HIGH CONTRAST STOCHASTIC SCREENWATERMARKS FOR COLOR HALFTONE PRINTS

Embedded watermarks in printed halftone images, which can subse-quently be detected using an visual aid or using a watermark detec-tion algorithm on a scan of the image, are of interest in wide range of applications. For black and white halftone printing using stochas-tic screens, digital watermarks that are embedded as correlations in the halftone screen have been previously proposed. Here we present a novel extension of these watermarks to color that produces a high contrast watermark by using the colorant separations coherently with a single watermarked stochastic screen and performing detection co-herently across the color separations. Compared with independent watermarking of the halftone separations, the resulting watermark offers significantly higher contrast in the detected image. Index Terms — color halftones, halftone watermarks, stochastic screens, visual watermarks 1