Bias Compensation for Photon Maps

Density estimation techniques such as the photon map method rely on a particle transport simulation to reconstruct indirect illumination, which is proportional to the particle density. In the photon map framework, particles are usually located using nearest‐neighbour methods due to their generality. However, these methods have an inherent tradeoff between local bias and noise in the reconstructed illumination, which depends on the density estimate bandwidth. This paper presents a bias compensating operator for nearest‐neighbour density estimation which adapts the bandwidth according to the estimated bias in the reconstructed illumination. ACM CSS: I.3.7 Three‐Dimensional Graphics and Realism Raytracing     

Adaptive Records for Irradiance Caching

Irradiance Caching is one of the most widely used algorithms to speed up global illumination. In this paper, we propose an algorithm based on the Irradiance Caching scheme that allows us (1) to adjust the density of cached records according to illumination changes and (2) to efficiently render the high‐frequency illumination changes. To achieve this, a new record footprint is presented. Although the original method uses records having circular footprints depending only on geometrical features, our record footprints have a more complex shape which accounts for both geometry and irradiance variations. Irradiance values are computed using a classical Monte Carlo ray tracing method that simplifies the determination of nearby objects and the pre‐computation of the shape of the influence zone of the current record. By gathering irradiance due to all the incident rays, illumination changes are evaluated to adjust the footprint’s records. As a consequence, the record footprints are smaller where illumination gradients are high. With this technique, the record density depends on the irradiance variations. Strong variations of irradiance (due to direct contributions for example) can be handled and evaluated accurately. Caching direct illumination is of high importance, especially in the case of scenes having many light sources with complex geometry as well as surfaces exposed to daylight. Recomputing direct illumination for the whole image can be very time‐consuming, especially for walkthrough animation rendering or for high‐resolution pictures. Storing such contributions in the irradiance cache seems to be an appropriate solution to accelerate the final rendering pass.     

基于梯度图的微结构表面全局光照实时绘制

针对带有微结构表面的几何模型全局光照计算复杂、难以达到实时性要求的问题,提出一种基于高度梯度图分析的全局光照实时绘制方法.首先,定义微结构高度梯度图,并据此构建可见点的局部最高点集合.其次,给出面向微结构表面对象实时绘制的全局光照计算模型,将光照计算近似分解为环境光入射、光源直接光照和一次交互漫反射这3种分量的计算.在环境光计算过程中,提出一种自适应环境光遮挡计算,借助局部最高点集合计算遮挡角.在直接光照中,给出一种微结构阴影的修正方法,搜索入射光方向的最近局部最高点剖面;通过比较剖面内光线投影与局部最高点的遮挡角,近似确定由微结构造成的阴影区域.最后,根据可见点的局部最高点集合确定一次交互漫反射的采样范围,进行渗色处理.整个全局光照计算方法在图像空间完成,较好地利用了延迟着色的思想和GPU并行计算的特点.算法可以在使用低精度几何模型时表现出带有微结构表面的高精度模型的全局光照效果,且适用于动态场景和可变形物体的全局光照计算.     

GPU‐Based Spherical Light Field Rendering with Per‐Fragment Depth Correction

Image‐based rendering techniques are a powerful alternative to traditional polygon‐based computer graphics. This paper presents a novel light field rendering technique which performs per‐pixel depth correction of rays for high‐quality reconstruction. Our technique stores combined RGB and depth values in a parabolic 2D texture for every light field sample acquired at discrete positions on a uniform spherical setup. Image synthesis is implemented on the GPU as a fragment program which extracts the correct image information from adjacent cameras for each fragment by applying per‐pixel depth correction of rays. We show that the presented image‐based rendering technique provides a significant improvement compared to previous approaches. We explain two different rendering implementations which make use of a uniform parametrisation to minimise disparity problems and ensure full six degrees of freedom for virtual view synthesis. While one rendering algorithm implements an iterative refinement approach for rendering light fields with per pixel depth correction, the other approach employs a raycaster, which provides superior rendering quality at moderate frame rates. GPU based per‐fragment depth correction of rays, used in both implementations, helps reducing ghosting artifacts to a non‐noticeable amount and provides a rendering technique that performs without exhaustive pre‐processing for 3D object reconstruction and without real‐time ray‐object intersection calculations at rendering time.     

Decoupled Shading for Real‐time Heterogeneous Volume Illumination

Existing real‐time volume rendering techniques which support global illumination are limited in modeling distinct realistic appearances for classified volume data, which is a desired capability in many fields of study for illustration and education. Directly extending the emission‐absorption volume integral with heterogeneous material shading becomes unaffordable for real‐time applications because the high‐frequency view‐dependent global lighting needs to be evaluated per sample along the volume integral. In this paper, we present a decoupled shading algorithm for multi‐material volume rendering that separates global incident lighting evaluation from per‐sample material shading under multiple light sources. We show how the incident lighting calculation can be optimized through a sparse volume integration method. The quality, performance and usefulness of our new multi‐material volume rendering method is demonstrated through several examples.     

