离散余弦变换数字水印的尺度系数研究

数字水印是一种应用于数字多媒体产品的版权的技术，基于离散余弦变换数字水印是一种鲁棒性较好的方法，在该方法中有一个非常关键的尺度系数，直接决定了水印不可见性的质量．对该系数的取值及其对水印的影响进行研究：首先把需要嵌入水印的图像进行离散余弦变换，然后选择变换后的低频系数作为水印的嵌入位置并将二值化的水印图像放入，最后通过改变尺度系数得到不同的水印图像．对该嵌入不同尺度系数的水印图像进行比较，得出尺度系数的取值范围．实验结果表明，基于离散余弦变换的数字水印嵌入方法在尺度系数小于0．0001时，其水印具有更好的不可见性，从而具有更实际的版权保护意义．

Research on Scale Factor of Digital Watermarking Method Based on DCT

Digital watermarking is one technology used in copyright of digital multimedia products. The ro- bustness of digital watermarking method based on DCT is very good. The scale factor, which is quite impor- tant in the method, directly determines the quality of watermark invisibility. This paper studies the value of this coefficient and its impact on the watermark. Firstly, the original image which needs watermark is trans- formed to DCT image according to DCT. Then, the binary watermark image is embedded to the location de- termined by the low-frequency factor of the Dcr image. At last, different watermarked images can be ob- tained by choosing different values of scale factor. By comparing the watermarked images with different val- ues of scale factor,we get the range of scale factor.The experimental results show that when scale factor is less than 0.0001, the watermark has better invisibility and has more practical significance of copyright pro- tection.