A Differential Expansion Reversible Watermarking Algorithm for Vector Map Based on Virtual Coordinates
Influenced by the limitations of data correlation,the traditional differential expansion technique applied directly to vec-tor data reversible watermarking schemes is prone to lower watermarking capacity and larger data distortion.For vector maps with low vertex correlation,the watermarking effect is even worse.In order to achieve higher watermarking capacity and control data distortion,two improvement methods are proposed for the traditional difference expansion technique.First,the virtual coor-dinates are inserted between vertex coordinates and the coordinate difference is calculated with the virtual coordinates as refer-ence points.Second,the histogram of the calculated coordinate differences is shifted to the left,so that the peak point of the his-togram coincides with the origin.The watermark is embedded in the shifted coordinate difference by the means of difference ex-pansion.The experimental results show that the improved reversible watermarking algorithm has a watermark capacity of 2 bit/vertex,which is at least 6 times of that of the traditional difference expansion.Compared with the traditional difference expan-sion algorithms,the proposed algorithm has less data distortion.The RMSE between the original map coordinates and the wa-termarked map coordinates and the maximum distortion of map coordinates Max-R are both significantly reduced.Moreover,the proposed algorithm is strictly reversible and still works well for watermarking vector maps with low vertex correlation.
万方数据
维普
