Lidé

prof. Ing. Vlastimil Havran, Ph.D.

Všechny publikace

General relations for optical design parameters under diffraction limited paraxial imaging

  • DOI: 10.1016/j.optlaseng.2023.107960
  • Odkaz: https://doi.org/10.1016/j.optlaseng.2023.107960
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We searched for fundamental relationships among general optical system parameters assuming diffraction limited imaging in paraxial space. We demonstrated that the total twelve optical system parameters describing the optical imaging problem are unambiguously determined with a set of four of them. This holds for a diffraction condition, where the image permitted blur is of the same size for both the spot due to defocus and the diffraction spot. Depending on the combinations of the four input parameters there can be found up to 314 different optical system design approaches to fully describe the diffraction limited imaging problem.

Different view on diffraction-limited imaging optics design

  • Autoři: Němcová, Š., prof. Ing. Vlastimil Havran, Ph.D., Hošek, J.
  • Publikace: Journal of the Optical Society of America A. 2023, 40(1), 149-154. ISSN 1520-8532.
  • Rok: 2023
  • DOI: 10.1364/JOSAA.474688
  • Odkaz: https://doi.org/10.1364/JOSAA.474688
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The task of imaging optics design starts with choosing a subset of imaging parameters such as the object distance, the image magnification, the image resolution, and the depth of field. It is clear that the imaging parameters are inter-related and their appropriate trade-off is the key problem of final optical design. We provide a novel analysis of the optical design considering diffractive imaging phenomena and thin lens approximation, and we derive formulas for the solution of individual parameters. We show that combinations of three independent optical design input variables determine all other optical and geometrical parameters under diffraction-limited optical imaging. We also formulate an invariant relation in the object space if the depth of field is one of the design’s target parameters.

Fast Ray Tracing of Trimmed NURBS Surfaces on a GPU for Industrial Applications

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Ray tracing of trimmed non-uniform rational basis spline (NURBS) surfaces is a must in the CAD industry, and has been widely applied in 3D modeling software. While most CAD software uses tessellation followed by rasterization to display surfaces, we show the performance of the 3D models by ray tracing can reach real-time performance even for large-scale models. We show the performance of ray tracing can reach from 50 to 1,000 mega rays per second for primary and random rays on the contemporary GPU RTX 3090, depending on the scene complexity between 10K to 1800K NURBS surfaces and 37K to 10,000K of trimming NURBS curves. We utilize the computing power of the GPU and new algorithmic ideas to accelerate the trimming in parametric space. The achieved performance of the ray tracing engine can be used for non-trivial rendering of high-quality images, including the global illumination with interactive and real-time rates.

Foreword

  • Autoři: Augusto Sousa, A., prof. Ing. Vlastimil Havran, Ph.D., Braz, J., Bouatouch, K.
  • Publikace: PROCEEDINGS OF THE 16TH INTERNATIONAL JOINT CONFERENCE ON COMPUTER VISION, IMAGING AND COMPUTER GRAPHICS THEORY AND APPLICATIONS - VOL. 1: GRAPP. Madeira: SciTePress, 2021. p. IX-X. vol. 1. ISSN 2184-4321. ISBN 978-989-758-488-6.
  • Rok: 2021
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    This book contains the proceedings of the 16th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP 2021) which was organized and sponsored by the Institute for Systems and Technologies of Information, Control and Communication (INSTICC), endorsed by the International Association for Pattern Recognition (IAPR), and in cooperation with the ACM Special Interest Group on Graphics and Interactive Techniques (SIGGRAPH), the European Association for Computer Graphics (EUROGRAPHICS), the EUROGRAPHICS Portuguese Chapter, the VRVis Center for Virtual Reality and Visualization Forschungs-GmbH, the French Association for Computer Graphics (AFIG), and the Society for Imaging Science and Technology (IS&T).

Optimizing Ray Tracing of Trimmed NURBS Surfaces on the GPU

  • DOI: 10.1111/cgf.14410
  • Odkaz: https://doi.org/10.1111/cgf.14410
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The representation of geometric models by trimmed NURBS surfaces has become a standard in the CAD industry. In CAD applications, the rendering of surfaces is usually solved by tessellation followed up by z-buffer rendering. Ray tracing of NURBS surfaces has not been widely used in industry due to its computational complexity that hinders achieving real-time performance in practice. We propose novel methods achieving faster point location search needed by trimming in the context of ray tracing trimmed NURBS surfaces. The proposed 2D data structure based on kd-trees allows for faster ray tracing while it requires less memory for its representation and less preprocessing time than previously published methods. Further, we show the current state of the art for ray tracing trimmed NURBS surfaces on a GPU. With careful design and implementation, the number of rays cast on a GPU may reach real-time performance in the order of tens to hundreds of million rays per second for moderately to large complex scenes containing hundreds of thousands of NURBS surfaces and trimming curves.

Alignment issues for any sample direction BTF measurement

  • Autoři: Hošek, J., prof. Ing. Vlastimil Havran, Ph.D., Čáp, J., Němcová, Š.
  • Publikace: Proceedings of the Regional Helix’18 Conference. Springer Nature, 2019. p. 487-493. Lecture Notes in Electrical Engineering. vol. 505. ISSN 1876-1100. ISBN 978-3-319-91333-9.
  • Rok: 2019
  • DOI: 10.1007/978-3-319-91334-6_66
  • Odkaz: https://doi.org/10.1007/978-3-319-91334-6_66
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Measurement of the bidirectional texture function (BTF) of the surfaces with portable instruments allowing on-site measurement outside the laboratory conditions is a newly emerging technique enabling data acquisition of the real objects without the necessity of their extraction from the environment. A practical issue of the sample measurement is the instrument alignment regarding the measured surface. The aim is to measure a sample surface under any orientation in space and to align the measurement instrument to the surface so to measure surface reflectance of the sample surface. This paper describes the design of two setups allowing adjustment of a portable BTF measurement instrument regarding the sample surface at any position. The final instrument alignment is performed with a help of feedback information provided by a simple laser autocollimator.

Increasing the Spatial Resolution of BTF Measurement with Scheimpflug Imaging

  • DOI: 10.1111/cgf.13594
  • Odkaz: https://doi.org/10.1111/cgf.13594
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present an improved way of acquiring spatially varying surface reflectance represented by a bidirectional texture function (BTF). Planar BTF samples are measured as images at several inclination angles which puts constraints on the minimum depth of field of cameras used in the measurement instrument. For standard perspective imaging, we show that the size of a sample measured and the achievable spatial resolution are strongly interdependent and limited by diffraction at the lens' aperture. We provide a formula for this relationship. We overcome the issue of the required depth of field by using Scheimpflug imaging further enhanced by an anamorphic attachment. The proposed optics doubles the spatial resolution of images compared to standard perspective imaging optics. We built an instrument prototype with the proposed optics that is portable and allows for measurement on site. We show rendered images using the visual appearance measured by the instrument prototype.

