Light Analysis of Paintings at Scale Using Spherical Harmonics

Abstract

Light is abstract. Light is difficult to describe with words. Unlike other pictorial motifs such as perspective, light depiction eludes fixed rules and defies straightforward measurement. This study presents a preliminary step towards measuring light information from paintings at scale. We use spherical harmonics to extract light environment features from depicted faces. Our initial evaluation assessed the model’s ability to accurately represent environmental lighting, using natural images with ground truth lighting information. To evaluate performance on paintings on a large-scale setting, we compare our light direction estimates with human annotations over the course of five centuries. Finally, our methodology undergoes validation through an art historical case study. We track the use of diffuse light across seventeenth century Netherlandish portrait painting to commensurate art historical literature with our quantitative measures.