An improved image watermarking algorithm based on NMF and DWT

In order to solve the shortages of present digital image watermarking algorithm, such as: perceptible quality degradation and the inherent conflict between imperceptibility and robustness. A novel image watermark algorithm based on non-negative matrix factorization (NMF) and discrete wavelet transform (DWT) is proposed in this paper. The processes of watermark embedding include three steps: Firstly, the preprocessing digital image is divided to not overlap image blocks and then decomposable coefficients are obtained by three-level DWT in each image blocks. Secondly, low frequency decomposition coefficients of block images are selected and then approximately represented as a product of a base matrix and a coefficient matrix using NMF. Finally, the feature vector represent original image is obtained by quantizing coefficient matrix, and then the copyright information is embedding by calculating the watermark and feature vector. Simulation results show that the scheme is robust against common signal processing attacks, and sensitive to malignity tamer, meanwhile security of the algorithm is guaranteed by using secret keys.