Optimal Deterministic Mixture Sampling

  • Autoři: Sbert, M., prof. Ing. Vlastimil Havran, Ph.D., Szirmay-Kalos, L.
  • Publikace: Eurographics 2019 - Short Papers. Aire-la-Ville: Eurographics Association, 2019. p. 73-76. ISSN 1017-4656.
  • Rok: 2019
  • DOI: 10.2312/egs.20191018
  • Odkaz: https://doi.org/10.2312/egs.20191018
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Multiple Importance Sampling (MIS) can combine several sampling techniques preserving their advantages. For example, we can consider different Monte Carlo rendering methods generating light path samples proportionally only to certain factors of the integrand. MIS then becomes equivalent to the application of the mixture of individual sampling densities, thus can simultaneously mimic the densities of all considered techniques. The weights of the mixture sampling depends on how many samples are generated with each particular method. This paper examines the optimal determination of this parameter. The proposed method is demonstrated with the combination of BRDF sampling and Light source sampling, and we show that it not only outperforms the application of the two individual methods, but is superior to other recent combination strategies and is close to the theoretical optimum.

Laser Imaging Approach for Portable BTF Measurement System Automatic Alignment

  • Autoři: Hošek, J., prof. Ing. Vlastimil Havran, Ph.D., Němcová, Š., Čáp, J.
  • Publikace: International Journal of Mechatronics and Applied Mechanics. 2018, 2(4), 232-237. ISSN 2559-4397.
  • Rok: 2018
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The paper presents a new alignment sensing possibility for automation of BTF instrument with regards to the sample surface. We have developed a portable bidirectional texture function (BTF) measurement instrument allowing for on-site measurement outside the laboratory. We propose a new approach for acquisition of the feedback information for the system alignment based on laser-imaging approach. We present theoretic relations of the proposed system and technical demands to reach the desired uncertainty of the system misalignment to the sample surface of less than 0.1°.

Multiple importance sampling characterization by weighted mean invariance

  • DOI: 10.1007/s00371-018-1522-x
  • Odkaz: https://doi.org/10.1007/s00371-018-1522-x
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper, we examine the linear combination of techniques and multiple importance sampling for Monte Carlo integration from a new perspective of quasi-arithmetic weighted means. The invariance property of these means allows us to define a new family of heuristics. We illustrate our results with several rendering examples, including environment mapping and path tracing.

Multiple importance sampling revisited: breaking the bounds

  • Autoři: Sbert, M., prof. Ing. Vlastimil Havran, Ph.D., Szirmay-Kalos, L.
  • Publikace: EURASIP Journal on Advances in Signal Processing. 2018, 2018(1), 7373-7384. ISSN 1687-6180.
  • Rok: 2018
  • DOI: 10.1186/s13634-018-0531-2
  • Odkaz: https://doi.org/10.1186/s13634-018-0531-2
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We revisit the multiple importance sampling (MIS) estimator and investigate the bound on the efficiency improvement over balance heuristic estimator with equal count of samples established in Veach's thesis. We revise the proof for this and come to the conclusion that there is no such bound and henceforth it makes sense to look for new estimators that improve on balance heuristic estimator with equal count of samples. Next, we examine a recently introduced non-balance heuristic MIS estimator that is provably better than balance heuristic with equal count of samples, and we improve it both in variance and efficiency. We then obtain an equally provably better one-sample balance heuristic estimator, and finally, we introduce a heuristic for the count of samples that can be used when the individual techniques are biased. All in all, we present three new sampling strategies to improve on both variance and efficiency on the balance heuristic using non-equal count of samples.

On the Advancement of BTF Measurement on Site

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Hošek, J., Němcová, Š., Čáp, J.
  • Publikace: MAM2018 - Workshop on Material Appearance Modeling. Aire-la-Ville: Eurographics Association, 2018. ISSN 2309-5059. ISBN 978-3-03868-055-0.
  • Rok: 2018
  • DOI: 10.2312/mam.20181191
  • Odkaz: https://doi.org/10.2312/mam.20181191
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present our progress to the on-site measurement of the spatially varying surface reflectance represented by bidirectional texture function (BTF). This requires a physical realization of a portable instrument that can be brought to the sample, outside the laboratory. We discuss our motivation, the main issues, and challenges for making such an instrument possible. We focus on the design of the mechanical parts that are required for an easy manipulation of the device on site and describe our experiences with the instrument in practice. The design uses a miniaturized rotary light stage. It allows for measurement of HDR images with the acquisition rate of 1000 HDR images per minute, where one HDR image consists of 4 individual exposures.

Adaptive multiple importance sampling for general functions

  • DOI: 10.1007/s00371-017-1398-1
  • Odkaz: https://doi.org/10.1007/s00371-017-1398-1
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a mathematical expression for the optimal distribution of the number of samples in multiple importance sampling (MIS) and also give heuristics that work well in practice. The MIS balance heuristic is based on weighting several sampling techniques into a single estimator, and it is equal to Monte Carlo integration using a mixture of distributions. The MIS balance heuristic has been used since its invention almost exclusively with an equal number of samples from each technique. We introduce the sampling costs and adapt the formulae to work well with them. We also show the relationship between the MIS balance heuristic and the linear combination of these techniques, and that MIS balance heuristic minimum variance is always less or equal than the minimum variance of the independent techniques. Finally, we give one-dimensional and two-dimensional function examples, including an environment map illumination computation with occlusion.

