A General Watermarking Framework for Optimal Energy Estimation
Rui Liu · Chinese Journal of Computers · 2001
Digital watermarking has been proposed as a solution to the problem of copyright protection of multimedia documents in network environments. Most of the current image watermarking schemes is based on unitary transforms, such as discrete cosine transform, discrete Fourier transform and discrete wavelet transform, etc. In general an effective watermarking scheme should satisfy the following two requirements: imperceptibility and robustness. It can be seen that the two requirements are in fact contrary to each other. For a particular watermarking scheme, we have to consider the trade off between imperceptibility and robustness. Thus how to determine the optimal watermark energy or capacity inserted into the original documents should be solved according to some evaluation criteria (such as the commonly used Peak Signal to Noise Ratio PSNR and Signal to Noise Ratio SNR). In this paper we addressed the issue of how to evaluate the energy and capacity of the inserted watermark. We define the two dimensional discrete unitary transform. Under the assumption of the transform, the digital watermarking is done in the unitary transform domain and the additive watermark embedding model is defined (which is adopted by many current watermarking schemes). Thus, given the permitted threshold of visual quality metrics (especially the most popular measurement PSNR and SNR), we can determine the best energy or capacity to be added to the original image. The estimation formula is given upon the assumption of unitary transforms and additive embedding models. Finally, we discuss two general watermark types (normal Gaussian white noise and binary noise) in our experiments to illustrate the correctness of the theoretical results. From the experimental results, we can see that the theoretical values are consistent with the experiments.