A method of light reflectance measurement

Abstract

The quality of light reflectance models in realistic image synthesis is directly related to the quality of computer generated images. In order to develop such models, actual light reflectance distribution data are required. One way to express the reflectance properties of a surface is called bidirectional reflectance distribution function, or BRDF. BRDF is a function with four degrees of freedom, two for the direction of incident light and two for the direction of reflected light. It requires acquiring large amount of data through measurements and the process is very time consuming. In this thesis, an automated measurement method is presented and implemented. A 3- channel CCD camera is calibrated and used as the light measuring device. The system used is called ACME (ACtive Measurement Facilities). Within ACME, all devices in the system are under robotics control. Experiments are written in Java, and can be loaded from any machine via Internet and run on the local server. Several material samples are measured by using this system including paper and silk, and reliable data were obtained. The overall error is estimated to be less than 8 % . It can be concluded that a CCD camera can be used to measure light reflectance properties for computer graphics, and it is relatively fast and convenient.