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Löw, Joakim
Publications (6 of 6) Show all publications
Löw, J., Kronander, J., Ynnerman, A. & Unger, J. (2013). ABC - BRDF Models for Accurate and Efficient Rendering of Glossy Surfaces. In: Eurographics 24th Symposium on Rendering: Posters. Paper presented at 24th Eurographics Symposium on Rendering, 19-21 June 2013, Zaragoza, Spain.
Open this publication in new window or tab >>ABC - BRDF Models for Accurate and Efficient Rendering of Glossy Surfaces
2013 (English)In: Eurographics 24th Symposium on Rendering: Posters, 2013Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Glossy surface reflectance is hard to model accuratley using traditional parametric BRDF models. An alternative is provided by data driven reflectance models, however these models offers less user control and generally results in lower efficency. In our work we propose two new lightweight parameteric BRDF models for accurate modeling of glossy surface refllectance, one inspired by Rayleigh-Rice theory for optically smooth surfaces and one inspired by microfacet-theory. We base our models on a thourough study of the scattering behaviour of measured reflectance data from the MERL database. The study focuses on two key aspects of BRDF models, parametrization and scatter distribution. We propose a new scattering distributuion for glossy BRDFs inspired by the ABC model for surface statistics of optically smooth surfaces. Based on the survey we consider two parameterizations, one based on micro-facet theory using the halfway vector and one inspired by the parametrization for the Rayleigh-Rice BRDF model considering the projected devaition vector. To enable efficent rendering we also show how the new models can be approximatley sampled for importance sampling the scattering integral.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-102871 (URN)
Conference
24th Eurographics Symposium on Rendering, 19-21 June 2013, Zaragoza, Spain
Available from: 2014-01-04 Created: 2014-01-04 Last updated: 2015-09-22Bibliographically approved
Unger, J., Kronander, J., Larsson, P., Gustavson, S., Löw, J. & Ynnerman, A. (2013). Spatially varying image based lighting using HDR-video. Computers & graphics, 37(7), 923-934
Open this publication in new window or tab >>Spatially varying image based lighting using HDR-video
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2013 (English)In: Computers & graphics, ISSN 0097-8493, E-ISSN 1873-7684, Vol. 37, no 7, p. 923-934Article in journal (Refereed) Published
Abstract [en]

Illumination is one of the key components in the creation of realistic renderings of scenes containing virtual objects. In this paper, we present a set of novel algorithms and data structures for visualization, processing and rendering with real world lighting conditions captured using High Dynamic Range (HDR) video. The presented algorithms enable rapid construction of general and editable representations of the lighting environment, as well as extraction and fitting of sampled reflectance to parametric BRDF models. For efficient representation and rendering of the sampled lighting environment function, we consider an adaptive (2D/4D) data structure for storage of light field data on proxy geometry describing the scene. To demonstrate the usefulness of the algorithms, they are presented in the context of a fully integrated framework for spatially varying image based lighting. We show reconstructions of example scenes and resulting production quality renderings of virtual furniture with spatially varying real world illumination including occlusions.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
High dynamic range video, HDR-video, image based lighting, photo realistic image synthesis
National Category
Media Engineering Signal Processing
Identifiers
urn:nbn:se:liu:diva-96949 (URN)10.1016/j.cag.2013.07.001 (DOI)000325834400015 ()
Projects
VPS
Funder
Swedish Foundation for Strategic Research , IIS11-0081Swedish Research Council
Available from: 2013-08-30 Created: 2013-08-30 Last updated: 2017-12-06Bibliographically approved
Löw, J., Kronander, J., Ynnerman, A. & Unger, J. (2012). BRDF Models for Accurate and Efficient Rendering of Glossy Surfaces. ACM Transactions on Graphics, 31(1)
Open this publication in new window or tab >>BRDF Models for Accurate and Efficient Rendering of Glossy Surfaces
2012 (English)In: ACM Transactions on Graphics, ISSN 0730-0301, E-ISSN 1557-7368, Vol. 31, no 1Article in journal (Refereed) Published
Abstract [en]

This article presents two new parametric models of the Bidirectional Reflectance Distribution Function (BRDF), one inspired by the Rayleigh-Rice theory for light scattering from optically smooth surfaces, and one inspired by micro-facet theory. The models represent scattering from a wide range of glossy surface types with high accuracy. In particular, they enable representation of types of surface scattering which previous parametric models have had trouble modeling accurately. In a study of the scattering behavior of measured reflectance data, we investigate what key properties are needed for a model to accurately represent scattering from glossy surfaces. We investigate different parametrizations and how well they match the behavior of measured BRDFs. We also examine the scattering curves which are represented in parametric models by different distribution functions. Based on the insights gained from the study, the new models are designed to provide accurate fittings to the measured data. Importance sampling schemes are developed for the new models, enabling direct use in existing production pipelines. In the resulting renderings we show that the visual quality achieved by the models matches that of the measured data.

Place, publisher, year, edition, pages
Association for Computing Machinery (ACM), 2012
Keywords
BRDF, gloss, Rayleigh-Rice, global illumination, Monte Carlo, importance sampling
National Category
Computer Systems
Identifiers
urn:nbn:se:liu:diva-75045 (URN)10.1145/2077341.2077350 (DOI)000300622500009 ()
Projects
CADICSELLIIT
Note
funding agencies|Swedish Foundation for Strategic Research through the Strategic Research Centre MOVIII| A3:05:193 |Swedish Knowledge Foundation| 2009/0091 |Forskning och Framtid| ITN 2009-00116 |Swedish Research Council through the Linnaeus Center for Control, Autonomy, and Decision-making in Complex Systems (CADICS)||Excellence Center at Linkoping and Lund in Information Technology (ELLIIT)||Available from: 2012-02-15 Created: 2012-02-15 Last updated: 2017-12-07
Kronander, J., Jönsson, D., Löw, J., Ljung, P., Ynnerman, A. & Unger, J. (2012). Efficient Visibility Encoding for Dynamic Illumination in Direct Volume Rendering: -. IEEE Transactions on Visualization and Computer Graphics, 18(3), 447-462
Open this publication in new window or tab >>Efficient Visibility Encoding for Dynamic Illumination in Direct Volume Rendering: -
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2012 (English)In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 18, no 3, p. 447-462Article in journal (Refereed) Published
Abstract [sv]

