Joint Image Halftoning and Watermarking in High-Resolution Digital Form

The existing halftone image watermarking methods were proposed to embed a watermark bit in a halftone dot, which corresponds to a pixel, to generate stego halftone image. This one-to-one mapping, however, is not consistent with the one-to-many strategy that is used by current high-resolution devices, such as computer printers and screens, where one pixel is first expanded into many dots and then a halftoning processing is employed to generate a halftone image. Furthermore, electronic paper or smart paper that produces high-resolution digital files cannot be protected by the traditional halftone watermarking methods. In view of these facts, we present a high-resolution halftone watermarking scheme to deal with the aforementioned problems. The characteristics of our scheme include: (i) a high-resolution halftoning process that employs a one-to-many mapping strategy is proposed; (ii) a many-to-one inverse halftoning process is proposed to generate gray-scale images of good quality; and (iii) halftone image watermarking can be directly conducted on gray-scale instead of halftone images to achieve better robustness