MAX渲染算法光线跟踪与光能传递的分析对比

光线跟踪（Raytracer）与光能传递（Radiosity）渲染是3D设计软件中常用的渲染方法,时场景使用光线跟踪与光能传递渲染可以生成十分逼真的光影效果。但两种渲染算法都需要进行大量复杂的运算,尤其是光能传递时计算机系统的性能要．求很高,时硬件平台的运算速度和能力都有很苛刻的要求。     

MAX渲染算法光线跟踪与光能传递的分析对比

光线跟踪(Raytracer)与光能传递(Radiosity)渲染是3D设计软件中常用的渲染方法,对场景使用光线跟踪与光能传递渲染可以生成十分逼真的光影效果。但两种渲染算法都需要进行大量复杂的运算,尤其是光能传递对计算机系统的性能要求很高,对硬件平台的运算速度和能力都有很苛刻的要求。     

半透明三维物体表面光泽真实感实时渲染方法

针对具有半透明特性玉石的真实感渲染问题,提出一种利用高光层、漫反射层、透射层三层光照模型叠加的解决方法。首先对散射层结合漫反射剖面来模拟半透明玉石的次表面散射效果,提出一种可改变漫反射剖面的散射方法,表达不同种类玉石漫反射剖面的特点;然后对透射层利用预计算的本地厚度贴图结合高斯线性和,实现基于表面厚度光的透射效果,再在能量守恒的基础上与基于微平面的高光反射项进行叠加,得到一个基于三层光照模型的真实感半透明材质表现。实验结果表明,所提出的方法能实现不同种类半透明玉石真实感渲染,且在片面数达160万时可保证30帧/秒的实时效率。     

基于VRay的龙泉青瓷真实感渲染研究

以龙泉青瓷真实感展现为背景,研究龙泉青瓷三维真实感展示,结合优秀的三维模型渲染插件VRay,从材质、灯光、环境等方面研究了基于VRay的龙泉青瓷真实感渲染。结果表明基于VRay的龙泉青瓷在材质、材光、环境等密切配合下可以渲染出非常真实的作品。     

基于复杂场景图的光线追踪渲染的Kd-tree构造

在基于光线跟踪等的全局光照绘制中,改良空间划分结构一直是各种加速策略中重要的方法之一。对常见的空间结构构建方法进行研究,针对复杂室内场景提出一种快速的分区构建方法。首先,算法并不直接将整个空间进行剖分,而是采用分组策略,结合包围盒进行判断,将具有一定空间联系的场景实体合并成一定数量的组;之后,对每个组使用优化后的Kd-tree构建细分结构,并提出合理的终止条件。与以往的方法相比,该方法构建的加速结构更适合于基于场景图构建的复杂室内环境,为快速生成真实感图形提供了有效的手段。     

一种非真实感的水墨画渲染方法

非真实感渲染是图形学的重要研究领域。本文利用Opengl实现了一种非真实感的水墨渲染的方法,方法首先通过模型定点的视线矢量和法线矢量的点乘积计算其夹角的余弦值,然后根据计算的余弦值进行纹理映射,最后进行显示完成了水墨渲染效果。     

基于WEB的VRML交互式光线追踪渲染

本文采用Java语言编制了一个Applet程序支持基于WEB的VRML2．0观察器。用户可以使用任何操作系统的浏览器来运行该程序，进行VRML文件的查看。该观察器采用了光线追踪算法对场景进行交互实时渲染，可以获得很好的效果。该算法对传统光线追踪算法作了适当改进以适用于交互式渲染，并采用包围盒和空间划分树(k—d树)等措施来加快渲染的速度。     

基于BRDF 和GPU 并行计算的全局光照实时渲染

基于光线追踪,将屏幕图像像素分解为投射光线与场景对象交点面片辐射亮度和 纹理贴图的合成,每个面片的辐射亮度计算基于双向反射分布函数(BRDF)基的线性组合,并通 过图形处理器(GPU)处理核心并行绘制进行加速,最后与并行计算的纹理映射结果进行合成。 提出了一种基于BRDF 和GPU 并行计算的全局光照实时渲染算法,利用GPU 并行加速,在提 高绘制效率的前提下,实现动态交互材质的全局光照实时渲染。重点研究：对象表面对光线的 多次反射用BRDF 基的线性组合来表示,将非线性问题转换为线性问题,从而提高绘制效率; 利用GPU 并行加速,分别计算对象表面光辐射能量和纹理映射及其线性组合,进一步提高计算 效率满足实时绘制需求。     

基于位图的点集表面表示及其渲染

提出了一种基于位图的点集表面表示形式：先对点集表面进行参数化，然后在参数域上进行曲面重构和重采样得到基于二维数组的点集表面表示。采用了切空间对齐的方法得到点集表面的参数坐标。该方法能寻找出点集代表的流型所在的二维参数空间，并存参数化过程中较好地保留了原曲面的尺度信息。位图形式表示点集表面具有数据结构简单和便于随机访问的优点。提出了基于位图表示形式的点渲染方法，该方法采用双线性插值来实现视角依赖的点集表面的重采样，解决了点渲染中采样点不足的问题。     

