A perceptually driven hybrid additive-multiplicative watermarking technique in the wavelet domain

This paper presents a hybrid watermarking technique which mixes additive and multiplicative watermark embedding with emphasis on its robustness versus the imperceptibility of the watermark. The embedding is performed in six wavelet sub-bands using independently three embedding equations and two parameters to modulate the embedding strength for multiplicative and additive embedding. The watermark strength is independently modulated into distinct image areas. Specifically, when a multiplicative embedding is used, the visibility threshold is first reached near the image edges, whereas using an additive embedding technique the visibility threshold is first reached into the smooth areas. A subjective experiment has been used to provide the optimal watermark strength for three distinct embedding equations. Observers were asked to tune the watermark amplitude and to set the strength at the visibility threshold. The experimental results showed that using an hybrid watermarking technique significantly improves the robustness performance. This work is a preliminary study for the design of an optimal wavelet domain Just Noticeable Difference (JND) mask.