一类新的纹理谱描述子

在纹理元的基础上提出了一类新的纹理谱描述子，新的纹理谱描述子在3个方面作了改进：将像素的灰度差量化为4个值；量化区间根据纹理对比度自动确定，并保证量化值具有灰度线性不变性；利用相关性弱的8邻域像素构建纹理谱描述子，从而降低了纹理谱维数。定义了基于新的纹理谱描述子的光照、旋转不变性纹理特征。利用该特征对Outex纹理进行光照、旋转不变性分类，分类准确率高于基于局部二值模式的光照、旋转不变性纹理特征。     

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。     

一种适应户外光照变化的背景建模及目标检测方法

针对户外视频监控存在光照变化这一问题, 提出一个用于准确完成目标检测的实时背景建模框架. 考虑到目标检测的准确性要求, 建立基于帧间像素亮度差统计直方图的像素亮度扰动阈值. 在此基础上, 针对背景建模的实时性要求, 提出一种基于自回归背景模型的参数快速更新方法. 鉴于不同光照变化的适应性要求, 定义对光照变化不敏感的背景纹理模型. 上述模型统称为自回归--纹理 (Auto regression and texture, ART) 模型, 该模型适应于户外光照变化. 基于该模型构建像素亮度和纹理置信区间用于目标检测. 实验结果表明, 该框架能适应和实时跟踪户外背景的光照变化, 并对目标进行准确检测.     

基于颜色统计不变性的纹理图像光照分析

针对目前纹理光照分析方法计算效率慢且需要过多用户交互的缺点,提出一种基于颜色统计不变性的快速纹理光照估算方法。首先,定义纹理图像的颜色统计特征、颜色统计不变性和窗口稳定尺寸,据此估算白色光照和彩色光照图像;其次,通过对纹理图像上-下采样的方法,降低彩色光照估算和本征图像提取的计算复杂度。实验结果表明该方法不但缓解了光照图像中含有纹理结构信息的问题,同时有效提高了运算效率。     

基于图形硬件的辐照度环境纹理图的计算方法

辐照度环境纹理图是绘制任意光照环境下漫反射物体表面的一种有效的方法。为了实现动态光照环境下辐照度环境纹理图的实时绘制,基于当前的通用图形硬件,提出了一种采用顶点着色器快速计算辐照度环境纹理图的方法。该方法从分析球面调和函数入手,首先得出环境贴图的二次多项式表达形式;然后用顶点着色程序对多项式系数和球面调和函数进行加速计算,以快速生成辐照度环境纹理图;最后对于动态光照环境,则通过对环境纹理图的分级细化来加快光照系数的计算,进而实现了动态光照环境下辐照度环境纹理图的重新绘制。实验表明,在动态光照条件下,采用该方法在获取真实感光照效果的同时,其运算速度也能满足交互系统的需求。     

基于颜色和纹理特征背景模型的多层差分运动目标检测算法

提出了一种可以剔除阴影、光照变化影响的运动目标检测算法.该算法分别建立基于颜色和梯度信息的背景差分模型,即为每一个像素建立了基于LBP的纹理特征模型,对于颜色信息采用了一种对颜色测量光度不变性的表示方法,背景模型的更新类似于Stauffer等提出的高斯模型,仅在权值更新中采用了具有滞后作用的策略的更新方法.在前景检测过程中采用了两层的判断过程,在像素层,通过用纹理和颜色的统计模型将每个像素划分为成前景或背景,在第二层,对于颜色特征差分得到前景区域的边界部分统计得到其LBP纹理信息,然后与纹理模型检测得到的同一区域边界的纹理信息进一步比较,剔除由于阴影、光照变化引起的前景误判.     

基于多策略融合的亚像素精度立体匹配研究

为了减少亚像素立体匹配中存在的错误匹配以及提高匹配精度,提出基于多策略融合的亚像素精度立体匹配方法。通过以下三个步骤实现:原图像插值处理结合基于最小生成树代价聚集策略估计分数视差;给出新的视差搜索范围确定关系,减少匹配代价计算;在大片低纹理区域引入视差平面拟合细化视差,在亚像素精度上平滑,减少错误匹配。实验表明,算法有效地将匹配精度提高到亚像素级,同时减少了错误匹配。     

辐射度场景中双向纹理函数表面的绘制

双向纹理函数(BTF)表面一般采用点采样数据来定义表面的光照属性,因而这类表面很难运用基于面片分割的辐射度方法进行绘制,提出一种将辐射度算法扩展到包括BTF表面场景的有效方法.对表面的BTF样本区域首先进行像素聚类,再在各个像素类内对视线采样方向做进一步自适应的聚类,在各个视线类内像素分别拟合一个低频光照甬数,并求它们在各个视线类内光照细节的高频光照函数.低频光照函数作为该表面区域的平均反射属性参与辐射度计算,生成场景的整体光照效果;然后利用计算的辐射度值和高频光照函数重建该表面区域的BTF材质细节.文中方法不仅取得了较高的压缩效率,而且在BTF材质表面产生了辉映等全局光照效果.最后利用硬件实现了视点快速改变时的场景绘制.     

