Reversible data hiding in dual encrypted halftone images using matrix embedding

Reversible data hiding (RDH) is a data-hiding technique that embeds data into cover media such that it can be recovered distortion-free after the embedded data are retrieved. Currently, for RDH in encrypted halftone images (RDH-EH), the original cover image cannot be recovered once the watermark is extracted. In this paper, we present a RDH method for encrypted halftone images based on matrix embedding, which can achieve a high embedding capacity with low distortion. Since minimal information redundancy exists in encrypted halftone images, perfectly reversible algorithms appear to be difficult to implement. Nevertheless, we proposed a completely reversible RDH method for encrypted halftone images with high embedding capacity. To address the drawback of information redundancy, the pixels of the cover image are copied into two images to guarantee reversibility. The watermark is embedded into the first cover image by changing one pixel of each block using syndrome encoding, and into the second cover image by bit replacement. The experimental results show that the halftone image can be completely recovered after the embedded data are extracted. Furthermore, our algorithm can achieve moderate computational complexity, high embedding capacity and high visual quality of marked images. This scheme is suitable for data-hiding applications such as the medical or printing applications where the reversibility is crucial.