PERCEPTUAL WATERMARKS IN THE WAVELET DOMAIN

In a watermarking system, robustness evaluation should be made if invisibility criteria are satisfied. For this purpose, perceptual watermarks are being used to overcome the issue of robustness against invisibility. In the literature, there was proposed a blind spread spectrum technique that uses a per-ceptual mask in the wavelet domain, taking into account the noise sensitivity, texture and the luminance content of all image subbands. In this paper, we describe new techniques proposed by the authors, based on the modifications of this perceptual mask, in order to increase robustness, while still maintaining imperceptibility. Moreover, using the new mask, information is successfully hidden in the lower fre-quency levels, thus increasing the capacity and making the mark more robust to common attacks that affect both high frequencies and low frequencies of the image. A good bal-ance between robustness and invisibility of the watermark is achieved when embedding is made in all detail subbands for all resolution levels, except the coarsest level. We also pre-sent three types of detectors that take advantage of the hier-archical wavelet decomposition. The effectiveness of the new perceptual mask is appreciated by comparison with the former watermarking system. Simulation results show the superiority of the proposed methods. 1