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doc. Ing. Jiří Bittner, Ph.D.

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Dynamic Diffuse Global Illumination: Implementation and Evaluation

  • Autoři: Hvězda, M., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Proceedings of CESCG 2022: The 26th Central European Seminar on Computer Graphics. Vienna: VRVis Center, 2022.
  • Rok: 2022
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We describe our implementation of a recent real-time global illumination method based on irradiance fields, which uses ray tracing to approximate multiple bounces of light transmission in a virtual scene. Furthermore, we present qualitative comparisons with a brute force path tracer and the method's performance results. Lastly, we discuss possible extensions, such as adaptive ray generation and probe placement.

Performance Comparison of Bounding Volume Hierarchies for GPU Ray Tracing

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Ray tracing is an inherent component of modern rendering algorithms. The bounding volume hierarchy (BVH) is a commonly used acceleration data structure employed in most ray tracing frameworks. Through the last decade, many methods addressing ray tracing with bounding volume hierarchies have been proposed. However, most of these methods were typically compared to only one or two reference methods. The acceleration provided by a particular BVH depends heavily on its construction algorithm. Even experts in the field dispute which method is the best. To add more insight into this challenge, we empirically compare the most popular methods addressing BVHs in the context of GPU ray tracing. Moreover, we combine the construction algorithms with other enhancements such as spatial splits, ray reordering, and wide BVHs. To estimate how close we are from the best performing BVH, we propose a novel method using global optimization with simulated annealing and combine it with the existing best-performing BVH builders. For the sake of fairness and consistency, all methods are evaluated in a single unified framework, and we make all source code publicly available. We also study the correlation between tracing times and the estimated traversal cost induced by the surface area heuristic (SAH).

A Survey on Bounding Volume Hierarchies for Ray Tracing

  • Autoři: Meister, D., Ogaki, S., Benthin, C., Doyle, M.J., Guthe, M., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: COMPUTER GRAPHICS FORUM. 2021, 40(2), 683-712. ISSN 0167-7055.
  • Rok: 2021
  • DOI: 10.1111/cgf.142662
  • Odkaz: https://doi.org/10.1111/cgf.142662
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Ray tracing is an inherent part of photorealistic image synthesis algorithms. The problem of ray tracing is to find the nearest intersection with a given ray and scene. Although this geometric operation is relatively simple, in practice, we have to evaluate billions of such operations as the scene consists of millions of primitives, and the image synthesis algorithms require a high number of samples to provide a plausible result. Thus, scene primitives are commonly arranged in spatial data structures to accelerate the search. In the last two decades, the bounding volume hierarchy (BVH) has become the de facto standard acceleration data structure for ray tracing-based rendering algorithms in offline and recently also in real-time applications. In this report, we review the basic principles of bounding volume hierarchies as well as advanced state of the art methods with a focus on the construction and traversal. Furthermore, we discuss industrial frameworks, specialized hardware architectures, other applications of bounding volume hierarchies, best practices, and related open problems.

QuadStack: An Efficient Representation and Direct Rendering of Layered Datasets

  • Autoři: Graciano, A., Rueda-Ruiz, A.J., Pospíšil, A., doc. Ing. Jiří Bittner, Ph.D., Beneš, B.
  • Publikace: IEEE Transactions on Visualization and Computer Graphics. 2021, 27(9), 3733-3744. ISSN 1077-2626.
  • Rok: 2021
  • DOI: 10.1109/TVCG.2020.2981565
  • Odkaz: https://doi.org/10.1109/TVCG.2020.2981565
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We introduce QuadStack, a novel algorithm for volumetric data compression and direct rendering. Our algorithm exploits the data redundancy often found in layered datasets that are common in science and engineering fields such as geology, biology, mechanical engineering, medicine, etc. QuadStack first compresses the volumetric data into vertical stacks that are then compressed into a quadtree that identifies and represents the layered structures at the internal nodes. The associated data (color, material, density, etc.) and shape of these layer structures are decoupled and encoded independently, leading to high compression rates (4× to 45×) of the original voxel model memory footprint in our experiments). We also introduce an algorithm for value retrieving from the QuadStack representation and we show that the access has logarithmic complexity. Because of the fast access, QuadStack is suitable for efficient data representation and direct rendering and we show that our GPU implementation performs comparable in speed with the state-of-the-art algorithms (18-79 MRays/s in our implementation), while maintaining a significantly smaller memory footprint

Rendering Wet Roads in Driving Simulations

  • Autoři: Nguyenová, G., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Proceedings of CESCG 2021: The 25th Central European Seminar on Computer Graphics. Vienna: VRVis Center, 2021.
  • Rok: 2021
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Rain and its impact can significantly enhance the realism and credibility of outdoor scene rendering. It further attributes to the environment's diversity by breaking the repeating patterns of a synthetic world. We describe our approach to visual simulation of the rain phenomena in driving simulations. We focus on varying intensity of the rain effects (e.g. drizzle or heavy rain) seen on roads with driving cars. The simulation includes adjustable wetness of the roads with puddle regions. When a car drives through a puddle, splashes are generated according to an assessment model. The puddles also react to contact with the tires, creating tiny wavy movements based on the wave equation. The simulation is implemented in a game engine, and we propose a way to render high-quality ray-traced outputs using an external ray tracer.

Spatio-temporal BRDF: Modeling and synthesis

  • Autoři: Meister, D., Pospíšil, A., Sato, I., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Computers & Graphics. 2021, 97 279-291. ISSN 0097-8493.
  • Rok: 2021
  • DOI: 10.1016/j.cag.2021.04.001
  • Odkaz: https://doi.org/10.1016/j.cag.2021.04.001
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a generalization of example-based texture synthesis to spatio-temporal BRDFs. A key com-ponent of our method is a novel representation of time-varying materials using polynomials describing time-varying BRDF parameters. Our representation allows efficient fitting of measured data into a com-pact spatio-temporal BRDF representation, and it allows an efficient analytical evaluation of distances be-tween spatio-temporal BRDF parameters. We show that even polynomials of low degree are sufficient to represent various time-varying phenomena and provide more accurate results than the previously proposed representation. We are the first who applied the example-based texture synthesis on abstract structures such as polynomial functions. We present two applications of synthesizing spatio-temporal BRDFs using our method: material enlargement and transfer of time-varying phenomenon from an ex-ample to a given static material. We evaluated the synthesized BRDFs in the context of realistic rendering and real-time rendering.

On Ray Reordering Techniques for Faster GPU Ray Tracing

  • Autoři: Meister, D., Bokšanský, J., Guthe, M., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: I3D '20: Symposium on Interactive 3D Graphics and Games. New York: ACM, 2020. p. 1-9. ISBN 978-1-4503-7589-4.
  • Rok: 2020
  • DOI: 10.1145/3384382.3384534
  • Odkaz: https://doi.org/10.1145/3384382.3384534
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We study ray reordering as a tool for increasing the performance of existing GPU ray tracing implementations. We focus on ray reordering that is fully agnostic to the particular trace kernel. We summarize the existing methods for computing the ray sorting keys and discuss their properties. We propose a novel modification of a previously proposed method using the termination point estimation that is well-suited to tracing secondary rays. We evaluate the ray reordering techniques in the context of the wavefront path tracing using the RTX trace kernels. We show that ray reordering yields significantly higher trace speed on recent GPUs (1.3 − 2.0 ×), but to recover the reordering overhead in the hardware-accelerated trace phase is problematic.

