Interactive rendering of NURBS surfaces

NURBS (Non-uniform rational B-splines) surfaces are one of the most useful primitives employed for high quality modeling in CAD/CAM tools and graphics software. Since direct evaluation of NURBS surfaces on the GPU is a highly complex task, the usual approach for rendering NURBS is to perform the conversion into Bézier surfaces on the CPU, and then evaluate and tessellate them on the GPU. In this paper we present a new proposal for rendering NURBS surfaces directly on the GPU in order to achieve interactive and real-time rendering. Our proposal, Rendering Pipeline for NURBS Surfaces (RPNS), is based on a new primitive KSQuad that uses a regular and flexible processing of NURBS surfaces, while maintaining their main geometric properties to achieve real-time rendering. RPNS performs an efficient adaptive discretization to fine tune the density of primitives needed to avoid cracks and holes in the final image, applying an efficient non-recursive evaluation of the basis function on the GPU. An implementation of RPNS using current GPUs is presented, achieving real-time rendering rates of complex parametric models. Our experimental tests show a performance several orders of magnitude higher than traditional approximations based on NURBS to Bézier conversion.     

Analysis of separating surfaces formed by a random subspace classifier

The discriminating capabilities of a random subspace classifier are considered. As a result of analysis of the probability density distribution of threshold values, an estimate is obtained for the minimum distinguishable distance. Real examples of separating surfaces for classical two-imensional problems are given. An algorithm is proposed for local averaging of a synapse matrix to improve the classifier performance in solving problems with overlapping probability distributions. The random subspace classifier is proved to be universal. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 55–70, November–December 2006.     

Interactive tensor field design and visualization on surfaces

Designing tensor fields in the plane and on surfaces is a necessary task in many graphics applications, such as painterly rendering, pen-and-ink sketching of smooth surfaces, and anisotropic remeshing. In this article, we present an interactive design system that allows a user to create a wide variety of symmetric tensor fields over 3D surfaces either from scratch or by modifying a meaningful input tensor field such as the curvature tensor. Our system converts each user specification into a basis tensor field and combines them with the input field to make an initial tensor field. However, such a field often contains unwanted degenerate points which cannot always be eliminated due to topological constraints of the underlying surface. To reduce the artifacts caused by these degenerate points, our system allows the user to move a degenerate point or to cancel a pair of degenerate points that have opposite tensor indices. These operations provide control over the number and location of the degenerate points in the field. We observe that a tensor field can be locally converted into a vector field so that there is a one-to-one correspondence between the set of degenerate points in the tensor field and the set of singularities in the vector field. This conversion allows us to effectively perform degenerate point pair cancellation and movement by using similar operations for vector fields. In addition, we adapt the image-based flow visualization technique to tensor fields, therefore allowing interactive display of tensor fields on surfaces. We demonstrate the capabilities of our tensor field design system with painterly rendering, pen-and-ink sketching of surfaces, and anisotropic remeshing     

Interactive design of fair hull surfaces using B-splines

Two related techniques for the interactive computer aided design of lines and molded surfaces are presented. The first technique is aimed at lines generation from hull form parameters. The second is aimed at fairing a mathematical surface that is based upon the lines. Both schemes employ B-splines to represent waterlines and stations in the lines drawing. The lines of a modern ship which have been generated by the first method are shown. A new indicator of surface fairness called Euler's net is illustrated. Indications are given of the expected future developments in these continuiing efforts.     

Efficient kinematical simulation of reflection high-energy electron diffraction streak patterns for crystal surfaces

An efficient program with a user-friendly graphical interface has been developed for simulating reflection high-energy electron diffraction patterns obtained on crystal surfaces. The calculations are based on a kinematical approach which considers single electron scattering events at the surface. This time-efficient approach is in most cases sensitive enough for distinguishing different structural models, even if they differ very subtly. The results are presented in realistic two-dimensional density plots which can be directly compared to experimental observations. This program provides a useful tool in studying different structural models for crystal surfaces.

Program summary

Program title: RHEEDsimCatalogue identifier: AEJC_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEJC_v1_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 2752No. of bytes in distributed program, including test data, etc.: 367 205Distribution format: tar.gzProgramming language: Matlab (version > 7.6.0)Computer: Personal ComputersOperating system: Windows with Matlab environmentRAM: Greater than 1 MBClassification: 7.4Nature of problem: Reflection high-energy electron diffraction (RHEED) has been widely used in studying crystal surface structures all over the world, especially in combination with ultra-high vacuum molecular beam epitaxy systems. In addition to determining the surface smoothness, RHEED is also a very useful tool in studying surface reconstructions, which are often encountered at the growth surfaces of semiconductors and alloys. While the positions of the fractional streaks can be used to determine the basic information of the surface supercells, the intensity modulations on the fractional streaks provide further insights on the details within these unit cells. Kinematic approach is an efficient method for simulating the RHEED patterns based on various surface structural models, which can help unraveling the surface atomic structure.Solution method: The kinematic approach utilized here assumes single scattering events. Furthermore, the Ewald sphere is approximated into a planar surface for computing the streak intensities (which are most relevant to real experiments). Structure factors are calculated based on a given input of atomic species and their coordinates, with user modifiable form factors. In addition to the intensity modulation within the surface plane, additional modulations extending into the z direction is also taken into consideration, resulting in realistic density maps of the RHEED streaks, which can be directly compared to experimental observations.Unusual features: The main program RHEEDsim.m calls several local subprograms for certain computational tasks. As a result, all programs should be extracted into a single folder, and that folder should be set as the main directory in Matlab.Running time: The computing time is computer and user parameter dependent, but typically ranges from few seconds to few minutes.     

