Variance, Noise, and Visual Artifacts in Real-Time Physically-Based Rendering
Published:
(work in progress…)
Noises are often referred to as error, visual artifacts, variance (especially in physically-based rendering (PBR)). The limited sample number is primary constraints of the real-time PBR. Higher variance represents noiser outputs as the number of samples has not converged enough to the right result of the integral (Light Transport Equation). Consequently, sophisticated denoising algorithm plays significant role in real-time PBR. The denoising process sometimes referred to as reconstruction in the literature. The denoisers can also referred to as reconstruction filters (a convolution process).
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
Resources and References
- Alian Galvan’s Ray Tracing Denoising blog
- Jacco Bikker’s Reprojection in a Ray Tracer blog
- NVidia OptiX AI-Accelerated a robust and low budged denoiser, however, limited to the offline PBR. A straight forward implementation could be find here. More, in the NVIdia-RTX git repository.