Ray Classification for Accelerated BVH Traversal

  • Autoři: Hendrich, J., Pospíšil, A., Meister, D., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: COMPUTER GRAPHICS FORUM. 2019, 38(4), 49-56. ISSN 0167-7055.
  • Rok: 2019
  • DOI: 10.1111/cgf.13769
  • Odkaz: https://doi.org/10.1111/cgf.13769
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    For ray tracing based methods, traversing a hierarchical acceleration data structure takes up a substantial portion of the total rendering time. We propose an additional data structure which cuts off large parts of the hierarchical traversal. We use the idea of ray classification combined with the hierarchical scene representation provided by a bounding volume hierarchy. We precompute short arrays of indices to subtrees inside the hierarchy and use them to initiate the traversal for a given ray class. This arrangement is compact enough to be cache-friendly, preventing the method from negating its traversal gains by excessive memory traffic. The method is easy to use with existing renderers which we demonstrate by integrating it to the PBRT renderer. The proposed technique reduces the number of traversal steps by 42% on average, saving around 15% of time of finding ray-scene intersection on average.

Ray Traced Shadows: Maintaining Real-Time Frame Rates

  • Autoři: Bokšanský, J., Wimmer, M., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Ray Tracing Gems. New York: Apress, 2019. p. 159-182. ISBN 978-1-4842-4426-5.
  • Rok: 2019
  • DOI: 10.1007/978-1-4842-4427-2_13
  • Odkaz: https://doi.org/10.1007/978-1-4842-4427-2_13
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Efficient and accurate shadow computation is a long-standing problem in computer graphics. In real-time applications, shadows have traditionally been computed using the rasterization-based pipeline. With recent advances of graphics hardware, it is now possible to use ray tracing in real-time applications, making ray traced shadows a viable alternative to rasterization. While ray traced shadows avoid many problems inherent in rasterized shadows, tracing every shadow ray independently can become a bottleneck if the number of required rays rises, e.g., for high-resolution rendering, for scenes with multiple lights, or for area lights. Therefore, the computation should focus on image regions where shadows actually appear, in particular on the shadow boundaries. We present a practical method for ray traced shadows in real-time applications. Our method uses the standard rasterization pipeline for resolving primary-ray visibility and ray tracing for resolving visibility of light sources. We propose an adaptive sampling algorithm for shadow rays combined with an adaptive shadowfiltering method. These two techniques allow computing high-quality shadows with a limited number of shadow rays per pixel. We evaluated our method using a recent real-time ray tracing API (DirectX Raytracing) and compare the results with shadow mapping using cascaded shadow maps.

Real-time External Labeling of Ghosted Views

  • DOI: 10.1109/TVCG.2018.2833479
  • Odkaz: https://doi.org/10.1109/TVCG.2018.2833479
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a new algorithm for calculating the external labeling of ghosted views of moderately complex 3D models. The algorithm uses multiple criteria decision making, based on fuzzy logic, to optimize positions of the labels associated with different parts of the input model. The proposed method can be used with various existing algorithms for creating ghosted views from 3D models. The method operates in real-time, which allows the user to acquire a good understanding of the structure of the input model by studying the model and its labels from different viewpoints. We have conducted a user study to evaluate label layouts produced by our algorithm and those created by humans. The results show that the proposed method can significantly improve user understanding of labeled ghosted views of complicated 3D models, and its label layouts are comparable with label layouts created by humans.

Parallel Locally-Ordered Clustering for Bounding Volume Hierarchy Construction

  • Autoři: Meister, D., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: IEEE Transactions on Visualization and Computer Graphics. 2018, 24(3), 1345-1353. ISSN 1077-2626.
  • Rok: 2018
  • DOI: 10.1109/TVCG.2017.2669983
  • Odkaz: https://doi.org/10.1109/TVCG.2017.2669983
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a novel massively parallel construction algorithm for Bounding Volume Hierarchies (BVHs) based on locally-ordered agglomerative clustering. Our method builds the BVH iteratively from bottom to top by merging a batch of cluster pairs in each iteration. To efficiently find the neighboring clusters, we keep the clusters ordered along the Morton curve. This ordering allows us to identify approximate nearest neighbors very efficiently and in parallel. We implemented our algorithm in CUDA and evaluated it in the context of GPU ray tracing. For complex scenes, our method achieves up to a twofold reduction of build times while providing up to 17 percent faster trace times compared with the state-of-the-art methods.

Parallel Reinsertion for Bounding Volume Hierarchy Optimization

  • DOI: 10.1111/cgf.13376
  • Odkaz: https://doi.org/10.1111/cgf.13376
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a novel highly parallel method for optimizing bounding volume hierarchies (BVH) targeting contemporary GPU architectures. The core of our method is based on the insertion‐based BVH optimization that is known to achieve excellent results in terms of the SAH cost. The original algorithm is, however, inherently sequential: no efficient parallel version of the method exists, which limits its practical utility. We reformulate the algorithm while exploiting the observation that there is no need to remove the nodes from the BVH prior to finding their optimized positions in the tree. We can search for the optimized positions for all nodes in parallel while simultaneously tracking the corresponding SAH cost reduction. We update in parallel all nodes for which better position was found while efficiently handling potential conflicts during these updates. We implemented our algorithm in CUDA and evaluated the resulting BVH in the context of the GPU ray tracing. The results indicate that the method is able to achieve the best ray traversal performance among the state of the art GPU‐based BVH construction methods.

Extended Morton Codes for High Performance Bounding Volume Hierarchy Construction

  • DOI: 10.1145/3105762.3105782
  • Odkaz: https://doi.org/10.1145/3105762.3105782
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose an extension to the Morton codes used for spatial sorting of scene primitives. The extended Morton codes increase the coherency of the clusters resulting from the object sorting and work better for non-uniform distribution of scene primitives. In particular, our codes are enhanced by encoding the size of the objects, applying adaptive ordering of the code bits, and using variable bit counts for diferent dimensions. We use these codes for constructing Bounding Volume Hierarchies (BVH) and show that the extended Morton code leads to higher quality BVH, particularly for the fastest available BVH build algorithms that heavily rely on spatial coherence of Morton code sorting. In turn, our method allows to achieve up to 54% improvement in the BVH quality especially for scenes with a non-uniform spatial extent and varying object sizes. Our method is easy to implement into any Morton code based build algorithm as it involves only a modifcation of the Morton code computation step.

Lightdrum-Portable Light Stage for Accurate BTF Measurement on Site

  • DOI: 10.3390/s17030423
  • Odkaz: https://doi.org/10.3390/s17030423
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a miniaturised light stage for measuring the bidirectional reflectance distribution function (BRDF) and the bidirectional texture function (BTF) of surfaces on site in real world application scenarios. The main principle of our lightweight BTF acquisition gantry is a compact hemispherical skeleton with cameras along the meridian and with light emitting diode (LED) modules shining light onto a sample surface. The proposed device is portable and achieves a high speed of measurement while maintaining high degree of accuracy. While the positions of the LEDs are fixed on the hemisphere, the cameras allow us to cover the range of the zenith angle from 0 degrees to 75 degrees and by rotating the cameras along the axis of the hemisphere we can cover all possible camera directions. This allows us to take measurements with almost the same quality as existing stationary BTF gantries. Two degrees of freedom can be set arbitrarily for measurements and the other two degrees of freedom are fixed, which provides a tradeoff between accuracy of measurements and practical applicability. Assuming that a measured sample is locally flat and spatially accessible, we can set the correct perpendicular direction against the measured sample by means of an auto- collimator prior to measuring. Further, we have designed and used a marker sticker method to allow for the easy rectification and alignment of acquired images during data processing. We show the results of our approach by images rendered for 36 measured material samples.

Lightdrum: Portable Surface-Reflectance Measurement Onsite

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Hošek, J., Němcová, Š., Čáp, J., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Special Interest Group on Computer Graphics and Interactive Techniques Conference, {SIGGRAPH} '17, Los Angeles, CA, USA, July 30 - August 03, 2017, Posters Proceedings. New York: ACM, 2017. p. 80:1-80:2. ISBN 978-1-4503-5015-0.
  • Rok: 2017
  • DOI: 10.1145/3102163.3102234
  • Odkaz: https://doi.org/10.1145/3102163.3102234
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    This portable dome-based instrument is designed for measuring surface reflectance (bidirectional texture function and bidirectional reflectance distribution function) outside the lab. Measurement of different surfaces (floor, wall, ceiling) acquires 16680 HDR RGB images (400x400 pixels) of a planar patch (36x36mm) in 17 minutes.