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

Optomechanical design of rotary kaleidoscope for bidirectional texture function acquisition

  • Autoři: Čáp, J., Hošek, J., prof. Ing. Vlastimil Havran, Ph.D., Němcová, Š., Macúchová, K.
  • Publikace: Applied Optics. 2017, 56(26), 7373-7384. ISSN 1559-128X.
  • Rok: 2017
  • DOI: 10.1364/AO.56.007373
  • Odkaz: https://doi.org/10.1364/AO.56.007373
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Optical systems are traditionally used for accurate recording and measurement of the real world's appearance. Present techniques allow us to form a computer-based virtual world, which is used in a variety of technical fields. The crucial issue for future applications of virtual reality is the fidelity of rendered images to real-world objects. This is strongly affected by the appearance of the rendered object's surfaces. Currently, the most applied method of describing a surface's visual appearance of spatially nonuniform surfaces is bidirectional texture function (BTF). We have designed, optimized, built, and tested a unique portable instrument based on a rotary kaleidoscope principle for BTF acquisition in situ. To the best of our knowledge, such an instrument has never been used before to measure BTF of a surface. We enhanced a common static kaleidoscope by adding rotation, which allows us to get a larger number of images of the sample for more combinations of illumination directions and viewing directions. This results in a higher directional and spatial resolution of measured BTF data. In this paper, we focus on the optomechanical design of the rotary BTF measurement instrument and issues related to its alignment to keep the desired mechanical precision. (C) 2017 Optical Society of America

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.

Gaze Analysis of BRDF Distortions

  • Autoři: Filip, J., prof. Ing. Vlastimil Havran, Ph.D., Myszkowski, K.
  • Publikace: MAM2016: Eurographics Workshop on Material Appearance Modeling. Aire-la-Ville: Eurographics Association, 2016. ISSN 2309-5059. ISBN 978-3-03868-007-9.
  • Rok: 2016
  • DOI: 10.2312/mam.20161252
  • Odkaz: https://doi.org/10.2312/mam.20161252
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    BRDFs are currently used as a standard representation of material surface reflectance properties either in the from of tabulated measurements or a parametric model. However, the compression of tabulated representations as well as their fitting into such a parametric model typically introduces some visual degradations. We describe our analysis of the human gaze behavior in two types of standard visual experiments, where the common task is to compare a pair of BRDFs. The analysis was carried out across six different isotropic/anisotropic materials and three application-relevant BRDF degradation models.

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 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.

Perceptually Motivated BRDF Comparison using Single Image

  • DOI: 10.1111/cgf.12944
  • Odkaz: https://doi.org/10.1111/cgf.12944
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Surface reflectance of real-world materials is now widely represented by the bidirectional reflectance distribution function (BRDF) and also by spatially varying representations such as SVBRDF and the bidirectional texture function (BTF). The raw surface reflectance measurements are typically compressed or fitted by analytical models, that always introduce a certain loss of accuracy. For its evaluation we need a distance function between a reference surface reflectance and its approximate version. Although some of the past techniques tried to reflect the perceptual sensitivity of human vision, they have neither optimized illumination and viewing conditions nor surface shape. In this paper, we suggest a new image-based methodology for comparing different anisotropic BRDFs. We use optimization techniques to generate a novel surface which has extensive coverage of incoming and outgoing light directions, while preserving its features and frequencies that are important for material appearance judgments. A single rendered image of such a surface along with simultaneously optimized lighting and viewing directions leads to the computation of a meaningful BRDF difference, by means of standard image difference predictors. A psychophysical experiments revealed that our surface provides richer information on material properties than the standard surfaces often used in computer graphics, e.g., sphere or blob.

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.

Practical Experiences from Using Autocollimator for Surface Reflectance Measurement

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: MAM2016: Eurographics Workshop on Material Appearance Modeling. Aire-la-Ville: Eurographics Association, 2016. ISSN 2309-5059. ISBN 978-3-03868-007-9.
  • Rok: 2016
  • DOI: 10.2312/mam.20161250
  • Odkaz: https://doi.org/10.2312/mam.20161250
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present our experiences with using an autocollimator to set up the surface reflectance measurement for both BRDF and BTF. Assuming the measured material appearance is put on a locally flat surface, the autocollimator allows us to set the perpendicularity of the measured sample in stationary measurement setups. The principle works also vice versa, we can align the measurement setup against a stationary sample for on-site measurements. The autocollimator requires to use a collimated beam of light, a mirror, a beam splitter, and a detector. We describe the autocollimator principle, problems, and the issues involved when using an autocollimator for surface reflectance measurement setups.

Variance Analysis of Multi-sample and One-sample Multiple Importance Sampling

  • DOI: 10.1111/cgf.13042
  • Odkaz: https://doi.org/10.1111/cgf.13042
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We reexamine in this paper the variance for the Multiple Importance Sampling (MIS) estimator for multi-sample and one-sample model. As a result of our analysis we can obtain the optimal estimator for the multi-sample model for the case where the weights do not depend on the count of samples. We extend the analysis to include the cost of sampling. With these results in hand we find a better estimator than balance heuristic with equal count of samples. Further, we show that the variance for the one-sample model is larger or equal than for the multi-sample model, and that there are only two cases where the variance is the same. Finally, we study on four examples the difference of variances for equal count as used by Veach, our new estimator, and a recently introduced heuristic.

Extensions to bidirectional texture function compression with multi-level vector quantization in OpenCL

  • DOI: 10.1016/j.cag.2015.01.005
  • Odkaz: https://doi.org/10.1016/j.cag.2015.01.005
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Bidirectional texture function (BTF) as an effective visual fidelity representation of surface appearance is becoming more and more widely used. In this paper we report on three contributions to BTF data compression. First, we propose novel decompositions for multi-level vector quantization in BTF data compression that improve the compression ratio by 12% in comparison with the original method, without loss of visual quality. This is achieved by a highly configurable software architecture that allows for different compression pipelines. Second, we show how for offline storage the compression ratio can be increased by 30% in total by Huffman coding. Third, we show how to efficiently parallelize this vector quantization algorithm in OpenCL for massively parallel architectures such as GPUs with a new modular design of the compression pipeline. The results for the new compression algorithm are shown on twelve low dynamic range BTFs and four high dynamic range publicly available BTF samples. Our method allows for real time synthesis on a GPU.

Geometric Accuracy Analysis of Stationary BTF Gonioreflectometers

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Proceedings of Workshop on Material Appearance Modeling 2015. Aire-la-Ville: Eurographics Association, 2015. ISSN 2309-5059. ISBN 978-3-905674-83-5.
  • Rok: 2015
  • DOI: 10.2312/mam.20151200
  • Odkaz: https://doi.org/10.2312/mam.20151200
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The accurate BTF data representation requires specialized measurement gantries, some of them designed as gonireflectometers. These consist of an illumination source and a camera mounted on two robotic arms, one degree of freedom possibly achieved by rotation stage which a measured sample is mounted on. While there are several variations of the gonioreflectometer gantry, the principle of all remains the same, positioning directly the illumination and detector on a hemispherical surface over a sample. We analyze the positioning error of such gonioreflectometers. The input parameters are the required spatial resolution of a BTF sample and the distance between the camera used as a detector and the BTF sample. Our analysis confirms that the requirements for mechatronic actuators for the positioning of the sample and arms are very high and near the limit of state of the art technology.

