Visually Encrypted Watermarking for Ordered-Dithered Clustered-Dot Halftones

Abstract

Visual encryption and show through watermarking are widely used techniques to hide secret data in halftone images. The secret watermark can be quickly revealed when the halftone images are printed in transparency and overlaid on each other. The present studies emphasize developing a show-through watermarking technique for the clustered-dot halftone types. The proposed method exploits the properties of various configurations of dither array screens constructed using distinct Gaussian filters to embed watermarks. Two approaches are proposed, i.e., adjacent dither array pairs and the dither array translations. The optimal configuration of dither array parameters is developed to obtain maximum contrast and imperceptibility. Moreover, a new edge screen dithering is proposed to eliminate the edge artifacts, resulting in smooth screen transitions. As efficient ordered dithering is adopted for the watermark embedding, the joint watermarking and halftoning can be performed without additional computations. In comparison to the existing state-of-the-art show-through watermarking techniques, the proposed method can present superior image quality, computational simplicity, and decoded watermarks can be perceived with clear contrast when the images are overlaid with each other.