A Combined Theory of Defocused Illumination and Global Light Transport

Projectors are increasingly being used as light-sources in computer vision applications. In several applications, they are modeled as point light sources, thus ignoring the effects of illumination defocus. In addition, most active vision techniques assume that a scene point is illuminated only directly by the light source, thus ignoring global light transport effects. Since both defocus and global illumination co-occur in virtually all scenes illuminated by projectors, ignoring them can result in strong, systematic biases in the recovered scene properties. To make computer vision techniques work for general real world scenes, it is thus important to account for both these effects.     

飞行模拟器成像系统延迟时间检测方法研究

为了检测飞行模拟器成像系统的延迟时间,首次设计了利用PIC单片机进行延迟时间检测的系统;深入分析了模拟器成像延迟的产生原因,并以某型模拟器的成像系统为研究对象,利用该系统对其进行检测,通过单片机与PC机通讯,观察并记录操纵杆与成像计算机亮度信息的变化的采样数据,根据采样程序周期和通讯程序的运行周期15ms,得出系统的延迟时间;解算结果与实际情况相符;此系统成本低、通用性较好,计算精度较高,可达到微秒级,误差较小,还可以为空军提供低成本的测试技术.     

Ultra-fast Lensless Computational Imaging through 5D Frequency Analysis of Time-resolved Light Transport

Light transport has been analyzed extensively, in both the primal domain and the frequency domain. Frequency analyses often provide intuition regarding effects introduced by light propagation and interaction with optical elements; such analyses encourage optimal designs of computational cameras that efficiently capture tailored visual information. However, previous analyses have relied on instantaneous propagation of light, so that the measurement of the time dynamics of light–scene interaction, and any resulting information transfer, is precluded. In this paper, we relax the common assumption that the speed of light is infinite. We analyze free space light propagation in the frequency domain considering spatial, temporal, and angular light variation. Using this analysis, we derive analytic expressions for information transfer between these dimensions and show how this transfer can be exploited for designing a new lensless imaging system. With our frequency analysis, we also derive performance bounds for the proposed computational camera architecture and provide a mathematical framework that will also be useful for future ultra-fast computational imaging systems.     

Sparsely Precomputing The Light Transport Matrix for Real‐Time Rendering

Precomputation‐based methods have enabled real‐time rendering with natural illumination, all‐frequency shadows, and global illumination. However, a major bottleneck is the precomputation time, that can take hours to days. While the final real‐time data structures are typically heavily compressed with clustered principal component analysis and/or wavelets, a full light transport matrix still needs to be precomputed for a synthetic scene, often by exhaustive sampling and raytracing. This is expensive and makes rapid prototyping of new scenes prohibitive. In this paper, we show that the precomputation can be made much more efficient by adaptive and sparse sampling of light transport. We first select a small subset of “dense vertices”, where we sample the angular dimensions more completely (but still adaptively). The remaining “sparse vertices” require only a few angular samples, isolating features of the light transport. They can then be interpolated from nearby dense vertices using locally low rank approximations. We demonstrate sparse sampling and precomputation 5 × faster than previous methods.     

用飞行时间相机优化可视外壳的实时三维重建算法

在基于图像的三维重建领域中,基于轮廓或立体匹配的实时三维重建算法精度很低,而高精度的三维重建算法需要像素级能量最优化,很难做到实时.针对这个问题,提出一种用飞行时间相机拍摄得到的深度图优化可视外壳方法的实时三维重建算法.首先使用一种简化的深度标定方法对深度数据进行误差修正;然后根据两种相机得到的数据构造粗糙网格模型;最后进行局部搜索匹配,对模型表面进行像素块的优化.实验结果表明,该算法比同类算法的实时性高,且能够有效地处理模型表面的凹多边形,比可视外壳算法的精度有较大改善.     

A Statistical Analysis of Global Economies Using Time Varying Copulas

Computational Economics - The application of time varying copulas has become popular in recent years. Here, we illustrate an application involving stock indices of ten major economies covering all...     

