Watermarking in dithered halftone images with embeddable cells selection and inverse halftoning

This work proposes a novel technique, named embeddable cells selection (ECS), for embedding flexible amounts of data in a ready-made dithered halftone image, while still achieving good quality results. The encoder embeds the secret data in the high-frequency regions with nearly the same number of black and white pixels and low pixel connections. A blind decoding technique without prior knowledge of the original dithered image but with some side information is adopted in the decoder. The inverse halftoning and the second round of halftoning are the key steps in locating the embedded information bits. Experimental results demonstrate that an objective good quality image with flexible capacity and reasonable complexity is obtained. Moreover, the correct decoding rate of 100% is maintained, and the original host halftone image can also be reconstructed in the decoder. Furthermore, by recording the embedded positions, this method can guard against distortions caused by tampering, cropping, and print-and-scan attacks.