JP2008017289A - Digital watermark embedding device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve proper digital watermark embedding control without inverting the relationship between watermark strength and deterioration in picture quality. <P>SOLUTION: When an original image and watermark information are input, a watermark pattern showing the change quantity of a pixel value applied to the original image is generated by the digital watermark embedding of the watermark information in the original image, and the watermark pattern is changed to generate a changed watermark pattern so that the error of watermark embedding target color components due to quantization to be generated in superimposing the watermark pattern on the original image can be reduced by referring to a reference change quantity storage means storing RGB reference change quantity as the pixel value change quantity of every RGB component, and the changed watermark pattern is superimposed on the original image and an image with a watermark is output. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a digital watermark embedding apparatus and method, and more particularly, to a digital watermark embedding apparatus and method in a digital watermark technique for embedding other sub-information in a content such as an image or video so as not to be perceived.

  Today, digital watermark technology is used in content copyright protection / management systems, content-related service provision systems, and the like.

When distributing content such as images and videos, there is a method of using digital watermark technology that embeds other information so that it cannot be perceived in the content for purposes such as content identification / management, copyright protection / management, and related information provision . In particular, in the digital watermark technology for image / video content, a method based on a minute change of a pixel value is common. In addition, there is a method of avoiding a luminance component with high visual sensitivity and finely changing a color component such as a color difference in order to suppress image quality deterioration due to digital watermark embedding (see, for example, Non-Patent Document 1).
Nakamura, Yamamoto, Kitahara, Miyatake, Katayama: "Mobile watermarking for moving images with real-time detection", 13th Multimedia Communication and Distributed Processing Workshop Proceedings, pp. 161-166, November 2005

  In general, a pixel value digitally expressed is, for example, a value quantized to 8 bits, that is, 256 values, and digital watermark embedding is a minute change of the pixel value. For example, consider 24-bit color data in which color image data is represented by 8 bits each for R, G, and B. The conversion from RGB data to luminance and color difference signals is, for example, a conversion formula defined by CCIR601 or the like.

Can be converted to each other. Now, in order to suppress image quality degradation, it is considered to avoid the luminance Y having high visual sensitivity, for example, to embed a digital watermark by changing the Cb component by a minute amount Δcb. In this case, for example, if Δcb ± 1, then the RGB changes Δr, Δg, Δb caused by embedding are Δr = 0, Δg = ± 0.336, Δb = ± 1.732, but when rounding error due to quantization is considered (assuming the rounding rule is used), ΔR = ΔG = 0 and ΔB ± 2. That is, in this case, the minute change amount of the Cb component is reflected only in the B component. At this time, if ΔrΔgΔb after quantization is converted into the YCbCr color space,
Δy = ± 0.114 × 2,
Δcb = ± 0.511 × 2,
Δcr = ± 0.083 × 2
Thus, it can be seen that the Y and Cr component values that were originally not changed have changed. In particular, there is a problem that visual deterioration due to digital watermark embedding becomes conspicuous when the luminance component Y changes.

  Further, from the conversion equation of equation (2), even if a change of | Δcb | <0.5 / 1.732 is given, Δr = Δg = Δb = 0 because of a rounding error due to quantization, and thus an image is obtained. It can be seen that the digital watermark is not embedded because no change is given.

  Further, when 0.5 / 1.732 ≦ | Δcb | <1.5 / 1.732, Δr = Δg = 0, Δb = ± 1, etc. Even if they are specified continuously, the actual pixel value change amount becomes discrete due to quantization.

In addition, when Δcb = ± 3, Δr = 0, Δg = ± 0.336 × 3, Δb = ± 1.732 × 3, and when quantization is performed, Δr = 0, Δg = ± 1, Δb = ± 5, and when ΔrΔgΔb after quantization is converted into the YCbCr color space,
Δy = ± (−0.587 × 1 + 0.114 × 5) = ± 0.017
Therefore, the amount of change is smaller than Δy = ± 0.114 × 2 when Δcb = ± 1. That is, even if the amount of change in the Cb component is reduced, the amount of change in the Y component, which is the main cause of image quality deterioration, may increase due to quantization. As can be seen from the above, in the prior art, it is difficult to finely and accurately control the trade-off balance between image quality degradation and durability by embedding strength, which is an important point in the operation of digital watermark technology. There was a problem.

In summary,
(1) Even if only the color component such as the Cb component is changed while avoiding the Y component in order to suppress the image quality deterioration, the final post-embedding pixel value (RGB value) can only take an integer. Ingredients fluctuate;
(2) Since the final post-embedding pixel value (RGB value) can only be an integer, the intensity cannot be finely adjusted;
(3) Since the image quality degradation may increase even if the intensity is lowered, the tolerance / image quality trade-off cannot be appropriately controlled by the intensity;
There was a problem.

  The present invention makes it possible to reduce the amount of change in luminance caused by minute changes in color signals, which was impossible with conventional technology, and to finely control the trade-off balance between image quality degradation and tolerance using embedding strength. An object of the present invention is to provide a digital watermark embedding apparatus and method that can be appropriately controlled without reversing the relationship between strength and image quality deterioration.

  FIG. 1 is a principle configuration diagram of the present invention.

The present invention (Claim 1) is an electronic watermark embedding apparatus for embedding an electronic watermark in a color image,
A reference change amount storage means 125 for storing a reference change amount for each color component of the color system used in the data format of the original image;
When an original image and watermark information are input, a watermark pattern generation unit 110 that generates a watermark pattern representing a change amount of a pixel value given to the original image by embedding the watermark information in the original image with the watermark,
Referring to the reference change amount stored in the reference change amount storage unit 125, the watermark pattern is changed and changed so that the error of the watermark embedding target color component due to quantization generated when the watermark pattern is superimposed on the original image is reduced. Watermark pattern changing means 120 for generating a completed watermark pattern;
Watermark pattern superimposing means for superimposing the changed watermark pattern on the original image and outputting a watermarked image.

The present invention (Claim 2) is a digital watermark embedding device for embedding a digital watermark in a color image,
A reference change amount storage means 125 for storing a reference change amount for each color component of the color system used in the data format of the original image;
When an original image and watermark information are input, a watermark pattern generation unit 110 that generates a watermark pattern representing a change amount of a pixel value given to the original image by embedding the watermark information in the original image with the watermark,
With reference to the reference change amount of the reference change amount storage means 125, the watermark pattern is reduced so that the change amount of the color components other than the watermark embedding target color component by quantization generated when the watermark pattern is superimposed on the original image is reduced. A watermark pattern changing unit 120 for generating a changed watermark pattern by changing
Watermark pattern superimposing means for superimposing the changed watermark pattern on the original image and outputting a watermarked image.

Further, the present invention (Claim 3) is provided in the watermark pattern changing means 120.
Pattern block dividing means for generating a watermark pattern block group by dividing a watermark pattern into blocks of a given size;
An in-block average change amount calculating means for calculating an average change amount that is an average value of the embedding target color components in each watermark pattern block;
A ratio between the average change amount and the embedding target color component value of the reference change amount of the reference change amount storage means in which the value of the color component other than the embedding target color component is small is calculated, and based on the calculated value of the ratio Density pattern modulation means for generating a modified watermark pattern block group by density-modulating the pixel value of each watermark pattern block using the reference change amount;
Pattern reconstructing means for reconstructing a modified watermark pattern block group and outputting a modified watermark pattern.