基于多粒度时间注意力RNN的航班客座率预测

准确预测航班客座率有利于处理航班机票超售、座位虚耗等问题,然而传统时间序列预测方法只关注航班近期每日客座率的变化特点,无法同时考虑其他因素的影响,预测效果不够理想。针对该问题,提出一种基于多粒度时间注意力机制的循环神经网络模型MTA-RNN。通过构建多级注意力机制获取航班客座率在不同时间粒度下的时序相关性,同时考虑航班自身属性及节假日等其他因素,得到未来一段时间内的目标航班客座率。在真实历史航班客座率数据集上的实验结果表明,MTA-RNN模型的预测准确率高于ARIMA模型、LSTM模型和Seq2seq模型。     

全局和时序结构特征并用的语音信号情感特征识别方法

在利用全局特征进行语音情感特征分析的基础上,提出了采用情感语句中各元音时序结构作为新的特征,并针对不同语句中包含不同元音个数的情况,提出了零补齐、分局均值补齐、前均值补齐三种不同的规整方法.以从10名话者中搜集的带有欢快、愤怒、惊奇、悲伤4种情感的1000句语句作为样本,本文对语音情感特征进行了分析.实验结果表明利用全局特征和时序特征相结合,对时序特征采用前均值补齐,同时使用修正二次判别函数(MQDF)进行情感识别能够获得94%的平均情感识别率.     

Replica Exchange Light Transport

We solve the light transport problem by introducing a novel unbiased Monte Carlo algorithm called replica exchange light transport, inspired by the replica exchange Monte Carlo method in the fields of computational physics and statistical information processing. The replica exchange Monte Carlo method is a sampling technique whose operation resembles simulated annealing in optimization algorithms using a set of sampling distributions. We apply it to the solution of light transport integration by extending the probability density function of an integrand of the integration to a set of distributions. That set of distributions is composed of combinations of the path densities of different path generation types: uniform distributions in the integral domain, explicit and implicit paths in light (particle/photon) tracing, indirect paths in bidirectional path tracing, explicit and implicit paths in path tracing, and implicit caustics paths seen through specular surfaces including the delta function in path tracing. The replica‐exchange light transport algorithm generates a sequence of path samples from each distribution and samples the simultaneous distribution of those distributions as a stationary distribution by using the Markov chain Monte Carlo method. Then the algorithm combines the obtained path samples from each distribution using multiple importance sampling. We compare the images generated with our algorithm to those generated with bidirectional path tracing and Metropolis light transport based on the primary sample space. Our proposing algorithm has better convergence property than bidirectional path tracing and the Metropolis light transport, and it is easy to implement by extending the Metropolis light transport.     

时间触发模式的任务调度与分解策略

在嵌入式系统设计中采用事件触发模式,很大程度上会增加系统的复杂性、代码的长度和复杂性,不适合普通开发人员构建,因此必须采用价格昂贵的商业实时操作系统;同时还需要很大的操作系统开销。采用时间触发模式简单、可靠,开发时间短,但系统的实时响应能力将被削弱,除非系统进程极其简短。本文探讨了基于时间触发模式的任务调度与分解策略,从而使时间触发模式可以满足绝大多数工程实际的需要。     

Forward Light Cuts: A Scalable Approach to Real‐Time Global Illumination

We present Forward Light Cuts, a novel approach to real‐time global illumination using forward rendering techniques. We focus on unshadowed diffuse interactions for the first indirect light bounce in the context of large models such as the complex scenes usually encountered in CAD application scenarios. Our approach efficiently generates and uses a multiscale radiance cache by exploiting the geometry‐specific stages of the graphics pipeline, namely the tessellator unit and the geometry shader To do so, we assimilate virtual point lights to the scene's triangles and design a stochastic decimation process chained with a partitioning strategy that accounts for both close‐by strong light reflections, and distant regions from which numerous virtual point lights collectively contribute strongly to the end pixel. Our probabilistic solution is supported by a mathematical analysis and a number of experiments covering a wide range of application scenarios. As a result, our algorithm requires no precomputation of any kind, is compatible with dynamic view points, lighting condition, geometry and materials, and scales to tens of millions of polygons on current graphics hardware.     

面向正点率提升的华北机场群航班时刻优化

近年来,区域机场群协同发展逐渐成为了未来民航发展的基本导向。然而,相比国外关于机场群的研究水平,我国尚处于萌芽阶段,出现了机场群内发展不均衡、缺乏协同、功能定位不清晰、空管运行难度大、服务品质降低等问题。因此,以京津冀机场群为研究对象,借鉴国外先进发展经验,从协同发展的角度对机场群航线优化进行研究。构建了以提升航班正点率为目标的机场群现有航班时刻优化模型,运用粒子群迭代寻优算法求解最优解,将优化后的航班时刻表用SIMMOD进行仿真验证,实验结果表明,经航线优化后的京津冀机场群航班延误得到了缓解,且多机场群系统的航班冲突得到了明显的降低。     

Bidirectional Rendering of Vector Light Transport

On the foundations of many rendering algorithms it is the symmetry between the path traversed by light and its adjoint path starting from the camera. However, several effects, including polarization or fluorescence, break that symmetry, and are defined only on the direction of light propagation. This reduces the applicability of bidirectional methods that exploit this symmetry for simulating effectively light transport. In this work, we focus on how to include these non‐symmetric effects within a bidirectional rendering algorithm. We generalize the path integral to support the constraints imposed by non‐symmetric light transport. Based on this theoretical framework, we propose modifications on two bidirectional methods, namely bidirectional path tracing and photon mapping, extending them to support polarization and fluorescence, in both steady and transient state.     

