Halftone Watermarking Using Multi layer Lookup Strategy

In this work, a halftoning-based multi-layer watermarking of low computational complexity is proposed. An additional data hiding technique is also employed to embed multiple watermarks into the watermark to be embedded to improve the security and embedding capacity. At the encoder, the Efficient Direct Binary Search (EDBS) method is employed to generate 256 reference tables to ensure the output is in halftone format. Subsequently, watermarks are embedded by a set of optimized compressed tables with various textural angles for table lookup. At the decoder, the Least-Mean-Square (LMS) metric is considered to increases the differences among those generated phenotypes of the embedding angles, and reduces the required number of dimensions for each angle.

Finally, the naïve Bayes classifier is employed to collect the possibilities of multi-layer information for classifying the associated angles to extract the embedded watermarks. These decoded watermarks can be further overlapped for retrieving the additional hidden-layer watermarks. Experimental results show that the proposed method only requires 8.4 milliseconds for embedding a watermark into an image of size 512×512, under the platform 32-bit Windows 7 running on 4GB RAM, Intel core i7 Sandy Bridge with 4GB RAM and IDE Visual Studio 2010. Finally, only 2MB is required to store the proposed compressed reference table.