【作者】 孙秋艳；

【导师】 雷仲魁；

【作者基本信息】 南京航空航天大学 ， 通信与信息系统， 2007， 硕士

【摘要】 图像置乱是图像信息隐藏技术的一种有效补充,来源于传统的加密技术,它使置乱后的图像看起来不可辨认,从而达到保护信息的目的,算法的优劣直接影响其安全性及其他处理的效果。基于骑士巡游变换的置乱算法是目前的研究热点,密钥量大,安全性高,但只能隐藏图像的细节。为了克服此缺点,本文讨论了基于骑士巡游变换的改进置乱算法。另外,对多种置乱效果的评价方法进行了分析比较,提出了两种新的置乱度计算公式。本文主要研究成果如下:1.给出了骑士巡游类生矩阵的生成算法。利用巡游类生矩阵进行图像置乱,不但可以隐藏图像中较大的轮廓和边缘,且对整幅图像都有模糊的效果。实验结果表明这是一种可行的算法。2.给出了一种分块分层的置乱算法。块的大小由图像的大小来决定,共分三层。该算法不仅简单易行、置乱效果好,而且对常见的剪裁、加噪、JPEG压缩等图像处理具有较强的稳健性。3.将骑士巡游变换和Arnold变换结合,提出了一种复合置乱算法。图像在此算法下可被充分置乱,象素分布均匀,看起来犹如随机噪声,加密解密速度快。4.在分析现有评价方法特点的基础上,基于Canny算子,提出了一种改进的图像置乱程度衡量公式,该置乱度计算量小,能够从图像的纹理结构上很好地反映置乱效果,且结果不受原图像影响。5.利用DCT系数的良好特性,结合人眼视觉掩蔽特点,提出了一种新的描述图像置乱程度的评价方法。该方法与人的主观评价相接近,能较好地反映同一图像和不同图像的置乱效果。更多还原

【Abstract】 The technology of digital image scrambling is an efficient supplement of image information hiding and it comes from the technology of encrypt. The scrambled image can’t be recognized then the information is protected. The algorithm influences directly the security of digital image and other processing results. The scrambling algorithm based on knight-tour transform is a hot topic because the number of its secret key is large and its security is high. But it can only scramble the details of digital image. This thesis discusses the improved scrambling algorithms based on knight-tour transform to overcome the shortage. In addition, by analyzing and comparing many different methods that are used to evaluate the image scrambling result, two new mathematical formulas are proposed.The major work involved is as follows:1. An algorithm of knight-tour producing matrix is proposed. The image which is scrambled by the producing matrix can not only hide the large contour and edge but also have a whole unclear effect. The results of experiment indicate that it is feasible.2. A block multilayer scrambling algorithm is given. The size of block is decided by the size of image and there are three layers. The algorithm is not only easy to realize and has satisfied scrambling effect but also robust enough to some common image processing such as cropping, noise and JPEG compression etc.3. A composite scrambling algorithm is proposed which is made of knight-tour transform and Arnold transform. The image using the algorithm can be scrambled enough and its pixels distributing is uniform. The scrambled image and random noise image is indistinguishable. Encrypting and decrypting is fast.4. An improved formula based on Canny operator is proposed for accessing the image scrambling degree by analyzing the existing assessments. The method, known as scrambling degree, has little calculating amount, can reflect the scrambling result better from the image texture and its result is not affected by the original image. 5. A novel method is proposed for accessing the image scrambling degree, which utilities the favorable performance of DCT coefficients and the feature of masking of human vision system. The method correlates with subjective assessment and its results can reflect scrambling effect better of the same image and different images.更多还原