Closed Form Solution of Local Shape from Shading at Critical Points

In the theory of shape from shading, behaviours of the local solution around a critical point of the image play an important role. This paper shows that the second derivatives of the object surface can be locally determined at these image critical points. Closed form expressions of the surface second derivatives in terms of the second derivatives of the image brightness and of the reflectance map are shown. They are derived as follows: By differentiating the image irradiance equation twice at an image critical point, a set of polynomial equations is obtained that contains the second derivatives of the surface, of the image brightness and of the reflectance map. Regarding these equations as simultaneous equations for unknown surface second derivatives, they are algebraically solved and their explicit expressions are derived. Such a derivation is possible only at image critical points and is impossible at any other image point. The applicability of the derived expressions to noisy images is tested using synthetic images.     

大幅面地图的快速自动地形晕渲

在提出一个建立三维规则数据场的新算法的基础上,提出了一个可用于大幅度地图的快速实用的地形自动晕渲算法,与传统数据网格化的方法不同,本算法采用了用网格点相邻等高线的高程值插值计算出网格点高程值的新思想,并且提出了相应的网格点相邻等高线的识别方法,该方法充分利用等高线所具有的先验知识,得到的网格点高程值质量很高,另外,该规则数据场的建立方法经改进后,其时间复杂性与数据点数（ｍ）和网格点数（ｎ）成线性关     

温州某办公大楼玻璃幕墙热工性能参数对空调冷负荷的影响

阐述了玻璃幕墙的传热系数K值与遮阳系数Sc的取值不同对空调冷负荷的影响;指出了不能单纯以K值来评估玻璃幕墙的热工性能的优劣,Sc值对热工性能影响更大,只有综合考虑K值和Sc值及环境因素,才能选择一个节能、环保的合适玻璃幕墙.     

Re-illuminating single images using Albedo estimation

Predicting the appearance of a scene under novel lighting conditions is of growing interest at the convergence of vision, graphics and virtual reality. In this paper, we develop a method for appearance prediction from a single image using the apparatus of shape from shading (SFS). We re-visit the reflectance estimation process first proposed by Blake (Graphics Image Process. 32 (1985) 314), and develop a novel approach to parameter selection within the Blake method based on the quality of images which can be produced by re-illuminating the recovered needle-map. Combining Blake's method with recent advances in SFS is demonstrated to yield significant improvements in the appearance prediction of real images under varying lighting conditions.     

A general framework for three-dimensional surface reconstruction by self-consistent fusion of shading and shadow features

In this paper a novel framework for three-dimensional surface reconstruction by self-consistent fusion of shading and shadow features is presented. Based on the analysis of at least two pixel-synchronous images of the scene under different illumination conditions, this framework combines a shape from shading approach for estimating surface gradients and altitude variations on small scales with a shadow analysis method that allows for the determination of the large-scale properties of the surface. As a first step, the result of shadow analysis is used for selecting a consistent solution of the shape from shading reconstruction algorithm. As a second step, an additional error term derived from the fine-structure of the shadow is incorporated into the reconstruction algorithm. This approach is extended to the analysis of two or more shadows under different illumination conditions leading to an appropriate initialization of the shape from shading algorithm. The framework is applied to the astrogeological task of three-dimensional reconstruction of regions on the lunar surface using ground-based CCD images and to the machine vision task of industrial quality inspection.     

Novel Lyapunov-based rapid and ripple-free MPPT using a robust model reference adaptive controller for solar PV system

