Light transport theory
Light transport theory deals with the mathematics behind calculating the energy transfers between media that affect visibility. This article is currently specific to light transport in rendering processes such as global illumination and high dynamic range imaging.
Light
Light transport
The amount of light transported is measured by flux density, or luminous flux per unit area on the point of the surface at which it is measured.Radiometry and energy transfer
is the science of measuring electromagnetic radiation, including visible light. It forms the foundation of light transport theory, which models how light interacts with surfaces, volumes, and media.- Energy Transfer Models: Light interacts with media through absorption, reflection, and transmission. These processes are governed by the rendering equation, which models the distribution of light in a scene.
Geometric models
Hemisphere
Given a surface S, a hemisphere H can be projected onto S to calculate the amount of incoming and outgoing light. If a point P is selected at random on the surface S, the amount of incoming and outgoing light can be calculated by its projection onto the hemisphere.Hemicube
The hemicube model works similarly to the hemisphere model, except that a hemicube is projected instead of a hemisphere. The similarity is only conceptual; the actual calculation, done through numerical integration, has a different form factor.Wave-particle duality
Light transport theory incorporates both wave-based and particle-based descriptions of light. While wave-based models rely on the principles of Maxwell's equations, particle models use ray optics and Monte Carlo methods to simulate light paths.- Monte Carlo Ray Tracing: A stochastic method used in light transport simulations to compute global illumination. This method leverages randomness to estimate solutions to the rendering equation, particularly in complex scenes with multiple light interactions.
Advanced models
The BRDF models how light is reflected on an opaque surface. It is defined as the ratio of reflected radiance in a given direction to the incident irradiance. BRDFs are crucial in light transport theory for simulating realistic material behavior.
Participating media
Light transport within volumes is modeled using the radiative transfer equation. Participating media are integral to achieving photorealism in scenes involving volumetric light effects.