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基于图像块的不可见性与鲁棒性均衡水印算法*

齐向明,高婷(辽宁工程技术大学)

摘 要
目的:为协调水印算法不可见性与鲁棒性之间的矛盾,提出一种基于图像块的不可见性与鲁棒性均衡水印算法。方法:将宿主图像分成互不重叠的图像块,利用人类视觉系统的掩蔽特性对每个块的纹理特征和边缘特征进行分析,提取掩蔽性好的图像块作小波变换,将其低频子带进行奇异值分解,通过修改U矩阵第一列元素间的大小关系嵌入Arnold置乱后的水印信息。在水印提取前,对几何失真的含水印图像利用图像尺度不变特征变换(SIFT)特征点的坐标关系和尺度特征进行几何校正,恢复水印的同步性。结果:对标准灰度图像进行实验,得到的含水印图像的峰值信噪比都能达到44以上,含水印图像受到常规攻击和几何攻击后提取出的水印图像与原始图像的归一化互相关系数大部分都能达到0.99以上,说明该算法不仅具有良好的不可见性,对常见攻击和几何攻击都具有较强的鲁棒性。结论:选择掩蔽性好的图像块作为水印嵌入位置能够充分保证水印算法的不可见性,特别是水印提取前对几何失真含水印图像实现几何校正,提高了含水印图像抵抗几何攻击的能力,较好地协调水印算法不可见性与鲁棒性之间的矛盾。
关键词
A watermarking algorithm with invisible and robust based on image-block

Qi Xiangming,Gao Ting(Liaoning Technical University)

Abstract
Objective: In order to balance the contradiction between invisibility and robustness of the watermarking algorithm , this paper proposed a watermarking algorithm with invisible and robust based on image-block. Method: The host image is divided into non overlapping image-blocks, the texture features and edge features of each block are analyzed by using the masking properties of human visual system and so to extract the image-blocks with good masking property , the singular value decomposition is applied to the low frequency sub-band after the wavelet transform of each selected image-block. By modifying the size relationship of the elements in the first column of the U orthogonal matrix, the watermark image with Arnold scrambling is embedded. Before the watermark extraction, geometric correction of the watermarked image with geometric distortion is realized by coordinate relations and scales features of the scale-invariant feature transform(SIFT) feature points, the approach of geometric correction restores the synchronization of the watermark. Result: Experiments on standard gray scale images, the peak signal to noise ratio values of the obtained watermarked images can reach more than 44, the normalized correlation coefficients between the original watermark image and the extracted watermark image from the watermarked image under conventional attacks and geometric attacks can mostly reach more than 0.99, which shows that this algorithm not only has good invisibility, but also has strong robustness against conventional attacks and geometric attacks. Conclusion: The image-blocks with good masking property are selected to fully ensure the invisibility of the watermarking algorithm. Especially before the watermark extraction, geometric correction is applied on the geometric distorted watermarked image to improve the ability of resisting geometric attacks , which greatly balances the contradiction between invisibility and robustness of the watermarking algorithm.
Keywords
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