基于层次多项式纹理的实时草地绘制

根据草的几何结构复杂性和材质的漫反射特性,提出层次多项式纹理(layered polynomial texture,简称LPT)来表示草,可以高效真实地实现这个目标.LPT是一个五维纹理,每一个纹理单元是一组多项式系数,记录分布在多层像素的不同光照方向下亮度的拟合信息,用于在绘制时计算出纹理像素的颜色.把草表示成3个沿已知视线方向的LPT,然后基于Wang Tile的LPT合成方法生成拼图块,再映射到地面上得到草地,从而获得动态光照环境下草地的实时绘制.实验结果表明,LPT的存储量小,运算代价低,而且LPT能推广到树的表示,也可以实现树的动态阴影效果.     

基于OpenGL的像素光照计算技术

首先介绍了基于像素的光照计算的理论基础；然后通过与基于顶点的光照计算技术的比较，分析了其优缺点；最后将其与新一代的硬件相结合，通过对基于像素计算的点光源的实现，展现了其在OpenGL下的强大功能和应用前景。     

Geometry‐Aware Framebuffer Level of Detail

This paper introduces a framebuffer level of detail algorithm for controlling the pixel workload in an interactive rendering application. Our basic strategy is to evaluate the shading in a low resolution buffer and, in a second rendering pass, resample this buffer at the desired screen resolution. The size of the lower resolution buffer provides a trade‐off between rendering time and the level of detail in the final shading. In order to reduce approximation error we use a feature‐preserving reconstruction technique that more faithfully approximates the shading near depth and normal discontinuities. We also demonstrate how intermediate components of the shading can be selectively resized to provide finer‐grained control over resource allocation. Finally, we introduce a simple control mechanism that continuously adjusts the amount of resizing necessary to maintain a target framerate. These techniques do not require any preprocessing, are straightforward to implement on modern GPUs, and are shown to provide significant performance gains for several pixel‐bound scenes.     

The truth about texture mapping

The author describes how the unique configuration of the planet Uranus influenced him to take a close look at how the layout of a texture map in memory affects the performance of the rendering algorithm. A planet rendering program that calculates, for each occupied pixel on the screen, the latitude and longitude visible at that pixel, is described. It uses this latitude and longitude to index into a texture map to get a surface color. The actual texture color comes from bilinearly interpolating the texture colors at the four texture map pixels that surround that latitude and longitude. This, along with the shading calculations, gives the net color of the pixel. The use of virtual memory, handling page faults, tiling, and address generation are considered     

基于OpenGL的等角插补明暗处理的软件实现

等角插补明暗处理具有Phong明暗处理的视觉效果,而且具有较Phong明暗处理更快的渲染效率,基于标准图形渲染管道,用Ｃ语言实现了OpenGL渲染管道的硬件计算部分,同时用Ｃ语言实现了等角插补明暗处理,并给出了实验结果。该方法的实现可为渲染算法的研究和实现提供参考。     

多视点成像的多边形模板法

该文提出一种对场景进行多视点成像的方法。该方法首先为场景中的多边形生成多边形模板，一个多边形模板，包括一条轮廓路径和一组纹条，而一个纹条是平行成像画的一个平面与多边形相交的直线段。由于纹条相对于不同视点的透视投影的变化是线性的，因此，绘制多边形时可以基于模板逐个纹条地处理，而不必按照传统的扫描转换方法逐个点地处理，绘制速度可以提高很多。同时，与视点无关的光照和纹理可以预先计算并保存在模板中，以便在成像时利用基于图像绘制的技术来生成高质量的图像。该方法中，视点可以放置在三维空间的任意位置，并且在场景漫游时可以根据视点位置自动地实现多分辨率绘制。     

Real-time triple product relighting using spherical local-frame parameterization

This paper addresses the problem of real-time rendering for objects with complex materials under varying all-frequency illumination and changing view. Our approach extends the triple product algorithm by using local-frame parameterization, spherical wavelets, per-pixel shading and visibility textures. Storing BRDFs with local-frame parameterization allows us to handle complex BRDFs and incorporate bump mapping more easily. In addition, it greatly reduces the data size compared to storing BRDFs with respect to the global frame. The use of spherical wavelets avoids uneven sampling and energy normalization of cubical parameterization. Finally, we use per-pixel shading and visibility textures to remove the need for fine tessellations of meshes and shift most computation from vertex shaders to more powerful pixel shaders. The resulting system can render scenes with realistic shadow effects, complex BRDFs, bump mapping and spatially-varying BRDFs under varying complex illumination and changing view at real-time frame rates on modern graphics hardware.     

