Per H. Christensen
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.
Available as IEEE Transactions on Visualization and Computer Graphics (TVCG),
Volume 9, Number 3, pages 329-340. IEEE, July 2003.