Embedding strategy and algorithm for image watermarking in DWT domain

Robustness is one of the most basic requirements for invisible image watermarks. Embedding strategy, embedding formula and the watermark strength all affect robustness of watermarks. A new embedding strategy for watermarking is proposed based on DWT domain. Based on the wavelet coefficient distribution and a quantitative analysis on the magnitudes of wavelet coefficients, watermarks should be embedded in the low frequency subband firstly, and the remains of the watermarks should be embedded in high frequency subbands according to the significance of subbands. Different embedding formulae should be applied on the low frequency subband and high frequency subbands respectively. Applying this strategy, an adaptive algorithm incorporating the feature of visual masking of human vision system into watermarking is proposed. The algorithm organizes wavelet coefficients to form wavelet blocks and applies a novel method to classify these wavelet blocks. Watermark components with different strength are inserted into different wavelet coefficients based on the results of classification. The experimental results show that the watermarks generated with the proposed algorithm are invisible and robust against noise and commonly used image processing techniques.