| dc.description.abstract | With explosive growth of the Internet and the development of digital content processing techniques, many valuable digitized materials are distributed and transmitted via the Internet. Various digital media can be embedded data for protecting digital materials from being accessed, duplicated, and modified. Most data-embedding techniques are applied to images. Work on other media is lacking. Recently, 3D models have become more accessible to most end-users in various applications. Thus, 3D models are suitable to serve as host media for various data-embedding purposes.
Most high-capacity, 3D data-hiding schemes introduce irreversible changes into the host models. For artistic or technical models, not modifying the original mesh models is sometimes very important. This dissertation describes two data-hiding schemes to solve this problem for 3D mesh models. The first one is a multi-layer reversible data-hiding scheme in the spatial domain such that the original model can be recovered after the retrieving of the hidden data. The second scheme hides data in the representation domain of 3D models. The vertex and face rearrangement procedures will not cause any distortion on the host model; thus the stego model is identical to the original one.
The first scheme starts with finding an independent set of vertices for embedding data. The prediction residues of the vertices of the independent set and the secret bit string are then encoded using the arithmetic coding method. The embedding procedure is done by substituting part of the mantissa of these vertices with the coded arithmetic decimal numbers. A maximum distortion constraint is set for each embedding vertex, such that the distortion on the cover model is controlled to be imperceptible. Users can construct a multi-layer embedding scheme by repeatedly applying the single-layer embedding procedure until the secret bit string is completely embedded. Experimental results show that the proposed scheme can successfully reconstruct the original model while extracting the secret bit string.
The second scheme embeds messages in triangle meshes by rearranging the vertex and face representation information in the mesh file. The main advantage of embedding messages in the representation domain is that the visual effect of the embedded models is identical to that of the original ones. After rearrangement, the secret messages are embedded in the new indices of vertices and faces of the cover model. The face rearrangement embedding scheme is integrated with a face formation type rearrangement scheme to increase the embedding capacity. The proposed method is robust against transformations such as translation, rotation and uniform resizing. Finally, a security enhancement algorithm is proposed to prevent malicious attackers retrieving the embedded information using a brute force method. Experimental results show that the proposed method is a high-capacity data-hiding approach with no distortion.
In short, this dissertation presents two data-hiding schemes for 3D mesh models. In the spatial domain, the proposed method achieves 4~8 bits/vertex embedding capacity while reserving the ability of rebuilding the original model. Currently, we consider an adaptive maximum distortion control mechanism for a good balance between capacity and distortion. Moreover, we try to develop a more effective way to predict the coordinates of the embedded vertices. In the representation domain, the proposed method can yield an embedding capacity of approximately 3lgn bits/vertex, where n presents the number of vertices. The bit-per-vertex (bpv) embedding capacity increases with the size of the mesh. The embedding capacity is the highest compared to that of other up-to-date 3D embedding schemes.
Future work includes constructing an embedding method which does not attract the attention of malicious users and is applicable to all model types. Many other issues of 3D data processing are also interesting and worth studying. In the future, we will extend our study in the fields of 3D texture mapping, compression, transmission, visualization, skeleton, deformation, animation, etc.
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