Spatio‐Temporal Filtering of Indirect Lighting for Interactive Global Illumination

We introduce a screen‐space statistical filtering method for real‐time rendering with global illumination. It is inspired by statistical filtering proposed by Meyer et al. to reduce the noise in global illumination over a period of time by estimating the principal components from all rendered frames. Our work extends their method to achieve nearly real‐time performance on modern GPUs. More specifically, our method employs the candid covariance‐free incremental PCA to overcome several limitations of the original algorithm by Meyer et al., such as its high computational cost and memory usage that hinders its implementation on GPUs. By combining the reprojection and per‐pixel weighting techniques, our method handles the view changes and object movement in dynamic scenes as well.     

一种点面混合的复杂三维模型加速绘制方法

在主流个人计算机硬件条件下,为加速百万以上三角面片构成的复杂稠密几何模型的绘制速度,综合基于几何的建模与绘制方法GBMR和基于点的建模与绘制方法PBMR的优点,提出了一种同时使用三角面片和点作为基本单元进行对象建模与绘制的点面混合方法．在预处理阶段,对模型表面进行网格分割,存储子块三角面片和顶点点云数据,同时对顶点点云按顶点重要度排序并序列化为线性结构．在实时绘制阶段,进行视相关的裁剪和背面剔除,不同子块按视点距离分别由三角形或点进行绘制．以上过程充分利用图形处理单元GPU,实现了基于GPU的点面混合的对象连续多分辨率绘制,有效地提高了复杂模型的绘制效率．     

Approximating global illumination on mesostructure surfaces with height gradient maps

Rendering global illumination for objects with mesostructure surfaces is a time-consuming task, and cannot presently be applied to interactive graphics. This paper presents a real-time rendering method based on a mesostructure height gradient map (MHGM) to exhibit lighting effects on meso-scale details in dynamic environments. We approximate global illumination using a lighting model including three components: incident ambient light, direct light and single bounce indirect light. MHGM is introduced to create local apex sets, which would help us to compute the three components adaptively. Our approach runs entirely on the graphics hardware, and uses deferred shading and the graphics pipeline to accelerate computation. We achieve high quality results which can render meso-scale details with approximate global illumination even for low-resolution geometric models. Moreover, our approach fully supports dynamic scenes and deformable objects.     

利用球谐方法分散计算场景的全局光照

作为一种特殊的光照模型,辐射度在图形学中有着重要的应用.然而,由于其计算的复杂性,辐射度方法一直得不到广泛的应用,特别是在动态场景中.提出一种基于辐射度算法的全局光照实时加速算法,在原有基于点采样进行场景的全局光照近似的基础上,提出了不同的点采样计算方法,以提高辐射度方法对动画场景的适应性.算法对场景中的物体建立六面体包围盒,并在包围盒各顶点设置采样点,这样就可以在环境变化对其光照影响不大的情况下采用原有的计算结果,实现辐射度算法在动态场景中的计算加速.同时,对场景中的每个物体的光照,利用立方体映射计算直接光照;而对物体间的能量交换采用点采样方法进行近似计算并利用附近采样点的光照插值作为物体的光照.实验结果表明,该算法可以减少大量的间接光照计算,提高了辐射度算法的效率.     

Sparse GPU Voxelization of Yarn‐Level Cloth

Most popular methods in cloth rendering rely on volumetric data in order to model complex optical phenomena such as sub‐surface scattering. These approaches are able to produce very realistic illumination results, but their volumetric representations are costly to compute and render, forfeiting any interactive feedback. In this paper, we introduce a method based on the Graphics Processing Unit (GPU) for voxelization and visualization, suitable for both interactive and offline rendering. Recent features in the OpenGL model, like the ability to dynamically address arbitrary buffers and allocate bindless textures, are combined into our pipeline to interactively voxelize millions of polygons into a set of large three‐dimensional (3D) textures (>10⁹ elements), generating a volume with sub‐voxel accuracy, which is suitable even for high‐density woven cloth such as linen.     

Scalable Realistic Rendering with Many‐Light Methods

Recent years have seen increasing attention and significant progress in many‐light rendering, a class of methods for efficient computation of global illumination. The many‐light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state‐of‐the‐art report, we give an easy‐to‐follow, introductory tutorial of the many‐light theory; provide a comprehensive, unified survey of the topic with a comparison of the main algorithms; discuss limitations regarding materials and light transport phenomena and present a vision to motivate and guide future research. We will cover both the fundamental concepts as well as improvements, extensions and applications of many‐light rendering.     

Efficient Image‐Based Proximity Queries with Object‐Space Precision

We present an efficient algorithm for object‐space proximity queries between multiple deformable triangular meshes. Our approach uses the rasterization capabilities of the GPU to produce an image‐space representation of the vertices. Using this image‐space representation, inter‐object vertex‐triangle distances and closest points lying under a user‐defined threshold are computed in parallel by conservative rasterization of bounding primitives and sorted using atomic operations. We additionally introduce a similar technique to detect penetrating vertices. We show how mechanisms of modern GPUs such as mipmapping, Early‐Z and Early‐Stencil culling can optimize the performance of our method. Our algorithm is able to compute dense proximity information for complex scenes made of more than a hundred thousand triangles in real time, outperforming a CPU implementation based on bounding volume hierarchies by more than an order of magnitude.