March 17, 2024

                                               [Runyi Yang](<https://runyiyang.github.io/>) / [Runyi’s Blogs](<https://runyiyang.notion.site/Runyi-s-Blogs-f52d6bf73e104c51a4f5e80529b6a9b6>)

What is Radiance Fields?

Since computer graphics started to develop, we always hoped to use computers to render a photorealistic image. Naturally, to talk about this, we need to briefly talk about optical and physical propagation laws and some academic terms.

• Lights come into human eyes through reflection, refraction, transmission, absorption, scattering, and so on physical processes. It’s so hard for a computer to simulate the whole process.
  • Reflection: When light hits a surface, it can be reflected. The laws of reflection dictate that the angle of incidence is equal to the angle of reflection.
  • Refraction: This is the bending of light as it passes from one medium into another with a different refractive index.
  • Transmission: Some materials allow light to pass through them, with or without some degree of refraction.
  • Absorption: Materials can also absorb light, converting the energy into other forms like heat.
  • Scattering: Light can be deflected in many directions when encountering particles or rough surfaces.
• 3D points in space radiate light (but not reflect), the radiance changes with different perspectives and obstructs the propagation of light. NeRF’s principle is to reconstruct the radiance field to describe a 3D scene.
  • If the points in front will block the points behind？
    • The points have the density, when light goes through solid points, the intensity decreases
    • Due to light and scattering, the light should be different in different views (highlight and shadow)

In conclusion, radiance fields are for computer graphic simplification, in order to simplify the complex electromagnetic field (physical principles) into the radiance fields, which discards details of reflection, refraction, transmission et. al. So, in this case, we could easily apply neural rendering or volume rendering (e.g. NeRF), such simple rendering methods to render the 3D representation.