Návrh a realizace přenosného zařízení pro měření BTF povrchů

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Článek popisuje realizaci nového typu zařízení pro rychlý záznam tisíců snímků měřeného povrchu kombinující různé směry osvětlení a směru pohledu na měřený vzorek. Pořízené snímky jsou následně zpracovány do BTF dat pro vizualizační počítačové aplikace například virtuální reality. Unikátnost navrženého zařízení spočívá v tom, že není nutné vzorek povrchu extrahovat ze svého prostředí a přinést k zařízení, ale měřicí zařízení je možné přenést k měřenému povrchu s libovolnou konfigurací v prostoru a provést jeho záznam obsahující 16680 HDR snímků během 17 minut. V článku je popsána optomechanická konstrukce celého zařízení a detaily problémů, které bylo nutné vhodným způsobem technicky vyřešit. V závěru jsou diskutovány možnosti aplikací BTF dat a ukázány první praktické výsledky.

Optomechanical design of a portable compact bidirectional texture function measurement instrument

  • DOI: 10.1364/AO.56.001183
  • Odkaz: https://doi.org/10.1364/AO.56.001183
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Recent developments in optoelectronics and material processing techniques make it possible to design and produce a portable and compact measurement instrument for bidirectional texture function (BTF). Parallelized optics, on-board data processing, rapid prototyping, and other nonconventional production techniques and materials were the key to building an instrument capable of in situ measurements with fast data acquisition. We designed, built, and tested a prototype of a unique portable and compact multi-camera system for BTF measurement which is capable of in situ measurement of temporally unstable samples. In this paper, we present its optomechanical design. (C) 2017 Optical Society of America

Parallel BVH Construction using Progressive Hierarchical Refinement

  • DOI: 10.1111/cgf.13143
  • Odkaz: https://doi.org/10.1111/cgf.13143
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a novel algorithm for construction of bounding volume hierarchies (BVHs) for multi-core CPU architectures. The algorithm constructs the BVH by a divisive top-down approach using a progressively refined cut of an existing auxiliary BVH. We propose a new strategy for refining the cut that significantly reduces the workload of individual steps of BVH construction. Additionally, we propose a new method for integrating spatial splits into the BVH construction algorithm. The auxiliary BVH is constructed using a very fast method such as LBVH based on Morton codes. We show that the method provides a very good trade-off between the build time and ray tracing performance. We evaluated the method within the Embree ray tracing framework and show that it compares favorably with the Embree BVH builders regarding build time while maintaining comparable ray tracing speed.

VAO++: Practical Volumetric Ambient Occlusion for Games

  • Autoři: Bokšanský, J., Pospíšil, A., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Rendering - Experimental Ideas & Implementations 2017. Aire-la-Ville: Eurographics Association, 2017. p. 31-39. ISSN 1727-3463. ISBN 978-3-03868-045-1.
  • Rok: 2017
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Ambient occlusion is one of the commonly used methods to increase visual fidelity in real-time rendering applications. We propose several extensions of the recently introduced volumetric ambient occlusion method. These extensions improve the properties of the methods with a particular focus on the quality vs performance tradeoff and wide applicability in contemporary games. We describe the implementation of the proposed algorithm and its extensions. We implemented the method as a camera effect within the Unity game engine. The results show that our implementation compares favorably with the standard ambient occlusion in Unity both in terms of quality and speed.

Compensating for color artifacts in the design of technical kaleidoscopes

  • DOI: 10.1117/1.OE.55.11.113104
  • Odkaz: https://doi.org/10.1117/1.OE.55.11.113104
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In the applications of computer graphics, bidirectional texture function (BTF) is used for realistic and predictive rendering. The goal of current research is to get a surface representation indistinguishable from the real world. We developed, built, and tested a portable instrument for BTF acquisition based on kaleidoscopic imaging. We discuss the color issues we experienced after the initial tests. We show that the same color balance cannot be applied to the whole image as the spectral response of the instrument varies depending on the position within the image. All optical elements were inspected for their contributions to the spectral behavior of the instrument. A software simulator of a mathematical model of the device was implemented. We found a way to implement all these contributions into the image processing pipeline. In this way, the correct white balance for each individual pixel in the image is found and applied, allowing for a more faithful color representation. Also proposed is an optimized dielectric protective layer for the kaleidoscope’s mirrors causing the least possible color aberration.

Compensating for colour artefacts in the design of technical kaleidoscopes

  • DOI: 10.1117/12.2225166
  • Odkaz: https://doi.org/10.1117/12.2225166
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In computer graphics and related fields, bidirectional texture function (BTF) is used for realistic and predictive rendering. BTF allows for the capture of fine appearance effects such as self-shadowing, inter-reflection and subsurface scattering needed for true realism when used in rendering algorithms. The goal of current research is to get a surface representation indistinguishable from the real world. We developed, produced and tested a portable instrument for BTF acquisition based on kaleidoscopic imaging. Here we discuss the colour issues we experienced after the initial tests. We show that the same colour balance cannot be applied to the whole picture as the spectral response of the instrument varies with the position in the image. All optical elements were inspected for their contributions to the spectral behaviour of the instrument. The off-the-shelf parts were either measured or the manufacturer’s data were considered. The custom made mirrors’ spectral reflectivity was simulated. The mathematical model of the instrument was made. We found a way how to implement all these contributions to the image processing pipeline. In this way, a correct white balance for each individual pixel in the image is found and applied, allowing for a more faithful colour representation. Also proposed is an optimized dielectric protective layer for the kaleidoscope’s mirrors.

Geometric calibration of rotational kaleidoscopic instrument

  • DOI: 10.1117/12.2257434
  • Odkaz: https://doi.org/10.1117/12.2257434
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The measurement of spatially varying surface reflectance is required for faithful reproduction of real world to allow for predictive look of computer generated images. One such proposed method uses a rotational kaleidoscopic imaging, where illumination and imaging paths are realized by subimages on kaleidoscopic mirrors and illumination is carried out by a DLP projector. We describe a novel geometric calibration method for a rotational kaleidoscope that is necessary to get aligned and accurate data from measurement. The calibration has two stages. The first stage mechanically adjusts the camera, the projector, and the autocollimator against the kaleidoscope mirrors. The second stage is based on the software. By random perturbation of camera and projector in corresponding mathematical model of the kaleidoscope we estimate better real positions of camera and projector in a physical setup, comparing the computed images from the software simulator and the acquired images from the physical setup.

Parallel BVH construction using k-means clustering

  • DOI: 10.1007/s00371-016-1241-0
  • Odkaz: https://doi.org/10.1007/s00371-016-1241-0
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a novel method for fast parallel construction of bounding volume hierarchies (BVH) on the GPU. Our method is based on a combination of divisible and agglomerative clustering. We use the k-means algorithm to subdivide scene primitives into clusters. From these clusters, we construct treelets using the agglomerative clustering algorithm. Applying this procedure recursively, we construct the entire bounding volume hierarchy. We implemented the method using parallel programming concepts on the GPU. The results show the versatility of the method: it can be used to construct medium-quality hierarchies very quickly, but also it can be used to construct high-quality hierarchies given a slightly longer computational time. We evaluate the method in the context of GPU ray tracing and show that it provides results comparable with other state-of-the-art GPU techniques for BVH construction. We also believe that our approach based on the k-means algorithm gives a new insight into how bounding volume hierarchies can be constructed.

