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Efficient Visibility Encoding for Dynamic Illumination in Direct Volume Rendering: -
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. (C-Research)
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. (C-Research)ORCID iD: 0000-0002-5220-633X
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. (C-Research)
Siemens. (Princeton Corporate Research)
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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, 447-462 p.Article 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. Vol. 18, no 3, 447-462 p.
Keyword [en]
Volumetric Illumination, Precomputed Radiance Transfer, Volume Rendering
National Category
Other Computer and Information Science
Identifiers
URN: urn:nbn:se:liu:diva-66839DOI: 10.1109/TVCG.2011.35ISI: 000299281700010OAI: oai:DiVA.org:liu-66839DiVA: diva2:405088
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: 2016-09-19Bibliographically approved
In thesis
1. Enhancing Salient Features in Volumetric Data Using Illumination and Transfer Functions
Open this publication in new window or tab >>Enhancing Salient Features in Volumetric Data Using Illumination and Transfer Functions
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The visualization of volume data is a fundamental component in the medical domain. Volume data is used in the clinical work-flow to diagnose patients and is therefore of uttermost importance. The amount of data is rapidly increasing as sensors, such as computed tomography scanners, become capable of measuring more details and gathering more data over time. Unfortunately, the increasing amount of data makes it computationally challenging to interactively apply high quality methods to increase shape and depth perception. Furthermore, methods for exploring volume data has mostly been designed for experts, which prohibits novice users from exploring volume data. This thesis aims to address these challenges by introducing efficient methods for enhancing salient features through high quality illumination as well as methods for intuitive volume data exploration.

Humans are interpreting the world around them by observing how light interacts with objects. Shadows enable us to better determine distances while shifts in color enable us to better distinguish objects and identify their shape. These concepts are also applicable to computer generated content. The perception in volume data visualization can therefore be improved by simulating real-world light interaction. This thesis presents efficient methods that are capable of interactively simulating realistic light propagation in volume data. In particular, this work shows how a multi-resolution grid can be used to encode the attenuation of light from all directions using spherical harmonics and thereby enable advanced interactive dynamic light configurations. Two methods are also presented that allow photon mapping calculations to be focused on visually changing areas.The results demonstrate that photon mapping can be used in interactive volume visualization for both static and time-varying volume data.

Efficient and intuitive exploration of volume data requires methods that are easy to use and reflect the objects that were measured. A value that has been collected by a sensor commonly represents the material existing within a small neighborhood around a location. Recreating the original materials is difficult since the value represents a mixture of them. This is referred to as the partial-volume problem. A method is presented that derives knowledge from the user in order to reconstruct the original materials in a way which is more in line with what the user would expect. Sharp boundaries are visualized where the certainty is high while uncertain areas are visualized with fuzzy boundaries. The volume exploration process of mapping data values to optical properties through the transfer function has traditionally been complex and performed by expert users. A study at a science center showed that visitors favor the presented dynamic gallery method compared to the most commonly used transfer function editor.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 61 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1789
National Category
Media and Communication Technology Computer Science Media Engineering Other Computer and Information Science
Identifiers
urn:nbn:se:liu:diva-131023 (URN)10.3384/diss.diva-131023 (DOI)9789176856895 (Print) (ISBN)
Public defence
2016-10-21, Domteatern, Visualiseringscenter C, Kungsgatan 54, Norrköping, 09:30 (English)
Opponent
Supervisors
Available from: 2016-10-04 Created: 2016-09-05 Last updated: 2016-10-04Bibliographically approved

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Kronander, JoelJönsson, DanielLöw, JoakimYnnerman, AndersUnger, Jonas
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