Jiaoying Shi

Robust mesh watermarking based on multiresolution processing

Abstract In this paper we propose a new mesh watermarking scheme for triangle meshes, which are widely used in computer graphics systems. Arbitrary meshes lack a natural parameterization for frequency-based signal processing, and thus they are harder to be watermarked. In this paper, we adopt Guskov’s multiresolution signal processing method for meshes and use his 3D non-uniform relaxation operator to construct a Burt–Adelson pyramid for the mesh, and then watermark information is embedded into a suitable coarser mesh. Since all the computation and data structures are the same as those used in the multiresolution signal processing, our mesh watermarking algorithm can be integrated naturally with the multiresolution mesh processing toolbox. To detect watermarks, registration and resampling are needed to bring the attacked mesh model back into its original location, orientation, scale, topology and resolution level. Experimental results and attack analysis are given to show that our watermarking algorithm is robust under a variety of attacks, including vertex reordering, noise addition, simplification, filtering and enhancement, cropping, etc. Our main contribution to the field of 3D watermarking is that we propose a generic applicable multiresolution framework in which other proposed techniques may fit in as well.

Interactive relighting with dynamic BRDFs

We present a technique for interactive relighting in which source radiance, viewing direction, and BRDFs can all be changed on the fly. In handling dynamic BRDFs, our method efficiently accounts for the effects of BRDF modification on the reflectance and incident radiance at a surface point. For reflectance, we develop a BRDF tensor representation that can be factorized into adjustable terms for lighting, viewing, and BRDF parameters. For incident radiance, there exists a non-linear relationship between indirect lighting and BRDFs in a scene, which makes linear light transport frameworks such as PRT unsuitable. To overcome this problem, we introduce precomputed transfer tensors (PTTs) which decompose indirect lighting into precomputable components that are each a function of BRDFs in the scene, and can be rapidly combined at run time to correctly determine incident radiance. We additionally describe a method for efficient handling of high-frequency specular reflections by separating them from the BRDF tensor representation and processing them using precomputed visibility information. With relighting based on PTTs, interactive performance with indirect lighting is demonstrated in applications to BRDF animation and material tuning.

Interactive relighting of dynamic refractive objects

We present a new technique for interactive relighting of dynamic refractive objects with complex material properties. We describe our technique in terms of a rendering pipeline in which each stage runs entirely on the GPU. The rendering pipeline converts surfaces to volumetric data, traces the curved paths of photons as they refract through the volume, and renders arbitrary views of the resulting radiance distribution. Our rendering pipeline is fast enough to permit interactive updates to lighting, materials, geometry, and viewing parameters without any precomputation. Applications of our technique include the visualization of caustics, absorption, and scattering while running physical simulations or while manipulating surfaces in real time.

3D surface filtering using spherical harmonics

Abstract This paper presents a novel approach for 3D surface filtering over two-manifold meshes. A robust spherical parameterization algorithm is proposed to transform the input surface into a spherical vector function/signal. This signal is then decomposed into frequency domain using spherical harmonic transforms. Finally, traditional filtering techniques are generalized to process such spherical signals in either the frequency or spatial domain. Our major contribution is the two-phase spherical parameterization algorithm, which can handle meshes with complex shapes by incorporating local parameterization into the progressive mesh. A number of experimental examples demonstrate the potential of our algorithm.

Virtual learning environment for medical education based on VRML and VTK

Virtual reality (VR) is being applied to a wide range of medical areas, including medical education/training, surgery and diagnostics assistance. In the medical education field, VR opens new realms in the teaching of medicine and creates new effective learning procedures for the students. In contrast with the expensive immersive virtual reality learning environment (VRLE) such as CAVE, ImmersaDesk, virtual reality modeling language (VRML) technology provides a cheap and simple way to create such an environment and can be easily deployed in the classroom. In this paper, we describe some traditional application of VR in medical education and design a prototype of VRLE system based on VRML and visualization toolkit (VTK). The system architecture and module design are described in detail and some results are presented.

