Objective

2

With the rapid development of internet technology

color digital image

the carrier of large amounts of information

not only brings great convenience to people

but also brings some infringements such as tampering and plagiarism. Thus

digital watermarking technology was proposed in the last century. Digital watermarking technology can effectively protect copyrights. However

at present

most of the studies on copyright protection of color digital images use non-blind watermarking methods

while blind watermarking methods mainly focus on binary watermarking techniques and gray-scale watermarking ones

which are difficult to meet the needs of copyright protection of color digital images. In addition

in terms of the robustness of color digital image copyright protection methods

most methods can only resist traditional image attacks

while the resistance to geometric attacks is very weak; that is

most algorithms cannot extract the watermark

or the effect of the extracted watermark is poor after some geometric attacks. At the same time

image geometric processing destroys the color watermarked carrier image

which complicates the blind detection of the color digital watermark image. Thus

a blind color image digital watermarking algorithm with a large watermark capacity

high concealment security

and strong robustness needs to be designed. This study proposes a blind color image watermarking method based on Hamming code and image correction

which can effectively solve the above-mentioned problems.

Method

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This algorithm uses the eigenvalue decomposition to obtain all eigenvalues of the pixel block of the host image and quantizes the sum of the absolute values of the eigenvalues to complete the hiding and blind detection of color watermark information. To improve the robustness of the algorithm

the attacks on watermarked images are judged by analyzing the geometric information of the image before extracting the watermark

so as to obtain the attack type of the color watermarked image and correct and restore them accordingly. In detail

when embedding the color watermark

affine transform based on private keys is used to encrypt the color watermark information in order to improve the security of the watermarking algorithm. Each encrypted watermark pixel is converted into an 8-bit binary information bit

and then it is encoded into more robust Hamming codes with the help of Hamming coding theory. Then

eigenvalue decomposition is used to calculate all the eigenvalues of the pixel block in the color carrier image

and the sum of the absolute value of all eigenvalues is quantified to embed the color watermark information. When extracting the color watermark information

the geometric attributes of the color watermarked image are used to judge and correct the watermarked image after various geometric attacks. In the process of judgment

the vertexes of the effective image inside the attacked color watermarked image are first obtained

and then the side and corner information of the effective image is calculated. According to the side and corner information of the effective image

the attack type of the attacked color watermarked image can be obtained. In the process of correction

the parameters of image transformation can be obtained according to the side and corner information of the effective image. Finally

the attacked color watermarked image can be corrected according to the parameters of image transformation and the attack type of the attacked color watermarked image. The extraction process of watermark is the inverse process of watermark embedding process. All the eigenvalues of the pixel block in the color corrected watermarked image are calculated

and the color watermark information is extracted by the proposed quantitative technique. In the recovery process

the extracted watermark information is reconstructed after the processing of the inverse affine transform based on private keys and inverse Hamming coding.

Result

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To accurately and effectively compare the performance of the algorithm

the experiments are compared with seven different methods based on the color standard image database. The simulation results show that the proposed algorithm has better performance in visual imperceptibility

robustness

algorithm security

efficiency

and embedding capacity than other methods. In detail

in terms of invisibility

the peak signal-to-noise ratio (PSNR) is 4 dB higher compared with the watermarking method using LU decomposition. In terms of the conventional robustness

the average normalized cross-correlation (NC) is slightly improved compared with the latest Schur decomposition method. In terms of geometric robustness

such as scaling

rotation

and shearing

the NC has certain advantages. At the same time

the extracted watermarks have good visual effect. In the aspect of watermark capacity

the watermark capacity is greatly improved (up to 0.25 bpp) compared with other anti-geometric attack methods. In terms of security

the watermarking algorithm has strong security; the key space of the proposed method reaches 2

432

. In terms of algorithm efficiency

the running time is greatly improved

which only takes about 3

compared with some watermarking methods that resist geometric attacks.

Conclusion

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Therefore

the experimental data show that the proposed method not only has better watermark invisibility and stronger robustness

but also has larger watermark capacity

higher security

and better real-time performance

which is suitable for the copyright protection of high-security large-capacity color digital images. Future work will focus on the reduction of time complexity of this watermarking algorithm and consider how to apply it in the copyright protection of color digital image in cloud storage.