We present an algorithm that enables real-time dynamic shading in direct volume rendering using general lighting, includingdirectional lights, point lights and environment maps. real-time performance is achieved by encoding local and global volumetricvisibility using spherical harmonic (SH) basis functions stored in an efficient multi-resolution grid over the extent of the volume. Ourmethod enables high frequency shadows in the spatial domain, but is limited to a low frequency approximation of visibility and illuminationin the angular domain. In a first pass, Level Of Detail (LOD) selection in the grid is based on the current transfer function setting.This enables rapid on-line computation and SH projection of the local spherical distribution of visibility information. Using a piecewiseintegration of the SH coefficients over the local regions, the global visibility within the volume is then computed. By representing thelight sources using their SH projections, the integral over lighting, visibility and isotropic phase functions can be efficiently computedduring rendering. The utility of our method is demonstrated in several examples showing the generality and interactive performanceof the approach.

Place, publisher, year, edition, pages
IEEE, 2012
Keywords
Volumetric Illumination, Precomputed Radiance Transfer, Volume Rendering
National Category
Other Computer and Information Science
Identifiers
urn:nbn:se:liu:diva-66839 (URN)10.1109/TVCG.2011.35 (DOI)000299281700010 ()
Projects
CADICSMOVIII
Note
©2011 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Joel Kronander, Daniel Jönsson, Joakim Löw, Patric Ljung, Anders Ynnerman and Jonas Unger, Efficient Visibility Encoding for Dynamic Illumination in Direct Volume Rendering, 2011, IEEE Transactions on Visualization and Computer Graphics. http://dx.doi.org/10.1109/TVCG.2011.35 Available from: 2011-03-24 Created: 2011-03-21 Last updated: 2018-01-12Bibliographically approved
Löw, J., Ynnerman, A., Larsson, P. & Unger, J. (2009). HDR Light Probe Sequence Resampling for Realtime Incident Light Field Rendering. In: Helwig Hauser (Ed.), Proceedings - SCCG 2009: 25th Spring Conference on Computer Graphics: . Paper presented at 25th Spring Conference on Computer Graphics, SCCG 2009; Budmerice; Slovakia (pp. 43-50). New York, USA: ACM New York
Open this publication in new window or tab >>HDR Light Probe Sequence Resampling for Realtime Incident Light Field Rendering
2009 (English)In: Proceedings - SCCG 2009: 25th Spring Conference on Computer Graphics / [ed] Helwig Hauser, New York, USA: ACM New York , 2009, p. 43-50Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a method for resampling a sequence of high dynamic range light probe images into a representation of Incident Light Field (ILF) illumination which enables realtime rendering. The light probe sequences are captured at varying positions in a real world environment using a high dynamic range video camera pointed at a mirror sphere. The sequences are then resampled to a set of radiance maps in a regular three dimensional grid before projection onto spherical harmonics. The capture locations and amount of samples in the original data make it inconvenient for direct use in rendering and resampling is necessary to produce an efficient data structure. Each light probe represents a large set of incident radiance samples from different directions around the capture location. Under the assumption that the spatial volume in which the capture was performed has no internal occlusion, the radiance samples are projected through the volume along their corresponding direction in order to build a new set of radiance maps at selected locations, in this case a three dimensional grid. The resampled data is projected onto a spherical harmonic basis to allow for realtime lighting of synthetic objects inside the incident light field.

Place, publisher, year, edition, pages
New York, USA: ACM New York, 2009
Keywords
Image Based Lighting, Incident Light Fields, Spherical Harmonics
National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:liu:diva-18052 (URN)10.1145/1980462.1980474 (DOI)978-1-4503-0769-7 (ISBN)
Conference
25th Spring Conference on Computer Graphics, SCCG 2009; Budmerice; Slovakia
Available from: 2009-05-04 Created: 2009-05-04 Last updated: 2018-01-13Bibliographically approved
Löw, J., Ynnerman, A. & Eldén, L. (2009). Numerical Analysis of BRDFs for Inverse Rendering. Göteborg: Chalmers University of Technology
Open this publication in new window or tab >>Numerical Analysis of BRDFs for Inverse Rendering
2009 (English)Report (Other academic)
Abstract [en]

The properties of materials which are present in a scene determine how geometry reflects and distributes light in the scene. This text presents work-in-progress on numerical analysis of bidirectional reflection distribution functions (BRDF) corresponding to various materials, with a focus on inverse rendering. An analysis of these functions is vital for the understanding of the behaviour of reflected light under different lighting conditions, and in the application of inverse rendering, it is important in order to determine what quality one can expect from recovered data. We discuss the singular value decompositions of a few materials, their effect on the ill-posedness of the inverse problem related to the reflectance equation and how regularization affects the solution of the problem.

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology, 2009. p. 4
Series
Chalmers University of Technology. Department of Architecture, ISSN 1650-6340 ; 2009:13
Keywords
bidirectional reflection distribution function, inverse rendering, singular value decomposition
National Category
Computer Vision and Robotics (Autonomous Systems) Computational Mathematics
Identifiers
urn:nbn:se:liu:diva-52357 (URN)
Available from: 2009-12-17 Created: 2009-12-17 Last updated: 2018-01-12
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