Real-world illumination and the perception of surface reflectance properties

TLDR

Recognizing materials from surface reflectance is difficult because illumination confounds, but people can use tacit knowledge of real‑world illumination statistics to reject unlikely interpretations and estimate reflectance even when illumination is unknown. The study employed a surface‑reflectance matching task and manipulated pixel‑ and wavelet‑level illumination properties, showing that observers rely on intermediate‑complexity cues such as edges and bright sources rather than high‑complexity object information. Participants matched surface reflectance accurately under realistic illumination, but performance deteriorated with non‑realistic lighting, indicating that they use stored assumptions about real‑world illumination statistics to estimate reflectance.

Abstract

Under typical viewing conditions, we find it easy to distinguish between different materials, such as metal, plastic, and paper. Recognizing materials from their surface reflectance properties (such as lightness and gloss) is a nontrivial accomplishment because of confounding effects of illumination. However, if subjects have tacit knowledge of the statistics of illumination encountered in the real world, then it is possible to reject unlikely image interpretations, and thus to estimate surface reflectance even when the precise illumination is unknown. A surface reflectance matching task was used to measure the accuracy of human surface reflectance estimation. The results of the matching task demonstrate that subjects can match surface reflectance properties reliably and accurately in the absence of context, as long as the illumination is realistic. Matching performance declines when the illumination statistics are not representative of the real world. Together these findings suggest that subjects do use stored assumptions about the statistics of real-world illumination to estimate surface reflectance. Systematic manipulations of pixel and wavelet properties of illuminations reveal that the visual system's assumptions about illumination are of intermediate complexity (e.g., presence of edges and bright light sources), rather than of high complexity (e.g., presence of recognizable objects in the environment).