Informed Coded Modulation and Host Rejection Techniques for Color Inkjet Hardcopy Watermarking in the Spatial Domain

This paper proposes improvements on the embedding and the detection watermarking techniques, aiming for improved color hardcopy watermarking using inkjet printers. We investigate informed coding along with a multibit spread spectrum modulation framework for watermarking color images to be deployed as printed media. The proposed approach aims to maximize the watermarking robustness with a modulation approach to achieve high payload with good transparency. At the encoding phase the impact of the color background on the detection metric is evaluated based on estimated color correlation and interference. This correlation is used to estimate and compare the robustness of sets of patterns which would be otherwise considered equivalent for modulating the same message. This allows a proper selection of sequences to be embedded for improved robustness. The detection is further improved by using a proposed whitening filter and a color rejection algorithm. Examples using real life images illustrate the performance enhancement achievable by employing the proposed approaches in color hardcopy watermarking systems.