Further, the present invention (Claim 4) is a density pattern modulating means,
Based on the value of the average change amount, referring to the reference change amount storage means, means for selecting one of a plurality of reference change amounts having small values of color components other than the embedding target color component;
Means for calculating a ratio between the average change amount and the embedding target color component value of the selected reference change amount;
Means for generating a changed watermark pattern block group by density-modulating the pixel value of each watermark pattern block using the selected reference change amount based on the calculated ratio value.

Further, according to the present invention (claim 5), in the reference change amount storage means 125,
Storing a set of a given reference change amount A and a reference change amount B in which the value of the embedding target color component has the same sign and the value of the color component other than the embedding target color component has the opposite sign;
In the watermark pattern changing means 110,
Watermark pattern block dividing means for dividing a watermark pattern into blocks of a given size to generate a watermark pattern block group;
An in-block average change amount calculating means for calculating an average change amount that is an average value of the embedding target color components in each watermark pattern block;
Referring to the reference change amount storage means 125, the ratio α of the absolute values of the embedding target color component values of the reference change amount A and the reference change amount B is calculated, and the pixel area having the same size as the watermark pattern block is represented by the area ratio α. : Find the embedding target component value per pixel in the pixel area when the reference change amount A and the reference change amount B are set in (1-α),
Refer to the ratio of the average change amount and the embedding target component value per pixel, and select a change target pixel group in each watermark pattern block based on the value of the ratio,
Dividing the selected pixel group to be changed into pixel groups of group A and group B with a pixel number ratio α: (1-α);
The pixel value of the group A pixel is set to the reference change amount A, the pixel value of the group B pixel is set to the reference change amount B, and other pixel values are set to 0 to generate a changed watermark pattern block group. Density pattern modulation means;
Pattern reconstructing means for reconstructing a modified watermark pattern block group and outputting a modified watermark pattern.

Further, according to the present invention (claim 6), in the reference change amount storage means 125,
A plurality of combinations of a given reference change amount A and a reference change amount B in which the value of the embedding target color component has the same sign and the values of the color components other than the embedding target color component are opposite signs are stored.
With reference to the reference change amount storage means 125, the ratio α of the absolute values of the embedding target color component values of the reference change amount A and the reference change amount B in each set is calculated, and pixels having the same size as the watermark pattern block Means for determining, for each set, an embedding target component value per pixel in a pixel region when the region is set to the reference change amount A and the reference change amount B with an area ratio α: (1−α);
Means for selecting one set of the reference change amount A and the reference change amount B of the reference change amount storage means based on the value of the embedding target component value per pixel of each set as the average change amount;
Means for calculating a ratio between the average change amount and the selected embedding target component value per pixel;
Means for selecting a pixel group to be changed in each watermark pattern block based on the calculated ratio value;
Means for dividing the pixel group to be changed into pixel groups of group A and group B with a pixel number ratio α: (1−α) using the ratio α in the selected set;
The pixel value of the group A pixel is set to the selected reference change amount A, the pixel value of the group B pixel is set to the selected reference change amount B, and the other pixel values are set to 0 to change the watermark. Generating a pattern block group.

Further, the present invention (Claim 7) is characterized in that in the watermark pattern changing means 120,
By referring to the reference change amount storage means, the watermark pattern is converted into a pseudo gradation using one or more reference change amount embedding target color component values whose color component values other than the embedding target color components are small. And means for generating a gradation conversion palette pattern,
The reference change amount of the reference change amount storage means is selected based on palette information that is an element value of the palette pattern subjected to gradation conversion corresponding to each pixel of the watermark pattern, and the watermark pattern is determined based on the selected reference change amount. And a means for setting the pixel value to output a changed watermark pattern.

Further, according to the present invention (claim 8), in the reference change amount storage means 125,
Storing a plurality of sets of given reference change amount A and reference change amount B in which the value of the embedding target color component is the same sign and the value of the color component other than the embedding target color component is the opposite sign;
The watermark pattern changing means 120
The ratio α of the absolute values of the embedding target color component values of the reference change amount A and the reference change amount B in each set of the reference change amount storage means is calculated, and the area ratio α :( 1-α) for each set, determine the embedding target component value per pixel in the pixel area when the reference change amount A and the reference change amount B are set.
Watermark pattern gradation conversion means for generating a gradation conversion palette pattern by performing pseudo gradation conversion of the watermark pattern using the embedding target component value per pixel of each set;
Based on palette information which is an element value of the gradation conversion palette pattern corresponding to each pixel of the watermark pattern, a set of reference change amounts in the reference change amount storage unit 125 is selected,
One of the selected reference change amount sets is selected with probability α and the other is selected with probability 1-α, and the watermark value is changed by setting the pixel value of the watermark pattern based on the selected reference change amount value. Pixel value mapping means for outputting a pattern.

  FIG. 2 is a diagram for explaining the principle of the present invention.

The present invention (Claim 9) is a digital watermark embedding method for embedding a digital watermark in a color image,
When an original image and watermark information are input in the watermark pattern generation means, a watermark pattern that generates a watermark pattern representing the amount of change in pixel value given to the original image by embedding the watermark information in the original image Generating step (step 1);
The watermark pattern changing means refers to the reference change amount storage means for storing the reference change amount for each color component of the color system used in the data format of the original image, and the quantum generated when the watermark pattern is superimposed on the original image. A watermark pattern changing step (step 2) for generating a changed watermark pattern by changing the watermark pattern so that an error of the watermark embedding target color component due to conversion is reduced;
The watermark pattern superimposing means performs a watermark pattern superimposing step (step 3) of superimposing the changed watermark pattern on the original image and outputting a watermarked image.

The present invention (Claim 10) is a digital watermark embedding method for embedding a digital watermark in a color image,
When an original image and watermark information are input in the watermark pattern generation means, a watermark pattern that generates a watermark pattern representing the amount of change in pixel value given to the original image by embedding the watermark information in the original image Generation step;
The watermark pattern changing means refers to the reference change amount storage means for storing the reference change amount for each color component of the color system used in the data format of the original image, and the quantum generated when the watermark pattern is superimposed on the original image. A watermark pattern changing step for generating a changed watermark pattern by changing the watermark pattern so that a change amount of a color component other than the color component to be embedded by watermarking is reduced;
The watermark pattern superimposing means performs a watermark pattern superimposing step of superimposing the changed watermark pattern on the original image and outputting a watermarked image.

  As described above, by using the present invention, it is possible to reduce the amount of change in luminance due to minute changes in color components, and to finely control the trade-off balance between image quality degradation and durability using embedding strength. It is possible to implement digital watermark embedding processing that can be appropriately controlled without reversing the relationship between image quality degradation and image quality degradation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Before describing each embodiment, a configuration and processing flow of a digital watermark embedding device common to all embodiments will be described.

  FIG. 3 shows a configuration of a digital watermark embedding apparatus common to the embodiments of the present invention. The digital watermark embedding apparatus 100 shown in FIG. 1 includes a watermark pattern generation unit 110, a watermark pattern change unit 120, and a watermark pattern superimposition unit 130.

  FIG. 4 shows a processing flow of the digital watermark embedding apparatus common to the embodiments of the present invention.

