Watermark embedding in optimal color direction
Robert Lyons, Alastair M. Reed, John Stach · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2013
To watermark spot color packaging images one modulates available spot color inks to create a watermark signal. By perturbing different combinations of inks one can change the color direction of the watermark signal. In this paper we describe how to calculate the optimal color direction that embeds the maximum signal while keeping the visibility below some specified acceptable value. The optimal color direction depends on the starting color for the image region, the ink density constraints and the definition of the watermark signal. After a description of the general problem of N spot color inks we shall describe two-ink embedding methods and try to find the optimal direction that will maximize robustness at a given visibility. The optimal color direction is usually in a chrominance direction and the resulting ink perturbations change the luminosity very little. We compare the optimal color embedder to a single-color embedder.