Index rendering: hardware-efficient architecture for 3-D graphics in multimedia system

Real-time three-dimensional (3D) graphics is emerging rapidly in multimedia applications, but it suffers from requirements for huge computation, high bandwidth, and large buffer. In order to achieve hardware efficiency for 3D graphics rendering, we propose a novel approach named index rendering. The basic concept of index rendering is to realize a 3D rendering pipeline by using asynchronous multi-dataflows. Triangle information can be divided into several parts with each part capable of being transferred independently and asynchronously. Finally, all data are converged by the index to generate the final image. The index rendering approach can eliminate unnecessary operations in the traditional 3D graphics pipeline, the unnecessary operations are caused by the invisible pixels and triangles in the 3D scene. Previous work, deferred shading, eliminates the operations relating to invisible pixels, but it requires huge tradeoffs in bandwidth and buffer size. With index rendering, we can eliminate operations on both invisible pixels and triangles with fewer tradeoffs as compared with the deferred shading approach. The simulation and analysis results show that the index rendering approach can reduce 10%-70% of lighting operations when using the flat and Gouraud shading process and decrease 30%-95% when using Phong shading. Furthermore, it saves 70% of buffer size and 50%-70% of bandwidth compared with the deferred shading approach. The result also indicates that this approach of index rendering is especially suitable for low-cost portable rendering devices. Hence, index rendering is a hardware-efficient architecture for 3D graphics, and it makes rendering hardware more easily integrated into multimedia systems, especially system-on-a-chip (SOC) designs.     

延迟着色的渲染管线优化

传统的GPU渲染方法是前向渲染,在当前的实时渲染领域中,一种叫做延迟着色的新管线利用了硬件的多渲染目标特性进行两个阶段的管线处理,在逐像素光照计算之前就完成了所有的可见性测试,将像素填充率降到最低。然而,延迟着色需要大量的视频存储空间,而且不能高效地渲染半透明物体,针对应用中的这些局限性提出可行的解决方案。     

基于图形硬件加速的体绘制关键技术综述

随着近年来计算机图形硬件性能的不断提高,利用硬件来实现体绘制过程中的某些环节以获取交互的绘制速率变为可能,并逐渐成为目前的研究热点。从体绘制的分类、明暗处理、重构、体积裁剪等4个角度对基于图形硬件加速的体绘制方法进行了分类综述,介绍了各种关键技术的研究进展和典型算法,并讨论了各自特点及其相互联系。     

Pixel History Linear Models for Real‐Time Temporal Filtering

We propose a new real‐time temporal filtering and antialiasing (AA) method for rasterization graphics pipelines. Our method is based on Pixel History Linear Models (PHLM), a new concept for modeling the history of pixel shading values over time using linear models. Based on PHLM, our method can predict per‐pixel variations of the shading function between consecutive frames. This combines temporal reprojection with per‐pixel shading predictions in order to provide temporally coherent shading, even in the presence of very noisy input images. Our method can address both spatial and temporal aliasing problems under a unique filtering framework that minimizes filtering error through a recursive least squares algorithm. We demonstrate our method working with a commercial deferred shading engine for rasterization and with our own OpenGL deferred shading renderer. We have implemented our method in GPU and it has shown significant reduction of temporal flicker in very challenging scenarios including foliage rendering, complex non‐linear camera motions, dynamic lighting, reflections, shadows and fine geometric details. Our approach, based on PHLM, avoids the creation of visible ghosting artifacts and it reduces the filtering overblur characteristic of temporal deflickering methods. At the same time, the results are comparable to state‐of‐the‐art real‐time filters in terms of temporal coherence.     

实时绘制带斑纹的毛发

提出一种将reaction-diffusion过程纹理与Lengyel的毛发绘制算法相结合，实时生成带有斑纹的毛发的方法。利用vertexshader和pixel shader等硬件扩展功能对Lengyel方法进行了改进，不但提高了绘制速度，而且使得毛发的光照计算更为准确．