Bi-directional reflectance of a varnished painting Part 1: Influence of the refractive indices without using the approximations of Saunderson correction – exact computation

✍ Scribed by Mady Elias; Lionel Simonot

• Publisher: Elsevier Science
• Year: 2004
• Tongue: English
• Weight: 250 KB
• Volume: 231
• Category: Article
• ISSN: 0030-4018
• DOI: 10.1016/j.optcom.2003.12.009

✦ Synopsis

An absorbing and non-scattering varnish layer applied on a diffuse painting modifies the colour appearance. The different refractive indices of air, varnish and painting are taken into account to express the diffuse reflectances of two systems: the three-layer system air/varnish/paint and the double-layer system air/paint. An exact relationship between the reflectance of the unvarnished and varnished painting is then deduced, for any bi-directional configuration. It is no more necessary to use the Saunderson correction, as implicitly done in a previous paper of the authors.

The result is compared with Kubelka-Munk two-flux theory and Saunderson correction applied at each interface air/varnish and varnish/painting. The comparison points out the insufficiency of the two-flux approach even in the case of a diffuse incident lighting and a scattered light collected in all directions.