Dual Watermarking Scheme via Sub-Sampling in WPT-SVD Domain

In this paper, a dual watermarking scheme based on wavelet packet transform(WPT), singular value decomposition (SVD) and sub-sampling is presented. After dividing original image into four sub-sample images, two sub-images are selected by taking into consideration of block variance singular analysis (BVSA). Then two watermarks are embedded in the selected subimages. First watermark is embedded into one of the selected sub-image by modifying the singular values. For second watermark embedding, another sub-image is transformed into wavelet packet transform domain and embedding is again done by modifying the singular values of the selected sub-bands. After embedding, modified sub-bands are mapped to their original positions for constructing watermarked sub-image. After both embedding, watermarked image is constructed by inverse sub-sampling. Experimental results show good robustness and security of the proposed scheme. A new measure BVSA is presented, which gives an image block from a set of image blocks, whose mean, standard deviation, entropy, gradient and sum of singular values is greater.