Parallel On-Demand Hierarchy Construction on Contemporary GPUs

  • DOI: 10.1109/TVCG.2015.2465898
  • Odkaz: https://doi.org/10.1109/TVCG.2015.2465898
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present the first parallel on-demand spatial hierarchy construction algorithm targeting ray tracing on many-core processors such as GPUs. The method performs simultaneous ray traversal and spatial hierarchy construction focused on the parts of the data structure being traversed. The method is based on a versatile framework built around a task pool and runs entirely on the GPU. We show that the on-demand construction can improve rendering times compared to full hierarchy construction. We evaluate our method on both object (BVH) and space (kd-tree) subdivision data structures and compare them mutually. The on-demand method is particularly beneficial for rendering large scenes with high occlusion. We also present SAH kd-tree builder that outperforms previous state-of-the-art builders running on the GPU.

Performance Comparison of Bounding Volume Hierarchies and Kd-Trees for GPU Ray Tracing

  • DOI: 10.1111/cgf.12776
  • Odkaz: https://doi.org/10.1111/cgf.12776
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a performance comparison of bounding volume hierarchies and kd-trees for ray tracing on many-core architectures (GPUs). The comparison is focused on rendering times and traversal characteristics on the GPU using data structures that were optimized for very high performance of tracing rays. To achieve low rendering times, we extensively examine the constants used in termination criteria for the two data structures. We show that for a contemporary GPU architecture (NVIDIA Kepler) bounding volume hierarchies have higher ray tracing performance than kd-trees for simple and moderately complex scenes. On the other hand, kd-trees have higher performance for complex scenes, in particular for those with high depth complexity. Finally, we analyse the causes of the performance discrepancies using the profiling characteristics of the ray tracing kernels.

CHC+RT: Coherent Hierarchical Culling for Ray Tracing

  • Autoři: Mattausch, O., doc. Ing. Jiří Bittner, Ph.D., Jaspe, A., Gobbetti, E., Wimmer, M., Pajarola, R.
  • Publikace: Computer Graphics Forum. 2015, 34(2), 537-548. ISSN 0167-7055.
  • Rok: 2015
  • DOI: 10.1111/cgf.12582
  • Odkaz: https://doi.org/10.1111/cgf.12582
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a new technique for in-core and out-of-core GPU ray tracing using a generalization of hierarchical occlusion culling in the style of the CHC++ method. Our method exploits the rasterization pipeline and hardware occlusion queries in order to create coherent batches of work for localized shader-based ray tracing kernels. By combining hierarchies in both ray space and object space, the method is able to share intermediate traversal results among multiple rays. We exploit temporal coherence among similar ray sets between frames and also within the given frame. A suitable management of the current visibility state makes it possible to benefit from occlusion culling for less coherent ray types like diffuse reflections. Since large scenes are still a challenge for modern GPU ray tracers, our method is most useful for scenes with medium to high complexity, especially since our method inherently supports ray tracing highly complex scenes that do not fit in GPU memory. For in-core scenes our method is comparable to CUDA ray tracing and performs up to 5.94x better than pure shader-based ray tracing.

Incremental BVH construction for ray tracing

  • DOI: 10.1016/j.cag.2014.12.001
  • Odkaz: https://doi.org/10.1016/j.cag.2014.12.001
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a new method for incremental construction of Bounding Volume Hierarchies (BVH). Despite the wide belief that the incremental construction of BVH is inefficient we show that our method incrementally constructs a BVH with quality comparable to the best SAH builders. We illustrate the versatility of the proposed method using a flexible parallelization scheme that opens new possibilities for combining different BVH construction heuristics. We demonstrate the usage of the method in a proof-of-concept application for real-time preview of data streamed over the network. We believe that our method will renew the interest in incremental BVH construction and it will find its applications in ray tracing based remote visualizations and fast previews or in interactive scene editing applications handling very large data sets.

Optimizing of functional design parameters of kaleidoscopes

  • DOI: 10.1117/12.2070343
  • Odkaz: https://doi.org/10.1117/12.2070343
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Imaging of surface textures requires many combinations of incident illumination angles and detector angles of view. Kaleidoscope is one of the means for measurement of bidirectional texture function of various sample surfaces. An optical system featuring the kaleidoscope is proposed in the paper. Optical parameters of such an imaging system are described and evaluated. We also discuss the optimization process of these parameters which influences the overall imaging performance of a kaleidoscope device. We provide the visualization of various kaleidoscope designs.

Přenosné zařízení pro BTF měření

  • Autoři: Hošek, J., Čáp, J., prof. Ing. Vlastimil Havran, Ph.D., Němcová, Š., doc. Ing. Jiří Bittner, Ph.D., Macúchová, K., Zicha, J.
  • Publikace: Sborník odborného semináře Nové metody a postupy v oblasti přístrojové techniky, automatického řízení a informatiky 2015. Praha: Ústav přístrojové a řídicí techniky FS ČVUT, 2015. pp. 17-19. ISBN 978-80-01-05758-2.
  • Rok: 2015
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Jednou z metod využívanou pro reálnou vizualizaci povrchů objektů v počítačové grafice je metoda označovaná jako bidirectional texture functions (BTF). Tato metoda využívá rozsáhlou databázi různých typů různě strukturovaných povrchů snímané a osvětlené pod mnoha různými prostorovými úhly, kterými je povrch virtuálního grafického tělesa rendrován. Pro první verzi takového zařízení realizované v prvním roce projektu jsme proto zvolili koncept využívající kaleidoskopického zobrazení, které umožňuje zvýšit rychlost snímání dat povrchu při zachování nízkých rozměrů a hmotnosti celého zařízení.

Prostorové hierarchie - klíč k rychlosti a detailu

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Proces, který od vstupního digitálního popisu 3D scény vede k vytvoření jejího 2D obrazu ze zvolené pozice pozorovatele včetně simulování světelných efektů (např. odrazů a lomů) se anglicky nazývá rendering. Čeští grafici sice pro něj nedokázali nalézt lepší pojmenování než nelibě znějící rendrování, zato dokázali tuto metodu výrazným způsobem urychlit. Klíčem k úspěchu bylo efektivní využití hierarchických struktur, tedy grafů doplňujících základní 3D geometrické informace o popis jejich prostorového uspořádání.

Realisation of Circular Motion for Portable BTF Measurement Instrument

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The paper contains analysis of possibilities for realization a large radius circular motion suitable for a portable measurement system for bidirectional texture functions (BTF) measurement. This circular motion will be used for changing the position of an array of detection cameras taking snapshots of sample illuminated by LED modules. The constrains for the proposed circular motion design are: large radius of motion about 300 mm limited to angular motion about 12°, non-accessibility of the centre of rotation which has to be kept free, total mass and price of the solution and motion deviation from centre point. We present three possible solutions comprising a single stiff curved guide with a ball roller, a curved guide with fixed rollers and two separated linear guides. We include an additional factor - the angular deviation of concentrically arranged array of cameras to - evaluate the optimal solution reaching BTF measurement instrument needs

Software simulator for design and optimization of the kaleidoscopes for the surface reflectance measurement

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., doc. Ing. Jiří Bittner, Ph.D., Čáp, J., Hošek, J., Macúchová, K., Němcová, Š.
  • Publikace: Proc. SPIE 9442, Optics and Measurement Conference 2014. Bellingham (stát Washington): SPIE, 2015. Proceedings of SPIE. vol. 9442. ISSN 0277-786X. ISBN 978-1-62841-557-5.
  • Rok: 2015
  • DOI: 10.1117/12.2086897
  • Odkaz: https://doi.org/10.1117/12.2086897
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Realistic reproduction of appearance of real-world materials by means of computer graphics requires accurate measurement and reconstruction of surface reflectance properties. We propose an interactive software simulation tool for modeling properties of a kaleidoscopic optical system for surface reflectance measurement. We use ray tracing to obtain fine grain simulation results corresponding to the resolution of a simulated image sensor and computing the reflections inside this system based on planar mirrors. We allow for a simulation of different geometric configurations of a kaleidoscope such as the number of mirrors, the length, and the taper angle. For accelerating the computation and delivering interactivity we use parallel processing of large groups of rays. Apart from the interactive mode our tool also features batch optimization suitable for automatic search for optimized kaleidoscope designs. We discuss the possibilities of the simulation and present some preliminary results obtained by using it in practice.

