Realistic Image Synthesis Using Photon Mapping
A practical guide to photon mapping, this book provides both the theory and the insight necessary to implement photon mapping and simulate all types of direct and indirect illumination efficiently.
TABLE OF CONTENTS Realistic Image Synthesis Using Photon Mapping
Chapter 5: Photon Tracing
Photon tracing is the process of emitting photons from the light sources and tracing them through a model. It is the technique used to build the photon map (Figure 5.1 illustrates the concept). This chapter contains the details of photon tracing. We describe how photons are generated at light sources and how they are traced efficiently through the model. The techniques in this chapter form a fundamental basis for building a good photon map.
Figure 5.1: The photon map is built using photon tracing in which photons are emitted from the light sources and stored as they interact with the diffuse surfaces in the model.
5.1 Photon Emission
Photons are created at the light sources in the model. These lights can be typical computer graphics light sources such as point lights, directional lights, and area light sources, or they can be physically based sources with arbitrary geometry and distributions. Any type of light source can be used.
Just as in nature, a large number of photons is typically emitted from each light source. The power ("wattage") of the light source is divided among all the emitted photons, and each photon therefore transports a fraction of the light source power. It is important to note that the power of the photons is proportional only to the number of emitted photons and not to the number of photons stored in the model (more detail later).
The following sections contain more detail on how to emit photons from different types of light sources.
Copyright A K Peters, Ltd. 2001 under license agreement with Books24x7
