VRML animated model watermarking scheme using geometry and interpolator nodes
Highlights
► We develop a multiple watermarking schemes of VRML animated model. ► Robust watermarking uses the vertex coordinates in geometric node. ► Fragile watermarking uses the position and orientation keyvalues in interpolator node. ► Our scheme is effective for the copyright protection and authentication simultaneously.
Introduction
With the increase in the 3D content market, 3D watermarking has been required for authentication, copyright protection, and illegal copy detection of 3D graphic model, 3D animation model, and CAD models. The 3D animation models, typical one of 3D model types, used in 3D CG/animation movies, 3D computer/mobile games, and 3D characters is defined by moving an object, including meshes, textures, and time movement, in 3D space. In particular, the 3D keyframe animation method is widely used to implement real 3D animation in 3D graphics. We address the management of authentication and copyright protection for the 3D keyframe animation model using the watermarking technique in this journal.
Most conventional 3D watermarking schemes cannot be applied to the 3D keyframe animation model because they are the robust schemes for the 3D polygon mesh [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], 3D NURBS [11], [12], [13], or 3D vector data models [14], [15], [16] and the fragile schemes for the 3D polygonal mesh [17], [18], [19], [20], [21]. Some researchers presented the watermarking scheme for specified animation model such as MPEG-4 facial animation [22], [23], MPEG-4 XMT(eXtensible MPEG-4 Textual Format) scene [24], [25], 3D skinning mesh animations [26]. The 3D mesh sequence in [10] comes from vertex animation with identical connectivity. This scheme cannot extract the watermark if the vertex coordinates and connectivity in each frame are not known or if the sequence is consisted of meshes with different time intervals.
In this study, we focused on a watermarking scheme for the 3D animation model that uses only the primitive data of the model, such as the vertex coordinates and the movement information; this animation model is based on VRML [27] and MPEG-4 BIFS (binary format for scenes) [28], [29]. This 3D animation model consists of a hierarchical transform of the nodes of objects. The transform node has geometric nodes that are vertex coordinates and the connectivity of an object and interpolator node to represent the moving properties for the position, orientation, scalar, and color as an object changes with respect to time. The interpolator node registers keyvalues of important frames and generates rest frames using the registered keyvalues. The registered frame is called the keyframe, and the time for each keyframe is called the keytime. The keyvalue is the value of the moving properties in each keyframe. The interpolator node is sensitive to changes in the geometric and timeline attacks. Therefore, the 3D animation model can be managed by both authentication and copyright protection because the watermark can be embedded in a robust way into geometric nodes and in a fragile way into interpolator nodes.
3D animation watermarking must consider various editing functions or attacks from 3D editing tools such as 3ds-max and Maya. The editing functions are categorized as geometric, topologic and timeline attacks. A geometric attack changes or deforms geometrically the shape of a 3D animation model like a 3D polygon model attack. This attack affects the vertex coordinate in geometry node and the keyvalues in interpolator node. Topologic attacks–such as re-meshing, mesh simplification, and subdivision–change the mesh connectivity. These attacks affect the connectivity and the number of vertices and meshes in the geometry nodes. A timeline attack changes or deforms the movement of time, position, orientation and scaling of the 3D animation model. This attack affects keyvalues and keytimes in interpolator nodes but does not affect the vertex coordinate or mesh object in geometry node because these make up the initial geometry shape.
We have previously presented robust watermarking for the 3D keyframe animation model using geometry node [30] and interpolators [31]. The geometry scheme [30], which is based on 2D projection of vertices, has the good robustness against geometric attack and timeline attack but has not the robustness against mesh simplification and subdivision. The interpolator scheme [31] is not good for robust watermarking since it does not have the robustness to defend against various geometric attacks as well as timeline attacks.
In this paper, we present concurrent robust and fragile watermarking schemes based on geometric properties for copyright protection and position and orientation interpolators for authentication of 3D keyframe animation models. We named a robust geometric watermarking and a fragile interpolator watermarking for the target transform nodes. The former normalizes the vertex coordinates in the geometric node of the target transform node to have a constant average distance and divides the distance range into uniform intervals. The watermark is then embedded robustly into the distribution of distances in each divided ranges. The latter resamples the position and orientation keyvalues in interpolator nodes by linear and slerp interpolations and divides the keytime range into uniform intervals. The watermark is fragilely embedded into the resampled keyvalues in each divided keytime range. From our experimental results, we verified that the geometric watermarking has robustness against various geometric, topologic, and timeline attacks and that the PSNR(Peak signal-to-noise ratio) of the watermarked vertex coordinates is above 35 dB. In addition, we verified that the interpolator watermarking is fragile against the above attacks and that the PSNR of the watermarked keyvalues is above 45 dB.
The rest of this paper is organized as follows. We explain the structure of 3D keyframe animation data and the watermarking schemes for 3D animation model in the next section, while the proposed geometric and interpolator watermarking are in Section 3. We then evaluate the proposed scheme using the experimental results and conclude in Section 5.
Section snippets
Related works
In this section, we explain the structure of the 3D keyframe animation model based on VRML [27] and MPEG-4 BIFS [28], [29], [30]and then discuss the embedding targets in the 3D keyframe animation model and the conventional watermarking schemes.
Proposed 3D animation watermarking
This paper presents a concurrent watermarking scheme for 3D animation models with robust geometric watermarking and fragile interpolator watermarking. The former embeds the robust watermark into the distance distribution of the vertex coordinate in the geometry node. The latter embeds the fragile watermark into the keyvalue gradients in the position and orientation interpolator nodes. Thus, one model has both the robust watermark for copyright protection and the fragile watermark for
Experimental results
In order to evaluate the proposed watermarking scheme, we transformed 3DS-MAX [32] animation models to VRML data and used them to test models. Table 3 shows the number of geometry node, position and orientation node and the number of average vertices per geometry node and the frame number in each test model. As shown in Table 3, each test model has a number of nodes and frames and each geometry node has a number of vertices and meshes. We used bit streams generated by random Gaussian
Conclusions
We pursued two goals in this study, unlike conventional 3D watermarking schemes. The first goal was to develop a watermarking scheme applicable to a 3D animation model. The second was to achieve both authentication and protection performing independently of each other. In general, 3D animation models have a hierarchical structure with a number of transform nodes. Each transform node has a transform matrix, geometry node and interpolator nodes. To achieve both authentication and protection in a
Acknowledgement
This work was supported by the Korea Research Foundation Grant funded by the Korean Government (MEST) (KRF-2010-0016835 and KRF-2010-0016684).
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