Decorating surfaces with bidirectional texture functions

We present a system for decorating arbitrary surfaces with bidirectional texture functions (BTF). Our system generates BTFs in two steps. First, we automatically synthesize a BTF over the target surface from a given BTF sample. Then, we let the user interactively paint BTF patches onto the surface such that the painted patches seamlessly integrate with the background patterns. Our system is based on a patch-based texture synthesis approach known as quilting. We present a graphcut algorithm for BTF synthesis on surfaces and the algorithm works well for a wide variety of BTF samples, including those which present problems for existing algorithms. We also describe a graphcut texture painting algorithm for creating new surface imperfections (e.g., dirt, cracks, scratches) from existing imperfections found in input BTF samples. Using these algorithms, we can decorate surfaces with real-world textures that have spatially-variant reflectance, fine-scale geometry details, and surfaces imperfections. A particularly attractive feature of BTF painting is that it allows us to capture imperfections of real materials and paint them onto geometry models. We demonstrate the effectiveness of our system with examples.

Easybowling: a small bowling machine based on virtual simulation

Abstract In this paper we describe a virtual bowling game machine called EasyBowling Machine, which is designed and implemented based on techniques such as Virtual Reality, animation, and image processing. To introduce Virtual Reality technique into this virtual bowling game, our system provides a real game mode: players play the game by throwing a real bowling ball, and then the EasyBowling system uses a PC Camera to detect the motion of the real bowling ball. After the motion parameters (ball direction, ball force, etc.) are computed, the movement of the bowling ball and its collision with pins are simulated in real-time and the result is displayed on a large display screen. The most obvious advantage of such bowling game machine over other existing bowling games is that the system integrates body exercise into game playing. The implementation techniques are discussed in detail, and the prototype system illustrates the feasibility and efficiency of our method.

Rendering with Spherical Radiance Transport Maps

In this paper, we propose a real‐time method for rendering soft shadows and inter‐reflections of dynamic objects under complex illumination. In previous methods, many efforts were taken to acquire occlusion and reflection informations for dynamic scene on the fly, and the result image cannot be generated in real time. In our approach, these informations for each object are pre‐computed and stored in well‐defined Spherical Radiance Transport Maps (SRTMs). For distant complex illumination such as environment illumination and area light source, we decompose the illumination to several hundred directional lights. In rendering, we search in SRTMs for occlusion info which may cause shadows, and reflection info which may cause inter‐reflections. Finally we produce realistic soft shadows and inter‐reflections efficiently. Our method is related with but different from previous Pre‐computed Radiance Transfer techniques which are only suitable for static scene.

Design and implementation of a large-scale hybrid distributed graphics system

Although modern graphics hardware has strong capability to render millions of triangles within a second, huge scenes are still unable to be rendered in real-time. Lots of parallel and distributed graphics systems are explored to solve this problem. However none of them is built for large-scale graphics applications.We designed AnyGL, a large-scale hybrid distributed graphics system, which consists of four types of logical nodes, Geometry Distributing Node, Geometry Rendering Node, Image Composition Node and Display Node. The first two types of logical nodes are combined to be a sort-first graphics architecture while the others compose images. A new state tracking method based on logical timestamp is also pro-posed for state tracking of large-scale distributed graphics systems. Besides, three classes of compression are employed to reduce the requirement of network bandwidth, including command code compression, geometry compression and image compression. A new extension, global share of textures and display lists, is also implemented in AnyGL to avoid memory explosion in large-scale cluster rendering systems.

A robust algorithm for feature point matching

Abstract Image matching is a key problem of computer vision and frequently used in 3D-model reconstruction, object recognition, image alignment, camera self-calibration and so on. Feature point matching is the most common one among all kinds of image matching. The result of feature point matching is affected greatly by many factors, such as object occlusions, lighting conditions and noises, therefore it is important to find a robust algorithm of feature point matching. In this paper, we extend the method for standard assignment algorithm to solve extended assignment problem and propose a new feature point matching algorithm. It employs the condition that the depth of the scene is local continuous as extra constraint, and uses the method for extended assignment problem to do global optimization. Moreover, this algorithm only needs two optimizations and can be implemented with almost complete matrix computation, so its efficiency is higher than the existing algorithms. Experiments show that the results of the algorithm are satisfactory.