| 1. |
- Akenine-Möller, Tomas, et al.
(författare)
-
Efficient Depth of Field Rasterization Using a Tile Test Based on Half-Space Culling
- 2012
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 31:1, s. 3-18
-
Tidskriftsartikel (refereegranskat)abstract
- For depth of field (DOF) rasterization, it is often desired to have an efficient tile versus triangle test, which can conservatively compute which samples on the lens that need to execute the sample-in-triangle test. We present a novel test for this, which is optimal in the sense that the region on the lens cannot be further reduced. Our test is based on removing half-space regions of the (u, v) -space on the lens, from where the triangle definitely cannot be seen through a tile of pixels. We find the intersection of all such regions exactly, and the resulting region can be used to reduce the number of sample-in-triangle tests that need to be performed. Our main contribution is that the theory we develop provides a limit for how efficient a practical tile versus defocused triangle test ever can become. To verify our work, we also develop a conceptual implementation for DOF rasterization based on our new theory. We show that the number of arithmetic operations involved in the rasterization process can be reduced. More importantly, with a tile test, multi-sampling anti-aliasing can be used which may reduce shader executions and the related memory bandwidth usage substantially. In general, this can be translated to a performance increase and/or power savings.
|
|
| 2. |
- Clarberg, Petrik, et al.
(författare)
-
An Optimizing Compiler for Automatic Shader Bounding
- 2010
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 29:4, s. 1259-1268
-
Tidskriftsartikel (refereegranskat)abstract
- Programmable shading provides artistic control over materials and geometry, but the black box nature of shaders makes some rendering optimizations difficult to apply. In many cases, it is desirable to compute bounds of shaders in order to speed up rendering. A bounding shader can be automatically derived from the original shader by a compiler using interval analysis, but creating optimized interval arithmetic code is non-trivial. A key insight in this paper is that shaders contain metadata that can be automatically extracted by the compiler using data flow analysis. We present a number of domain-specific optimizations that make the generated code faster, while computing the same bounds as before. This enables a wider use and opens up possibilities for more efficient rendering. Our results show that on average 42-44% of the shader instructions can be eliminated for a common use case: single-sided bounding shaders used in lightcuts and importance sampling.
|
|
| 3. |
- Clarberg, Petrik, et al.
(författare)
-
Exploiting visibility correlation in direct illumination
- 2008
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 27:4, s. 1125-1136
-
Tidskriftsartikel (refereegranskat)abstract
- The visibility function in direct illumination describes the binary visibility over a light source, e.g., an environment map. Intuitively, the visibility is often strongly correlated between nearby locations in time and space, but exploiting this correlation without introducing noticeable errors is a hard problem. In this paper, we first study the statistical characteristics of the visibility function. Then, we propose a robust and unbiased method for using estimated visibility information to improve the quality of Monte Carlo evaluation of direct illumination. Our method is based on the theory of control variates, and it can be used on top of existing state-of-the-art schemes for importance sampling. The visibility estimation is obtained by sparsely sampling and caching the 4D visibility field in a compact bitwise representation. In addition to Monte Carlo rendering, the stored visibility information can be used in a number of other applications, for example, ambient occlusion and lighting design.
|
|
| 4. |
- Clarberg, Petrik, et al.
(författare)
-
Practical product importance sampling for direct illumination
- 2008
-
Ingår i: Computer Graphics Forum. - : Wiley. - 0167-7055 .- 1467-8659. ; 27:2, s. 681-690
-
Konferensbidrag (refereegranskat)abstract
- We present a practical algorithm for sampling the product of environment map lighting and surface reflectance. Our method builds on wavelet-based importance sampling, but has a number of important advantages over previous methods. Most importantly, we avoid using precomputed reflectance functions by sampling the BRDF on-the-fly. Hence, all types of materials can be handled, including anisotropic and spatially varying BRDFs, as well as procedural shaders. This also opens up for using very high resolution, uncompressed, environment maps. Our results show that this gives a significant reduction of variance compared to using lower resolution approximations. In addition, we study the wavelet product, and present a faster algorithm geared for sampling purposes. For our application, the computations are reduced to a simple quadtree-based multiplication. We build the BRDF approximation and evaluate the product in a single tree traversal, which makes the algorithm both faster and more flexible than previous methods.
|
|
| 5. |
- Hasselgren, Jon, et al.
(författare)
-
A family of inexpensive sampling schemes
- 2005
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 24:4, s. 843-848
-
Tidskriftsartikel (refereegranskat)abstract
- To improve image quality in computer graphics, antialiazing techniques such as supersampling and multisampling are used. We explore a family of inexpensive sampling schemes that cost as little as 1.25 samples per pixel and up to 2.0 samples per pixel. By placing sample points in the corners or on the edges of the pixels, sharing can occur between pixels, and this makes it possible to create inexpensive sampling schemes. Using an evaluation and optimization framework, we present optimized sampling patterns costing 1.25, 1.5, 1.75 and 2.0 samples per pixel.
|
|
| 6. |
- Larsson, Thomas, et al.
