数字图像水印算法研究
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摘要
随着计算机网络技术的飞速发展、公众版权保护意识的增强,数字信息的安全问题越来越重要,数字水印技术应运而生,在数字产品版权保护领域得到越来越多的关注。
本文主要研究了空间域和DCT域的数字图像水印技术。空间域技术是通过修改像素的亮度来实现水印的嵌入,具有简单易行,时效性好的特点。离散余弦变换(DCT)是数字信号处理技术中最常用的线性变换之一,该变换具有良好的能量压缩以及去相关的能力,因此将离散余弦变换应用到数字水印处理的技术中逐渐受到重视。通过研究,本文提出了两种基于空域和一种基于DCT域的数字图像水印算法。
1.提出了两种基于空域的数字水印算法。
利用了将水印能量均匀分布在载体图像的能量上可以提高算法安全性的特性,通过有规律地改变图像像素的数值,实现水印信息的均匀、平滑地嵌入。在嵌入水印前对水印数据进行Arnold变换和混沌加密,增强了水印的抗攻击性能。虽然这是一种明水印算法,提取水印时,需要读取原始图像,但是由于使用了多个密钥,算法的安全性得到了提高。
基于量化嵌入可以实现盲提取以及块均值具有良好的承受攻击的能力的特性,根据各个子块的纹理复杂度选择不同的量化步长,保证了水印的不可感知性。计算图像子块的均值,对每个子块的均值进行量化,每个图像子块的整体数据的改变代表一个水印信息。由于使用了量化的方法,提取水印时不需要原始载体图像的参与。
2.提出了一种基于DCT域的数字水印算法。该算法利用HVS的空间频率特性,选择合适的嵌入区域嵌入水印,并且对于具有不同纹理特性的区域采用不同的嵌入强度,保证了水印的不可感知性。由于经过各种图像处理后,嵌入位置周围参数的变化可能改变图像子块的原有特性,因此计算嵌入位置周围的DCT系数的均值与水印信息之和嵌入相应的位置,增强了水印的鲁棒性。
实验结果表明,本文提出的算法均满足数字图像水印技术不可感知性和鲁棒性的要求。仿真实验中,以有意义的二值图像作为水印信号,结果直观可信。同时,基于均值量化的空域水印算法和基于DCT域的水印算法是盲水印算法,具有一定的实用性。
With the rapid development of computer network technology and the enhancement of public consciousness of copyright protection, the security of digital information becomes very important. The digital watermarking technology emerges as the times require. As an effective method for copyright protection, the digital watermarking technology has acquired more and more attention.
The main task in this paper is focused on digital image watermarking that based on spatial domain and DCT domain. The principle of digital watermarking based on spatial domain algorithms is that, the watermarker is embedded by modifying the pixel, so it is simple and easy. Discrete cosine transform is one of the most common linear transformations in digital signal processing technology. This transformation has good energy compression and the ability to remove correlation. So it is getting more and more attention in watermarking technology. Through the research, two kinds of digital watermarking algorithms based on spatial domain and one based on DCT domain are proposed.
1. Two kinds of digital watermarking algorithms based on spatial domain are brought forward in this paper.
(1)When the watermark energy is distributed uniformly in the energy of the carrier image, the safety of the algorithm will be improved. This characteristic is fully utilized in the first algorithm. The watermark is embedded evenly and smoothly by changing the pixels of the image sub-block regularly. Adding a series of pre-processing including Arnold transform、chaos encryption to watermark data before embedding enhanced the anti-attack performance of watermark. The raw carrier image is needed when extracting the watermark, so it is not a blind watermarking algorithm, but by using multiple keys, the algorithm becomes more safety.
(2)The mean value of sub-block has good ability to withstand the attack, based on that, the second algorithm is proposed. According to the various sub-block texture complexities, quantization step length is selected, so that the requirements of imperceptibility are satisfied. Then, the mean value of the sub-block is calculated and quantified. Each watermark data is represented by the change of the overall data of the sub-block. By using the method of quantization, the blind image watermarking extraction is realized.
2. One kind of digital watermarking algorithm based on frequency domain is presented. Using the spatial frequency characteristics of HVS, appropriate areas are selected for watermark embedding. And each image sub-block which has different texture characteristic is embedded by different strength.
Because of that after several kinds of image processing, the parameters around the embedding positions may be changed; the mean value of the DCT coefficients around it is calculated. The values on the embedding positions are replaced by the sum of the mean value and the value of the watermark, so the robustness of the watermark is enhanced.
In the simulation experiments, gray image is used as carrier image, and a meaningful binary picture used as watermark signal, the result is intuitionistic and believable. Experimental results demonstrate that the three algorithms can satisfy the requirements of imperceptibility and robustness. And the last two algorithms are more practical, because they do not need the original carrier data when extracting the watermark.
