Grouping strategies for promoting image quality of watermarking on the basis of vector quantization
In this paper, a novel vector quantization (VQ)-based digital image watermarking scheme is proposed which retains high image quality even after embedding. The general scheme of watermarking is to embed a representative digital watermark in the protected image to claim the ownership. The robustness of watermark is important; however, the imperceptibility of embedded images also cannot be ignored. In previous papers, existing greedy technique to group codewords often results in low quality of stego-images. As an improvement to the existing techniques, two new grouping strategies, codebook-sort grouping and bipartite-match grouping are proposed in this paper to improve the quality of stego-images. Moreover, a new VQ encoder, called as shortest-group encoding method is proposed to replace the traditional VQ encoder in the purpose of embedding. Finally, in order to improve the grouping flexibility, two kinds of weights are considered in our approach. Experimental results show that all of the above approaches can improve the quality of stego-images on VQ-based watermarking.
image quality watermarking vector quantization robustness stego-image bipartite-matching copyright protection peak-signal-noise-ratio