(författare)
-
Bounding Volume Hierarchies of Slab Cut Balls
- 2009
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 28:8, s. 2379-2395
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce a bounding volume hierarchy based on the Slab Cut Ball. This novel type of enclosing shape provides an attractive balance between tightness of fit, cost of overlap testing, and memory requirement. The hierarchy construction algorithm includes a new method for the construction of tight bounding volumes in worst case O(n) time, which means our tree data structure is constructed in O(n log n) time using traditional top-down building methods. A fast overlap test method between two slab cut balls is also proposed, requiring as few as 28-99 arithmetic operations, including the transformation cost. Practical collision detection experiments confirm that our tree data structure is amenable for high performance collision queries. In all the tested benchmarks, our bounding volume hierarchy consistently gives performance improvements over the sphere tree, and it is also faster than the OBB tree in five out of six scenes. In particular, our method is asymptotically faster than the sphere tree, and it also outperforms the OBB tree, in close proximity situations.
|
|
| 7. |
- Munkberg, Jacob, et al.
(författare)
-
Per-Vertex Defocus Blur for Stochastic Rasterization
- 2012
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 31:4, s. 1385-1389
-
Tidskriftsartikel (refereegranskat)abstract
- We present user-controllable and plausible defocus blur for a stochastic rasterizer. We modify circle of confusion coefficients per vertex to express more general defocus blur, and show how the method can be applied to limit the foreground blur, extend the in-focus range, simulate tilt-shift photography, and specify per-object defocus blur. Furthermore, with two simplifying assumptions, we show that existing triangle coverage tests and tile culling tests can be used with very modest modifications. Our solution is temporally stable and handles simultaneous motion blur and depth of field.
|
|
| 8. |
- Munkberg, Jacob, et al.
(författare)
-
Practical HDR texture compression
- 2008
-
Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 27:6, s. 1664-1676
-
Tidskriftsartikel (refereegranskat)abstract
- The use of high dynamic range (HDR) textures in real-time graphics applications can increase realism and provide a more vivid experience. However, the increased bandwidth and storage requirements for uncompressed HDR data can become a major bottleneck. Hence, several recent algorithms for HDR texture compression have been proposed. In this paper, we discuss several practical issues one has to confront in order to develop and implement HDR texture compression schemes. These include improved texture filtering and efficient offline compression. For compression, we describe how Procrustes analysis can be used to quickly match a predefined template shape against chrominance data. To reduce the cost of HDR texture filtering, we perform filtering prior to the color transformation, and use a simple trick to reduce the incurred errors. We also introduce a number of novel compression modes, which can be combined with existing compression schemes, or used on their own.
|
|
| 9. |
- Auer, Cornelia, et al.
(författare)
-
Complete Tensor Field Topology on 2D Triangulated Manifolds embedded in 3D
- 2011
-
Ingår i: Computer graphics forum (Print). - : Wiley. - 0167-7055 .- 1467-8659. ; 30:3, s. 831-840
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is concerned with the extraction of the surface topology of tensor fields on 2D triangulated manifoldsembedded in 3D. In scientific visualization topology is a meaningful instrument to get a hold on the structure of agiven dataset. Due to the discontinuity of tensor fields on a piecewise planar domain, standard topology extractionmethods result in an incomplete topological skeleton. In particular with regard to the high computational costs ofthe extraction this is not satisfactory. This paper provides a method for topology extraction of tensor fields thatleads to complete results. The core idea is to include the locations of discontinuity into the topological analysis.For this purpose the model of continuous transition bridges is introduced, which allows to capture the entiretopology on the discontinuous field. The proposed method is applied to piecewise linear three-dimensional tensorfields defined on the vertices of the triangulation and for piecewise constant two or three-dimensional tensor fieldsgiven per triangle, e.g. rate of strain tensors of piecewise linear flow fields.
|
|
| 10. |
- Günther, D., et al.
(författare)
-
Extraction of Dominant Extremal Structures in Volumetric Data using Separatrix Persistence
- 2012
-
Ingår i: Computer graphics forum (Print). - : Wiley-Blackwell. - 0167-7055 .- 1467-8659. ; 31:8, s. 2554-2566
-
Tidskriftsartikel (refereegranskat)abstract
- Extremal lines and surfaces are features of a 3D scalar field where the scalar function becomes minimal or maximal with respect to a local neighborhood. These features are important in many applications, e.g., computer tomography, fluid dynamics, cell biology. We present a novel topological method to extract these features using discrete Morse theory. In particular, we extend the notion of Separatrix Persistence from 2D to 3D, which gives us a robust estimation of the feature strength for extremal lines and surfaces. Not only does it allow us to determine the most important (parts of) extremal lines and surfaces, it also serves as a robust filtering measure of noise-induced structures. Our purely combinatorial method does not require derivatives or any other numerical computations.
|
|