本文主要研究了空间域和DCT域的数字图像水印技术。空间域技术是通过修改像素的亮度来实现水印的嵌入,具有简单易行,时效性好的特点。离散余弦变换(DCT)是数字信号处理技术中最常用的线性变换之一,该变换具有良好的能量压缩以及去相关的能力,因此将离散余弦变换应用到数字水印处理的技术中逐渐受到重视。通过研究,本文提出了两种基于空域和一种基于DCT域的数字图像水印算法。
1.提出了两种基于空域的数字水印算法。
利用了将水印能量均匀分布在载体图像的能量上可以提高算法安全性的特性,通过有规律地改变图像像素的数值,实现水印信息的均匀、平滑地嵌入。在嵌入水印前对水印数据进行Arnold变换和混沌加密,增强了水印的抗攻击性能。虽然这是一种明水印算法,提取水印时,需要读取原始图像,但是由于使用了多个密钥,算法的安全性得到了提高。
基于量化嵌入可以实现盲提取以及块均值具有良好的承受攻击的能力的特性,根据各个子块的纹理复杂度选择不同的量化步长,保证了水印的不可感知性。计算图像子块的均值,对每个子块的均值进行量化,每个图像子块的整体数据的改变代表一个水印信息。由于使用了量化的方法,提取水印时不需要原始载体图像的参与。
2.提出了一种基于DCT域的数字水印算法。该算法利用HVS的空间频率特性,选择合适的嵌入区域嵌入水印,并且对于具有不同纹理特性的区域采用不同的嵌入强度,保证了水印的不可感知性。由于经过各种图像处理后,嵌入位置周围参数的变化可能改变图像子块的原有特性,因此计算嵌入位置周围的DCT系数的均值与水印信息之和嵌入相应的位置,增强了水印的鲁棒性。
实验结果表明,本文提出的算法均满足数字图像水印技术不可感知性和鲁棒性的要求。仿真实验中,以有意义的二值图像作为水印信号,结果直观可信。同时,基于均值量化的空域水印算法和基于DCT域的水印算法是盲水印算法,具有一定的实用性。
With the rapid development of computer network technology and the enhancement of public consciousness of copyright protection, the security of digital information becomes very important. The digital watermarking technology emerges as the times require. As an effective method for copyright protection, the digital watermarking technology has acquired more and more attention.
The main task in this paper is focused on digital image watermarking that based on spatial domain and DCT domain. The principle of digital watermarking based on spatial domain algorithms is that, the watermarker is embedded by modifying the pixel, so it is simple and easy. Discrete cosine transform is one of the most common linear transformations in digital signal processing technology. This transformation has good energy compression and the ability to remove correlation. So it is getting more and more attention in watermarking technology. Through the research, two kinds of digital watermarking algorithms based on spatial domain and one based on DCT domain are proposed.
1. Two kinds of digital watermarking algorithms based on spatial domain are brought forward in this paper.
(1)When the watermark energy is distributed uniformly in the energy of the carrier image, the safety of the algorithm will be improved. This characteristic is fully utilized in the first algorithm. The watermark is embedded evenly and smoothly by changing the pixels of the image sub-block regularly. Adding a series of pre-processing including Arnold transform、chaos encryption to watermark data before embedding enhanced the anti-attack performance of watermark. The raw carrier image is needed when extracting the watermark, so it is not a blind watermarking algorithm, but by using multiple keys, the algorithm becomes more safety.
(2)The mean value of sub-block has good ability to withstand the attack, based on that, the second algorithm is proposed. According to the various sub-block texture complexities, quantization step length is selected, so that the requirements of imperceptibility are satisfied. Then, the mean value of the sub-block is calculated and quantified. Each watermark data is represented by the change of the overall data of the sub-block. By using the method of quantization, the blind image watermarking extraction is realized.
2. One kind of digital watermarking algorithm based on frequency domain is presented. Using the spatial frequency characteristics of HVS, appropriate areas are selected for watermark embedding. And each image sub-block which has different texture characteristic is embedded by different strength.
Because of that after several kinds of image processing, the parameters around the embedding positions may be changed; the mean value of the DCT coefficients around it is calculated. The values on the embedding positions are replaced by the sum of the mean value and the value of the watermark, so the robustness of the watermark is enhanced.
In the simulation experiments, gray image is used as carrier image, and a meaningful binary picture used as watermark signal, the result is intuitionistic and believable. Experimental results demonstrate that the three algorithms can satisfy the requirements of imperceptibility and robustness. And the last two algorithms are more practical, because they do not need the original carrier data when extracting the watermark.
引文
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[15]陈曦,田俊峰,杨茂宝.利用HVS特性的DCT数字水印算法[J].软件导刊,2008,7(11):216~217.
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[19]纪震,李慧慧,肖薇薇等.基于混沌序列的数字水印信号研究[J].电子学报,2004,32(7):1131~1134.
[20]张俊萍,谭月辉,梁欣等.Arnold变换的置乱恢复研究[J].军械工程学院学报,2006,18(4):52~55.
[21]丁纬,闫伟奇,齐东旭.基于Arnold变换的数字图像置乱技术[J].计算机辅助设计与图形学学报,2001,13(4):338~341.
[22]孙伟.关于Arnold变换的周期性[J].北方工业大学学报,1999,11(1):29~32.
[23]赵慧.n维Arnold变换及其周期性[J].北方工业大学学报,2002,14(1):21~25.