机械零件的非真实感渲染研究

针对机械零件CAD模型在二维载体上显示时特征不明显的问题,提出对零件模型进行非真实感渲染,使结果类似于手绘轴测图中的黑白润饰样式。根据手绘轴测图的润饰策略,对零件模型的特征进行了分析和分类,并制订出针对主要特征的识别规则;在此基础上,用计算机模拟出多种润饰笔触效果,并与特征识别结果相结合,最终生成表达型的轴测图样。通过实例验证了渲染工具的有效性。     

Computer-aided appearance design based on BRDF measurements

This paper presents a comprehensive and efficient framework for computer-aided appearance design based on BRDF (bidirectional reflectance distribution function) measurements. It covers all stages of a new product development including acquisition, processing and modeling of reflectance data, interactive rendering and evaluation of material appearance, and manufacturing operations. The proposed method eliminates the need of making a real physical prototype by providing a reliable surface appearance design process in which he/she can faithfully simulate the final surface appearance in the early design stage of a product. In addition, it enables us to manufacture the coating surface the same as the computer simulated surface from the known coating specification. The accuracy test between a real sample and the computer simulated one demonstrates that the proposed method satisfies an acceptable level of accuracy for industrial applications. A case study has been conducted to evaluate the user preference on the surface appearance of a digital handheld device which contains a combination of different coating surfaces. The case study successfully demonstrates that the user preference can be identified using the proposed method while changing the combination of different coating surfaces represented by BRDFs considering factors such as surrounding environments and age groups.     

An Adaptive BRDF Fitting Metric

We propose a novel image-driven fitting strategy for isotropic BRDFs. Whereas existing BRDF fitting methods minimize a cost function directly on the error between the fitted analytical BRDF and the measured isotropic BRDF samples, we also take into account the resulting material appearance in visualizations of the BRDF. This change of fitting paradigm improves the appearance reproduction fidelity, especially for analytical BRDF models that lack the expressiveness to reproduce the measured surface reflectance. We formulate BRDF fitting as a two-stage process that first generates a series of candidate BRDF fits based only on the BRDF error with measured BRDF samples. Next, from these candidates, we select the BRDF fit that minimizes the visual error. We demonstrate qualitatively and quantitatively improved fits for the Cook-Torrance and GGX microfacet BRDF models. Furthermore, we present an analysis of the BRDF fitting results, and show that the image-driven isotropic BRDF fits generalize well to other light conditions, and that depending on the measured material, a different weighting of errors with respect to the measured BRDF is necessary.     

Integration and Case Analysis of BRDF Model based on Linear Kernel\|driven Model#br#

Anisotropic reflectance is the intrinsic characteristic of an object surface.over the past few decades,various BRDF models have been developed for investigating the relationship between the vegetation canopy and reflectance anisotropy.This helps to retrieve biophysical parameters from the anisotropic reflectance patterns of vegetation canopy.In this study,for the purpose of assisting potential users to use these models,and to improve the understanding of the BRDF modeling,several BRDF models that are widely used in the remote sensing community have been integrated with the current version of the MaKeMAT (Multi\|angular Kernel\|driven Model Analysis Tool),based on the Interactive Data Language (IDL).This work retains all functions of the current version of the MaKeMAT model,meanwhile,adds some new functions by integrating these physical BRDF models.Undoubtedly,this work facilitates the potential users to process BRDF data and make further analysis in their work by operating a simpler visual interface.This helps to build a rapid communication between the kernel\|driven BRDF models and the physical BRDF models.Our initial results show that this model\|integration practice is a valuable reference for potential users to devise a similar technique.Our case study in coupling these physical BRDF models with the kernel\|driven models present a high correlation between them,with the determination of coefficients (R²) reaching 0.899~0.989 in the red and NIR bands.     

Two-dimensional BRDF estimation from polarisation

This paper presents a novel technique for reflectance function (BRDF) estimation, which uses polarisation information and photometric stereo. The first stage of the technique is standard and involves the acquisition of polarisation information (angle and degree of polarisation) using a linear polariser and a digital camera. This yields a field of ambiguous surface normal estimates for an arbitrarily shaped object. A photometric stereo algorithm is then used with three different light source directions to disambiguate the surface normals. Next, the proposed algorithm constructs a 3D histogram of the surface normals and pixel brightnesses. A surface, representing the BRDF, is then fitted to the histogram data using simulated annealing optimisation. The result is a set of Cartesian triples that relate the surface normals to the observed pixel brightnesses. Unlike most previous techniques for BRDF estimation, the technique is image-based and does not require sophisticated equipment or intrusive light sources. Although the technique is restricted to smooth and slightly rough dielectric objects, no prior knowledge about the surface geometry is assumed.     

