05: Variance, Noise, and Artifacts in Real-Time Path Tracing

(work in progress…) Noise is also referred as error, visual artifacts. In ray tracing-based rendering, it is referred to as variance. High variance represents more noise as the number of samples has not converged enough to the actual right result of the integral (Light Transport Equation).

Denoising also referred to as reconstruction. Therefore, denoisers are referred to as reconstruction filters.

Firefly

• lighting artifact.
• a pixel that is unusually bright compared to the neighboring pixels, appearing much like a firefly in the dark.
• typically happens when a ray bounces off a surface and randomly hits a very bright, small light source.
• The small size of the light means it isn’t hit very often, but when it is, it contributes a large amount of energy to a pixel.
• read

Temporal stability

• Reproject past denoised frame
• To ensure temporal coherence, warp the previous frame’s denoised using screen-space motion vectors (motion vector estimation)
• Optical flow algorithms
• time warping
• Interactive Stable Ray Tracing