Dual watermarking algorithm exploiting the logarithmic characteristic of the Human eye´s sensitivity to luminance

The proposed colour image watermarking algorithm exploits the human visual system to optimise the trade off between the visibility and the robustness of the watermark. A less sensitive colour channel is selected to be watermarked and central watermarking is used to give the algorithm an extra robustness to image cropping. The DWT and DCT transforms are combined to pack the most energy into a few coefficients. The logarithmic sensitivity of the Human eye to luminance is exploited by assigning pixels into groups with different luminance ranges and watermarking them with different insertion powers. Test results show that the proposed algorithm has very good performance and is robust to several common image manipulations.