gn−Gm becomes a negative value while ΔG takes only 0 or a positive value.

  The range conversion unit 7 performs binarization using R / 2 as a threshold value. If the output is P, it can be expressed by the following equation.

  The digital watermark detection unit 43 receives the differential image stored in the differential image frame buffer 45 and detects additional information embedded as a digital watermark. Here, the detection algorithm corresponds to that of the watermark pattern generation unit 3 of the digital watermark embedding apparatus according to the first embodiment.

  The moving image data embedded with the digital watermark used in the digital watermark detection apparatus may be used as it is generated by the digital watermark embedding apparatus, and may be once displayed on the display and captured by the camera. FIG. 6 is a diagram showing a state in which the moving image data 27a embedded with a watermark is copied to the display 71, the image on the display screen 71a is captured by the camera 73, and the moving image data 77a is stored in the memory via the image output unit 75. It is.

  As described above, according to the digital watermark embedding device according to the present embodiment, the watermark pattern can be made difficult to be perceived by human eyes by making the range of the embedded pattern sufficiently small with respect to the fluctuation of the input image. Can do.

  Further, according to the digital watermark embedding device according to the present embodiment, since the embedding pattern is inverted with respect to one of the pair of frames and embedded, the embedded component is temporally averaged. It becomes difficult for human eyes to perceive the pattern.

  On the other hand, according to the digital watermark detection apparatus of the present embodiment, it is easy to detect a digital watermark pattern by taking a frame difference. This is particularly effective when the images of two frames are hardly moving, and this can be expressed by a mathematical expression. For example, substituting equation (2) into equation (4), ignoring the range restriction from 0 to R-1, and assuming that Fn = Fm, the frame difference is as follows.

  That is, it can be seen that only the watermark pattern is extracted and the range is further doubled. However, as can be seen from equation (6), ΔG has a distribution centered on R / 2.

  In general, two-dimensional code or OCR is intended for a binarized image. Therefore, by binarizing the frame difference ΔG with R / 2 as a threshold value, the two-dimensional code or OCR can be used in place of a digital watermark for still images. When used for the above, the detection accuracy thereof can be increased.

  In other words, according to the digital watermark embedding device and the digital watermark detection device according to the present embodiment, not only a generally known digital watermark algorithm for still images but also a two-dimensional symbol algorithm or OCR can be used. There is an advantage that you can.

  The present invention is applicable to digital watermark technology.

It is a figure which shows the structural example of the digital watermark embedding apparatus by the 1st Embodiment of this invention. It is a figure which shows the input and output of a watermark pattern embedding part. In watermark pattern embedding, it is a figure which shows the relationship between a watermark pattern and the frame embedded as it is, and the frame embedded reversely. It is a figure which shows the example of 1 structure of the digital watermark detection apparatus by the 2nd Embodiment of this invention. It is a figure which shows the input and output of a flame | frame difference extraction part. It is a figure which shows a mode that the image copied on the display is taken in with a camera.

Explanation of symbols

  DESCRIPTION OF SYMBOLS A ... Digital watermark embedding apparatus, 3 ... Digital watermark pattern production | generation part, 5 ... Digital watermark pattern frame buffer, 11 ... Digital watermark pattern embedding part, 7 ... Range conversion part, 15 ... Image input frame buffer, 17 ... Image output Frame buffer, 21... Image input unit, 23... Image output unit, 25.

Claims (18)

An electronic watermark embedding method for embedding an electronic watermark in an image, comprising: an image input step for inputting a moving image; an electronic watermark pattern storing step for storing an electronic watermark pattern; and an electronic watermark for embedding an electronic watermark pattern in a frame of the moving image A pattern embedding step, and an image output step for outputting a moving image in which a digital watermark pattern is embedded,
An electronic watermark embedding method comprising embedding an electronic watermark pattern and an inverted pattern of the electronic watermark pattern in the moving image in the step of embedding an electronic watermark pattern in the moving image.   2. The digital watermark embedding method according to claim 1, wherein the digital watermark pattern is embedded in a first frame, and the inverted pattern is embedded in a second frame adjacent to the first frame. An electronic watermark embedding method for embedding an electronic watermark in an image,
An electronic watermark embedding method comprising a range conversion step of converting a range of a watermark pattern to be embedded in the step of embedding a watermark pattern in a moving image.   4. The digital watermark embedding method according to claim 3, wherein a frame of a watermark pattern and a frame of an inverted pattern of the watermark pattern are embedded in the moving image.   The step of embedding a digital watermark pattern in the moving image embeds a watermark pattern frame and a reverse pattern frame of the watermark pattern by inverting and embedding the other one of a pair of frames as they are. The digital watermark embedding method according to claim 4.   The digital watermark embedding method according to any one of claims 3 to 5, wherein the range conversion in the range conversion step is performed to make it smaller than the original range.   The method according to claim 1, wherein the digital watermark is additional information for an image. An electronic watermark embedding device for embedding an electronic watermark in an image,
An image input means for inputting a moving image;
Digital watermark pattern storage means for storing a digital watermark pattern;
Digital watermark pattern embedding means for embedding a digital watermark pattern in a frame of a moving image;
An electronic watermark embedding apparatus comprising: an image output means for outputting a moving image in which an electronic watermark pattern is embedded.   9. The digital watermark embedding apparatus according to claim 8, further comprising range conversion means for converting a range of a watermark pattern stored in the digital watermark pattern storage unit.   10. The digital watermark embedding apparatus according to claim 9, wherein the range conversion of the range conversion means is made smaller than the original range.   The digital watermark embedding apparatus according to any one of claims 8 to 10, wherein the digital watermark pattern embedding means includes means for inverting a part of a frame.   11. The digital watermark pattern embedding means includes means for leaving one of a pair of frames of a digital watermark pattern as it is and inverting the other frame. Digital watermark embedding device. An electronic watermark detection method for detecting additional information embedded in an image,
An image input step for inputting a moving image in which a digital watermark pattern is embedded;
And a frame difference extracting step for extracting a frame difference in which a digital watermark pattern of a moving image is embedded. An electronic watermark detection method for detecting additional information embedded in an image,
An image input step for inputting a moving image in which a digital watermark pattern is embedded;
A frame difference extraction step for extracting a frame difference in which a digital watermark pattern of a moving image is embedded;
A digital watermark detection method comprising: a histogram conversion step of converting a histogram of extracted frame differences.   15. The digital watermark detection method according to claim 14, wherein the histogram conversion in the histogram conversion step is binarization. An electronic watermark detection apparatus for detecting additional information embedded in an image,
Image input means for inputting a moving image in which a digital watermark pattern is embedded;
A digital watermark detection apparatus comprising: frame difference extraction means for extracting a frame difference in which a digital watermark pattern of a moving image is embedded.   17. The digital watermark detection apparatus according to claim 16, further comprising histogram conversion means for converting the histogram of the extracted frame difference.   18. The digital watermark detection apparatus according to claim 17, wherein the histogram conversion of the histogram conversion means is binarization.

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