A robust public watermark for halftone images
In many printing and publishing applications, it is desirable to embed data in halftone images for copyright control and authentication purposes. While intentional attacks on printed matter may not be likely, unintentional attacks such as cropping and distortion due to dirt or human writing/marking are likely. In this paper, we proposed a novel halftone image watermarking method called Watermarking Error Diffusion (WED) to embed a robust, invisible, public watermark in the parity domain of halftone images during halftoning while introducing minimal distortion. Since WED uses the local stochastic properties of the halftone image to embed the watermark throughout the whole image, WED is robust to cropping and distortion due to dirt or human writing/marking. Experimental results suggest that WED can give halftone images with good visual quality and the watermark is robust to crop and human marking.