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.

Light Chisel: 6DOF Pen Tracking

  • DOI: 10.1111/cgf.12563
  • Odkaz: https://doi.org/10.1111/cgf.12563
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a novel interaction device tracked in 6 degrees of freedom by two commodity cameras. The inexpensive Light Chisel is statically illuminated with two LEDs, and uses no additional sensor (e.g. inertial or magnetic) or means of communication or synchronization. Its form factor is well suited for a screwdriver or chisel grip, allowing the Light Chisel to be rolled between the fingers. The position and orientation of the tool is tracked absolutely, making the Light Chisel suited for complex interaction, e.g. geometric modeling in augmented reality. The Light Chisel is physically small, limiting the physical and optical collisions with the real world. The orientation of the tool is tracked in a wide range of angles: pitch and yaw 90 , roll 180 . We evaluated our system against the OptiTrack optical tracking system. Our system achieved mean differences from OptiTrack reference of 2:07mm in position, 1:06 in yaw and pitch, and 5:26 in roll using a pair of VGA cameras. We demonstrate usefulness of our Light Chisel in four applications: character animation, modeling by swirls, volumetric modeling, and docking of CAD models

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.

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

Register Efficient Dynamic Memory Allocator for GPUs

  • DOI: 10.1111/cgf.12666
  • Odkaz: https://doi.org/10.1111/cgf.12666
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We compare five existing dynamic memory allocators optimized for GPUs and show their strengths and weaknesses. In the measurements, we use three generic evaluation tests proposed in the past and we add one with a real workload, where dynamic memory allocation is used in building the k-d tree data structure. Following the performance analysis we propose a new dynamic memory allocator and its variants that address the limitations of the existing dynamic memory allocators. The new dynamic memory allocator uses few resources and is targeted towards large and variably sized memory allocations on massively parallel hardware architectures.

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.

Surface Reflectance Characterization by Statistical Tools

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Sbert, M.
  • Publikace: Proceedings of Spring Conference on Computer Graphics 2015. Bratislava: Comenius University Bratislava, 2015. p. 39-46. ISBN 978-80-223-3844-8.
  • Rok: 2015
  • DOI: 10.1145/2788539.2788544
  • Odkaz: https://doi.org/10.1145/2788539.2788544
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The classification of surface reflectance functions as diffuse, specular, and glossy has been introduced by Heckbert more than two decades ago. Many rendering algorithms are dependent on such a classification, as different kinds of light transport will be handled by specialized methods, for example caustics require specular bounce or refraction. Due to the increasing wealth of surface reflectance models including those based on measured data, it has not been possible to keep such a characterization simple. Each surface reflectance model is mostly handled separately, or alternatively, the rendering algorithm restricts itself to the use of some subset of reflectance models. We suggest a characterization for arbitrary surface reflectance representation by standard statistical tools, namely normalized variance known as Squared-Coefficient-of-Variation (SCV). We show by videos that there is even a weak perceptual correspondence with the proposed reflectance characterization, when we use monochromatic surface reflectance and the images are normalized so they have the unit albedo.

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.

Optimal Combination of Techniques in Multiple Importance Sampling

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Sbert, M.
  • Publikace: Proceedings of VRCAI 2014 conference. New York: ACM SIGGRAPH, 2014. p. 141-150. ISBN 978-1-4503-3254-5.
  • Rok: 2014
  • DOI: 10.1145/2670473.2670496
  • Odkaz: https://doi.org/10.1145/2670473.2670496
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Multiple Importance Sampling (MIS) technique has been widely used in Computer Graphics in rendering algorithms. MIS is based on weighting several sampling techniques into a single estimator. When the combination weights are taken such that the sample contributions are balanced, i.e. they are the same for all techniques, it becomes balance heuristic. It has been used since its invention almost exclusively on equal sampling for all techniques. The question whether unequal sampling can give better variance, has raised till now little interest. Based on the properties of balance heuristic MIS as a weighted mixture of distributions, where weights are proportional to the number of samples, we obtain for this kind of integral an implicit closed formula for the sampling, where we get the minimum variance for MIS. We also take into account the cost of each sampling technique. Although this closed formula can not be written in an explicit way, we outline an iterative procedure to obtain the optimal values. To bypass the combinatorially growing cost of the iterative procedure, we introduce a sound heuristic approximation based on the optimal combination of two independent estimators with known variance. We validate our theory by the results from implementation of 1-dimensional function examples and 2-dimensional examples of environment map illumination.

Parallel BTF Compression with Multi-Level Vector Quantization in OpenCL

  • Autoři: Egert, P., prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Proceedings of Pacific Graphics 2014. Aire-la-Ville: Eurographics Association, 2014. p. 131-134. ISBN 978-3-905674-73-6.
  • Rok: 2014
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Bidirectional Texture Function (BTF) as an effective visual fidelity representation of surface appearance is becoming more and more widely used. In this paper we report on contributions to BTF data compression for multi-level vector quantization. We describe novel decompositions that improve the compression ratio by 15% in comparison with the original method, without loss of visual quality. Further, we show how for offline storage the compression ratio can be increased by 33% in total by Huffman coding. We also show that efficient parallelization of the vector quantization algorithm in OpenCL can reduce the compression time by factor of 9 on a GPU. The results for the new compression algorithm are shown on six low dynamic range BTFs and four high dynamic range publicly available BTF samples. Our method allows for real time synthesis on a GPU.

Register Efficient Memory Allocator for GPUs

  • Autoři: Vinkler, Marek, prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: High-Performance Graphics 2014. Lyon: Eurographics Association, 2014. p. 19-27. ISSN 2079-8679. ISBN 978-3-905674-60-6.
  • Rok: 2014
  • DOI: 10.2312/hpg.20141090
  • Odkaz: https://doi.org/10.2312/hpg.20141090
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We compare four existing dynamic memory allocators optimized for GPUs and show their strengths and weaknesses. In the measurements we use three generic evaluation tests proposed in the literature and add one with a real workload where dynamic memory allocation is used for building the kd-tree data structure. Following the performance analysis we propose a new dynamic memory allocator and its variants that address the limitations of the existing dynamic memory allocators. The new dynamic memory allocator uses few resources and is targeted towards large and variably sized memory allocations on massively parallel hardware architectures.

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.

