Spread Spectrum based M-ary Modulated Robust Image Watermarking

Spread Spectrum (SS) modulation principle has been widely used in digital watermarking due to its distinguishing characteristics viz. excellent security and robustness in performance. The use of wide spectrum of the host signal in message hiding process puts a limit on the data rate subject to a given embedding distortion. In SS communication the use of M– ary modulation is a popular extension to binary antipodal signaling usually resulting in a significant performance improvement. Moreover, with the increasing M and for certain schemes, M–ary modulation works at the channel capacity. The present work investigates on how to use M–ary modulation in the context of transform domain SS watermarking for performance improvement over binary signaling schemes. Furthermore, relevant computational complexity issue of M–ary watermarking is also reduced to a greater extent by the implementation of M– ary phase modulation. The present work also suggests data embedding in selected sub bands (DWT) or channels (M–band) of wavelet transform decomposition. Performance improvement of M–ary signaling principle in SS scheme with respect to error rate, complexity and superiority of wavelet domain embedding approach are supported by experimental results against lossy compressions.