  Step 101) The digital watermark embedding apparatus 100 first generates a watermark pattern based on the watermark information in the watermark pattern generation unit 110 and outputs the generated watermark pattern to the intra-block average change amount calculation unit 122 and the density pattern modulation unit 123. The watermark pattern is made up of three execution columns (ΔR, ΔG, ΔB) having the same size as the pixel size of the original image, and the pixel value change amount given to each pixel of the original image by embedding the digital watermark. This is specified for each RGB component. According to the definition of this watermark pattern, it is obvious that a watermark pattern can be obtained by any digital watermarking method (since the difference image between the pixel after embedding and the original image becomes the watermark pattern, By creating a difference from the original image, a watermark pattern can be obtained by any digital watermark method). Also, for example, Document A (T. Nakamura, H. Ogawa, A. Tomioka, and Y. Takashima, Improved Digital Watermark Robustness against Translation and / or Cropping of an Image Area, IEICE Trans. Fundamentals, Vol. E83-A, No.1, pp. 68-76, January 2000), the amplitude of the watermark pattern is amplified by the watermark strength parameter, and the embedding strength is adaptively changed depending on the image content. It is assumed that all factors that affect the amount of change are also included in the watermark pattern generation unit 110. That is, it is assumed that the watermark pattern generated by the watermark pattern generation unit 110 is a pixel value change amount finally given to the original image in consideration of factors such as watermark strength and adaptive embedding. However, the pixel value change amount represented by the watermark pattern is a real number, that is, the pixel value change amount is directly taken as a real value without being rounded by quantization. For example, when the amount of change in the pixel value of the R component is +0.8, it is actually +1.0 by adding 0.8 to the R component of the original image and rounding off by rounding off. However, this means that the element value of the ΔR component of the watermark pattern remains +0.8.

  Step 102) Next, the watermark pattern changing unit 120 changes the watermark pattern so as to reduce the image quality degradation caused by the quantization rounding performed when the pixel value of the original image is actually changed, and generates a changed watermark pattern. . A specific method of change will be described later.

  Step 103) Finally, the watermark pattern superimposing unit 130 superimposes the changed watermark pattern on the original image to obtain a watermarked image.

  Further, in the embodiment of the present invention, for the sake of simplicity of description, description will be made using a specific digital watermark method as described below.

  As shown in FIG. 5, digital watermarking is performed by subjecting 1-bit watermark information to spread spectrum modulation with a pseudo-random number sequence and changing the Cb component value of each block of the original image with the value of each term of the spread watermark information. Is to be embedded. For this reason, the watermark pattern ΔR, ΔG, ΔB is divided into blocks, and for the elements in the nth block, the value obtained by converting the change amount of the Cb component into the RGB component using the equation (2) (real number) Will be set as an element value.

  In addition, as shown in FIG. 6, the detection of the digital watermark is performed by dividing the detection target image into blocks, obtaining the detection target sequence from the average Cb component value in each block, and using the pseudo random number sequence for spread spectrum demodulation. Then, the bit value of the detected watermark information is determined based on the sign of the correlation value.

  The present invention is not limited to application to the above-described digital watermark method example. For example, a watermark is embedded in each frame of a moving image as in Non-Patent Document 1 described above, or a watermark pattern is not a block but a texture as in Document A, or It does not have to be based on spread spectrum modulation. Further, in the above example, in order to avoid image quality deterioration, the Cb component of the YCbCr color system is embedded, but this can be arbitrarily set as a Cr component or any other color system component. Selectable.

[First Embodiment]
FIG. 7 shows the configuration of the watermark pattern changing unit in the first embodiment of the present invention, and FIG. 8 is a flowchart of the processing of the watermark pattern changing unit in the first embodiment of the present invention. These are the figures for demonstrating the process of the watermark pattern change part in the 1st Embodiment of this invention.

  The watermark pattern changing unit 120 includes a watermark pattern block dividing unit 121, an in-block average change amount calculating unit 122, a density pattern modulating unit 123, a pattern reconstruction unit 124, and an RGB reference change amount storage unit 125. The watermark pattern changing unit 120 receives the watermark pattern from the watermark pattern generating unit 110 and outputs the changed watermark pattern.

  Step 201) The watermark pattern changing unit 120 first divides the watermark pattern input from the watermark pattern generating unit 110 into watermark pattern blocks in the watermark pattern block dividing unit 121. At this time, the block division size may be the same as or different from the block size of the digital watermark method shown in FIGS.

  Step 202) Next, the average change amount calculation unit 122 in block calculates the average change amount of the Cb component in one watermark pattern block. Since the watermark pattern is data representing the change amount of the RGB component in each pixel, the change of the Cb component is obtained by using the expression (1) for the RGB component change amounts Δr, Δg, Δb of each pixel. The quantity Δcb can be determined. By performing this for all the pixels in the block, the average change amount μ (Δcb) can be obtained.

Step 203) Next, the density pattern modulation unit 123 performs density pattern modulation on the watermark pattern block using the RGB reference change amount acquired from the RGB reference change amount storage unit 125 to obtain a changed watermark pattern block. . Specifically, as shown in FIG. 9, when the RGB reference change amount is (Δr ₁ , Δg ₁ , Δb ₁ ), the Cb component change amount Δcb ₁ based on the RGB reference change amount is expressed by the above-described equation. (1) is used, and the ratio of Δcb ₁ to the in-block average change amount μ (Δcb) β = μ (Δcb) / Δcb ₁
Ask for. Here, the RGB reference change amount is Δcb ₁ > 0 and sufficiently large (meaning that it is equal to or more than the pixel value change amount by the strongest digital watermark embedding strength assumed in the digital watermark method). In addition, it is preferable to select a value that reduces the luminance change amount Δy ₁ due to the RGB reference change amount (generated by quantization rounding). For example, in the case of (Δr ₁ , Δg ₁ , Δb ₁ ) = (0, 0, 2), Δcb ₁ = 1.022 and Δy ₁ = 0.228, but (Δr ₁ , Δg ₁ , Δb ₁ ) = (0, −1,5), Δcb ₁ = 2.894 and Δy ₁ = 0.017. If Δcb ₁ = 1.022 can be determined to be too small, or if both Δcb1 can be determined to be sufficiently large, the smaller Δy ₁ is selected, so (Δr ₁ , Δg ₁ , Δb ₁ ) = (0, ₋₁ , 5) should be the RGB reference change amount.

  Next, assuming that the number of pixels in the block is k pixels, the change amount of the block is modulated into a density pattern by selecting βk pixels in the block as change target pixels. As a selection method, there may be various methods such as selecting at random, or attaching 1 to k labels at pixel positions in the block, and selecting pixels labeled up to βk among these.

Next, all the pixels of ΔR, ΔG, and ΔB in the watermark pattern block are once cleared to zero, and the pixel values of the ΔR, ΔG, and ΔB planes at the selected pixel position are set to Δr ₁ , Δ, respectively. It is set to be g ₁ , Δb ₁ , that is, the RGB reference change amount, and is output as a changed watermark pattern block.

  As shown in FIG. 10, βk pixels are selected for each color plane as change locations for the number k of pixels in the block, and the RGB reference change amount corresponds to each color plane of the watermark pattern block. You may make it modulate to a density pattern using a component value.

  Step 204) If the above-described processing of the density pattern modulation unit 123 is performed on all the watermark pattern blocks, the process proceeds to step 205. If not, the process proceeds to step 202.

  Step 205) After the processing from the watermark block average change amount calculation unit 122 to the density pattern modulation unit 123 is applied to all the watermark pattern blocks, the watermark pattern reconstruction unit 124 changes the changed watermark pattern block. A modified watermark pattern is generated and output by replacing each of the groups with the original watermark pattern block.

