Robust digital image watermarking based on joint DWT-DCT”, International journal of digital content technology and its applications

In this paper, a new robust digital image watermarking algorithm based on Joint DWT-DCT Transformation is proposed. A binary watermarked logo is scrambled by Arnold cat map and embedded in certain coefficient sets of a 3-level DWT transformed of a host image. Then, DCT transform of each selected DWT sub-band is computed and the PN-sequences of the watermark bits are embedded in the middle frequencies coefficients of the corresponding DCT block. In extraction procedure, the watermarked image, which maybe attacked, is pre-filtered by combination of sharpening and Laplassian of Gaussian filters to increase distinction between host image and watermark information. Subsequently, the same procedures as the embedding process is used to extract the DCT middle frequencies of each sub-band. Finally, correlation between mid-band coefficients and PN-sequences is calculated to determine watermarked bits. Experimental results show that high imperceptibility is provided as well as higher robustness against common signal processing attacks. In compare to current watermarking algorithms which are based on the joint of DWT-DCT, proposed system is achieved significantly higher robustness against enhancement and noise addition attacks