Blind Binary Watermarking Method Using Maximum Wavelet Coefficient Quantization of the Third and Fourth Sub-bands

To improve transparency, as an important parameter in watermarking, and maintain robustness, a new quantization coefficient of the third and fourth sub-bands of Discrete Wavelet Transform (DWT) is being proposed. In this method, all coefficients of four-level Haar DWT sub-bands of a host image (HL4, LH4, HL3 and LH3) are divided into different non-overlapping blocks. Then, each block is divided into some sets consisting of several wavelet coefficients as their members. Depending on whether a zero or one needs to be embedded, one or all sets are selected. By quantizing the first and second largest coefficient values in each selected set, a watermark bit is embedded. In decoding stage, the lowest difference between the first and second largest coefficient values in each block is compared with an empirical threshold, in order to estimate the watermark bit. In comparison with other methods, the implementation results show that the proposed method significantly improves transparency, while enhancing the robustness for most attacks. Moreover, the proposed method establishes a trade-off between transparency and robustness by tuning a threshold value in the decoding stage.