<Effect of the first embodiment>
In the first embodiment, the pixel value finally output by the digital watermark embedding apparatus is (0, 0, 0), that is, no change, or the RGB reference change amount (Δr ₁ , Δ g ₁ , Δb ₁ ). As described above, since the RGB reference change amount is selected as a small change amount of the luminance component, there is no luminance change in each pixel (when there is no change) or only a slight luminance change (RGB reference change) If the average Cb component is viewed macroscopically for each block, the amount of change in luminance relative to the original image of the watermarked image is small when viewed as the entire image. The product of the changed pixel ratio β based on the RGB reference change amount and the Cb component change amount Δcb ₁ based on the RGB reference change amount, that is,
μ (Δcb) / Δcb ₁ × Δcb ₁ = μ (Δcb)
Thus, the value of the Cb component does not change before and after the watermark pattern change. This ensures that the watermark is embedded and can be detected.

The watermark pattern is modulated into a density pattern in a state before quantization rounding. Accordingly, when the amplitude of the original watermark pattern has fluctuated due to the digital watermark embedding strength or adaptive embedding, the conventional technique changes independently for each pixel.
0.5 / 1.732 ≦ | Δcb | <1.5 / 1.732
In such a Cb component change amount, fluctuations are not expressed due to quantization rounding errors, and all change amounts are the same. However, according to the present embodiment, the average Cb component change amount in the block is finely controlled by the ratio β of changed pixels based on the RGB reference change amount in the block.

Furthermore, according to the present embodiment, an increase in embedding strength corresponds to an increase in the number of changed pixels due to the RGB reference change amount in the block, and since the change amount of the luminance component in the block is βy ₁ , embedding is performed. The change amount of the luminance component is monotonously increasing with respect to the intensity. That is, the reverse phenomenon that the image quality deterioration increases even if the embedding strength is lowered due to the quantization error, which has been a problem in the prior art, does not occur, and the tolerance / image quality trade-off can be appropriately determined.

[Second Embodiment]
This embodiment is the same as the first embodiment described above except for the parts described below.

  FIG. 11 shows the configuration of the watermark pattern changing unit in the second embodiment of the present invention, and FIG. 12 is a flowchart of the processing of the watermark pattern changing unit in the second embodiment of the present invention.

  The watermark pattern changing unit 120 of this embodiment is different from the configuration of the first embodiment in that the RGB reference change amount storage unit 225 stores a plurality of predetermined RGB reference change amounts.

  The operation of the watermark pattern changing unit 120 is the same as that of the first embodiment until the process of calculating the average change amount of the Cb component in each watermark pattern block (step 202) in the intra-block average change amount calculating unit 122. is there.

  Step 301) Next, the density pattern modulation unit 123 selects one of the RGB reference change amounts stored in the RGB reference change amount storage unit 225 depending on the calculated average change amount. The accompanying part is different from the first embodiment.

FIG. 13 shows an example of a method for selecting the RGB reference change amount. Now, it is assumed that n RGB reference change amounts (1) to (n) are prepared. Further, the respective RGB reference change amount with respect to (i), the value _{x 1} associated. At this time, as the subscript of the RGB reference change amount increases, the change amount of the Cb component accompanying the change of the pixel value increases. That is, as the watermark is embedded strongly, _{also, 0 <x 1 <x 2} <... < such that _{x n,} should define a _{x i.} Further, as for each RGB reference change amount (i), it is preferable to select one with a small change amount of the luminance component, as in the first embodiment. In the selection process, the absolute value y of the average change amount of the input Cb component is obtained, and when y is a value in a section where x _j−1 <y ≦ x _j , the j-th RGB reference change amount (j ) Is selected. In the example of FIG. 13, since the input average change amount (black circle in the figure) is x ₁ <y ≦ x ₂ , the RGB reference change amount (2) is selected. Processing after selecting one RGB reference change amount in this way (steps 203 to 205) is the same as that in the first embodiment.

<Effects of Second Embodiment>
In the present embodiment, the RGB reference change amount is selected stepwise in accordance with the average change amount in the watermark block pattern. When there is only one RGB reference change amount as in the first embodiment, when one relatively large change amount is selected based on the assumed maximum pixel value change amount, In order to express a slight change amount, it is possible to change a small number of pixels in the block pattern. However, since the change amount per pixel is large, there is a risk that visual deterioration will increase. there were. In addition, the watermark intensity can be controlled only at a level of the value that the number of changed pixels in the block can take, and fine control cannot be performed especially when the block is small. In contrast, according to the present embodiment, when the average change amount in the watermark block pattern is small, the RGB reference change amount with a small change amount is selected, and when the average change amount is large, the RGB reference change amount with a large change amount is selected. Therefore, improvement in image quality can be expected.

  Furthermore, there is an effect that by switching a plurality of RGB reference change amounts, the watermark strength can be controlled more finely than in the first embodiment.

[Third Embodiment]
FIG. 14 shows the configuration of the watermark pattern changing unit in the third embodiment of the present invention. FIG. 15 shows the flowchart of the processing of the watermark pattern changing unit in the third embodiment of the present invention. These are the figures for demonstrating the process of the watermark pattern change part in the 3rd Embodiment of this invention.

  The watermark pattern changing unit 120 includes a watermark pattern block dividing unit 121, an intra-block average change amount calculating unit 122, a density pattern modulating unit 123, a pattern reconstruction unit 124, and an RGB reference change amount storage unit 325. The RGB reference change amount storage unit 325 according to the present embodiment stores a predetermined set of RGB reference change amount A and RGB reference change amount B.

  The watermark pattern changing unit 120 receives the watermark pattern from the watermark pattern generating unit 110 and outputs the changed watermark pattern.

  Step 401) The watermark pattern changing unit 120 first divides the watermark pattern input from the watermark pattern generating unit 110 into watermark pattern blocks in the watermark pattern block dividing unit 121. The block division size at this time may be the same as or different from the block size of the digital watermark method shown in FIGS. The watermark pattern block dividing unit 121 outputs the watermark pattern block to the intra-block average change amount calculating unit 122 and the density pattern modulating unit 123.

  Step 402) Next, the average change amount calculation unit 122 between blocks calculates the average change amount of the Cb component in one watermark pattern block. Since the watermark pattern is data representing the RGB component change amount in each pixel, the Cb component change amount Δ can be obtained by using the equation (1) for the RGB component change amounts Δr, Δg, Δb of each pixel. cb can be determined. By performing this for all the pixels in the block, the average change amount μ (Δcb) can be obtained.

Next, the density pattern modulation unit 123 performs density pattern modulation on the watermark pattern block using the RGB reference change amount stored in advance in the RGB reference change amount storage unit 325 to obtain a changed watermark pattern block. . Specifically, first, when the RGB reference change amount A is (Δr _A , Δg _A , Δb _A ) and the RGB reference change amount B is (Δr _B , Δg _B , Δb _B ). , Y component changing amount by RGB reference change amount a △ y _a and RGB reference change amount due to B Y component changing amount △ a y _B advance calculated using equation (1), by using the absolute value of the ratio of the two values α
α = │ △ y _A │ / (│ △ y _A │ + │ △ y _B │)
Find it like this. Here, Δy _A and Δy _B are such that the signs are reversed, and the Cb component change amount Δcb _{A by the} RGB reference change amount _A and the Cb component change amount Δcb _B by the RGB reference change amount _B are Assume that a set of RGB reference change amount A and RGB reference change amount B is stored in the RGB reference change amount storage unit 325 in advance so as to have the same sign (positive in the present embodiment). For example, the RGB reference change amount A is (Δr _A , Δg _A , Δb _A ) = (0, 0, 1), and the RGB reference change amount B is (Δr _B , Δg _B , Δb _B ) = Assuming that (−1, 0, 0), Δy _A = 0.114,
Δy _B = −0.299,
Δcb _A = 0.511,
Δcb _B = 0.172
Therefore, this is a set that satisfies the condition.

