Pan Ri-jing

Watermarking T-Spline surfaces

This paper proposes two data embedding algorithms for T-spline surfaces, one is suitable for steganography, and the other for robust shape-preserving watermarking. For steganography, we embed data into the points on T-spline surfaces by using constrained optimization method. For robust shape-preserving watermarking, we use the local knot insertion of T-spline surfaces. The experiment results and their analyses are also presented.

Robust watermarking for T-spline surfaces based on nonuniform B-spline wavelets transformation

T-spline surfaces are widely used in entertainment, engineering, science and medicine. Nonuniform B-spline wavelets transformation is introduced into T-spline surfaces watermarking, and a scheme is proposed for embedding watermarks into T-spline surfaces. In watermark embeding stage, firstly, the points are selected from the standard T-spline surfaces. Secondly, the points are decomposited by nonumiform B-spline wavelets transformation, then the watermarks are embedded into its lower resolution coefficients, and then the watermarked points are obtained by the B-spline wavelets reconstruction. Finally, the watermarked T-spline surfaces are obtained by modifing the T-spline control points. In watermark extracting stage, the same points selection and wavelets decomposition processes are performed to both the original surfaces and the watermarked surfaces, then the watermarks are obtained according to the differences of their lower resolution coefficients. Experimental results show that the proposed scheme is robust against attacks such as translation, rotation, uniform scaling, noise addition, control points modification, weights modification, local knot insertion and control point removal.

A fragile watermarking algorithm for T-Spline surfaces

T-Spline surface is an important parametric surface, which is widely used in entertainment, engineering, science and medicine. A fragile watermarking algorithm is proposed for integrity authentication of T-Spline surfaces. In this algorithm, some points on T-Spline surfaces are selected by a special algorithm, then the watermark is embedded by modifing the selected points, and then the watermarked surfaces is acquired by modifying the control points with constrained optimization method. The experiment results show that the watermark is fragile to many attacks, and the tampered area can be detected. Additionally, when preprocessing is used before watermark extracting, the algorithm can modified to be semi-fragile that is robust to translating, rotating and uniformly scaling.