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Historygrams: Enabling Interactive Global Illumination in Direct Volume Rendering using Photon Mapping
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-5220-633X
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-9466-9826
2012 (English)In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 18, no 12, 2364-2371 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we enable interactive volumetric global illumination by extending photon mapping techniques to handle interactive transfer function (TF) and material editing in the context of volume rendering. We propose novel algorithms and data structures for finding and evaluating parts of a scene affected by these parameter changes, and thus support efficient updates of the photon map. In direct volume rendering (DVR) the ability to explore volume data using parameter changes, such as editable TFs, is of key importance. Advanced global illumination techniques are in most cases computationally too expensive, as they prevent the desired interactivity. Our technique decreases the amount of computation caused by parameter changes, by introducing Historygrams which allow us to efficiently reuse previously computed photon media interactions. Along the viewing rays, we utilize properties of the light transport equations to subdivide a view-ray into segments and independently update them when invalid. Unlike segments of a view-ray, photon scattering events within the volumetric medium needs to be sequentially updated. Using our Historygram approach, we can identify the first invalid photon interaction caused by a property change, and thus reuse all valid photon interactions. Combining these two novel concepts, supports interactive editing of parameters when using volumetric photon mapping in the context of DVR. As a consequence, we can handle arbitrarily shaped and positioned light sources, arbitrary phase functions, bidirectional reflectance distribution functions and multiple scattering which has previously not been possible in interactive DVR.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE) , 2012. Vol. 18, no 12, 2364-2371 p.
Keyword [en]
Volume rendering, photon mapping, global illumination, participating media
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-86634DOI: 10.1109/TVCG.2012.232ISI: 000310143100040OAI: oai:DiVA.org:liu-86634DiVA: diva2:580109
Projects
CADICSCMIV
Note

Funding Agencies|Excellence Center at Linkoping and Lund in Information Technology (ELLIIT)||Swedish e-Science Research Centre (SeRC)||

Available from: 2012-12-20 Created: 2012-12-20 Last updated: 2017-12-06
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 (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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Jönsson, DanielKronander, JoelRopinski, TimoYnnerman, Anders

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