Statistical Characterization of Surface Reflectance

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Sbert, Mateu
  • Publikace: Workshop on Material Appearance Modeling: Issues and Acquisition 2014. Aire-la-Ville: Eurographics Association, 2014. pp. 15-18. Eurographics workshops and symposia. ISSN 2309-5059. ISBN 978-3-905674-64-4.
  • Rok: 2014
  • DOI: 10.2312/mam.20141294
  • Odkaz: https://doi.org/10.2312/mam.20141294
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The classification of surface reflectance functions as diffuse, specular, and glossy has been introduced by Heckbert more than two decades ago. Many rendering algorithms are dependent on such a classification, as different kinds of light transport will be handled by specialized methods, for example caustics require specular bounce or refraction. Due to the increasing wealth of surface reflectance models including those based on measured data, it has not been possible to keep such a characterization simple. Each surface reflectance model is mostly handled separately, or alternatively, the rendering algorithm restricts itself to the use of some subset of reflectance models. We suggest a characterization for arbitrary surface reflectance representation by standard statistical tools, namely normalized variance known as Squared-Coefficient-of-Variation (SCV).We show by videos that there is even a weak perceptual correspondence with the proposed reflectance characterization, when we use monochromatic surface reflectance and the images are normalized so they have the unit albedo.

BRDF Slices: Accurate Adaptive Anisotropic Appearance Acquisition

  • Autoři: Filip, Jiri, Vavra, Radomir, Haindl, Michal, Zid, Pavel, Krupicka, Mikulas, prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: CVPR: 2013 IEEE Computer Society Conference on Computer Vision and Pattern Recognition. Los Alamitos: IEEE Computer Society Press, 2013. p. 1468-1473. ISSN 1063-6919.
  • Rok: 2013
  • DOI: 10.1109/CVPR.2013.193
  • Odkaz: https://doi.org/10.1109/CVPR.2013.193
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we introduce unique publicly available dense anisotropic BRDF data measurements. We use this dense data as a reference for performance evaluation of the proposed BRDF sparse angular sampling and interpolation approach. The method is based on sampling of BRDF subspaces at fixed elevations by means of several adaptively-represented, uniformly distributed, perpendicular slices. Although this proposed method requires only a sparse sampling of material, the interpolation provides a very accurate reconstruction, visually and computationally comparable to densely measured reference. Due to the simple slices measurement and method’s robustness it allows for a highly accurate acquisition of BRDFs. This in comparison with standard uniform angular sampling, is considerably faster yet uses far less samples.

Efficient Stack-less BVH Traversal for Ray Tracing

  • Autoři: Hapala, M., Davidovič, T., Wald, I., prof. Ing. Vlastimil Havran, Ph.D., Slusallek, P.
  • Publikace: Proceedings of the 27th Spring Conference on Computer Graphics. New York: ACM, 2013. pp. 7-12. ISBN 978-1-4503-1978-2.
  • Rok: 2013
  • DOI: 10.1145/2461217.2461219
  • Odkaz: https://doi.org/10.1145/2461217.2461219
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a new, completely iterative traversal algorithm for ray tracing bounding volume hierarchies that is based on storing a parent pointer with each node, and on using simple state logic to infer which node to traverse next. Though our traversal algorithm does re-visit internal nodes, it intersects each visited node only once, and in general performs exactly the same ray-box tests and ray-primitive intersection tests---and in exactly the same order---as a traditional stack-based variant. The proposed algorithm can be used for computer architectures that need to minimize the use of local memory for processing rays or those that need to minimize the data transport such as distributed multi-CPU architectures.

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.

Visibility Driven BVH Build Up Algorithm for Ray Tracing

  • DOI: 10.1016/j.cag.2012.02.013
  • Odkaz: https://doi.org/10.1016/j.cag.2012.02.013
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The minimization of traversal cost using surface area heuristic is extensively used to build high quality spatial subdivisions and bounding volume hierarchies for ray tracing. Despite the fair performance of trees built with the cost model, it is known that the underlying assumptions for surface area heuristics are not realistic. In this paper we show how the cost function of the surface area heuristic can be improved on using the assumed visibility of geometric primitives such as triangles. This way the build algorithm utilizes the exact or assumed visibility to construct more efficient BVHs by traversing smaller portion of the hierarchy. We show that by these inexpensive modifications to the cost function we can speed up the ray traversal by approximately 102% on average for path tracing of highly occluded scenes compared to standard surface area heuristics. Moreover, it is also possible to lower the construction time and memory usage by subdividing only those parts of the animated scene through which rays are expected to be traversed.

Efficient Stack-less Traversal Algorithm for Ray Tracing with BVH

  • Autoři: Hapala, M., Davidovic, T., Wald, I., prof. Ing. Vlastimil Havran, Ph.D., Slusallek, P.
  • Publikace: SCCG 2011 - 27th Spring conference on Computer Graphics. Bratislava: Comenius University, 2011. pp. 29-34. ISBN 978-80-223-3018-3.
  • Rok: 2011
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We propose a new, completely iterative traversal algorithm for ray tracing bounding volume hierarchies that is based on storing a parent pointer with each node, and on using simple state logic to infer which node to traverse next. Though our traversal algorithm does re-visit internal nodes, it intersects each visited node only once, and in general performs exactly the same ray-box tests and ray-primitive intersection tests---and in exactly the same order---as a traditional stack-based variant. The proposed algorithm can be used for computer architectures that need to minimize the use of local memory for processing rays or those that need to minimize the data transport such as distributed multi-CPU architectures.

Path Regeneration for Random Walks

  • Autoři: Novák, J., prof. Ing. Vlastimil Havran, Ph.D., Dachsbacher, C.
  • Publikace: GPU Computing Gems, Emerald Edition. San Francisco: Morgan Kaufmann Publishers, 2011. p. 401-412. Emerald Edition. ISBN 978-0-12-384988-5.
  • Rok: 2011
  • DOI: 10.1016/B978-0-12-384988-5.00026-7
  • Odkaz: https://doi.org/10.1016/B978-0-12-384988-5.00026-7
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this chapter, we present a method for efficiently generating random walks on the GPU. We analyze the main drawback of naive random walk generators resulting in low GPU utilization over time, and propose an intuitive scheme for keeping all the processing units busy during the entire computation. The algorithm does not require inter-thread communication, collective operations, or intricate handling of work queues. Instead, full utilization is achieved by intelligently regenerating terminated walks. We discuss our optimization in the context of rendering global illumination images where random walks are used to compute the propagation of energy between light sources and cameras. Algorithms such as (bidirectional) path tracing, photon mapping, and irradiance caching directly benefit from the higher throughput; however, our technique is also applicable to non-graphical problems that explore the domain of interest by random walks.

