Roughness-Adaptive 3D Watermarking of Polygonal Meshes

We present a general method to improve watermark robustness by exploiting the masking effect of surface roughness on watermark visibility, which, to the best of our knowledge, has not been studied in 3D digital watermarking. Our idea is to adapt watermark strength to local surface roughness based on the knowledge that human eyes are less sensitive to changes on a rougher surface patch than those on a smoother surface. We implemented our idea in a modified version of a well known method proposed by Benedens [3]. As an additional contribution, we modified Benedens’s method in two ways to improve its performance. The first improvement led to a blind version of Benedens’s method that no longer requires any key that depends on the surface mesh of the cover 3D object. The second improvement concerned the robustness of bit ‘1’ in the watermark. Experimental results showed that our new method permits to improve watermark robustness by 41% to 56% as compared to the original Benedens’s method. Further analyses indicated that the average watermark strength by our roughness-adaptive method was larger than that by the original Benedens’s method while ensuring watermark imperceptibility. This was the main reason for the improvement in robustness observed in our experiments. We conclude that exploiting the masking property of human vision is a viable way to improve the robustness of 3D watermarks in general, and therefore could be applied to other 3D digital watermarking techniques.