Image synthesis using adjoint photons
R. Keith Morley, Solomon Boulos, Jared M. Johnson, David Edwards, Peter Shirley, Michael Ashikhmin, Simon Premože · 2006
Figure 1: An image generated using adjoint photon tracing in a scene with millions of instanced polygons, a heterogeneous medium from simulation data, and Rayleigh scattering for the sky. The Sun is the only source of light in the scene (i.e. there is no background radiance or sky map) and uses a spectral radiance emission function. 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.