结合汉明码和图像矫正的彩色图像盲水印

目的 随着互联网技术的飞速发展，彩色数字图像带来极大便利的同时，也产生了一些篡改、剽窃等侵权行为；同时，几何处理对含水印载体的破坏使水印盲检测的难度增加，因此，本文提出一种基于汉明码和图像矫正的彩色图像盲水印方法，旨在解决当前图像版权保护的难点问题。方法 嵌入水印时，使用仿射变换加密彩色水印，并将已加密的信息编为汉明码，然后利用特征值分解计算出像素块的全部特征值，并通过对特征值绝对值的和进行量化来完成水印的嵌入；提取水印时，利用图像的几何属性对多种几何攻击后的图像进行判断、矫正，并借助量化技术提取水印。结果 基于彩色图像标准数据库，将本文方法与7种相关方法进行了对比实验：在不可见性方面，与LU分解的水印方法相比，本文算法峰值信噪比（peak signal-to-noise ratio，PSNR）提高了4 dB；在常规攻击鲁棒性方面，与Schur分解的最新方法相比，本文算法平均归一化互相关（normalized cross-correlation，NC）的值稍有提高；在几何攻击鲁棒性方面，本文算法NC值具有一定的优势；同时，本文算法的水印容量达到了0.25 bit/像素，密钥空间达到了2⁴³²，运行时间仅需3 s左右。结论 所提方法不仅具有较好的水印不可见性和较强的鲁棒性，而且具有较大的水印容量、较高的安全性和实时性。

Blind color image watermarking method combining Hamming code with image correction

Objective 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 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 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 2⁴³². 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 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.