Softwarová simulace návrhu a optimalizace kaleidoskopu pro měření odrazivosti povrchu

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Realistická a prediktivní počítačová syntéza obrazu včetně vzhledu materiálů vyžaduje přesné měření a následnou rekonstrukci odrazivosti povrchu materiálů. K měření lze použít kaleidoskopický systém, jehož optické vlastnosti lze interaktivně modelovat dále popisovaným simulačním software. Simulátor využívá metodu sledování paprsků pro získání výsledků v rozlišení, které odpovídá zvolenému rozlišení použitého detektoru. Lze tak porovnat výsledky z různých geometrických konfigurací kaleidoskopu. Kromě interaktivního režimu je možné použít i dávkové zpracování zadání vhodné pro optimalizaci parametrů kaleidoskopu. V závěru jsou diskutovány možnosti simulace a ukázány první praktické výsledky.

T-SAH: Animation Optimized Bounding Volume Hierarchies

  • DOI: 10.1111/cgf.12581
  • Odkaz: https://doi.org/10.1111/cgf.12581
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a method for creating a bounding volume hierarchy (BVH) that is optimized for all frames of a given animated scene. The method is based on a novel extension of surface area heuristic to temporal domain (T-SAH). We perform iterative BVH optimization using T-SAH and create a single BVH accounting for scene geometry distribution at different frames of the animation. Having a single optimized BVH for the whole animation makes our method extremely easy to integrate to any application using BVHs, limiting the per-frame overhead only to refitting the bounding volumes.We evaluated the T-SAH optimized BVHs in the scope of real-time GPU ray tracing. We demonstrate, that our method can handle even highly complex inputs with large deformations and significant topology changes. The results show, that in a vast majority of tested scenes our method provides significantly better run-time performance than traditional SAH and also better performance than GPU based per-frame BVH rebuild.

Bounding Volume Hierarchies versus Kd-trees on Contemporary Many-Core Architectures

  • DOI: 10.1145/2643188.2643196
  • Odkaz: https://doi.org/10.1145/2643188.2643196
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a performance comparison of bounding volume hierarchies and kd-trees for ray tracing on many-core architectures (GPUs). The comparison is focused on rendering times and traversal characteristics on the GPU using data structures that were optimized for maximum performance of tracing rays irrespective of the time needed for their build. We show that for a contemporary GPU architecture (NVIDIA Kepler) bounding volume hierarchies have higher ray tracing performance than kd-trees for simple and moderately complex scenes. Kd-trees, on the other hand, have higher performance for complex scenes, in particular for those with occlusion.

Efficient Sorting and Searching in Rendering Algorithms

  • DOI: 10.2312/egt.20141024
  • Odkaz: https://doi.org/10.2312/egt.20141024
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In the tutorial we show the connection between rendering algorithms and sorting and searching as classical problems studied in computer science. We provide both theoretical and empirical evidence that for many rendering techniques most time is spent by sorting and searching. In particular we discuss problems and solutions for visibility computation, density estimation, and importance sampling. For each problem we mention its speci c issues such as dimensionality of the search domain or online versus oine searching. We will present the underlying data structures and their enhancements in the context of speci c rendering algorithms such as ray tracing, photon mapping, and hidden surface removal.

Simple kaleidoscope design for reflectance measurement

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we describe simple design of a kaleidoscope used for measuring the bidirectional reflectance distribution function with aim to obtain the bidirectional texture function of various surface samples. The first prototype of the kaleidoscope was designed in symmetrical configuration with four tapered mirror walls. We discuss the influence of different design parameters with respect to expected results. The proposed kaleidoscope was manufactured and his performance evaluated.

DCGI Laboratories at CTU Prague, Czech Republic

  • DOI: 10.2312/conf/EG2013/lab/L04
  • Odkaz: https://doi.org/10.2312/conf/EG2013/lab/L04
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The Department of Computer Graphics and Interaction (DCGI) covers education and research activities in Computer Graphics and HumanComputer Interaction areas at the Czech Technical University in Prague (CTU). This paper presents the staff, laboratories, projects, and selected scientific achievements of the DCGI.

Fast Insertion-Based Optimization of Bounding Volume Hierarchies

  • DOI: 10.1111/cgf.12000
  • Odkaz: https://doi.org/10.1111/cgf.12000
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present an algorithm for fast optimization of bounding volume hierarchies (BVH) for efficient ray tracing. We perform selective updates of the hierarchy driven by the cost model derived from the surface area heuristic. In each step, the algorithm updates a fraction of the hierarchy nodes to minimize the overall hierarchy cost. The updates are realized by simple operations on the tree nodes: removal, search and insertion. Our method can quickly reduce the cost of the hierarchy constructed by the traditional techniques, such as the surface area heuristic. We evaluate the properties of the proposed method on fourteen test scenes of different complexity including individual objects and architectural scenes. The results show that our method can improve a BVH initially constructed with the surface area heuristic by up to 27% and a BVH constructed with the spatial median split by up to 88%.

Massively Parallel Hierarchical Scene Processing with Applications in Rendering

  • DOI: 10.1111/cgf.12140
  • Odkaz: https://doi.org/10.1111/cgf.12140
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a novel method for massively parallel hierarchical scene processing on the GPU, which is based on sequential decomposition of the given hierarchical algorithm into small functional blocks. The computation is fully managed by the GPU using a specialized task pool which facilitates synchronization and communication of processing units. We present two applications of the proposed approach: construction of the bounding volume hierarchies and collision detection based on divide-and-conquer ray tracing. The results indicate that using our approach we achieve high utilization of the GPU even for complex hierarchical problems which pose a challenge for massive parallelization.

Multiple Live Video Environment Sampling

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a framework that captures multiple high dynamic range environment maps and decomposes them into sets of directional light sources in real-time. The environment maps, captured and processed on stand-alone devices (e.g. Nokia N900 smartphone), are available to rendering engines via a server that provides wireless access. We compare three different importance sampling techniques in terms of the quality of sampling pattern, temporal coherence, and performance. Furthermore, we propose a novel idea of merging the directional light sources from multiple cameras by interpolation. We then discuss the pros and cons when using multiple cameras.

Temporally Coherent Adaptive Sampling for Imperfect Shadow Maps

  • DOI: 10.1111/cgf.12154
  • Odkaz: https://doi.org/10.1111/cgf.12154
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a new adaptive algorithm for determining virtual point lights (VPL) in the scope of real-time instant radiosity methods, which use a limited number of VPLs. The proposed method is based on Metropolis-Hastings sampling and exhibits better temporal coherence of VPLs, which is particularly important for real-time applications dealing with dynamic scenes. We evaluate the properties of the proposed method in the context of the algorithm based on imperfect shadow maps and compare it with the commonly used inverse transform method. The results indicate that the proposed technique can significantly reduce the temporal flickering artifacts even for scenes with complex materials and textures. Further, we propose a novel splatting scheme for imperfect shadow maps using hardware tessellation. This scheme significantly improves the rendering performance particularly for complex and deformable scenes. We thoroughly analyze the performance of the proposed techniques on test scenes with detailed materials, moving camera, and deforming geometry.

