Printed image watermarking using direct binary search halftoning

A novel framework using direct binary search (DBS) is proposed for printed image watermarking. Watermarks are embedded in the halftone by forcing pairs of pixels to be positively or negatively correlated, halftone image quality and watermark detection are two goals to be jointly maximized, and a modified toggle and swap strategy of DBS is employed to find the optimal halftone. Experiment results are presented for watermark rate (WMR) equal to 4.62%, 9.77%, 27.81%, and 46.73%. Excellent performance is demonstrated, e.g. when the WMR is below 10%, the image quality degradation is negligible, and the error rate (BER) is about 1%.