Review: Kd-tree Traversal Algorithms for Ray Tracing

  • DOI: 10.1111/j.1467-8659.2010.01844.x
  • Odkaz: https://doi.org/10.1111/j.1467-8659.2010.01844.x
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we review the traversal algorithms for kd-trees for ray tracing. Ordinary traversal algorithms such as sequential, recursive, and those with neighbor-links have different limitations, which led to several new developments within the last decade. We describe algorithms exploiting ray coherence and algorithms designed with specific hardware architecture limitations such as memory latency and consumption in mind. We also discuss the robustness of traversal algorithms as one issue that has been neglected in previous research.

When it is More Efficient to Use Uniform Grids for Ray Tracing

  • Autoři: Hapala, M., Karlík, O., prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Workshop 2011,CTU Student Grant Competition in 2010 (SGS 2010). Praha: ČVTVS, 2011. pp. 1-3.
  • Rok: 2011
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Commonly used hierarchical data structures such as bounding volume hierarchies and kdtrees have rather high build times, which can be a bottleneck for applications rebuilding or updating the acceleration structure required by data changes. On the other hand uniform grids can be built almost instantly in linear time, however, they can suffer from severe performance penalty, in particular in scenes with non uniformly populated geometry. We improve on performance using a two-step approach that selects a more efficient data structure given a particular implementation of the algorithms which yields with high probability an overall smaller computational time.

When It Makes Sense to Use Uniform Grids for Ray Tracing

  • Autoři: Hapala, M., Karlík, O., prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: WSCG'2011 - 19-th International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision'2011, Communication Papers. Plzeň: UNION Agency - Science Press, 2011, pp. 193-200. ISBN 978-80-86943-82-4. Available from: http://wscg.zcu.cz/WSCG2011/!_2011_WSCG-Short_Papers.pdf
  • Rok: 2011
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Commonly used hierarchical data structures such as bounding volume hierarchies and kd-trees have rather high build times, which can be a bottleneck for applications rebuilding or updating the acceleration structure required by data changes. On the other hand uniform grids can be built almost instantly in linear time, however, they can suffer from severe performance penalty, in particular in scenes with non-uniformly populated geometry. We improve on performance using a two-step approach that combines both approaches: first we build a uniform grid and test its performance. Second, using an estimate on the number of rays to be queried we either continue using the grid or build a hierarchical data structure instead. This way we select a more efficient data structure given a particular implementation of the algorithms which yields with high probability an overall smaller computational time. We evaluate the properties of this method for a set of 28 scenes.

Bidirectional Texture Function Compression Based on Multi-Level Vector Quantization

  • DOI: 10.1111/j.1467-8659.2009.01585.x
  • Odkaz: https://doi.org/10.1111/j.1467-8659.2009.01585.x
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    The model resamples input BTF data into a parametrization, allowing decomposition of individual view and illumination dependent texels into a set of multi-dimensional conditional probability density functions. These functions are compressed in turn using a novel multi-level vector quantization algorithm. The result of this algorithm is a set of index and scale code-books for individual dimensions. BTF reconstruction from the model is then based on fast chained indexing into the nested stored code-books. In the proposed model, luminance and chromaticity are treated separately to achieve further compression. The proposed model achieves low distortion and compression ratios 1:233-1:2040, depending on BTF sample variability. These results compare well with several other BTF compression methods with predefined compression ratios, usually smaller than 1:200.

Interactive Ray Tracing of Distance Fields

  • Autoři: Jamriška, O., prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Proceedings of the 14th Central European Seminar on Computer Graphics. Vienna: Impressum, 2010. p. 91-98. ISBN 978-3-9502533-2-0.
  • Rok: 2010
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Distance field is a flexible surface representation used in many applications. We study the algorithms for direct rendering of distance field surfaces representation via ray tracing in interactive frame rates. To accelerate the ray tracing we represent the distance fields by sparse block grid data structure. We compare the visual quality and the computation time for different methods of ray-surface intersection test and for surface normal estimation. We present a technique to accelerate the computation for primary rays from the camera by projection. We also describe another technique for faster computation of shadow rays via volumetric occlusion. We show the results on four scenes of different complexities.

Path Regeneration for Interactive Path Tracing

  • Autoři: Novák, J., prof. Ing. Vlastimil Havran, Ph.D., Dachsbacher, C.
  • Publikace: Eurographics 2010 Short Papers. Aire-la-Ville: Eurographics Association, 2010. p. 61-64.
  • Rok: 2010
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Rendering of photo-realistic images at interactive frame rates is currently an extensively researched area of computer graphics. Many of these approaches attempt to utilize the computational power of modern graphics hardware for ray tracing based methods. When using path tracing algorithms the ray paths are highly incoherent, hence we propose an efficient technique that minimizes the divergence in execution flow and ensures full utilization by intelligently regenerating the paths. We analyze the conditions under which our improvements provide the highest speedup, and demonstrate the performance of the overall system by rendering interactive previews of global illumination solutions using (bidirectional) path tracing with progressive refinement.

Ray Tracing on a GPU with CUDA - Comparative Study of Three Algorithms

  • Autoři: Zlatuška, M., prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: WSCG2010 Communication Papers Proceedings. Pilsen: University of West Bohemia, 2010. pp. 69-75. ISBN 978-80-86943-87-9.
  • Rok: 2010
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a comparative study of ray tracing algorithms implemented on a GPU for three published papers using different spatial data structures evaluated for performance on nine static scenes in walk-through animation. We compare the performance for uniform grids, bounding volume hierarchies (BVHs), and kd-trees evaluated on a GPU for ray casting and Whitted-style ray tracing. We show that performance of ray tracing with BVHs exceeds the performance of ray tracing with kd-trees for coherent rays. Contrary, the ray tracing with kd-trees is faster than that with BVHs for incoherent rays. The performance of ray tracing with uniform grids is slower than both ray tracing with BVHs and kd-trees except for uniformly populated scenes. We show that the performance is highly sensitive to details of implementation on kd-trees.

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.

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.

About the Relation between Spatial Subdivisions and Object Hierarchies Used in Ray Tracing

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Spring Conference on Computer Graphics SCCG 2007. Conference Proceedings. Bratislava: Comenius University, 2007. pp. 55-60. ISBN 978-80-223-2292-8.
  • Rok: 2007
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we study the relation between object hierarchies (such as bounding volume hierarchies) and spatial subdivisions (such as kd-trees and octrees) in the context of ray tracing for static scenes. First, we recall the principles used in efficient ray tracing algorithms and discuss the changes to the performance model more appropriate to current computer architectures. Second, we show how kd-trees can be emulated via bounding volume hierarchies. More importantly we show how bounding volume hierarchies can be emulated via kd-trees in six-dimensional space. Through emulation of one data structure via the second one we show that both data structures are computationally equivalent, assuming that their construction is carried out in top-down fashion.