Efficient Online Visibility for Shadow Maps

  • Autoři: Mattausch, O., doc. Ing. Jiří Bittner, Ph.D., Silvennoinen, A., Scherzer, D., Wimmer, M.
  • Publikace: GPU PRO 3: Advanced Rendering Techniques. Boca Raton: CRC Press, 2012. p. 233-242. ISBN 978-1-4398-8782-0.
  • Rok: 2012
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Standard online occlusion culling is able to vastly improve the rasterization performance of walkthrough applications by identifying large parts of the scene as invisible from the camera and rendering only the visible geometry. However, it is of little use for the acceleration of shadow map generation, so that typically a high percentage of the geometry will be visible when rendering shadow maps. Our algorithm remedies this situation by quickly detecting and culling the geometry that does not contribute to the shadow in the final image. The main idea is to use camera-view visibility information to create a mask of potential shadow receivers in the light view, which restricts the areas where shadow casters have to be rendered.

On Tools for Game Interaction Analysis

  • DOI: 10.2316/P.2012.766-008
  • Odkaz: https://doi.org/10.2316/P.2012.766-008
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Improving accessibility of games was recently identified as one of approaches how to increase the number of potential players. In this paper we propose and discuss several tools for analysing the interaction of a player and a computer game in order to increase accessibility of the game. We focus on interaction devices that use key presses, a mouse cursor movement and mouse clicks for the interaction with the game. Our tools monitor the user interactions during game play and then visualize the interaction of the user through the devices with the game.

Using Annotated Task Models for Accessibility Evaluation

  • DOI: 10.1007/978-3-642-31522-0_47
  • Odkaz: https://doi.org/10.1007/978-3-642-31522-0_47
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Evaluation of application accessibility is a challenging task that requires an intensive testing with potential application users. An alternative to user tests is the model based testing using simulations. The simulations provide important feedback about application accessibility particularly when it is hard to involve the target users in the tests which is often the case for users with disabilities. In this paper we propose a methodology of providing the quickly and easily necessary data for the simulations. In particular we show how to annotate task models using application walkthroughs logs that is data obtained by recording the application usage. We create annotated task models, which together with the user models are suitable for simulation of application usage by virtual users with various disabilities. We present tools for recording and processing of the application walkthrough logs and tools for the interactive task model annotation. Finally, we provide actual examples of task model annotation on three scenarios involving the Second Life metaverse.

Shadow caster culling for efficient shadow mapping

  • Autoři: doc. Ing. Jiří Bittner, Ph.D., Mattausch, O., Silvennoinen, A., Wimmer, M.
  • Publikace: Proceedings of Symposium on Interactive 3D Graphics and Games. New York: ACM Press, 2011. pp. 81-88. ISBN 978-1-4503-0565-5.
  • Rok: 2011
  • DOI: 10.1145/1944745.1944759
  • Odkaz: https://doi.org/10.1145/1944745.1944759
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a novel method for efficient construction of shadow maps by culling shadow casters which do not contribute to visible shadows. The method uses a mask of potential shadow receivers to cull shadow casters using a hierarchical occlusion culling algorithm. We propose several variants of the receiver mask implementations with different culling efficiency and computational costs. For scenes with statically focused shadow maps we designed an efficient strategy to incrementally update the shadow map, which comes close to the rendering performance for unshadowed scenes. We show that our method achieves 3x-10x speedup for rendering large city like scenes and 1.5x-2x speedup for rendering an actual game scene.

VR and HCI Labs at the Czech Technical University in Prague

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    This paper describes the mission, objectives, and research directions of the Department of Computer Graphics and Interaction of the Czech Technical University in Prague. It also gives a brief overview of the running research projects and collaborations.

Layout-aware optimization for interactive labeling of 3D models

  • DOI: 10.1016/j.cag.2010.05.002
  • Odkaz: https://doi.org/10.1016/j.cag.2010.05.002
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a novel method for computing labeling of 3D illustrations in real-time. We solve a multiple criteria optimization problem in which we consider the desired layout already in the stage of searching for salient points of the labeled areas. In the solution we employ fuzzy logic combined with greedy optimization. The method runs on the GPU and achieves interactive rates on medium sized models. The results indicate that the method compares favorably to the state-of-the-art interactive labeling techniques.

Adaptive Global Visibility Sampling

  • DOI: 10.1145/1531326.1531400
  • Odkaz: https://doi.org/10.1145/1531326.1531400
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we propose a global visibility algorithm which computes from-region visibility for all view cells simultaneously in a progressive manner. We cast rays to sample visibility interactions and use the information carried by a ray for all view cells it intersects. The main contribution of the paper is a set of adaptive sampling strategies based on ray mutations that exploit the spatial coherence of visibility. Our method achieves more than an order of magnitude speedup compared to per-view cell sampling. This provides a practical solution to visibility preprocessing and also enables a new type of interactive visibility analysis application, where it is possible to quickly inspect and modify a coarse global visibility solution that is constantly refined.

Game Engine Friendly Occlusion Culling

  • Autoři: doc. Ing. Jiří Bittner, Ph.D., Mattausch, O., Wimmer, M.
  • Publikace: ShaderX7: Advanced Rendering Techniques. Boston: Charles River Media, 2009. p. 637-653. ISBN 1-58450-598-2.
  • Rok: 2009
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    "This article presents a method which minimizes the overhead associated with occlusion queries. The method reduces the number of required state changes and should integrate easily with most game engines. The key ideas are batching of the queries and interfacing with the game engine using a dedicated render queue. We also present some additional optimizations which reduce the number of queries issued as well as the number of rendered primitives. The algorithm is based on the well-known Coherent Hierarchical Culling algorithm.",

RDH: Ray Distribution Heuristics for Construction of Spatial Data Structures.

  • DOI: 10.1145/1980462.1980475
  • Odkaz: https://doi.org/10.1145/1980462.1980475
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Surface area heuristics is currently the most popular method for view independent construction of spatial hierarchies for ray tracing. We present a method which modifies the surface area heuristics by taking into account the actual distribution of rays in the scene. This is achieved by subsampling the rays to be cast and using these rays in order to estimate the probabilities of rays traversing through nodes of the constructed hierarchy. The main aim of our paper is to analyze the potential of taking the ray distribution into account.

CHC++: Coherent Hierarchical Culling Revisited

  • DOI: 10.1111/j.1467-8659.2008.01119.x
  • Odkaz: https://doi.org/10.1111/j.1467-8659.2008.01119.x
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a new algorithm for efficient occlusion culling using hardware occlusion queries. The algorithm significantly improves on previous techniques by making better use of temporal and spatial coherence of visibility. This is achieved by using adaptive visibility prediction and query batching. As a result of the new optimizations the number of issued occlusion queries and the number of rendering state changes are significantly reduced. We also propose a simple method for determining tighter bounding volumes for occlusion queries and a method which further reduces the pipeline stalls. The proposed method provides up to an order of magnitude speedup over the previous state of the art. The new technique is simple to implement, does not rely on hardware calibration and integrates well with modern game engines.

Estimación de Densidades usando GPUs

  • Autoři: Lastra, M., Ureňa, C., doc. Ing. Jiří Bittner, Ph.D., García, R., Montes, R.
  • Publikace: CEIG 2008 Congreso Espaool de Informática Gráfica. Barcelona: Universidad Politechnica de Catalunya, 2008. pp. 37-46. ISBN 978-3-905673-69-2.
  • Rok: 2008
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Este artículo presenta un método de estimación de densidades basado en rayos que ha sido implementado completamente en la GPU. La estimación de densidades basada en rayos reduce el sesgo de los enfoques clásicos basados en fotones aunque tiene un costo computacional más alto. Proponemos algoritmos y estructuras de datos para la implementación en GPUs de la estimación de densidades basada en rayos y mostramos que la técnica propuesta da hasta un orden de magnitud de aceleración comparada con su variante CPU. La aceleración obtenida se incrementa al aumentar el número de rayos y por tanto el método es muy útil en aplicaciones que requieran renderización de alta calidad.

