Abstract
The most straightforward image synthesis algorithm is to follow photon-like particles from luminaires through the environment. These particles scatter or are absorbed when they interact with a surface or a volume. They contribute to the image if and when they strike a sensor. Such an algorithm implicitly solves the light transport equation. Alternatively. adjoint photons can be traced from the sensor to the luminaires to produce the same image. This "adjoint photon" tracing algorithm is described, and its strengths and weaknesses are discussed, as well as details needed to make adjoint photon tracing practical.
