Moving toward more abstract concepts, we introduce the physics of light transport in semi-transparent media, the foundational theory for Neural Radiance Fields.
The Emission-Absorption Model describes how radiance L accumulates along a
ray path through a cloud of particles.
| Variable | Definition | Role in Rendering |
|---|---|---|
| σ(x) | Volume Density | Probability of light hitting a particle at point x |
| c(x, d) | Radiance (Color) | Light emitted from point x in direction d |
| T(t) | Transmittance | Cumulative occlusion from camera to distance t |
| α_i | Alpha (Opacity) | Discretized opacity of a single ray segment |
Use the simulator on the right to "paint" density into a 3D grid and observe how the transmittance curve drops as the ray passes through dense regions.