BRDF模型及其反演研究的现状及展望

介绍了二向性反射的物理模型及半经验模型在理论研究中的新进展,并分析了各个模型的优缺点,为模型选择提供了依据;同时对模型反演的策略和方法及最新研究进展进行了概述。在此基础上,对实验研究、理论研究以及应用研究中存在的主要问题及目前的一些解决方案进行了分析,并讨论了遥感反演研究的未来发展方向。     

基于Ross Thick—LiSparseR及Ross Thick—LiTransit的核驱动BRDF计算与评价

核驱动BRDF模型是MODIS传感器用于计算全球地表反照率的AMBRALS算法系统所使用的模型。目前AMBRALS算法系统的几何光学散射核为LiSparseR核,它不能完全避免反射率为负的情况,并在遥感像元尺度应用互易原理的理论依据不充足。几何光学核LiTransit核兼有LiSparse核向LiDense核过渡的优点,比LiSparseR核更符合几何光学模型的基本原理。本文研究了基于LiSparseR核及LiTransit核驱动的方向反射率计算方法,并进行了比较验证。     

基于表观BRDF的泡沫金属辐射特性反演测量方法

泡沫金属是通过在金属基体上形成大量孔隙结构而得到的一类新型多功能材料,在太阳能利用、强化换热等领域有重要应用价值,其辐射特性参数是分析其内部辐射传递的必要物性数据。提出一种基于表观双向反射分布函数（ BRDF）测量数据反演泡沫金属热辐射物性的方法,利用测量的多角度入射的表观BRDF数据结合辐射传递方程求解来反演泡沫金属的等效辐射特性。对泡沫铁镍（50 ppi ）、泡沫铜（90 ppi）及泡沫镍（30 ppi）三种泡沫金属样品在波长660 nm激光照射下1/2半球空间的表观BRDF分布进行了实验测量,并对其辐射特性进行了反演,首次获得了这三种材料的辐射特性参数,其辐射物性表现出明显的半透明性质,散射反照率随着孔隙数密度的增加而增加,散射相函数呈后向散射占优。     

Noiseless GPU rendering of isotropic BRDF surfaces

Illumination at a surface point is formulated as an integral of a BRDF using the incident radiance over the hemisphere domain. A popular method to compute the integral is Monte Carlo integration, in which the surface illumination is computed as the sum of the integrand evaluated with stochastically sampled rays. Although its simple nature is practically attractive, it incurs the serious drawback of noise artifacts due to estimator variance. In this paper, we propose a novel noiseless Monte Carlo rendering algorithm running in real time on a GPU. The main contribution is a novel importance sampling scheme, which constructs spatially continuous sample rays over a surface. For each evenly spaced polar angle of the eye ray, denoted by θ, incident rays are sampled with a PDF (probability density function) derived from a target BRDF lobe. We develop a force-based update method to create a sequence of consistent ray sets along θ’s. Finally, corresponding rays in the sequence of ray sets are linearly connected to form a continuous ray curve, referred to as a sample thread. When rendering, illumination at a surface point is computed with rays, each of which is given as a point on a sample thread. Because a thread provides a sample ray that continuously varies on a surface, the random variance of the illumination, causing visual noise during the Monte Carlo rendering process, is eliminated. A thread set is precomputed for each BRDF to free the GPU from the burden of sampling during real-time rendering. According to extensive experiments, approximately 100 threads are sufficient for most measured BRDFs with acceptable rendering quality for interactive applications.     

Use of a Kalman filter for the retrieval of surface BRDF coefficients with a time-evolving model based on the ECOCLIMAP land cover classification

The goal of this study is to demonstrate the asset in using a Kalman filter to improve the spatial coherence and time consistency of surface Bidirectional Reflectance Distribution Function (BRDF) and albedo retrievals from moderate resolution sensor data sets. For this purpose, we use a simple surface model describing BRDF seasonal evolution for the land cover classes of the ECOCLIMAP database. The application of temporal composition windows used so far for BRDF retrieval is limited in regions characterized by a high frequency of cloud coverage, which induces a lot of gaps in the temporal series. Instead, the present method ensures a continuous production of surface BRDF parameters thanks to the Kalman filter recursive data processing. An application of the method is performed with SPOT/VEGETATION data over the western Africa equatorial region for the year 2003. Compared to presently available products from VEGETATION and MODIS instruments, this new approach allows to fill the gaps and improves the retrieved parameters time consistency. Another interesting possibility of the Kalman filter is the production of surface biophysical variables in quasi-real-time for applications that require a frequent update of the surface parameters.     

一种Blinn-Phong BRDF红外反射模型的研究

针对红外场景仿真中辐射反射分量运算复杂、真实感欠缺等问题,提出一种Blinn-Phong BRDF红外反射模型,并基于Unity平台将其应用于三维红外仿真场景。该方法在对实测红外图像进行阈值分割的基础上,利用简化辐亮度运算和红外成像过程的仿真链路反演模型,求解目标表面温度值,根据红外辐射原理与可见光光照模型的理论相似性,将改进的Blinn-Phong光照模型移植到红外波段,并引入双向反射分布函数提高仿真精度,提出Blinn-Phong BRDF红外反射模型;最后基于该辐射反射模型构建零视距仿真场景,同时将仿真图像与实测图像进行比对,验证了反射模型的可信度和有效性。实验结果表明,提出的红外反射模型既有较高的仿真效率,又能够较好地模拟红外反射的高光现象,满足红外视景仿真对辐射反射的要求。