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。     

一种超大规模地形场景的实时渲染算法

超大规模地形场景包含大量的数据,无法一次性载入内存进行实时渲染.基于Geometrical Mipmapping算法,结合动态调度技术,提出一种高效的超大规模地形场景实时渲染算法.算法对海量地形数据进行分块,在实时运行时,根据视点的位置动态地载入所需的地形块和释放无用的地形块,使得内存中的地形数据维持在一定范围内.然后,通过LOD技术和视域剔除对内存中的地形数据进行简化,大量减少送入GPU的三角形数量,从而达到实时渲染.实验结果表明,算法渲染速度快,内存开销较小,适合于超大规模地形场景的实时渲染.     

基于连续HLOD的大规模场景快速绘制算法

大规模场景的快速绘制是虚拟现实技术重要的研究课题之一.为了加速场景的绘制,一般采用层次细节模型和可见性裁剪方法,但是现有算法在处理大规模场景时存在着局限性.本文提出了一种新的大规模场景快速绘制算法,该算法在场景层次划分的基础上,利用拓扑结构可变的网格简化方法为场景层次计算连续的分层层次细节模型（HLOD）;然后在实时绘制阶段,对场景分层层次细节模型进行视点相关的全局和局部细化,并结合快速有效的视域裁剪,从而大大加速了场景绘制速度.实验结果表明该算法是简单有效的,并且算法还可以进一步扩展到外存方式.     

基于重要性采样的动态场景全频阴影实时绘制算法

由于环境光源下的柔和阴影绘制需要针对每像素对来自全景方向的上千个光源进行昂贵的可见性计算,这给实时绘制带来了巨大的挑战.在消除预计算的前提下,提出了一种环境光源下动态场景全频阴影实时绘制算法.通过基于光照强度的环境图重要性采样、场景几何信息近似采样、阴影图预滤波、BRDF重要性采样等方法,实现了环境光源下动态场景的全频阴影及其环境映射绘制.实验表明,算法可满足环境光源、场景物体及其材质动态变化的要求,并可在保证实时绘制效率的前提下,取得近似于预计算算法的绘制质量.     

视野驱动的自适应阴影图

阴影图是当前实时阴影绘制中的一种经典算法。该算法基于图像空间,当有限分辨率的阴影图映射到较大场景中时,就会由于采样不足造成锯齿形变走样。提出了一种实时的反走样阴影图算法,该算法首先获取当前视点所能够看到的场景范围,然后绘制该范围内的阴影图,并映射到场景中生成实时阴影。该方法同经典的阴影图算法相比,避免了场景中不必要的阴影绘制,提高了阴影图的利用率,反走样的效果很好。而且,该方法只需要绘制一到两幅阴影图,算法的实时性很强,可以满足一个上百万面片的大规模场景中实时阴影绘制的需要。     

三维虚拟漫游技术的研究

三维虚拟现实漫游技术目前是国内外的研究热点之一.主要研究和探讨了利用五点定位LOD四又树组织和管理大规模地形数据,并以井地算法实现大规模地形实时渲染,能有效地提升三维场景的渲染速度.提出了一种基于场景投影图矩阵的自动漫游路径生成的钢丝算法,该算法适用于各种复杂的三维虚拟场景并能生成光滑的自动漫游路径.     

基于环境映照自动对齐的高质量虚实融合技术

要实现高品质的增强现实效果需要解决虚拟物体与现实场景的光照一致性问题.虽然采用HDR技术能获取场景的环境映照,但需要解决所获取的光照环境信息与真实场景的对齐问题.为此提出一种基于特征自动匹配的环境映照对齐方法.首先采用Affine-SIFT算法和随机抽样一致性算法对环境映照和拍摄场景进行特征匹配并优化匹配结果,然后利用基于运动推断结构的摄像机定标算法求得匹配对的三维位置,从而计算出环境映照与真实场景的对应关系,实现了二者的自动对齐.基于该技术搭建的高真实感实时虚实融合系统采用基于关键帧的相机跟踪技术,可以实时地将虚拟物体注册到拍摄的视频场景里,并允许对其进行实时的交互编辑.在渲染时有效地利用了自动对齐后的光照环境信息,采用重要性采样算法和阴影映射技术实现了实时的高质量渲染.实验结果表明,所搭建的增强现实系统很好地解决了实时虚实融合中的几何一致性和光照一致性问题.     

自适应背景提取算法的比较

介绍几种背景自适应提取算法的原理,分析算法在交通视频检测中的仿真效果.依据交通场景提取中实时性、准确性等关键技术指标,采用基于"真理图"的量化评估方法,在多种复杂交通场景中利用recall,precision评价参数对背景提取算法的效果进行比较分析,明确被评价算法的性能特点与适用的交通场景.     

基于OpenCL的实时KD-Tree与动态场景光线跟踪

目前,基于GPU或多核CPU加速的光线跟踪算法是与硬件相关的.研究具有跨平台性能的实时光线跟踪算法既具有挑战性,又具有很强的应用价值.为此,提出一种基于OpenCL并且跨平台的动态场景实时光线跟踪绘制算法.首先通过对通用GPU并行处理性能进行发掘,将光线跟踪中KD-Tree建立、场景遍历和绘制3个过程均设计在GPU上,而CPU只负责其中各过程的调度,从而充分利用了GPU的计算性能,并有效地降低了数据传输开销;通过设计并行分区、并行SAH、紧密的数据管理以及区间性叶结点存储等算法,在GPU中高效、高质量地建立动态场景的KD-Tree,同时高质量的KD-Tree也有效地加速了场景的遍历速度.该算法以广度优先和大规模并行模式建立K D-Tree,更具通用性,既可以运行于NVIDIA GPU(CUDA GPU),也可以运行于AMD GPU.实验结果表明,文中算法可以在NVIDIA GPU和AMD GPU上对中等规模的动态场景实现实时光线跟踪绘制.     