Step 403) Further, the density pattern modulation unit 123
Δcb _AB = α · Δcb _A + (1-α) · Δcb _B
Ask for. Δcb _AB is a pixel value change using the RGB reference change amount A in the RGB reference change amount storage unit 325 at an area ratio α with respect to the pixels in the block, and an RGB reference change amount at the area ratio (1−α). This is the average Cb component change amount per pixel when the pixel value change is performed using the GB reference change amount B of the storage unit 325. As in the first embodiment, the set of RGB reference change amounts A and B is Δcb _AB > 0 and sufficiently large (the pixel value change amount based on the strongest digital watermark embedding strength assumed in the digital watermark method) It means that the luminance change amounts Δy _A and Δy _B (which are caused by quantization rounding) are reduced by the RGB reference change amount A or B. It is good to do.

Step 404) Next, the concentration pattern modulation unit 123, △ _{cb AB} average change amount and the block mu (△ cb) ratio beta = mu a (△ cb) / △ seek _{cb AB.}

  Step 405) Then, assuming that the number of pixels in the block is k pixels, βk pixels in the block are selected as change target pixels. As a selection method, there may be various methods such as selecting at random, or attaching 1 to k labels at pixel positions in the block, and selecting pixels labeled up to βk among these.

  Step 406) Next, the selected βk change target pixels are divided into two groups, a group A of αβk pixels and a group of (1-α) βk pixels. This division method is also selected at random, or a label of 1... K is previously attached to the pixel position in the block, and whether the j-th pixel position belongs to group A or group B is mapped ( In this block, the number of pixels in group A is αk and the number of pixels in group B is (1−α) k), and this map is used for each of the selected βk change target pixels. There can be various methods such as grouping into group A and group B.

Step 407) Next, the density pattern modulation unit 123 once clears all the pixels of ΔR, ΔG, and ΔB of the watermark pattern block to zero, and ΔR, β at the βk pixel positions selected in Step 406 above. Regarding the pixel values of the ΔG and ΔB planes, those belonging to group A are set to be (Δr _A , Δg _A , Δb _A ), that is, the RGB reference change amount A, and those belonging to group B are (Δr _B , Δg _B , Δb _B ), that is, the RGB reference change amount B is set, and the changed watermark pattern block is output to the pattern reconstruction unit 124.

  Step 408) If the above-described processing of the density pattern modulation unit 123 is applied to all the watermark pattern blocks, the process proceeds to step 409, and if not, the process proceeds to step 404.

  Step 409) The pattern reconstruction unit 124 reconstructs the changed watermark pattern block by replacing it with the corresponding original watermark pattern block, and generates and outputs a modified watermark pattern.

  As shown in FIG. 17, βk pixels for the number k of pixels in the block are selected as changed portions for each color plane, and group A and group B are divided independently for each color plane. The group A pixels and the group B pixels may be set for each color plane using the corresponding component values of the RGB reference change amount A or B stored in the RGB reference change amount storage unit 325. Good.

<Effect of the third embodiment>
In this embodiment, the pixel value finally output from the digital watermark embedding apparatus is (0, 0, 0), that is, no change, but the RGB reference change amount A = (Δr _A , Δg _A , Δb _A ) Or RGB reference change amount B = (Δr _B , Δg _B , Δb _B ). Further, as described above, since according to the RGB reference change amount A △ by y _A and RGB reference change amount B △ y _B are opposite sign, change by changing the RGB reference change amount B by RGB reference change amount A during block When there is a mixture of brightness and brightness, an increase / decrease in luminance can be offset if viewed from a macro viewpoint, not a pixel but a block. As in the present embodiment, the ratio α of the absolute values of Δy _A and Δy _B determines the area ratio of the pixels to be changed by the RGB reference change amount A and the change by the RGB reference change amount B. For example, when viewed macroscopically, the increase or decrease in luminance is completely offset. That is, the change of the unintended luminance component, which is a main cause of the image quality degradation, which has been a problem in the past, can be made zero (macro), which greatly contributes to the reduction of image quality degradation due to digital watermark embedding. In this respect, the present embodiment is superior to the first embodiment.

In addition, since Δcb _B has the same sign as Δcb _A by the RGB reference change amount _A and RGB reference change amount B, the Cb component which is a watermark embedding channel is not canceled out. That is, a digital watermark can be reliably embedded.

  Furthermore, as in the first embodiment, since the watermark embedding level can be controlled by the number of pixels to be changed in the block, the problem of rounding error due to quantization can be avoided, and a more accurate value than in the prior art can be embedded. Fine control is also possible.

[Fourth Embodiment]
This embodiment is the same as the third embodiment except for the parts described below.

  FIG. 18 shows the configuration of the watermark pattern changing unit in the fourth embodiment of the present invention, and FIG. 19 is a flowchart of the processing of the watermark pattern changing unit in the fourth embodiment of the present invention.

  The watermark pattern changing unit 120 according to the present embodiment is different from the third embodiment in that a plurality of RGB reference change amounts A and RGB reference change amounts B are stored in the RGB change amount storage unit 425.

  The watermark pattern changing unit 120 is the same as that of the third embodiment until the process of calculating the average change amount of the Cb component in each watermark pattern block in the intra-block average change amount calculating unit 122 (steps 401 to 404). .

Step 501) In the density pattern modulation unit 123, a plurality of RGB reference change amounts A / B stored in the RGB change amount storage unit 425 depending on the average change amount calculated by the intra-block average change amount calculation unit 122. The part accompanied by the process of selecting one set from the set is different from the third embodiment. FIG. 20 shows an example of a method for selecting a set of RGB reference change amounts. Assume that n sets of RGB reference change amounts A / B are prepared from (1) to (n). Further, it is assumed that a value x _i is associated with each RGB reference change amount A / B (i). At this time, as the subscript of the RGB reference change amount A / B increases, the change amount of the Cb component accompanying the change of the pixel value increases, that is, the watermark is strongly embedded, and 0 <x ₁ <x ₂ <... <x _i is determined so that x _n is satisfied. In addition, for each RGB reference change amount A / B (i), the change amount of the luminance component has the opposite sign and the change amount of the Cb component has the same sign as in the third embodiment. To do. Further, it is desirable that each of the RGB reference change amounts A / B has a small luminance change amount. The absolute value y of the average change amount of the input Cb component is obtained, and when y is a value in a section where x _j−1 <y ≦ x _j , the set RGB reference change amount of the jth RGB reference change amount Select A / B (j). In the example of FIG. 20, since the input average change amount (black circle in the figure) is x ₁ <y ≦ x ₂ , the RGB reference change amount A / B (2) is selected.

  Thus, the processing after selecting one set of RGB reference change amounts is the same as that of the third embodiment.

<Effect of the fourth embodiment>
In the present embodiment, the same effect as that of the second embodiment with respect to the first embodiment can be further added to the effect of the third embodiment. That is, in addition to the effects of the third embodiment, the RGB reference change amount A / B pair is selected stepwise according to the average change amount in the watermark block pattern, so that visual degradation is reduced. It is possible to simultaneously obtain the effect of suppressing and finely controlling the strength.

