一种压缩域低灰度平滑块数字水印方案

Digital Watermarking Scheme with Low Luminance Smooth Blocks in Discrete Cosine Transform Domains

针对数字水印信息嵌入位置问题,提出一种在低灰度平滑块中嵌入水印信息的方案.该方案首先对图像做8×8离散余弦变换(DCT),得到量化取整后的DCT块,然后分别按照每个DCT块DC系数的大小,以及AC系数的方差大小对DCT块进行排序,由两个排序序列确定出一定数量的低灰度平滑块,通过修改这些平滑块低频系数的相位来嵌入水印信息,根据这些平滑块的低频系数均值的正负来提取水印信息,实验结果表明,该方案不仅具有较好的不可感知性,而且对于滤波、压缩、噪声具有较强的鲁棒性,对裁减、缩放和直方图均衡等也具有一定的抗攻击性.

Focusing on the problem of the embedding position for digital watermarking, a new digital watermarking scheme is presented in which watermarks can be embedded in low luminance smooth blocks. The low luminance smooth blocks are selected by sorting the 8 × 8 disperse cosine transform （DCT） blocks according to the values of DC coefficients and the variance of AC coefficients, respectively. The watermark is embedded by shifting the phases of a subset with low-frequency coefficients and the watermark extraction can be performed according to the signs of these low-frequency coefficients＇ averages. Experimental results show that the watermarked images look visually identical to the original ones and that the watermarks are robust to low-pass filtering and JPEG compression, and have certain resistance to some operations such as image cropping,scaling and histogram equalizing.