Joint Screening Halftoning and Visual Cryptography for Image Protection

Since digital right management of digital media data has received considerable attention recently, protection of halftone image documents becomes another important topic. Image-based visual cryptography is found to provide an alternative for applications of copyright protection by overlapping more than one secret embedded image to show the hidden information. In this paper, we propose a novel screening halftoning-based visual cryptography method for halftone image protection. Compared with the existing methods, the major contributions of our method contain (i) improved quality of the halftone images and extracted secrets; (ii) unlimited database size of protected halftone images; (iii) more than two halftone images can be overlapped to show the hidden secret; (iv) only one conjugate screen pair in our method is able to achieve the maximum clarity of extracted secrets in random screening. Experimental results and comparisons with a state of the art method demonstrate the effectiveness of our method.