The technological, economic, and environmental benefits of photovoltaic (PV) systems have led to their widespread adoption in recent years as a source of electricity generation. However, precisely identifying a PV system''s maximum power point (MPP) under normal and shaded weather conditions is crucial to conserving the maximum generated power. One of the biggest concerns with a PV system is the existence of partial shading, which produces multiple peaks in the P–V characteristic curve. In these circumstances, classical maximum power point tracking (MPPT) approaches are prone to getting stuck on local peaks and failing to follow the global maximum power point (GMPP). To overcome such obstacles, a new Lyapunov-based Robust Model Reference Adaptive Controller (LRMRAC) is designed and implemented to reach GMPP rapidly and ripple-free. The proposed controller also achieves MPP accurately under slow, abrupt and rapid changes in radiation, temperature and load profile. Simulation and OPAL-RT real-time simulators in various scenarios are performed to verify the superiority of the proposed approach over the other state-of-the-art methods, i.e., ANFIS, INC, VSPO, and P&O. MPP and GMPP are accomplished in less than 3.8 ms and 10 ms, respectively. Based on the results presented, the LRMRAC controller appears to be a promising technique for MPPT in a PV system.     

一种基于改进羊群算法的光伏系统最大功率跟踪策略

针对传统控制算法在局部遮蔽条件下无法持续准确地跟踪最大输出功率点,提出一种基于改进羊群算法的光伏系统最大功率跟踪策略.在羊群算法中引入扰动算子、反向种群和自适应放牧概率,以增强算法的局部开发能力,提高算法的寻优精度.均匀光照、局部遮蔽和变照度3种条件下的实验结果表明,改进羊群算法在不同环境条件下均能持续稳定地跟踪最大功率点,在收敛时间和收敛精度上均有较大优势,验证了该算法在最大功率点跟踪控制中的可行性.     

基于明暗信息的胶囊内镜图像三维形状恢复

利用明暗恢复形状技术,将视频胶囊内镜二维图像的明暗信息重构小肠内腔表面的三维场景信息。针对传统的明暗恢复形状技术的约束条件,提出了一种针对胶囊内镜图像的预处理方法,利用预处理后的图像恢复出更为平滑的视觉场景,同时保留被检查对象的结构信息。基于临床数据的实验结果表明,三维形状恢复技术可以增强胶囊内镜视频的可读性,提高小肠疾病的诊断准确率。     

Enhanced Texture‐Based Terrain Synthesis on Graphics Hardware

Curvilinear features extracted from a 2D user‐sketched feature map have been used successfully to constraint a patch‐based texture synthesis of real landscapes. This map‐based user interface does not give fine control over the height profile of the generated terrain. We propose a new texture‐based terrain synthesis framework controllable by a terrain sketching interface. We enhance the realism of the generated landscapes by using a novel patch merging method that reduces boundary artefacts caused by overlapping terrain patches. A more constrained synthesis process is used to produce landscapes that better match user requirements. The high computational cost of texture synthesis is reduced with a parallel implementation on graphics hardware. Our GPU‐accelerated solution provides a significant speedup depending on the size of the example terrain. We show experimentally that our framework is more successful in generating realistic landscapes than current example‐based terrain synthesis methods. We conclude that texture‐based terrain synthesis combined with sketching provides an excellent solution to the user control and realism challenges of virtual landscape generation.     

Pre‐convolved Radiance Caching

The incident indirect light over a range of image pixels is often coherent. Two common approaches to exploit this inter‐pixel coherence to improve rendering performance are Irradiance Caching and Radiance Caching. Both compute incident indirect light only for a small subset of pixels (the cache), and later interpolate between pixels. Irradiance Caching uses scalar values that can be interpolated efficiently, but cannot account for shading variations caused by normal and reflectance variation between cache items. Radiance Caching maintains directional information, e.g., to allow highlights between cache items, but at the cost of storing and evaluating a Spherical Harmonics (SH) function per pixel. The arithmetic and bandwidth cost for this evaluation is linear in the number of coefficients and can be substantial. In this paper, we propose a method to replace it by an efficient per‐cache item pre‐filtering based on MIP maps — such as previously done for environment maps — leading to a single constant‐time lookup per pixel. Additionally, per‐cache item geometry statistics stored in distance‐MIP maps are used to improve the quality of each pixel's lookup. Our approximate interactive global illumination approach is an order of magnitude faster than Radiance Caching with Phong BRDFs and can be combined with Monte Carlo‐raytracing, Point‐based Global Illumination or Instant Radiosity.