Posted ·Updated · v2
Characterising Per-Pixel Rendering Difficulty by Transport Mechanism
- 1 Independent Researcher
Per-pixel rendering difficulty is conventionally characterised by one noisy scalar: the sample variance of a Monte Carlo estimator. We argue that it should instead be characterised through transport structure — a discrete description of how each contribution's energy reaches the sensor, deterministic under stated renderer conventions — with variance treated as a measurement whose reliability that structure helps predict. We make this concrete with a seven-class transport-mechanism descriptor assigned per contribution event, evaluate it on eleven scenes, and measure variance reliability on the seven first-party ones. The dominant label agrees 87–99.6% between 64 and 4096 samples per pixel, where quantile-binned variance agrees as little as 21%; its stability on unseen scenes is predicted from their pilots. Conditioning a pilot variance on the label improves equal-budget sample allocation wherever heavy-tailed buckets carry appreciable population, reduces to the incumbent where they are absent or negligible, and is neither reproduced by a random partition nor absorbed by a median-of-means estimator; where the pilot fails for other reasons, as on the classical ajar-door scene (6.8 dB below uniform), the label says so from the pilot alone.
- Monte Carlo rendering
- path tracing
- light transport
- rendering difficulty
- sample variance
- heavy-tailed estimators
- adaptive sampling
@misc{lin2026characterising,
title = {Characterising Per-Pixel Rendering Difficulty by Transport Mechanism},
author = {Po-Ting Lin},
year = {2026},
howpublished = {arXiv},
note = {Under review at Computer Graphics Forum.},
doi = {10.48550/arXiv.2608.16730},
eprint = {2608.16730v2},
archivePrefix = {arXiv}
}