Ray tracing- Is luminance being traced?

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SUMMARY

This discussion focuses on the principles of ray tracing, specifically the relationship between luminance and radiance in rendering scenes. It establishes that in backwards ray tracing, each ray can indeed have an associated luminance value. For perfectly diffuse surfaces, the mean luminance of secondary rays (L1, L2, L3, L4, L5) can be used to calculate the primary ray's luminance (L0). The conversation emphasizes that rays in ray tracing are linked to radiance, measured in W/(m²*sr), which quantifies the power propagating in a specific direction, while luminance serves as the photometric equivalent of radiance, adjusted for human visual perception.

PREREQUISITES
  • Understanding of ray tracing techniques, particularly backwards ray tracing.
  • Familiarity with the concepts of luminance and radiance in photometry.
  • Knowledge of diffuse surfaces and their impact on light propagation.
  • Basic grasp of radiometric units, specifically W/(m²*sr).
NEXT STEPS
  • Research the mathematical models used in backwards ray tracing.
  • Explore the differences between luminance and radiance in depth.
  • Study the impact of surface properties on ray tracing outcomes.
  • Learn about advanced ray tracing algorithms and their applications in graphics rendering.
USEFUL FOR

This discussion is beneficial for graphics programmers, visual effects artists, and anyone involved in computer graphics who seeks to deepen their understanding of ray tracing and its implications for rendering realistic scenes.

kingsna1
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My understanding of ray tracing is that it maps out luminance for a scene. Now with ray tracing (backwards ray tracing that starts from the camera outwards) does each ray have a luminance value associated with it? In the case of a perfectly diffuse surface, can one simply take the mean of all of the secondary rays luminance to arrive at a luminance value for the primary ray or is this assumption wrong? If L0 are the primary rays luminance, and L1 ,L2 ,L3, L4 ,L5 are the secondary rays that are created due to the diffuse surface. (see Diagram for explanation).
 

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Interesting question- in radiometric terms, rays in a ray trace are associated with radiance- a conserved quantity with units of W/(m^2*sr)- the quantity tells you how much power is propagating in a given direction.

Luminance is the photometric equivalent to radiance- radiance that has been corrected for the spectral response of normal human eyes.