The article addresses the problem of copyright protection for 3D motion-captured data by designing a robust blind watermarking mechanism. The mechanism segments motion capture data and identifies clusters of 3D points per segment. A watermark can be embedded and extracted within these clusters by using a proposed extension of 3D quantization index modulation. The watermarking scheme is blind in nature and the encoded watermarks are shown to be imperceptible, and secure. The resulting hiding capacity has bounds based on cluster size. The watermarks are shown to be robust against attacks such as uniform affine transformations (scaling, rotation, and translation), cropping, reordering, and noise addition. The time complexity for watermark embedding and extraction is estimated as O(nlogn) and O(n2logn), respectively.

Digital watermarking for copyright protection of 3-D meshes cannot be directly applied to point clouds, since we need to derive consistent connectivity information, which might change due to attacks, such as noise addition and cropping. Schemes for point clouds operate only on the geometric data and, hence, are generic and applicable to mesh-based representations of 3-D models. For building generic copyright schemes for 3-D models, this paper presents a robust blind watermarking mechanism for 3-D point-sampled geometry. The basic idea is to find a cluster tree from clusters of 3-D points. Using the cluster tree, watermarks can be embedded and extracted by deriving an order among points at global (intracluster) and local levels (intercluster). The multiple bit watermarks are encoded/decoded inside each cluster based on an extension of the cluster structure-based 3-D quantization index modulation. The encoding mechanism makes the technique robust against uniform affine transformations (rotation, scaling, and transformation), reordering, cropping, simplification, and noise addition attacks. The technique when applied to 3-D meshes also achieves robustness against retriangulation and progressive compression techniques. Customization of the bit-encoding scheme achieves high hiding capacity with embedding rates that are equal to 4 b/point, while maintaining the imperceptibility of the watermark with low distortions. The estimated time complexity isO(nlogn), wherenis the number of 3-D points.

Different compression methods (Jingliang Peng et al., 2005) such as progressive meshes and single refinement mesh compression exist for mesh representation for 3D models and improving them is a challenge. This paper is a step in this direction, where we show that data hiding methods can be used to significantly improve the compression achieved for such methods. 3D meshes are made up of connectivity (edge set E) and geometric (vertices set V) information. The data hiding method should provide a very high embedding rate in order to achieve a desirable compression ratio. This can be modeled mathematically, given 'V points or vertices in 3D space; for a given compression ratio we use 'AT' points and hide rest of the connectivity and geometric information inside it. These points are termed as the encoding points and the encoded information is termed is the compressed information.