Visibility-driven Mesh Analysis and Visualization through Graph Cuts

  • Autoři: Zhou, K., Zhang, E., doc. Ing. Jiří Bittner, Ph.D., Wonka, P.
  • Publikace: IEEE Transactions on Visualization and Computer Graphics. 2008, 14(6), 1667-1674. ISSN 1077-2626.
  • Rok: 2008
  • DOI: 10.1109/TVCG.2008.176
  • Odkaz: https://doi.org/10.1109/TVCG.2008.176
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we present an algorithm that operates on a triangular mesh and classifies each face of a triangle as either inside or outside. We present three example applications of this core algorithm: normal orientation, inside removal, and layer-based visualization. The distinguishing feature of our algorithm is its robustness even if a difficult input model that includes holes, coplanar triangles, intersecting triangles, and lost connectivity is given. Our algorithm works with the original triangles of the input model and uses sampling to construct a visibility graph that is then segmented using graph cut.

Optimized HLOD Refinement Driven by Hardware Occlusion Queries

  • Autoři: Charalambos, J.P., doc. Ing. Jiří Bittner, Ph.D., Wimmer, M.
  • Publikace: Advances in Visual Computing (Third International Symposium on Computer Vision -- ISVC 2007). New York: Springer, 2007. pp. 106-117. ISBN 978-3-540-76857-9.
  • Rok: 2007
  • Pracoviště: Katedra počítačů
  • Anotace:
    We present a new method for integrating hierarchical levels of detail (HLOD) with occlusion culling. The algorithm refines the HLOD hierarchy using geometric criteria as well as the occlusion information. For the refinement we use a simple model which takes into account the possible distribution of the visible pixels. The traversal of the HLOD hierarchy is optimized by a new algorithm which uses spatial and temporal coherence of visibility. We predict the HLOD refinement condition for the current frame based on the results from the last frame.

Optimized Subdivisions for Preprocessed Visibility

  • Autoři: Mattausch, O., doc. Ing. Jiří Bittner, Ph.D., Wonka, P., Wimmer, M.
  • Publikace: Proceedings of International Symposium on Visual Computing. Mississauga, Ontario: Canadian Human-Computer Communications Society, 2007. pp. 335-342. ISSN 0713-5424. ISBN 978-1-56881-337-0.
  • Rok: 2007
  • Pracoviště: Katedra počítačů
  • Anotace:
    This paper describes a new tool for preprocessed visibility. It puts together view space and object space partitioning in order to control the render cost and memory cost of the visibility description generated by a visibility solver. The presented method progressively refines view space and object space subdivisions while minimizing the associated render and memory costs. Contrary to previous techniques, both subdivisions are driven by actual visibility information. We show that treating view space and object space together provides a powerful method for controlling the efficiency of the resulting visibility data structures.

Ray Tracing with Sparse Boxes

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a new method for ray tracing acceleration by modification of current spatial data structures. We augment a spatial hierarchy such as kd-tree with sparsely distributed bounding boxes that are linked from bottom to top. The augmented data structures can be viewed as a hybrid between kd-trees and uniform grids. The augmentation by boxes is used in new traversal algorithms, which are not restricted to start the hierarchy traversal at the root node. This is in particular efficient for short rays where we significantly reduce the number of traversal steps through the hierarchy. Further we make use of ray coherence as well as explicit knowledge of ray distribution and initiate the traversal near the leaf nodes where the intersection is expected.

Stackless Ray Traversal for kD-Trees with Sparse Boxes

  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    We present a new stackless ray traversal algorithm which makes use of kD-tree augmented with sparsely distributed bounding boxes. The proposed traversal algorithm is not restricted to start the hierarchy traversal at the root node and so it can exploit the knowledge of the ray origin. The algorithm achieves traversal times comparable with the traditional hierarchical traversal as well as recently introduced bottom-up traversal with sparse boxes. The stackless nature of the algorithm lends itself towards implementation of the method on the architectures with limited number of registers.

Adaptive Visibility-Driven View Cell Construction

  • Autoři: Mattausch, O., doc. Ing. Jiří Bittner, Ph.D., Wimmer, M.
  • Publikace: Rendering Techniques 2006. Aire-la-Ville: Eurographics Association, 2006. pp. 195-205. ISSN 1727-3463. ISBN 3-905673-35-5.
  • Rok: 2006
  • Pracoviště: Katedra počítačů
  • Anotace:
    We present a new method for the automatic partitioning of view space into a multi-level view cell hierarchy. We use a cost-based model in roder to minimize the average rendering time. Unlike previous methods, our model takes into account the actual visibility in the scene, and the partition is not restricted to planes given by the scene geometry. We show tat the resulting view cell hierarchy works for different types of scenes and gives lower average rendering time than previously used methods.

Efficient Sorting and Searching in Rendering Algorithms. Eurographics 2006 Tutorial T4

  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    In the proposed tutorial we would like to highlight the connection between rendering algorithms and sorting and searching as classical problems studied in computer science. We will provide both theoretical and empirical evidence that for many rendering techniques most time is spent by sorting and searching. In particular we will discuss problems and solutions for visibility computation, density estimation, and importance sampling. For each problem we mention its specific issues such as dimensionality of the search domain or online versus offline searching. We will present the underlying data structures and their enhancements in the context of specific rendering algorithms such as ray shooting, photon mapping, and hidden surface removal.

Fast Exact From-Region Visibility in Urban Scenes

  • Autoři: doc. Ing. Jiří Bittner, Ph.D., Wonka, P.W., Wimmer, M.W.
  • Publikace: Eurographics Symposium on Rendering. Aire-la-Ville: Eurographics Association, 2005. p. 223-230. ISSN 1727-3463. ISBN 3-905673-23-1.
  • Rok: 2005
  • Pracoviště: Katedra počítačů
  • Anotace:
    We present a fast exact from-region visibility algorithm for 2.5D urban scenes. The algorithm uses a subdivision of line space for identifying visibility interactions in a 2D footprint of the scene. Visibility in the remaining vertical dimension is resolved by testing for the existence of lines stabbing sequences of virtual portals. Our results show that exact analytic from-region visibility in urban scenes can be computed at times comparable or even superior to recent conservative methods.

Hardware Occlusion Queries Made Useful

  • Autoři: Wimer, M.W., doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: GPU Gems 2: Programming Techniques for High-Performance Graphics and General-Purpose Computation. Boston: Addison Wesley Professional, 2005. p. 91-108. ISBN 0-321-33559-7.
  • Rok: 2005
  • Pracoviště: Katedra počítačů
  • Anotace:
    In this chapter, we present a simple but powerful algorithm that solves these problems (Bittner et al. 2004): it minimizes the number of issued queries and reduces the impact of delays due to the latency of query results. To achieve this, the algorithm exploits the spatial and temporal coherence of visibility by reusing the results of occlusion queries from the previous frame in order to initiate and schedule the queries in the current frame. This is done by storing the scene in a hierarchical data structure (such as a k-d tree or octree [Cohen-Or et al. 2003]), processing nodes of the hierarchy in a front-to-back order, and interleaving occlusion queries with the rendering of certain previously visible nodes

Ray Maps for Global Illumination

  • DOI: 10.1145/1186223.1186319
  • Odkaz: https://doi.org/10.1145/1186223.1186319
  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    We describe a novel data structure for representing light transport called ray map. The ray map extends the concept of photon maps: it stores not only photon impacts but the whole photon paths. We demonstrate the utility of ray maps for global illumination by eliminating boundary bias and reducing topological bias of density estimation in global illumination. Thanks to the elimination of boundary bias we could use ray maps for fast direct visualization with the image quality being close to that obtained by the expensive final gathering step. We describe in detail our implementation of the ray map using a lazily constructed kD-tree. We also present several optimizations bringing the ray map query performance close to the performance of the photon map.