[Fifth Embodiment]
In the present embodiment, unlike the first to fourth embodiments, not only the watermark pattern based on the block average pixel value but also an arbitrary watermark pattern as shown in FIG. . For example, the present invention can be applied to a digital watermark method such as Document A.

  FIG. 22 shows the configuration of the watermark pattern changing unit in the fifth embodiment of the present invention, and FIG. 23 is a flowchart of the processing of the watermark pattern changing unit in the fifth embodiment of the present invention.

  The watermark pattern changing unit 120 according to the present embodiment includes a watermark pattern gradation converting unit 510, a pixel value mapping unit 520, and an RGB reference change amount storage unit 501 storing one or more predetermined RGB reference change amounts. Composed. The watermark pattern changing unit 120 receives the watermark pattern from the watermark pattern generating unit 110 and outputs the changed watermark pattern. As the plurality of RGB reference change amounts, the one having the small Y component change amount is selected as in the first to fourth embodiments.

Step 601) The watermark pattern changing unit 120 first performs pseudo gradation conversion on the input Cb component change amount of the watermark pattern in the watermark pattern gradation converting unit 510 to obtain a gradation conversion palette pattern. The pseudo gradation level in the watermark pattern gradation conversion unit 510 will be described with reference to FIG. First, for each of the n RGB reference change amounts (i) (i = 1... N) stored in the RGB reference change amount storage unit 501 in advance, the Cb component change amount Δcb _i is expressed by equation (1). And ask. Next, the Cb component change amount x of each pixel value of the watermark pattern (takes a positive or negative value obtained by applying Expression (1) to ΔR, ΔG, ΔB) is expressed as −Δcb _i , 0. , Δcb _i (i = i... N), 2n + 1 values are used to define a mapping to be quantized. Specifically, as shown in FIG. 24, when Cb of the watermark pattern, component change amount x is positive, 0 ≦ x <△ For _cb 1/2 are quantized to _{0, △ cb 1/2 ≦} x < △ in the case of _{cb 1 + △ cb 2/2} , and quantized to △ cb _1, ...,

Quantize to Δcb _i , ...

In the case of, the procedure of quantizing to Δcb _n is performed. The same may be done when x is negative. In this way, the Cb component change amount x of the watermark pattern, which was originally a real value, is mapped to a discrete value of 2n + 1 levels. At this time, if the palette number representing -Δcb _i is [-i], the palette number representing [0] is [0], and the palette number representing Δcb _i is [i], the real value x is [± i] (i = 0,..., n) is mapped to 2n + 1 pieces of palette information.

Using the mapping, pseudo gradation conversion of the watermark pattern is performed to generate a gradation conversion palette pattern. Specifically, as shown in FIG. 25, for example, pseudo gradation conversion using the Floyd-Steinberg error diffusion method is performed. As in the case of well-known binarization, the Cb component change amount of each pixel is replaced with a quantized value by mapping as described above, and an error from the original Cb component change amount generated by the replacement is not changed. Multilevel error diffusion can be performed by the procedure of diffusing to the neighboring pixels of the process. In FIG. 25, since the RGB reference change amount is 1, that is, n = 1, the pseudo gradation expression is performed at the ternary level. Figure 23 (B) black pixels pallet number [-1] in the gradation conversion palette pattern in, that - the △ Cb _1, gray pixels [0], i.e. 0, white images [1], i.e. △ it represents the Cb _1. In this embodiment, the Floyd-Steinberg error diffusion method is used. However, another pseudo gradation expression method such as a systematic dither method may be used.

  Step 602) Next, the image value mapping unit 520 changes each pixel value of the watermark pattern using each palette information of the gradation change palette pattern, and outputs the changed watermark pattern. Processing in the pixel value mapping unit 520 will be described with reference to FIG.

Each element value of the gradation conversion palette pattern is palette information [i] associated with the RGB reference change amount (i) as described above. Therefore, the pixel value mapping unit 520 generates the changed watermark pattern by setting the RGB reference change amount corresponding to each palette information of the gradation conversion palette pattern as the pixel value of the corresponding watermark pattern. At this time, if the palette information is negative, the RGB reference change amount (| _i |) = (Δr _i ) corresponding to the absolute value | _i | of the palette information according to the association between the palette information and the RGB reference change amount. , Δg _i , Δb _i ), the corresponding pixel value of the watermark pattern is set to (−Δr _i , −Δg _i , −Δb _i ). FIG. 26 shows a case where there is only one RGB reference change amount, but processing is performed in the same procedure when there are a plurality of RGB reference change amounts.

<Effect of Fifth Embodiment>
In the present embodiment, the watermark pattern is subjected to pseudo gradation conversion, the quantized value is associated with the RGB reference change amount, and based on this, the changed watermark pattern is obtained. As in the embodiment, the image quality can be improved without causing block distortion that occurs in the case of block-based processing. In particular, it is suitable for a textured watermark pattern as shown in FIG. Further, since each RGB reference change amount is a small change amount of the Y component, the Y component change amount of the changed watermark pattern can be suppressed to be low, so that the image quality can be improved. Further, the amplitude level of the watermark pattern can be expressed finely by the pseudo gradation expression, and fine control of the trade-off balance between image quality degradation and resistance can be performed.

[Sixth Embodiment]
The present embodiment is the same as the fifth embodiment except for the points described below.

  FIG. 27 shows a configuration of a watermark pattern changing unit in the sixth embodiment of the present invention, and FIG. 28 shows a flowchart of processing of the watermark pattern changing unit in the sixth embodiment of the present invention.

  The watermark pattern changing unit 120 in this embodiment includes a watermark pattern gradation converting unit 510, a pixel value mapping unit 520, and one or more predetermined pairs of RGB reference change amount A and RGB reference change amount B. The stored RGB reference change amount storage unit 502 is configured. The watermark pattern changing unit 120 receives the watermark pattern from the watermark pattern generating unit 110 and outputs the changed watermark pattern.

  In the RGB reference change amount storage unit 502, it is assumed that n sets of RGB reference change amounts A / B from (1) to (n) are prepared as in the fourth embodiment. Further, the larger the subscript of the RGB reference change amount A / B, the larger the change amount of the Cb component accompanying the change of the pixel value. That is, it is assumed that the watermark is strongly embedded, and in A and B in each set, the change amount of the luminance component is the opposite sign and the change amount of the Cb component is the same sign.

  Step 701) The watermark pattern changing unit 120 first performs pseudo gradation conversion on the input Cb component change amount of the watermark pattern in the watermark pattern gradation changing unit 510 to obtain a gradation conversion palette pattern.

The pseudo gradation label in the watermark pattern gradation conversion unit 510 will be described with reference to FIG. First, for each set of n predetermined RGB reference change amounts A / B (i) (i = 1... N) stored in the RGB reference change amount storage unit 502, the RGB reference change amount A (i ) Is (Δr _Ai , Δg _Ai , Δb _Ai ), and the RGB reference change amount B (i) is (Δr _Bi , Δg _Bi , Δb _Bi ), the RGB reference change amount A (i ) Y component change amount Δy _Ai and RGB reference change amount B (i) Y component change amount Δy _Bi are obtained using equation (1), and the absolute value of both is used to determine the ratio value αi. ,
αi = │ △ y _Ai │ / (│ △ y _Ai │ + │ △ y _Bi │)
Find it like this.

Step 702) Next, using the Cb component change amount Δcb _Ai based on the RGB reference change amount A (i), the Cb component change amount Δcb _Bi based on the RGB reference change amount B (i), and the α _i thus obtained. ,
Δcb _i = α _i · Δcb _Ai + (1−α _i ) · Δcb _Bi is obtained.