[24]刘德鹏,蔡翔云,水印图像的混沌置乱算法[J].云南大学学报(自然科学版),2006,28(S1):145～148.
[25]武拴虎,谈正.基于混沌序列的视频图像数字水印隐藏与多分辨检测[J].西安交通大学学报,2000,34(6):35~39.
[26]纪震,肖薇薇,王建华等.基于混沌序列的多重数字图像水印算法[J].计算机学报,2003,23(11):1555~1561.
[27]姚敏.数字图像处理[M].北京:机械工业出版社,2006:22.
[28] Peter Adjei Fordjour Wang Shuozhong. Spatial Domain Technique for Visible Watermarking[J] . JOURNAL OF SHANGHAI UNIVERSITY(ENGLISH EDITION) .2003,7(4):384~388.
[29] Sun Yue,SunHong,Yao TianRen.Blind watermarking scheme for a spatial-domain digital image. JOURNAL OF HUAZHONG UNIVERSITY OF SCIENCE AND TECHNOLOGY(NATURE SCIENCE EDITION),2002,30(2):81~83.
[30]刘宏伟,谢维信,喻建平等.基于人类视觉系统的自适应水印算法[J].上海交通大学学报,2008,42(7):1144~1148.
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[2]吴金海,林福宗.基于数字水印的图像认证技术[J].计算机学报,2004,27(9):1153~1161.
[3]李冠华,赵耀,袁保宗.一种基于局部迭代函数系统的数字水印技术[J].北方交通大学学报,2002,26(1):11~14.
[4]蒋建国,宣曼,齐美彬.数字水印技术的研究现状及进展[J].计算机应用,2006,(26):60~62.
[5]华先胜,石青云.易损数字水印若干问题的研究[J].2001,5(11):1089~1095.
[6]易开祥,孙鑫,王道顺等.一种新的基于图像内容的半易损水印技术[J].系统仿真学报,2000,14(9):1203~1207.
[7]李会方,渠长红,朱波等.基于小波的彩色图象半盲水印算法[J].信息安全与通保密,2007,(3):92~93.
[8] PIVA A,BARNI M,BARTOLINI E,etal.DCT-based Watermark Recovering without Resorting to the Uncorrupted Original Image[J].1997 International Conference on Image Processing (ICIP'97),1997,(1):520~523.
[9]王振夺,李杰.试探数字水印技术的概念、应用及其未来[J].大众科技,2006,(3):50~51.
[10]朱清祥,张蕊.信息隐藏技术的研究与进展[J].中国科技信息,2007,(5):286~287.
[11]石培新,王颖.数字水印技术及其应用和发展[J].微型机与应用,2004,(5):58~60.
[12]陈伟,刘淑英.数字水印技术综述[J].计算机与现代化,2009,(9):96~102.
[13]李华,朱光喜,朱耀庭.一种基于人眼视觉感知模型的数字水印隐藏方法[J].电子学报,2000,28(10):110~113.
[14]曹岭,杨小帆,柏森.一种基于视觉掩盖的数字图像水印技术[J].重庆大学学报,2005,28(6):64~67.
[15]陈曦,田俊峰,杨茂宝.利用HVS特性的DCT数字水印算法[J].软件导刊,2008,7(11):216~217.
[16]李华,朱光喜,朱耀庭.一种基于人眼视觉感知模型的数字水印隐方法[J].电子学报,2000,28(10):108~110.
[17]孟兵,王文惠,周良柱等.信息安全中的数字水印技术[J].信息安全与通信保密,2003,(3):70~74.
[18]王淑琴.数字水印测评标准研究[D].成都:四川大学,2004.
[19]纪震,李慧慧,肖薇薇等.基于混沌序列的数字水印信号研究[J].电子学报,2004,32(7):1131~1134.
[20]张俊萍,谭月辉,梁欣等.Arnold变换的置乱恢复研究[J].军械工程学院学报,2006,18(4):52~55.
[21]丁纬,闫伟奇,齐东旭.基于Arnold变换的数字图像置乱技术[J].计算机辅助设计与图形学学报,2001,13(4):338~341.
[22]孙伟.关于Arnold变换的周期性[J].北方工业大学学报,1999,11(1):29~32.
[23]赵慧.n维Arnold变换及其周期性[J].北方工业大学学报,2002,14(1):21~25.
[24]刘德鹏,蔡翔云,水印图像的混沌置乱算法[J].云南大学学报(自然科学版),2006,28(S1):145～148.
[25]武拴虎,谈正.基于混沌序列的视频图像数字水印隐藏与多分辨检测[J].西安交通大学学报,2000,34(6):35~39.
[26]纪震,肖薇薇,王建华等.基于混沌序列的多重数字图像水印算法[J].计算机学报,2003,23(11):1555~1561.
[27]姚敏.数字图像处理[M].北京:机械工业出版社,2006:22.
[28] Peter Adjei Fordjour Wang Shuozhong. Spatial Domain Technique for Visible Watermarking[J] . JOURNAL OF SHANGHAI UNIVERSITY(ENGLISH EDITION) .2003,7(4):384~388.
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