A Combination of DWT and QR Decomposition for Color Image Watermarking

Abstract

For the purpose of protecting copyright of digital images, many published articles indicate that combining DWT with matrix decomposition can improve robustness of watermark. In this paper, a hybrid image watermarking scheme is represented by using a combination of 1-level $DWT$ transform and $QR$ decomposition. The first, Haar transform is applied on the channel B of the host color image and $LL$ sub-band is partitioned in $4 \times 4$ non-overlapping blocks. After that, $QR$ factorization is executed on each block where $Q$ matrix and $R$ matrix are calculated separately by our proposal. Watermark bits are embedded into the first element of $R$ matrix instead of the whole row as previous published articles to improve the quality of watermarked image. In addition, the original watermark image is permuted by Arnold transform and it helps the proposed method is more secure. In this study, we also perform experiments to select the most suitable sub-band for embedding information. The experimental results show that this combination gives a better invisibility of watermarked image which is compared to the $QR$ decomposition based approach. Furthermore, the proposed algorithm is more effective to against many common attacks.