  Step 703) Using this, a gradation conversion palette pattern is generated as in the fifth embodiment.

Step 704) Next, the pixel value mapping unit 520 changes each pixel value of the watermark pattern using each palette information of the gradation conversion palette pattern, and outputs the changed watermark pattern. Processing in the pixel value mapping unit will be described with reference to FIG. Each element value of the gradation conversion palette pattern is palette information [i] associated with the RGB reference change amount A / B (i). Therefore, the pixel value mapping unit 520 generates a changed watermark pattern using the RGB reference change amount A / B corresponding to each palette information of the gradation conversion palette pattern. Specifically, the above-mentioned ratio α _i is regarded as the probability that the RGB reference change amount A (i) is selected, and (1-α _i ) is regarded as the probability that the RGB reference change amount B (i) is selected. The pixel value of i] is set to the RGB reference change amount A (i) or the RGB reference change amount B (i) according to this probability. As shown in FIG. 29, this corresponds to randomly grouping pixel regions having the same palette information into an area ratio α _i : 1−α _i . When the palette information is negative, the changed pixel value is set using the RGB reference change amount A / B (| i |) corresponding to the absolute value | i | of the palette information, as in the fifth embodiment. What is necessary is just to reverse positive / negative.

  In each of the above embodiments, the digital watermark embedding in the Cb component has been described, but it goes without saying that the Cr component may be used. Further, it may be an H component or S component in the HSV display color (in this case, the V (brightness) component is considered to be equivalent to Y in the YcbCr component, and the present invention is applied so as to suppress the change amount of V. do it). The same applies to other color systems.

  In the present embodiment, the case where the data format of the original image is based on the RGB color system has been described, but the present invention is not limited to this. In other words, the present invention is applicable even if the original image data format is based on the YCbCr color system such as JPEG or MPEG, or the HSV color system. In the present embodiment, the case where the data format of the original image is the RGB color system and the digital watermark embedding is performed in the YCbCr color system has been described. However, as in the first, second, and fifth embodiments, the density has been described. When modulating, these two color systems may be the same. Further, when the change amount of the specific color component is canceled as in the third, fourth, and sixth embodiments, the color system of the original image data format and the color system of the digital watermark embedding target color component are different. Any combination is applicable to the present invention.

  Further, in each of the above-described embodiments, the digital watermark to the still image has been described. However, when considering the digital watermark to the moving image as in Non-Patent Document 1, each frame image or field image of the moving image is The present invention may be applied as a still image.

  The operation of each component of the digital watermark embedding device in the above first to sixth embodiments is constructed as a program, installed in a computer used as the digital watermark embedding device, and executed, or a network It is possible to circulate through.

  Further, the constructed program can be stored in a portable storage medium such as a hard disk, a flexible disk, or a CD-ROM, and can be installed or distributed in a computer used as a digital watermark embedding apparatus.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made within the scope of the claims.

  The present invention can be applied to a digital watermark technique used in a content copyright protection / management system, a content-related service providing system, and the like.

It is a principle block diagram of this invention. It is a figure for demonstrating the principle of this invention. It is a block diagram of the digital watermark embedding apparatus common to the embodiments of the present invention. It is a flowchart of a process of the digital watermark embedding apparatus common to the embodiments of the present invention. It is a figure for demonstrating the digital watermark embedding method used for description of this invention. It is a figure for demonstrating the digital watermark detection method used for description of this invention. It is a block diagram of the watermark pattern change part in the 1st Embodiment of this invention. It is a flowchart of the process of the watermark pattern change part in the 1st Embodiment of this invention. It is FIG. (1) for demonstrating the process of the watermark pattern change part in the 1st Embodiment of this invention. It is FIG. (2) for demonstrating the process of the watermark pattern change part in the 1st Embodiment of this invention. It is a block diagram of the watermark pattern change part in the 2nd Embodiment of this invention. It is a flowchart of the process of the watermark pattern change part in the 2nd Embodiment of this invention. It is a figure for demonstrating the selection process of the RGB reference | standard change amount of the density pattern modulation part in the 2nd Embodiment of this invention. It is a block diagram of the watermark pattern change part in the 3rd Embodiment of this invention. It is a flowchart of the process of the watermark pattern change part in the 3rd Embodiment of this invention. It is FIG. (1) for demonstrating the process of the watermark pattern change part in the 3rd Embodiment of this invention. It is FIG. (2) for demonstrating the process of the watermark pattern change part in the 3rd Embodiment of this invention. It is a block diagram of the watermark pattern change part in the 4th Embodiment of this invention. It is a flowchart of the process of the watermark pattern change part in the 4th Embodiment of this invention. It is a figure for demonstrating the selection process of the RGB reference | standard change amount of the density pattern modulation part in the 4th Embodiment of this invention. It is an example of the watermark pattern to which the 5th Embodiment of this invention is applied. It is a block diagram of the watermark pattern change part in the 5th Embodiment of this invention. It is a flowchart of the process of the watermark pattern change part in the 5th Embodiment of this invention. It is FIG. (1) for demonstrating the process of the watermark pattern gradation conversion part in the 5th Embodiment of this invention. It is FIG. (2) for demonstrating the process of the watermark pattern gradation conversion part in the 5th Embodiment of this invention. It is a figure for demonstrating the process of the pixel value mapping part in the 5th Embodiment of this invention. It is a block diagram of the watermark pattern change part in the 6th Embodiment of this invention. It is a flowchart of the process of the watermark pattern change part in the 6th Embodiment of this invention. It is a figure for demonstrating the process of the pixel value mapping part in the 6th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Digital watermark embedding apparatus 110 Watermark pattern production | generation means, Watermark pattern production | generation part 120 Watermark pattern change means, Watermark pattern change part 121 Watermark pattern block division | segmentation part 122 Block average change amount calculation part 123 Density pattern modulation part 124 Pattern reconstruction part 125 Reference change amount storage means, RGB reference change amount storage section 130 Watermark pattern superimposing means, watermark pattern superposition section 225 RGB reference change amount storage section 325 RGB reference change amount storage section 425 RGB reference change amount storage section 501 RGB reference change amount storage section 502 RGB reference change amount storage unit 510 Watermark pattern gradation conversion unit 520 Pixel value mapping unit

Claims (10)