Interactive rendering of Catmull/Clark surfaces with crease edges

Published online: 23 July 2002     

Interactive modeling of implicit surfaces using a direct visualization approach with signed distance functions

Modeling appealing virtual scenes is an elaborate and time-consuming task, requiring not only training and experience, but also powerful modeling tools providing the desired functionality to the user. In this paper, we describe a modeling approach using signed distance functions as an underlying representation for objects, handling both conventional and complex surface manipulations. Scenes defined by signed distance functions can be stored compactly and rendered directly in real-time using sphere tracing. Hence, we are capable of providing an interactive application with immediate visual feedback for the artist, which is a crucial factor for the modeling process. Moreover, dealing with underlying mathematical operations is not necessary on the user level. We show that fundamental aspects of traditional modeling can be directly transferred to this novel kind of environment, resulting in an intuitive application behavior, and describe modeling operations which naturally benefit from implicit representations. We show modeling examples where signed distance functions are superior to explicit representations, but discuss the limitations of this approach as well.     

Interactive machinability analysis of free-form surfaces using multiple-view image space techniques on the GPU

In this paper we present a set of graphics hardware accelerated algorithms to interactively evaluate the machinability of complex free-form surfaces. These algorithms work in image space and easily interface with all common formats available on CAD systems. The running time of these algorithms is independent of the complexity of the surface to be analyzed and depends only on the size of the projected image of the surface and the largest available tool head. Interactive speed is achieved through clever use of data-parallel techniques that map nicely onto the programming model of modern programmable graphics processing units. We demonstrate a method for pre-calculating and storing the machinability of a surface within a texture to further reduce rendering costs. The algorithms are implemented and tested on a complex set of parts and their performance has been analyzed.     

Rain streak removal by multi-frame-based anisotropic filtering

Dynamic weather conditions, such as rain and snow, often produce strong intensity discontinuity among frames, thus seriously degrade their visual or compression performance. How to remove these artifacts is a challenging task and has been intensively studies recently. The state-of-the-art algorithms detect these scratches before removing them from the scene. Visual effect of rain or snow is complex and difficult to be distinguished from the background; hence the precision of its detection and segmentation by hard decision is usually unsatisfactory. As an anisotropic filter performs well in structural noise removal, such as linear, planar as well as isotropic noise, it is utilized in this paper to analyze image content and suppress scratch noise simultaneously. Compared with the state-of-the-art algorithms, the proposed algorithm is better and more robust in dynamic scenes.     

Towards separating nondeterminism from determinism

The main result of this paper is a separation result: there is a positive integerk such that for all well-behaving functionst(n), there is a language accepted by a nondeterministic (multi-tape) Turing machine in timet(n) which cannot be accepting by any deterministic (multitape) Turing machine in timeO(t(n)) and simultaneously spaceo((t(n)) ^1/k ). This implies, for example that for any positive integer,l,l k, there is a language accepted by an ^l time bounded NDTM which cannot be accepted by a DTM in time and spaceO(n ^l ) andO((logn) ^l ) respectively for anyl. Such a result is not provable by direct diagonalization because we do not have time to simulate and do the opposite". We devise a different method for accomplishing the result: We first use an alternating Turing machine to speed up the simulation of a time and space bounded DTM and then argue that if our separation result did not hold, every NDTM can itself be simulated faster by another NDTM producing a contradiction to the standard hierarchy results. Some other applications of this method are also presented.Supported by NSF Grant No. MCS-8105557     

自然场景图像去雨的可学习混合MAP网络

目的 近年来,人工智能成为新兴研究领域,得到越来越多研究机构的关注。图像恢复问题一直是低层次计算机视觉领域的一个研究热点,其中,图像去雨由于其雨线分布的未知性及其求解的病态性,导致难以解决。现有方法存在雨线和背景之间的估计具有依赖性,难以平衡雨线去除效果与估计背景的清晰程度之间的关系;局限性比较大,训练数据很难涵盖各种场景下的雨图,而测试结果受训练数据的影响,导致难于泛化。针对上述不足,借鉴一般图像恢复问题思路,将模型与以数据驱动的网络相结合,凸显网络与模型各自的优势,提出可学习的混合MAP网络有效地解决图像去雨问题。方法 首先基于最大后验估计（MAP）建立含有隐式先验的能量模型,然后通过优化算法将模型分解为背景估计模型和雨线估计模型两部分,以减少背景估计和雨线估计之间的依赖性。对于背景估计模型,通过对模型及优化目标分析采用以数据驱动的去噪残差网络进行建模,保证估计出的背景更清晰;对于雨线估计模型,为避免直接对未知的雨线建模失去准确性,利用高斯混合模型实时刻画输入雨图的雨线先验。结果 在合成数据集Rain12及真实雨图上进行实验,通过综合考虑定量分析和定性分析,并与3种基于模型的方法及两种基于深度网络的方法相比,本文方法在去除雨线的同时能够损失的背景信息最少,合成数据集上的平均结构相似性（SSIM）值达到0.92。结论 本文通过将基于模型的方法与基于深度网络的方法相结合,既去除了雨线又保证了估计背景的清晰程度,同时也验证了将传统模型与深度网络相结合是一种解决图像恢复问题的有效途径。     

