Improved quantization index modulation watermarking robust against amplitude scaling and constant change distortions

The original quantization index modulation watermarking is largely vulnerable to valumetric scaling and constant change attacks. To overcome these two drawbacks, the normalized dither modulation (NDM) is presented in this paper. The main idea of it is to construct a gain-invariant vector with zero mean for quantization. Performance analysis shows that NDM is theoretically invariant to valumetric scaling and constant change and achieves similar performance to dither modulation (DM) in other aspects. Some useful strategies are further provided to improve the performance of NDM. Experiments on real data (images) demonstrate that not only the proposed method is extremely robust to amplitude scaling and constant change, and outperform the original DM subject to several other typical attacks.