A Radiosity Solution for Curved Surface Environments

Radiosity has been a popular method for photorealistic image generation.But the determination of form factors between curved patches is the most difficult and time consuming procedure,and also the errors caused by approximating source patch‘s radiosity with average values are obvious.In this paper,a radiosity algorithm for rendering curved surfaces represented by parameters is described.The contributed radiosity from differential areas on four vertices of the source patch to a receiving point is calculated firstly,then the contribution from the inner area of the source patch is evaluated by interpolating the values on four corners.Both the difficult problem of determining form-factors between curved surfaces and errors mentioned above have been avoided.Comparison of the experimental results using the new algorithm has been made with the ones obtained by traditional method.Some associated techniques such as the visibility test and the adaptive subdivision are also described.     

Bounded Radiosity – Illumination on General Surfaces and Clusters

Traditionally, Radiosity algorithms have been restricted to scenes made from planar patches. Most algorithms for computing form factors and the subdivision criterion for hierarchical methods implicitly assume planar patches. In this paper, we present a new radiosity algorithm that is solely based on simple geometric information about surface elements, namely their bounding boxes and cone of normals. Using this information allows to compute efficient error bounds that can be used for the subdivision oracle and for computing the energy transfer. Due to the simple interface to geometric objects, our algorithm not only allows for computing illumination on general curved surfaces, but it can also be directly applied to a hieararchy of clusters. Several examples demonstrate the advantages of the new approach.     

Tone reproduction for realistic images

Radiosity and other global illumination methods for image synthesis calculate the real world radiance values of a scene instead of the display radiance values that will represent them. Though radiosity and ray tracing methods can compute extremely accurate and wide-ranging scene radiances, modern display devices emit light only in a tiny fixed range. The radiances must be converted, but ad-hoc conversions cause serious errors and give little assurance that the evoked visual sensations are truly equivalent. Sensation-preserving conversions for display, already known in photography, printing, and television as tone reproduction methods, are discussed. Computer graphics workers can apply the existing photographic methods, but may also extend them to include more complex and subtle effects of human vision using the published findings of vision researchers. Ways of constructing a sensation-preserving display converter, or tone reproduction operator, for monochrome images are demonstrated     

曲面环境的一般辐射度方法

基于两微面元间的能量传递理论,本文提出了一种适用于曲面环境的一般辐射度方法.与传统辐射度方法不同的是,本方法假定每一面片上的辐射度是变化的,并引入双线性插值将辐射度系统方程中未知数转化为各面片顶点处的辐射度,从而建立起一整套辐射度系统方程.同时,该一般辐射度方程被拓广至非漫射环境,并导出了一组描述多重镜面和透明面间光能传递的递推公式.理论分析与实验结果证明该方法具有很大的潜力.     

Radiosity in Flatland

The radiosity method for the simulation of interreflection of light between diffuse surfaces is such a common image synthesis technique that its derivation is worthy of study. We here examine the radiosity method in a two dimensional, flatland world. It is shown that the radiosity method is a simple finite element method for the solution of the integral equation governing global illumination. These two-dimensional studies help explain the radiosity method in general and suggest a number of improvements to existing algorithms. In particular, radiosity solutions can be improved using a priori discontinuity meshing, placing mesh boundaries on discontinuities such as shadow edges. When discontinuity meshing is used along with piecewise-linear approximations instead of the current piecewise-constant approximations, the accuracy of radiosity simulations can be greatly increased.     

A Progressive Radiosity Algorithm for Scenes Containing Curved Surfaces

Based on the theory of light energy transfer between two differential diffuse surface areas, a generalized radiosity approach is presented. Unlike the conventional radiosity method, curved surfaces are subdivided into triangular surface patches, radiosity is assummed to be vary across each triangular surface patch. By adopting linear interpolation scheme over each triangular surface patch, we have established a complete set of approximated radiosity equations. Their unknowns are radiosities of differential surface areas located at all vertices of surface patches. The generalized radiosity equation has also been extended to non-diffuse environments. Theoretical analysis and experimental results demonstrate the great potential of this method,     

Radiosity: A method for computing global illumination

The radiosity method for computing the interreflection of light within diffuse environments is described. The development of the method for realistic image synthesis over the past three years is outlined. A short discussion of the underlying theory and implementation is followed by a real life example which illustrates the power and accuracy of the radiosity method and points out the different results from ray tracing procedures. Current and future developments of the radiosity method are outlined.     

辐射度技术用于随机分维几何面的全局光照计算

分维几何为模拟自然体和景物提供了十分卓越的工具，然而，分维几何的造型是一个无限细分的随机造型过程，这就为分维几何的绘制带来了极大的困难，到目前为止，只有某些特殊的光线跟踪技术能够用于绘制分维几何曲面，主要产生高光效果。     

Multiresolution B-spline Radiosity

This paper introduces a kind of new wavelet radiosity method called multiresolution B-spline radiosity, which uses B-splines of different scales to represent radiosity distribution functions. A set of techniques and algorithms, such as function extrapolation, adaptive quadrature, scale adjustment and octree, are proposed to implement it. This method sets up hierarchical structures on surfaces, keeps radiosity distribution continuous at element boundaries, does not need postprocessing, and does not prevent the use of any surface whose parameter domain is rectilinear.