基于环链的多面体剖分快速算法研究

利用环链提出了一种对任意多面体不添加顶点的凸剖分快速方法 ,它对多面体的剖分个数接近最少 .该方法首先从多面体的棱和对角棱所构成的所有环中 ,以最小周长选取一个最好的环 ,然后利用这个环的各个边所形成的一系列面 ,对多面体进行一次剖分 .实验证明 ,这种方法可找到对多面体不添加顶点剖分的最好剖分面 ,使剖分的次数接近最少 ,具有较好的实用价值和广泛的应用前景 .     

Decomposing the global financial crisis: A Self-Organizing Time Map

A key starting point for financial stability surveillance is understanding past, current and possible future risks and vulnerabilities. Through temporal data and dimensionality reduction, or visual dynamic clustering, this paper aims to present a holistic view of cross-sectional macro-financial patterns over time. The Self-Organizing Time Map (SOTM) is a recent adaptation of the Self-Organizing Map for exploratory temporal structure analysis, which disentangles cross-sectional data structures over time. We apply the SOTM, as well as its combination with classical cluster analysis, in financial stability surveillance. Thus, this paper uses the SOTM for decomposing and identifying temporal structural changes in macro-financial data before, during and after the global financial crisis of 2007–2009.     

Light Fields and Computational Imaging

A survey of the theory and practice of light field imaging emphasizes the devices researchers in computer graphics and computer vision have built to capture light fields photographically and the techniques they have developed to compute novel images from them.     

Visualization of Coherent Structures of Light Transport

Inspired by vector field topology, an established tool for the extraction and identification of important features of flows and vector fields, we develop means for the analysis of the structure of light transport. For that, we derive an analogy to vector field topology that defines coherent structures in light transport. We also introduce Finite‐Time Path Deflection (FTPD), a scalar quantity that represents the deflection characteristic of all light transport paths passing through a given point in space. For virtual scenes, the FTPD can be computed directly using path‐space Monte Carlo integration. We visualize the FTPD field for several example scenes and discuss the revealed structures. Lastly, we show that the coherent regions visualized by the FTPD are closely related to the coherent regions in our new topologically‐motivated analysis of light transport. FTPD visualizations are thus also visualizations of the structure of light transport.     

Improved Half Vector Space Light Transport

In this paper, we present improvements to half vector space light transport (HSLT) [ KHD14 ], which make this approach more practical, robust for difficult input geometry, and faster. Our first contribution is the computation of half vector space ray differentials in a different domain than the original work. This enables a more uniform stratification over the image plane during Markov chain exploration. Furthermore, we introduce a new multi chain perturbation in half vector space, which, if combined appropriately with half vector perturbation, makes the mutation strategy both more robust to geometric configurations with fine displacements and faster due to reduced number of ray casts. We provide and analyze the results of improved HSLT and discuss possible applications of our new half vector ray differentials.     

On the Effective Dimension of Light Transport

Light transport is often characterized within a high‐dimensional space although practitioners have long known that it commonly behaves as a much lower‐dimensional phenomenon. We study the effective dimension of light transport over a neighborhood on the scene manifold and show that under plausible assumptions the dimensionality is characterized by the spectrum of the spatio‐spectral concentration problem. This allows us to improve existing estimates for the dimension in computer graphics using a more insightful derivation and for the first time we obtain optimal representations. The relevance of our results for existing rendering applications is discussed.     

Quantifying the Error of Light Transport Algorithms

This paper proposes a new methodology for measuring the error of unbiased physically based rendering algorithms. The current state of the art includes mean squared error (MSE) based metrics and visual comparisons of equal‐time renderings of competing algorithms. Neither is satisfying as MSE does not describe behavior and can exhibit significant variance, and visual comparisons are inherently subjective. Our contribution is two‐fold: First, we propose to compute many short renderings instead of a single long run and use the short renderings to estimate MSE expectation and variance as well as per‐pixel standard deviation. An algorithm that achieves good results in most runs, but with occasional outliers is essentially unreliable, which we wish to quantify numerically. We use per‐pixel standard deviation to identify problematic lighting effects of rendering algorithms. The second contribution is the error spectrum ensemble (ESE), a tool for measuring the distribution of error over frequencies. The ESE serves two purposes: It reveals correlation between pixels and can be used to detect outliers, which offset the amount of error substantially.