Controllable Image‐Based Transfer of Flow Phenomena

Modelling flow phenomena and their related weathering effects is often cumbersome due their dependence on the environment, materials and geometric properties of objects in the scene. Example‐based modelling provides many advantages for reproducing real textures, but little effort has been devoted to reproducing and transferring complex phenomena. In order to produce realistic flow effects, it is possible to take advantage of the widespread availability of flow images on the Internet, which can be used to gather key information about the flow. In this paper, we present a technique that allows the transfer of flow phenomena between photographs, adapting the flow to the target image and giving the user flexibility and control through specifically tailored parameters. This is done through two types of control curves: a fitted theoretical curve to control the mass of deposited material, and an extended colour map for properly adapting to the target appearance. In addition, our method filters and warps the input flow in order to account for the geometric details of the target surface. This leads to a fast and intuitive approach to easily transfer phenomena between images, providing a set of simple and intuitive parameters to control the process.     

基于GPU加速的锥束CT重建算法研究

锥束计算机断层扫描（Cone-Beam Computed Tomography，CBCT）具有采集速度快和空间分辨率高等特点，被生物医学等领域广泛关注。然而通过CPU串行处理CBCT重建中海量投影数据非常耗时，难以满足实时性的需求。GPU的发展为CBCT重建的并行加速提供了条件。根据三角函数周期性的特点对FDK算法进行了改进，并利用GPU实现了12幅投影数据同时并行计算。实验结果表明，相比于传统基于CPU的重建算法，基于GPU的CBCT重建算法在保证图像质量的前提下，将重建速度提高了超过310倍。     

A high performance crashworthiness simulation system based on GPU

Crashworthiness simulation system is one of the key computer-aided engineering (CAE) tools for the automobile industry and implies two potential conflicting requirements: accuracy and efficiency. A parallel crashworthiness simulation system based on graphics processing unit (GPU) architecture and the explicit finite element (FE) method is developed in this work. Implementation details with compute unified device architecture (CUDA) are considered. The entire parallel simulation system involves a parallel hierarchy-territory contact-searching algorithm (HITA) and a parallel penalty contact force calculation algorithm. Three basic GPU-based parallel strategies are suggested to meet the natural parallelism of the explicit FE algorithm. Two free GPU-based numerical calculation libraries, cuBLAS and Thrust, are introduced to decrease the difficulty of programming. Furthermore, a mixed array and a thread map to element strategy are proposed to improve the performance of the test pairs searching. The outer loop of the nested loop through the mixed array is unrolled to realize parallel searching. An efficient storage strategy based on data sorting is presented to realize data transfer between different hierarchies with coalesced access during the contact pairs searching. A thread map to element pattern is implemented to calculate the penetrations and the penetration forces; a double float atomic operation is used to scatter contact forces. The simulation results of the three different models based on the Intel Core i7-930 and the NVIDIA GeForce GTX 580 demonstrate the precision and efficiency of this developed parallel crashworthiness simulation system.     

Turning a Digital Camera into an Absolute 2D Tele‐Colorimeter

We present a simple and effective technique for absolute colorimetric camera characterization, invariant to changes in exposure/aperture and scene irradiance, suitable in a wide range of applications including image‐based reflectance measurements, spectral pre‐filtering and spectral upsampling for rendering, to improve colour accuracy in high dynamic range imaging. Our method requires a limited number of acquisitions, an off‐the‐shelf target and a commonly available projector, used as a controllable light source, other than the reflected radiance to be known. The characterized camera can be effectively used as a 2D tele‐colorimeter, providing the user with an accurate estimate of the distribution of luminance and chromaticity in a scene, without requiring explicit knowledge of the incident lighting power spectra. We validate the approach by comparing our estimated absolute tristimulus values (XYZ data in ) with the measurements of a professional 2D tele‐colorimeter, for a set of scenes with complex geometry, spatially varying reflectance and light sources with very different spectral power distribution.     