Global Illumination using Photon Ray Splatting

  • Autoři: Herzog, R., prof. Ing. Vlastimil Havran, Ph.D., Kinuwaki, S., Myszkowski, K., Seidel, H.-P.
  • Publikace: Computer Graphics Forum. 2007, 2007(3), 503-513. ISSN 0167-7055.
  • Rok: 2007
  • DOI: 10.1111/j.1467-8659.2007.01073.x
  • Odkaz: https://doi.org/10.1111/j.1467-8659.2007.01073.x
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a novel framework for efficiently computing the indirect illumination in diffuse and moderately glossy scenes using density estimation techniques. Many existing global illumination approaches either quickly compute an overly approximate solution or orders of magnitude more slowly compute high-quality results for the indirect illumination. The proposed method improves photon density estimation and leads to significantly better visual quality in particular for complex geometry, while only s lightly increasing the computation time. We perform direct splatting of photon rays, which allows us to use simpler search data structures. Our novel li ghting computation combines photon splatting and density estimation. Since the density estimation is carried out in ray space rather than on surfaces, as in the commonly used photon mapping algorithm, the results are more robust against geometrically incurred sources of bias.

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.

Applying Ray Tracing for Virtual Reality and Industrial Design

  • Autoři: Wald, I., Dietrich, A., Benthin, C., Efremov, A., Dahmen, T., Guenther, J., prof. Ing. Vlastimil Havran, Ph.D., Seidel, H.P., Slusallek, P.
  • Publikace: Proceedings of IEEE Symposium on Interactive Ray Tracing 2006. USA: IEEE Computer Society, 2006. p. 177-185. ISBN 1-4244-0693-5.
  • Rok: 2006
  • DOI: 10.1109/RT.2006.280229
  • Odkaz: https://doi.org/10.1109/RT.2006.280229
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Computer aided design (CAD) and virtual reality (VR) are becoming increasingly important tools for industrial design applications. Unfortunately, there is a huge and growing gap between what data CAD engineers are working on, what rendering quality is needed by designers and executives to faithfully judge a design variant, and what rendering capabilities are offered by commonly available VR frameworks. In particular, existing VR systems cannot currently cope with the accuracy demanded by CAD engineers, nor can they deliver the photo-realistic rendering quality and reliability required by designers and decision makers. In this paper, we describe a ray tracing based virtual reality framework that closes these gaps. In particular, the proposed system supports direct ray tracing of trimmed freeform surfaces even for complex models of thousands of patches, allows for accurately simulating reflections and refraction for glass and car paint effects, offers support for direct integration of me

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.

On building fast kd-trees for ray tracing, and on doing that in O(N log N)

  • Autoři: Wald, I., prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Proceedings of IEEE Symposium on Interactive Ray Tracing 2006. USA: IEEE Computer Society, 2006. p. 61-70. ISBN 1-4244-0693-5.
  • Rok: 2006
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Though a large variety of efficiency structures for ray tracing exist, kd-trees today seem to slowly become the method of choice. In particular, kd-trees built with cost estimation functions such as a surface area heuristic (SAH) seem to be important for reaching high performance. Unfortunately, most algorithms for building such trees have a time complexity of O(N log2 N), or even O(N2). In this paper, we analyze the state of the art in building good kdtrees for ray tracing, and eventually propose an algorithm that builds SAH kd-trees in O(N logN), the theoretical lower bound.

On the Fast Construction of Spatial Hierarchies for Ray Tracing

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Herzog, W., Seidel, H.-P.
  • Publikace: Proceedings of IEEE Symposium on Interactive Ray Tracing 2006. USA: IEEE Computer Society, 2006. p. 71-80. ISBN 1-4244-0693-5.
  • Rok: 2006
  • DOI: 10.1109/RT.2006.280217
  • Odkaz: https://doi.org/10.1109/RT.2006.280217
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we will address the problem of fast construction of spatial hierarchies for ray tracing with applications in animated environments including non-rigid animations. We will discuss the properties of currently used techniques with O(N logN) construction time for kd-trees and bounding volume hierarchies. Further, we will propose a hybrid data structure blending a spatial kd-tree with bounding volume primitives.

Fast final gathering via reverse photon mapping

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present a new algorithm for computing indirect illumination based on density estimation similarly to photon mapping. We accelerate the search for final gathering by reorganizing the computation in the reverse order. We use two trees that organize spatially not only the position of photons but also the position of final gather rays. The achieved speedup is algorithmic, the performance improvement takes advantage of logarithmic complexity of searching in trees. The algorithm requires almost no user settings unlike many known acceleration techniques for photon mapping. The image quality is the same as for traditional photon mapping with final gathering, since the algorithm does not approximate or interpolate. Optionally, the algorithm can be combined with other techniques such as density control and importance sampling.

Interactive System for Dynamic Scene Lighting using Captured Video Environment Maps

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Smyk, M., Krawczyk, G., Myszkowski, K., Seidel, H.-P.
  • Publikace: Eurographics Symposium on Rendering. Aire-la-Ville: Eurographics Association, 2005. p. 31-42. ISSN 1727-3463. ISBN 3-905673-23-1.
  • Rok: 2005
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We present an interactive system for fully dynamic scene lighting using captured high dynamic range (HDR) video environment maps. The key component of our system is an algorithm for efficient decomposition of HDR video environment map captured over hemisphere into a set of representative directional light sources, which can be used for the direct lighting computation with shadows using graphics hardware. The resulting lights exhibit good temporal coherence and their number can be adaptively changed to keep a constant framerate while good spatial distribution (stratification) properties are maintained. We can handle a large number of light sources with shadows using a novel technique which reduces the cost of BRDF-based shading and visibility computations. We demonstrate the use of our system in a mixed reality application in which real and synthetic objects are illuminated by consistent lighting at interactive framerates.

