Graphics Reference
In-Depth Information
2
Global Illumination
The basic ray-tracing method implemented by Whitted was a significant advance
in realistic rendering. However, it does not account for the indirect light reflected
between diffuse surfaces, which is an important component of illumination in
real environments. As discussed in the previous chapter,
global illumination
(GI)
refers to the overall lighting of an environment, particularly indirect illumination
caused by light bouncing between objects.
The mathematical foundations of GI were essentially complete by the middle
of the 1980s, but the cost of computing indirect lighting to a visually acceptable
accuracy was a major obstacle to its practical use. Techniques such as image-
based lighting were developed to mimic some of the effects of GI in a more cost-
effective way. Even as computing power has increased, much of the research in
GI continues to be about achieving the essential effects in GI efficiently. This
chapter explores the history of GI and some of the most recent developments in
its computation.
2.1 The Rendering Equation and Its Solutions
2.1.1 The Rendering Equation
Whitted's original ray-tracing paper was published in 1979. The early and middle
1980s saw major developments in algorithms for indirect lighting, such as the
radiosity method and Monte Carlo ray tracing (MCRT). Jim Kajiya formulated
the GI problem as a single integral
rendering equation
in a classic 1986 paper
of the same name [Kajiya 86]. How to solve this equation efficiently has since
become the ultimate goal of much of GI research.
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