Integer-DCT-based reversible image watermarking by adaptive coefficient modification

We investigate in this paper several possible methods to improve the performance of the bit-shifting operation based reversible image watermarking algorithm in the integer DCT domain. In view of the large distortion caused by the modification of high-amplitude coefficients in the integer DCT domain, several coefficient selection methods are proposed to provide the coefficient modification process with some adaptability to match the coefficient amplitudes’ status of different 8-by-8 DCT coefficient blocks. The proposed adaptive modification methods include global coefficient-group distortion sorting, zero-tree DCT prediction, and a low frequency based coefficient prediction method for block classification. All these methods are supposed to optimize the bit-shifting based coefficient modification process so as to improve the watermarking performance in terms of capacity/distortion ratio. Comparisons are presented for these methods in aspects of performance in terms of capacity/distortion ratio, performance stability, performance scalability, algorithm complexity and security. Compared to our old integer DCT based scheme and other recently proposed reversible image watermarking algorithms, some of the proposed methods exhibit much improved performances, among which the low frequency based coefficient prediction methods bear highest efficiency to predict the coefficient amplitudes’ status, leading to distinct improved watermarking performance in most aspects. Detailed experimental results and performance analysis are also given for all the proposed algorithms and several other reversible watermarking algorithms.