D.A. Karras (Greece), R.C. Papademetriou and T. Dimitrakopoulos (UK)
Watermarking, Spread Spectrum Modulation
The goal of this paper is to introduce an integrated approach in using spread spectrum modulation techniques and FEC methodology in modeling low error probability digital image watermarking. The combination of Modulation Schemes, Multiplexing and Multiple Access techniques constitute the stage of channel coding. The approach adopted here is the direct sequence spread spectrum modulation on the frequency domain, but after modulating the digital watermark signal with an analog (simple sinusoidal summation). This modulation is imposed to the watermark in order to enhance its resistance in noisy signal/image transmission environments. It is imposed after application of the Forward Error Correction (FEC-RS) methodology. The paper evaluates the merits of this technique in different SNR ratios concerning binary sequences based watermarks embedded in 2-D images, using the probability of error in the watermark detection as a criterion. The novelty of the proposed approach lies in that while modeling spread spectrum watermarking usually involves embedding a watermark in the spread spectrum of a signal/image, it is herein attempted to improve the robustness of the transform domain watermarking approach by properly modulating the watermark and not the signal/image so that even complete destruction of image blocks, with embedding data bits, will gracefully degrade extracted watermark quality. That is, fault tolerant or noise resistant watermarking modeling is attempted.
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