Rain streak removal based on non-negative matrix factorization

A rain streak in an image can degrade visual quality of that image to the human eye. Unfortunately, removing the rain streak from a single image represents a very challenging task. In this paper, a single image rain removal process based on non-negative matrix factorization is proposed. First, the rain image is broken down into a low-frequency and high-frequency part by a Gaussian filter. Therefore, the rain component, which lies mostly in the middle frequency range, can be discarded in high and low frequency domains. Next, non-negative matrix factorization (NMF) method is applied to deal with the rain streak in the low frequency domain. Finally, Canny edge detection and block copy strategy are performed separately to remove the rain component in the high frequency domain to improve image quality. In comparison with state-of-the-art approaches, the proposed method achieves competitive results without the need for an extra image database to train the dictionary.

     

Classifying matrices separating rows and columns

The classification problem transforms a set of N numbers in such a way that none of the first N/2 numbers exceeds any of the last N/2 numbers. A comparator network that solves the classification problem on a set of r numbers is commonly called an r-classifier. We show how the well-known Leighton's Columnsort algorithm can be modified to solve the classification problem of N=rs numbers, with 1 /spl les/ s /spl les/ r, using an r-classifier instead of an r-sorting network. Overall, the r-classifier is used O(s) times, namely, the same number of times that Columnsort applies an r-sorter. A hardware implementation is proposed that runs in optimal O(s+logr) time and uses an O(rlogr(s + logr)) work. The implementation shows that, when N= rlogr, there is a classifier network solving the classification problem on N numbers in the same O(logr) time and using the same O(rlogr) comparators as an r-classifier, thus saying a logr factor in the number of comparators over an (rlogr)-classifier.     

一种改进的重叠细胞分离算法

在细胞图像识别中,经常会遇到细胞重叠的现象,需要有一种有效的方法将重叠在一起的细胞分离成单个的细胞。目前很多分离算法都是基于数学形态学的,但这些算法都存在着一定的局限性。为此,提出了一种改进的基于数学形态学的分离算法,该算法首先采用一种简单、快速的边界剥离方法得到距离变换结果,然后再用分水岭方法对细胞图像进行分离。实验结果表明,算法获得了较好的分离效果。     

WAV音频分句的算法设计

随着网络信息技术的迅猛成长,我们正快步走进信息时代,世界经济、文化等信息交流变得十分频繁与快捷。基于语言学习的需要,本文提出了一种基于语音端点检测技术的音频分句算法。本算法对音频文件进行分帧后,通过提取语音帧特征项,判别其特征值后对其进行归类。在特征项提取时,为短时过零率设定正负门限,可大大增强判别特征值的准确性。提出上升沿与下降沿的概念对语音端点进行精确定位,并最终存储音频分句的端点,实现音频分句功能。     

Numerical simulation of separating boundary-layer flow

A two-dimensional boundary-layer flow over a bump has been studied computationally by solving the incompressible Navier–Stokes equations. The numerical solution procedure uses a mapping transforming the physical coordinate system into a Cartesian one. The resulting system is solved using a mixed finite differences––Chebyshev collocation discretization. We compare the influence matrix technique with a fractional time-step procedure used to enforce the divergence-free condition. Numerical experiments are performed for bumps with different aspect ratios. The separation structure is investigated for increasing Reynolds number and self-induced vortex shedding is reproduced numerically.     

Interactive documentation

Documents are increasingly often read from computer screens rather than from paper. This paper describes a tool, called GUIDE, which allows readers of computer-based documents to peruse these documents at any desired level of detail. GUIDE covers any kind of textual document, and is designed for environments where both author and readers are lay users.     

Interactive Workspaces

We are rapidly entering a world in which people equip themselves with a small constellation of mobile devices and pass through environments rich in embedded technology. However, we are still a long way from harnessing the power of this technology in a way that seamlessly and invisibly assists users in their day-to-day activities. Bringing pervasive computing to maturity requires innovations in systems integration and human-computer interaction (HCI). To investigate these challenges, Stanford University's Interactive Workspaces project (http://iwork.stanford.edu/) is exploring team-based collaboration in technology-augmented environments. These workspaces are designed to allow groups of five to ten people to work together using computing and interaction devices on many scales.