Abstract: This survey gives an overview of the use of importance, an adjoint of light, in speeding up rendering. The importance of a light distribution indicates its contribution to the region of most interest -- typically the directly visible parts of a scene. Importance can therefore be used to concentrate global illumination and ray tracing calculations where they matter most for image accuracy, while reducing computations in areas of the scene that do not significantly influence the image. In this paper, we attempt to clarify the various uses of adjoints and importance in rendering by unifying them into a single framework. While doing so, we also generalize some theoretical results -- known from discrete representations -- to a continuous domain.
Index terms: Rendering, adjoints, importance, light, ray tracing, global illumination, participating media, literature survey.
One-line summary: What is importance, how is it used in rendering, and what is the difference between all those different types of importance?
Published in: IEEE Transactions on Visualization and Computer Graphics (TVCG), volume 9, number 3, pages 329-340. IEEE, July 2003.
Download paper here: paper.pdf.
Annotated bibliography: see my importance web page.
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