Estimation of amplitude modifications before SCS watermark detection

New blind digital watermarking schemes that are optimized for additive white Gaussian noise (AWGN) attacks have been developed by several research groups within the last two years. Currently, the most ef£cient schemes, e.g., the scalar Costa scheme (SCS), involve scalar quantization of the host signal during watermarking embedding and watermark reception. Reliable watermark reception for these schemes is vulnerable to amplitude modi£cation of the attacked host signal. In this paper, a method for the estimation of possible amplitude modi£cations before SCS watermark detection is proposed. The estimation is based on a securely embedded SCS pilot watermark. We focus on linear amplitude modi£cations, but investigate also the extension to nonlinear amplitude modi£cations. Further, the superiority of our proposal over an estimation method based on a spread-spectrum pilot watermark is demonstrated.