Coherent Hierarchical Culling: Hardware Occlusion Queries Made Useful

  • Autoři: doc. Ing. Jiří Bittner, Ph.D., Wimmer, M.W., Piringer, H.P., Purgathofer, W.P.
  • Publikace: Computer Graphics Forum. 2004, 23(3), 615-624. ISSN 0167-7055.
  • Rok: 2004
  • DOI: 10.1111/j.1467-8659.2004.00793.x
  • Odkaz: https://doi.org/10.1111/j.1467-8659.2004.00793.x
  • Pracoviště: Katedra počítačů
  • Anotace:
    We present a simple but powerful algorithm for optimizing the usage of hardware occlusion queries in arbitrary complex scenes. Our method minimizes the number of issued queries and reduces the delays due to the latency of query results. We reuse the results of occlusion queries from the last frame in order to initiate and schedule the queries in the next frame. This is done by processing nodes of a spatial hierarchy in a front-to-back order and interleaving occlusion queries with rendering of certain previously visible nodes. The proposed scheduling of the queries makes use of spatial and temporal coherence of visibility. Despite its simplicity, the algorithm achieves good culling efficiency for scenes of various types. The implementation of the algorithm is straightforward and it can be easily integrated in existing real-time rendering packages based on common hierarchical data structures.

Delivering Interactivity to Complex Tone Mapping Operators

  • Autoři: Artusi, A.A., doc. Ing. Jiří Bittner, Ph.D., Wimmer, M.W., Wilkie, A.W.
  • Publikace: Proceedings of the Eurographics Symposium on Rendering. Aire-la-Ville: Eurographics Association, 2003. p. 38-44.
  • Rok: 2003
  • Pracoviště: Katedra počítačů
  • Anotace:
    The accurate display of high dynamic range images requires the application of complex tone mapping operators. These operators are computationally costly, which prevents their usage in interactive applications. We propose a general framework that delivers interactive performance to an important subclass of tone mapping operators, namely global tone mapping operators. The proposed framework consists of four steps: sampling the input image, applying the tone mapping operator, fitting the point-sampled tone mapping curve, and reconstructing the tone mapping curve for all pixels of the input image. We show how to make use of recent graphics hardware while keeping the advantage of generality by performing tone mapping in software. We demonstrate the capabilities of our method by accelerating several common global tone mapping operators and integrating the operators in a real-time rendering application.

Exact Regional Visibility Using Line Space Partitioning

  • DOI: 10.1016/S0097-8493(03)00101-8
  • Odkaz: https://doi.org/10.1016/S0097-8493(03)00101-8
  • Pracoviště: Katedra počítačů
  • Anotace:
    We present a new method for computing visibility from a polygonal region in the plane considering a set of line segments as occluders. The proposed method provides a comprehensive description of visibility from the given region. We represent sets of occluded rays using a hierarchical partitioning of dual space (line space). The line space partitioning is maintained by a BSP tree that provides efficient operations on the sets of lines. The implementation shows that the method is suitable for computing potentially visible sets in large scenes with various visibility characteristics.

Exploiting Temporal Coherence in Ray Casted Walkthroughs

  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    We present a technique that aims at exploiting temporal coherence of ray casted walkthroughs. Our goal is to reuse ray/object intersections computed in the last frame of the walkthrough for acceleration of ray casting in the current frame. In particular we aim at eliminating the ray traversal and computing only a single ray/object intersection per pixel. If our technique does not succeed in determining visibility, it falls back to the classical ray traversal. Visible point samples from the last frame are reprojected to the current frame. To identify whether these samples can be reused we apply splatting and epipolar geometry constraints. We discuss two additional techniques that handle correct appearanceof small objects.

Visibility in Computer Graphics

  • Autoři: doc. Ing. Jiří Bittner, Ph.D., Wonka, P.
  • Publikace: Environment and Planning B: Planning and Design. 2003, 30(5), 729-755. ISSN 0265-8135.
  • Rok: 2003
  • Pracoviště: Katedra počítačů
  • Anotace:
    Visibility computation is crucial for computer graphics from its very beginning. The first visibility algorithms in computer graphics aimed to determine visible surfaces in a synthesized image of a 3D scene. Nowadays there are many different visibility algorithms for various visibility problems. We propose a new taxonomy of visibility problems that is based on a classification according to the problem domain. We provide a broad overview of visibility problems and algorithms in computer graphics grouped by the proposed taxonomy. The paper surveys visible surface algorithms, visibility culling algorithms, visibility algorithms for shadow computation, global illumination, point-based and image-based rendering, and global visibility computations. Finally, we discuss common concepts of visibility algorithm design and several criteria for the classification of visibility algorithms.

Efficient Construction of Visibility Maps using Approximate Occlusion Sweep

  • Autoři: doc. Ing. Jiří Bittner, Ph.D.,
  • Publikace: Spring Conference on Computer Graphics - SCCG 2002. New York: ACM, 2002. p. 167-175. ISBN 1-58113-608-0.
  • Rok: 2002

On Improving Kd-Trees for Ray Shooting

  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    Efficient ray shooting algorithm is inherently required by many computer graphics algorithms, particularly in image synthesis. Practical ray shooting algorithms aiming at the average-case complexity use some underlying spatial data structure such as kd-tree. We show the new termination criteria algorithm that improves the space and time complexity of the kd-tree construction. It provides efficient ray-shooting queries and does not require any specific constants from a user. Further, we show how to apply a novel clipping algorithm into the kd-tree within construction phase in order to improve its properties.

Exploiting Coherence in Hierarchical Visibility Algorithms

  • DOI: 10.1002/vis.269
  • Odkaz: https://doi.org/10.1002/vis.269
  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    We present a series of simple improvements that make use of temporal and spatial coherence in the scope of hierarchical visibility algorithms. The hierarchy updating:avoids visibility tests of certain interior nodes of the hierarchy. The visibility propagation algorithm reuses information about visibility of neighbouring spatial regions. Finally, the conservative hierarchy updating avoids visibility tests of the hierarchy nodes that are expected to remain visible. We evaluate the presented methods in the context of hierarchical visibility culling using occlusion trees. Copyright (C) 2002 John Wiley Sons, Ltd.

Exploiting Temporal and Spatial Coherence in Hierarchical Visibility Algorithms

Visibility Preprocessing for Urban Scenes using Line Space Subdivision

  • Autoři: doc. Ing. Jiří Bittner, Ph.D., Wonka, P., Wimmer, M.
  • Publikace: Proceedings of Pacific Graphics 2001. Los Alamitos: IEEE Computer Society Press, 2001. p. 276-284. ISBN 0-7695-1227-5.
  • Rok: 2001

LCTS: Ray Shooting using Longest Common Traversal Sequences

Adaptive Data Structures for Visibility Computing

Constructing Rectilinear BSP Trees for Preferred Ray Sets

Rectilinear BSP Trees for Preferred Ray Sets

Hierarchical Visibility Algorithms

Hierarchical Visibility Culling with Occlusion Trees

Ray Tracing with Rope Trees

Fast Robust BSP Tree Traversal Algorithm for Ray Tracing

  • DOI: 10.1080/10867651.1997.10487481
  • Odkaz: https://doi.org/10.1080/10867651.1997.10487481
  • Pracoviště: Katedra počítačů, Katedra počítačové grafiky a interakce
  • Anotace:
    An orthogonal BSP (binary space partitioning) tree is a commonly used spatial subdivision data structure for ray tracing acceleration. While the construction of a BSP tree takes a relatively short time, the efficiency of a traversal algorithm significantly influences the overall rendering time. We propose a new fast traversal algorithm based on statistical evaluation of all possible cases occurring during traversing a BSP tree. More frequent cases are handled simply, while less frequent ones are more computationally expensive. The proposed traversal algorithm handles all singularities correctly. The algorithm saves from 30% up to 50% of traversal time comparing with the commonly-known Sung and Arvo algorithms.

Global Visibility

Za stránku zodpovídá: Ing. Mgr. Radovan Suk