On Cross-Validation and Resampling of BRDF Data Measurements

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Neumann, A., Zotti, G., Purgathofer, W., Seidel, H.-P.
  • Publikace: Proceedings of the 21st spring conference on Computer graphics. New York: ACM, 2005. p. 161-168. ISBN 1-59593-204-6.
  • Rok: 2005
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    We discuss the validation of BTF data measurements by means used for BRDF measurements. First, we show how to apply the Helmholtz reciprocity and isotropy for a single data set. Second, we discuss a cross-validation for BRDF measurement data obtained from two different measurement setups, where the measurements are not calibrated or the level of accuracy is not known. We show the practical problems encountered and the solutions we have used to validate physical setup for four material samples. We describe a novel coordinate system suitable for resampling the BRDF data from one data set to another data set. Further, we show how the perceptually uniform color space CIE 1976 L a b is used for crosscomparison of BRDF data measurements, which were not calibrated.

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.

Robust and Numerically Stable Bézier Clipping Method for Ray Tracing NURBS Surfaces

  • Autoři: Efremov, A., prof. Ing. Vlastimil Havran, Ph.D., Seidel, H.-P.
  • Publikace: Proceedings of the 21st spring conference on Computer graphics. New York: ACM, 2005. p. 127-135. ISBN 1-59593-204-6.
  • Rok: 2005
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Raytracing has become a popular method for generating realistic images and movies. The progress in hardware development shows that the real time raytracing on a single PC might be possible in the ongoing future. Obviously, that new generation of raytracing based applications will require more visualization precision and flexibility. Most of the modern raytracing based applications only deal with triangles as basic primitives, which brings limitations to an application and may cause visual artifacts to appear. NURBS surface representation is common for most of 3D modeling tools because of its compactness and useful geometric properties of NURBS surfaces. Using the direct raytracing NURBS surfaces, one can achieve better quality of rendered images.This paper presents a modifed Bézier clipping method for finding ray - NURBS surface intersection points, which is fast, robust, and numerically stable.

Exploiting Temporal Coherence in Global Illumination

  • Autoři: Tawara, T., Myszkowski, K., Dmitriev, K., prof. Ing. Vlastimil Havran, Ph.D., Damez, C., Seidel, J.-P.
  • Publikace: Spring Conference on Computer Graphics SCCG 2004 - Conference Proceedings. New York: ACM SIGGRAPH, 2004. p. 16-26. ISBN 1-58113-914-4.
  • Rok: 2004
  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Producing high quality animations featuring rich object appearance and compelling lighting effects is very time consuming using traditional frame-by-frame rendering systems. In this paper we present a number of global illumination and rendering solutions that exploit temporal coherence in lighting distribution for subsequent frames to improve the computation performance and overall animation quality. Our strategy relies on extending into temporal domain well-known global illumination techniques such as density estimation photon tracing, photon mapping, and bi-directional path tracing, which were originally designed to handle static scenes only.

An Efficient Spatio-Temporal Architecture for Animation Rendering

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Damez, C., Myszkowski, K., Seidel, H.-P.
  • Publikace: Proceedings of the Eurographics Symposium on Rendering. Aire-la-Ville: Eurographics Association, 2003. p. 106-117.
  • Rok: 2003

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.

Goniometric Diagram Mapping for Hemisphere

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Dmitriev, K., Seidel, H.-P.
  • Publikace: Eurographics 2003 Short Presentations. Aire-la-Ville: Eurographics Association, 2003. p. 293-300. ISSN 1017-4656.
  • Rok: 2003

On Comparing Ray Shooting Algorithms

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    In this paper we discuss a methodology for comparing various ray shooting algorithms through a set of experiments performed on a set of scenes. We develop a computational model for ray shooting algorithms, which allows us to map any particular ray shooting algorithm to the computational model. Further, we develop a performance model for ray shooting algorithms, which establishes the correspondence between the computational model and the running time of the ray shooting algorithm for a sequence of ray shooting queries. Based on these computational and performance models, we propose a set of parameters describing the use of a ray shooting algorithm in applications. These parameters allows us to make a fair comparison of various ray shooting algorithms for the same set of input data, i.e., the same scene and the same sequence of ray shooting queries, but virtually independently of hardware and implementation issues.

Mailboxing, yea or nay?

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.

On the Efficiency of Ray-shooting Acceleration Schemes

  • Autoři: Szirmay-Kalos, L., prof. Ing. Vlastimil Havran, Ph.D., Balázs, B., Szecsi, L.
  • Publikace: Spring Conference on Computer Graphics - SCCG 2002. New York: ACM, 2002. p. 89-98. ISBN 1-58113-608-0.
  • Rok: 2002

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

LCTS: Ray Shooting using Longest Common Traversal Sequences

VIS-RT: A Visualization System for RT Spatial Data Structures

A Summary of Octree Ray Traversal Algorithms

Adaptive Data Structures for Visibility Computing

Analysis of Cache Sensitive Representation for Binary Space Partitioning Trees

  • Pracoviště: Katedra počítačové grafiky a interakce
  • Anotace:
    Several variants of binary search trees were designed to solve various types of searching problems including geometrical ones as point location and range search queries. In complexity analysis we usually abstract from the real implementation and easily derive that the time complexity of traversal from the root of a balanced tree to any leaf is O(log m), where m is the number of leaves. In this paper we analyse a new method for memory mapping of a binary tree aiming to improve spatial locality of data represented by binary trees and thus performance of traversal algorithms applied on these data structures.

Comparison of Hierarchical Grids

Constructing Rectilinear BSP Trees for Preferred Ray Sets

Rectilinear BSP Trees for Preferred Ray Sets

Hierarchical Visibility Culling with Occlusion Trees

Ray Tracing with Rope Trees

Statistically Optimized Traversal Algorithm for BSP Trees

View Dependent Data Structures for Ray Tracing

Cache Sensitive Representation for the BSP Tree

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Proceedings of Compugraphics'97 conference. Oxford: Elsevier Ltd, 1997, pp. 369-376. Available from: http://www.cgg.cvut.cz/~havran/ARTICLES/compugr97.pdf
  • Rok: 1997

Evaluation of BSP Properties for Ray-tracing

Evaluation of BSP Trees for Ray-Tracing

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Poster 1997. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 1997, pp. 12.
  • Rok: 1997

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.

Parallel Merge Sort on Shared Memory Multicomputer

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D., Šimek, P., Šoch, M., Tvrdík, P.
  • Publikace: Workshop 97. Praha: České vysoké učení technické v Praze, 1997. pp. 287-288.
  • Rok: 1997

Parallel Ray-Tracer on Shared Memory Multiprocessor Machines Connected via Internet

Load Balancing Techniques for Ray-tracer on Shared Memory Machine

  • Autoři: prof. Ing. Vlastimil Havran, Ph.D.,
  • Publikace: Poster 1996. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 1996, pp. 74.
  • Rok: 1996

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