Watermarking of dither halftoned images

Image watermarking concerns embedding information in images, in a manner that does not affect the visual quality of the image. This paper focusses on watermarking of dither halftone images. The basic idea is to use a sequence of two dither matrices (instead of one) to encode the watermark information. Analysing a specific statistical model of input images, leads to an optimal decoding algorithm in term of the rate-distortion trade-off. Furthermore, we characterize optimal dither matrix pairs (i.e: dither matrix pairs whose use results in the most favorable rate-distortion). Finally, the results are demonstrated in a synthetic example. The example is synthetic in the sense that it does not resort to printing and re-scanning of the image.