Data hiding in halftone images with parity coding

In this paper, we propose a novel halftone image data hiding method called Data Hiding in Block Parity (DHBP), which hides data in the block-sum parity. DHBP assumes that the original multi-tone image is available and the halftoning method is ordered dithering. DHBP can hide a relatively large amount of invisible watermarking data in halftone images while retaining good visual quality. In DHBP, one bit of information is hidden in a block of size MxN by forcing the parity of the sum of the MN pixels to be even or odd according to the data bit to be embedded. To alter the parity, one out of the MN pixels is chosen by minimizing the local image intensity change. Some custom-made quality measures are proposed to evaluate DHBP. Simulation results suggest that DHBP can hide a large amount of data while maintaining good visual quality