Watermarking MPEG-4 2-D mesh animation in multiresolution an

Abstract. Although watermarking techniques have been successfully applied to natural images and videos, little progress is made in the area of graphics animation. In particular, the MPEG-4 dynamic 2D mesh that provides efficient coding for animated graphic

Watermarking MPEG-4 2D Mesh Animation in

Multiresolution Analysis

Shih-Hsuan Yang, Chun-Yen Liao, and Chin-Yun Hsieh

Department of Computer Science and Information Engineering

National Taipei University of Technology

1, Sec.3, Chung-Hsiao E. Rd.

Taipei 106, Taiwan

shyang@ntut.edu.tw

Abstract. Although watermarking techniques have been successfully applied to natural images and videos, little progress is made in the area of graphics anima-tion. In particular, the MPEG-4 dynamic 2D mesh that provides efficient cod-ing for animated graphics data imposes several realistic constraints for water-marking. In this paper, we propose a robust watermarking technique for MPEG-4 2D mesh animation. A multiresolution analysis is applied to locate feature motions of the animated mesh. The watermark signal is inserted based on a spread-spectrum approach by perturbing the extracted feature motions. We have also incorporated a spatial-domain registration technique to restore geo-metrically transformed mesh data. A variety of attacks, including the affine transformation, smoothing, enhancement and attenuation, and random noise, are used to verify the robustness of the proposed system. Experimental results show that our watermarks can withstand the aforementioned attacks. We also compare the performance of several common integer-to-integer wavelet trans-forms under the proposed framework.

1. Introduction

In the last decade digital multimedia have proliferated owing to the remarkable growth of PC and Internet. Many content owners, however, are reluctant to offer digi-tal services because their revenues may be jeopardized due to perfect and rapid dis-semination of unprotected digital contents. One of the most promising skills proposed for copyright protection is the digital watermarking, which inserts identifiable but usually imperceptible code into the host media. The embedded watermark remains present and detectable when the media are consumed by users, and therefore can be taken for ownership verification.

A digital watermarking system used for copyright protection should satisfy the fol-lowing requirements [1]:

Transparency. The perceptual degradation introduced by the watermark should be unnoticeable.

Robustness. The embedded watermark should remain identifiable unless the attack has rendered the host data useless.

Abstract. Although watermarking techniques have been successfully applied to natural images and videos, little progress is made in the area of graphics animation. In particular, the MPEG-4 dynamic 2D mesh that provides efficient coding for animated graphic

Security. A watermarking system should be secure in a sense that an unauthorized party is unable to remove the watermark even with full knowledge of the water-marking algorithm.

Adequate complexity. This issue is critical especially for real-time applications. Digital watermarking has been extensively developed for images, videos, and audios, either in the original domain or in the transform domain. Among the trans-formations widely adopted in the literature are the DCT (discrete cosine transform) and the DWT (discrete wavelet transform). Besides the natural image and video data, the synthetic graphics data in terms of the geometric model find many important ap-plications. Two basic attributes, geometry and topology, are associated with a geo-metric model. In addition to its different constituent components, watermarking of graphics data is more intricate since the perceptual model in this domain is little un-derstood. The pioneering work done by Ohbuchi et al. [2] proposes to embed water-marks on geometric or topological primitives including triangle similarity quadruple, tetrahedral volume ratio, and mesh density pattern. Benedens [3] develops a robust watermarking scheme where the watermark is cast on the surface normal distribution of a polygon model. Praun et al. [4] develop a general spread-spectrum robust mesh watermarking scheme where the watermark is superimposed upon the original mesh by a set of surface basis functions. In [5], a spectral analysis that derives from the ei-gen-property of the Kirchhoff matrix is employed for watermarking 3D polygonal meshes. Yin et al. [6] propose to use the Burt-Adelson pyramid to obtain the mul-tiresolution representation of a mesh and embed the watermark information in the co-efficients of a suitable scale. All the above techniques are performed on a single frame of polygon models and may not be adequate to be directly applied to animated graphics. Kim el al. [7] propose a watermarking scheme for the articulated figure, in which the position, orientation, and a rigid transformation of a body segment are specified. They develop a temporal-domain multiresolution framework and insert the watermark by perturbing large detail coefficients. The proposed method is robust against common signal processing and time warping.

In contrast of the former MPEG-1 and MPEG-2 standards that focuses on efficient compression of frame-based natural audio-visual data, the emerging MPEG-4 stan-dard encompasses the synthetic media within an object-based framework [8]. For ex-ample, an MEPG-4 dynamic 2D mesh uses a temporal sequence of 2D triangular meshes to tessellate a 2D visual object plane into triangular patches. The dynamic 2D mesh can be used to create 2D animations by mapping texture onto successive meshes. One such example is shown in Fig. 1, in which the frame is composed of three different objects, namely the fish mesh, the fish texture, and the ‘MPEG-4’ ban-ner.

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