An electronic watermark embedding device for embedding an electronic watermark in a color image,
Reference change amount storage means for storing a reference change amount for each color component of the color system used in the data format of the original image;
When an original image and watermark information are input, a watermark pattern generating means for generating a watermark pattern representing a change amount of a pixel value given to the original image by embedding the watermark information in the original image with the watermark,
With reference to the reference change amount of the reference change amount storage means, the watermark pattern is changed so that the error of the watermark embedding target color component due to quantization generated when the watermark pattern is superimposed on the original image is reduced. Watermark pattern changing means for generating a changed watermark pattern
Watermark pattern superimposing means for superimposing the changed watermark pattern on the original image and outputting a watermarked image;
A digital watermark embedding apparatus comprising: An electronic watermark embedding device for embedding an electronic watermark in a color image,
Reference change amount storage means for storing a reference change amount for each color component of the color system used in the data format of the original image;
When an original image and watermark information are input, a watermark pattern generating unit that generates a watermark pattern representing a change amount of a pixel value given to the original image by embedding the watermark information into the original image, and
With reference to the reference change amount of the reference change amount storage means, the change amount of the color components other than the watermark embedding target color component due to quantization generated when the watermark pattern is superimposed on the original image is reduced. Watermark pattern changing means for generating a changed watermark pattern by changing the watermark pattern;
Watermark pattern superimposing means for superimposing the changed watermark pattern on the original image and outputting a watermarked image;
A digital watermark embedding apparatus comprising: The watermark pattern changing means includes
Pattern block dividing means for dividing the watermark pattern into blocks of a given size to generate a watermark pattern block group;
An in-block average change amount calculating means for calculating an average change amount that is an average value of the embedding target color components in each watermark pattern block;
The ratio between the average change amount and the embedding target color component value of the reference change amount stored in the reference change amount storage means in which the value of the color component other than the embedding target color component is small is calculated, and the calculated ratio Density pattern modulation means for generating a modified watermark pattern block group by performing density modulation on the pixel value of each watermark pattern block using the reference change amount based on the value of
Pattern reconstruction means for reconstructing the modified watermark pattern block group and outputting the modified watermark pattern;
The digital watermark embedding apparatus according to claim 1, comprising: The density pattern modulating means includes
Based on the value of the average change amount, referring to the reference change amount storage unit, means for selecting one of a plurality of reference change amounts having small values of color components other than the embedding target color component;
Means for calculating a ratio between the average change amount and the embedding target color component value of the selected reference change amount;
Means for generating a modified watermark pattern block group by density-modulating the pixel value of each watermark pattern block using the selected reference change amount based on the calculated ratio value;
4. The digital watermark embedding apparatus according to claim 3. The reference change amount storage means includes
Storing a set of a given reference change amount A and a reference change amount B in which the value of the embedding target color component has the same sign and the value of the color component other than the embedding target color component has the opposite sign;
The watermark pattern changing means includes
Watermark pattern block dividing means for dividing the watermark pattern into blocks of a given size to generate a watermark pattern block group;
An in-block average change amount calculating means for calculating an average change amount that is an average value of the embedding target color components in each watermark pattern block;
Referring to the reference change amount storage means, the ratio α of the absolute values of the embedding target color component values of the reference change amount A and the reference change amount B is calculated, and a pixel region having the same size as the watermark pattern block is calculated. An embedding target component value per pixel in the pixel area when the reference change amount A and the reference change amount B are set at an area ratio α: (1−α) is obtained,
Referencing the ratio between the average change amount and the embedding target component value per pixel, and selecting a change target pixel group in each watermark pattern block based on the ratio value;
The selected pixel group to be changed is divided into pixel groups of group A and group B with a pixel number ratio α: (1-α),
The pixel value of the group A pixel is set to the reference change amount A, the pixel value of the group B pixel is set to the reference change amount B, and other pixel values are set to 0 to change the watermark pattern block A density pattern modulating means for generating a group;
Pattern reconstructing means for reconstructing the modified watermark pattern block group and outputting a modified watermark pattern;
The digital watermark embedding apparatus according to claim 1, comprising: The reference change amount storage means includes
A plurality of sets of a given reference change amount A and a reference change amount B in which values of embedding target color components have the same sign and values of color components other than the embedding target color component have opposite signs; ,
Referring to the reference change amount storage means, calculates a ratio α of absolute values of the embedding target color component values of the reference change amount A and the reference change amount B in each set, and has the same size as the watermark pattern block Means for obtaining for each set an embedding target component value per pixel in the pixel area when the pixel area is set to the reference change amount A and the reference change amount B at an area ratio α: (1−α);
Means for selecting one set of reference change amount A and reference change amount B of the reference change amount storage means based on the value of the embedding target component value per pixel of each set for the average change amount;
Means for calculating a ratio between the average change amount and the selected embedding target component value per pixel;
Means for selecting a pixel group to be changed in each watermark pattern block based on the calculated ratio value;
Means for dividing the pixel group to be changed into pixel groups of group A and group B with a pixel number ratio α: (1-α) using the ratio α in the selected set;
The pixel value of the group A pixel is set to the selected reference change amount A, the pixel value of the group B pixel is set to the selected reference change amount B, and the other pixel values are set to 0. Means for generating a modified watermark pattern block group,
The digital watermark embedding apparatus according to claim 5. The watermark pattern changing means includes
With reference to the reference change amount storage means, the watermark pattern is converted into a pseudo gradation using one or more reference change amount embedding target color component values whose color component values other than the embedding target color component are small. Generating a gradation conversion palette pattern by converting
Based on palette information which is an element value of the palette pattern after gradation conversion corresponding to each pixel of the watermark pattern, a reference change amount of the reference change amount storage means is selected, and based on the selected reference change amount Means for setting the pixel value of the watermark pattern and outputting the changed watermark pattern;
The digital watermark embedding apparatus according to claim 1, comprising: The reference change amount storage means includes
Storing a plurality of sets of given reference change amount A and reference change amount B in which the value of the embedding target color component is the same sign and the value of the color component other than the embedding target color component is the opposite sign;
The watermark pattern changing means includes
A ratio α of absolute values of embedding target color component values of the reference change amount A and the reference change amount B in each set of the reference change amount storage means is calculated, and an area of a pixel region having the same size as the watermark pattern block is calculated. The component value to be embedded per pixel in the pixel area when the reference change amount A and the reference change amount B are set at a ratio α: (1−α) is obtained for each set,
Watermark pattern gradation conversion means for generating a gradation conversion palette pattern by performing pseudo gradation conversion on the watermark pattern using the embedding target component value per pixel of each set;
Based on palette information that is an element value of the gradation conversion palette pattern corresponding to each pixel of the watermark pattern, a set of reference change amounts of the reference change amount storage means is selected,
One of the selected reference change amount sets is selected with probability α and the other is selected with probability 1-α, and the watermark value is changed by setting the pixel value of the watermark pattern based on the selected reference change amount value. Pixel value mapping means for outputting a pattern;
The digital watermark embedding apparatus according to claim 1, comprising: An electronic watermark embedding method for embedding an electronic watermark in a color image,
When an original image and watermark information are input in the watermark pattern generation means, a watermark pattern that generates a watermark pattern representing the amount of change in pixel value given to the original image by embedding the watermark information in the original image Generation step;
In the watermark pattern changing means, with reference to the reference change amount storage means for storing the reference change amount for each color component of the color system used in the data format of the original image, when the watermark pattern is superimposed on the original image A watermark pattern changing step for generating a changed watermark pattern by changing the watermark pattern so that an error of a watermark embedding target color component caused by quantization is reduced;
In a watermark pattern superimposing unit, a watermark pattern superimposing step of superimposing the changed watermark pattern on the original image and outputting a watermarked image;
An electronic watermark embedding method comprising: An electronic watermark embedding method for embedding an electronic watermark in a color image,
When an original image and watermark information are input in the watermark pattern generation means, a watermark pattern that generates a watermark pattern representing the amount of change in pixel value given to the original image by embedding the watermark information in the original image Generation step;
In the watermark pattern changing means, with reference to the reference change amount storage means for storing the reference change amount for each color component of the color system used in the data format of the original image, when the watermark pattern is superimposed on the original image A watermark pattern changing step for generating a changed watermark pattern by changing the watermark pattern so that a change amount of a color component other than a watermark embedding target color component by the generated quantization is reduced;
In a watermark pattern superimposing unit, a watermark pattern superimposing step of superimposing the changed watermark pattern on the original image and outputting a watermarked image;
An electronic watermark embedding method comprising: