Watermarking in halftone images with noise balance strategy

Two novel and robust methods for embedding watermarks into error‐diffused halftone images are presented in this study. The first method is referred to as Dither‐Referenced Error Diffusion (DREDF), where the proposed Average Ordered Dithering (AOD) is adopted to produce the referenced halftone image. The Noise‐ Balanced Error diffusion (NBEDF) is then applied to embed the watermark. The other method is referred to as Parity‐Matched Error Diffusion (PMEDF). This approach achieves good image quality and capacity as high as 6.25 to 25%. Since the two techniques are blind, the decoder does not need any priori knowledge of the original halftone image or watermark. The capacity of the two approaches is also flexible to accommodate all kinds of applications. As the experimental results demonstrated, both techniques are able to guard against degradation due to cropping, tampering, and the print‐and‐scan process in error‐diffused halftone images. Moreover, both methods have features of low computational complexity, low memory demand, and good image quality. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 202–214, 2010.