基于变阈值量化误差分散的半调水印算法

Halftone watermarking algorithm by threshold-altered error diffusion

为解决半调(二值)图中直接嵌入水印引起的图像质量下降问题,提出一种基于变阈值量化误差分散的水印算法.通过分析打印-扫描(P-S)过程对图像的影响,得出抵抗P-S过程的半调图应具有绿噪声特性的结论;在构造水印模板和量化阈值变化规则的基础上,充分利用误差分散半调过程嵌入水印.仿真结果表明:在嵌入相同数据量时,该算法较直接嵌入法有更好的水印不可感知性;当图像遭受随机涂改、裁剪、加噪、对比度降低和低通滤波攻击时,仍能够正确提取其中嵌入的水印.

Watermark to be directly embedded into halftone images would degrade the image quality. A new algorithm is proposed via threshold-altered error diffusion. Effects of print and scan （P-S） on the images were analyzed. It is concluded that halftone images to resist P-S process should feather greennoise. The watermark screens and threshold-altered rule were constructed to be embed watermark by using halftone process fully. Experiments show the proposed method has better watermark imperceptibility than that of directly embedding method when equal data was embedded. Watermark can still be extracted correctly when the watermarked halftone is attacked by marking, cropping, noise, lower contrast operation and low-pass filtering.