Dither modulation: a new approach to digital watermarking and information embedding

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Abstract
We consider the problem of embedding one signal (e.g., a digital watermark), within another 'host' signal to form a third, 'composite' signal. The embedding must be done in such a way that minimizes distortion between the host signal and composite signal, maximizes the information-embedding rate, and maximizes the robustness of the embedding. In general, these three goals are conflicting, and the embedding process must be designed to efficiently trade-off the three quantities. We propose a new class of embedding methods, which we term quantization index modulation (QIM), and develop a convenient realization of a QIM system that we call dither modulation in which the embedded information modulates a dither signal and the host signal is quantized with an associated dithered quantizer. QIM and dither modulation systems have considerable performance advantages over previously proposed spread-spectrum and low-bit(s) modulation systems in terms of the achievable performance trade-offs among distortion, rate, and robustness of the embedding. We also demonstrate these performance advantages in the context of 'no-key' digital watermarking applications, in which attackers can access watermarks in the clear. We also examine the fundamental limits of digital watermarking from an information theoretic perspective and discuss the achievable limits of QIM and alternative systems.

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