High-capacity reversible watermarking for 2D vector data
Michael Voigt, Bian Yang, Christoph Busch · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2005
We propose a reversible embedding watermarking algorithm for georeferenced 2D-vectordata which provides a promising solution to GIS (geographic information system) data hiding and authentication applications with a high requirement of fidelity or bit-by-bit exactness with the original point coordinates. The proposed scheme uses an 8-point integer DCT-transform to exploit the high correlation among neighboring coordinates in the same polygon. There exist two kinds of distributions of DCT-coefficients where the typical one shows energy concentration in the low frequency range while in the other case the highest frequency coefficient holds the maximum DCT-coefficient. In the first step of our scheme a distinction between these two cases has to be done. For this discrimination the DCT-coefficient of the highest frequency is compared with the coefficients of the lower frequency range. Only for the typical cases the information is embedded. This is accomplished with a bit-shift procedure where the DCT-coefficients of certain frequencies are shifted by one or two bits. The watermarking information is embedded in the resulting gaps. The frequencies are lying in the range not being used for the discrimination task of step one. Depending on a key there is an alternating sequence of shifts by one ore two bits.