一种新型的工程绘图软件及其开发应用

随着计算机技术的飞速发展，计算机辅助绘图ＣＡＧ已逐步取代传统设计，这就需要选择合适的绘图软件。本文介绍了一种工程绘图软件ＭｉｃｒｏＣＡＤＤＳＧＣＤ。它可构造真正的三维几何模型，其命令结构简单，显示操作灵活，具有开发工具──用户编程语言ＵＰＬ。最后介绍了ＧＣＤ软件在机械工程设计中的应用技巧．     

Real‐Time Modelling of Fibrous Muscle

Relatively recently it has become apparent that providing human kind with a better healthcare requires personalized, predictive and integrative medicine, for which the building of virtual physiological human (VPH) framework accessible via virtual patient avatar is necessary. Real‐time modelling and visual exploration of such a complex avatar is a challenging task. In this paper, we propose a real‐time method for automatic modelling of an arbitrarily large number of muscle fibres in the volume of a muscle represented by its surface mesh. The method is based on an iterative morphing of predefined fibres template into the muscle volume exploiting harmonic scalar field computed on the surface of muscle. Experiments with muscles of thighs and pelvis show that the method produces realistic shapes of fibres. Our sequential VTK‐based C++ implementation is capable of producing 64 fine fibres within a muscle of 10K triangles in less than 170 ms on commodity hardware making the method suitable for VPH purposes as well as for interactive educational medical software.     

Visualization of the Centre of Projection Geometrical Locus in a Single Image

Single view reconstruction (SVR) is an important approach for 3D shape recovery since many non‐existing buildings and scenes are captured in a single image. Historical photographs are often the most precise source for virtual reconstruction of a damaged cultural heritage. In semi‐automated techniques, that are mainly used under practical situations, the user is the one who recognizes and selects constraints to be used. Hence, the veridicality and the accuracy of the final model partially rely on man‐based decisions. We noticed that users, especially non‐expert users such as cultural heritage professionals, usually do not fully understand the SVR process, which is why they have trouble in decision making while modelling. That often fundamentally affects the quality of the final 3D models. Considering the importance of human performance in SVR approaches, in this paper we offer a solution that can be used to reduce the amount of user errors. Specifically, we address the problem of locating the centre of projection (CP). We introduce a tool set for 3D visualization of the CP's geometrical loci that provides the user with a clear idea of how the CP's location is determined. Thanks to this type of visualization, the user becomes aware of the following: (1) the constraint relevant for CP location, (2) the image suitable for SVR, (3) more constraints for CP location required, (4) which constraints should be used for the best match, (5) will additional constraints create a useful redundancy. In order to test our approach and the assumptions it relies on, we compared the amount of user made errors in the standard approaches with the one in which additional visualization is provided.     

Implicit Decals: Interactive Editing of Repetitive Patterns on Surfaces

Texture mapping is an essential component for creating 3D models and is widely used in both the game and the movie industries. Creating texture maps has always been a complex task and existing methods carefully balance flexibility with ease of use. One difficulty in using texturing is the repeated placement of individual textures over larger areas. In this paper, we propose a method which uses decals to place images onto a model. Our method allows the decals to compete for space and to deform as they are being pushed by other decals. A spherical field function is used to determine the position and the size of each decal and the deformation applied to fit the decals. The decals may span multiple objects with heterogeneous representations. Our method does not require an explicit parametrization of the model. As such, varieties of patterns, including repeated patterns like rocks, tiles and scales can be mapped. We have implemented the method using the GPU where placement, size and orientation of thousands of decals are manipulated in real time.     

Self‐similarity for accurate compression of point sampled surfaces

Most surfaces, be it from a fine‐art artifact or a mechanical object, are characterized by a strong self‐similarity. This property finds its source in the natural structures of objects but also in the fabrication processes: regularity of the sculpting technique, or machine tool. In this paper, we propose to exploit the self‐similarity of the underlying shapes for compressing point cloud surfaces which can contain millions of points at a very high precision. Our approach locally resamples the point cloud in order to highlight the self‐similarity of the shape, while remaining consistent with the original shape and the scanner precision. It then uses this self‐similarity to create an ad hoc dictionary on which the local neighborhoods will be sparsely represented, thus allowing for a light‐weight representation of the total surface. We demonstrate the validity of our approach on several point clouds from fine‐arts and mechanical objects, as well as a urban scene. In addition, we show that our approach also achieves a filtering of noise whose magnitude is smaller than the scanner precision.     

基于图形处理器的形态学重建系统

形态学重建是医学图像处理中非常基础和重要的操作。它根据掩膜图像的特征对标记图像反复进行膨胀操作，直到标记图像中的像素值不再变化为止。对于传统基于中央处理器（CPU）的形态学重建系统计算效率不高的问题，提出了使用图形处理器（GPU）来加速形态学重建。首先，设计了适合GPU处理的数据结构：并行堆集群；然后，基于并行堆集群，设计和实现了一套基于GPU的形态学重建系统。实验结果表明，相比传统基于CPU的形态学重建系统，基于GPU的形态学重建系统可以获取超过20倍的加速比。基于GPU的形态学重建系统展示了如何把基于复杂数据结构的软件系统高效地移植到GPU上。