The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Theory and Algorithms for Efficient Physically-Based Illumination

Jaakko Lehtinen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Computer Science and Engineering for public examination and debate in Auditorium TU1 at Helsinki University of Technology (Espoo, Finland) on the 31st of August, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8900-4)   [1362 KB]
Dissertation is also available in print (ISBN 978-951-22-8899-1)


Realistic image synthesis is one of the central fields of study within computer graphics. This thesis treats efficient methods for simulating light transport in situations where the incident illumination is produced by non-pointlike area light sources and distant illumination described by environment maps. We describe novel theory and algorithms for physically-based lighting computations, and expose the design choices and tradeoffs on which the techniques are based.

Two publications included in this thesis deal with precomputed light transport. These techniques produce interactive renderings of static scenes under dynamic illumination and full global illumination effects. This is achieved through sacrificing the ability to freely deform and move the objects in the scene. We present a comprehensive mathematical framework for precomputed light transport. The framework, which is given as an abstract operator equation that extends the well-known rendering equation, encompasses a significant amount of prior work as its special cases. We also present a particular method for rendering objects in low-frequency lighting environments, where increased efficiency is gained through the use of compactly supported function bases.

Physically-based shadows from area and environmental light sources are an important factor in perceived image realism. We present two algorithms for shadow computation. The first technique computes shadows cast by low-frequency environmental illumination on animated objects at interactive rates without requiring difficult precomputation or a priori knowledge of the animations. Here the capability to animate is gained by forfeiting indirect illumination. Another novel shadow algorithm for off-line rendering significantly enhances a previous physically-based soft shadow technique by introducing an improved spatial hierarchy that alleviates redundant computations at the cost of using more memory.

This thesis advances the state of the art in realistic image synthesis by introducing several algorithms that are more efficient than their predecessors. Furthermore, the theoretical contributions should enable the transfer of ideas from one particular application to others through abstract generalization of the underlying mathematical concepts.

This thesis consists of an overview and of the following 4 publications:

  1. J. Lehtinen. A Framework for Precomputed and Captured Light Transport. ACM Transactions on Graphics, accepted for publication, ACM Press, 36 pages.
  2. J. Lehtinen and J. Kautz. Matrix Radiance Transfer. In Proceedings of ACM Siggraph 2003 Symposium on Interactive 3D Graphics, pages 59-64, ACM Press, 2003.
  3. J. Kautz, J. Lehtinen and T. Aila. Hemispherical Rasterization for Self-Shadowing of Dynamic Objects. In Rendering Techniques 2004 (Eurographics Symposium on Rendering), pages 179-184, Eurographics Association, 2004.
  4. J. Lehtinen, S. Laine and T. Aila. An Improved Physically-Based Soft Shadow Volume Algorithm. Computer Graphics Forum, 25 (3): 303-312, Eurographics Association, 2006.

Keywords: computer graphics, shading, global illumination, indirect illumination, precomputed radiance transfer

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© 2007 Helsinki University of Technology

Last update 2011-05-26