Data hiding in halftone images by conjugate error diffusion

In this paper, we propose a method called Data Hiding by Conjugate Error Diffusion (DHCED) to hide invisible patterns in two or more error diffused halftone images such that the hidden patterns would appear on the halftone images when they are overlaid. A binary visual pattern is hidden in two halftone images by applying Conjugate Error Diffusion. Simulation results show that the two halftone images have good visual quality, and the hidden pattern is visible when the two halftone images are overlaid. Compared with the old proposed method, Data Hiding by Stochastic Error Diffusion (DHSED), the contrast between the hidden pattern and the background is greatly improved. The minor trace of edge generated by the phase change of DHSED is also eliminated.