Development of a Dynamic Relighting System for Moving Planar Objects with Unknown Reflectance

Relighting is a technique to modify an image to account for alternate illumination conditions. Conventionally, the reflectance characteristics of an object are provided, and a relighted image is calculated using input light source information. In this paper, we propose a dynamic relighting system for moving planar objects with unknown reflectance. By acquiring the surface spectral reflectance of moving objects, our system is able to reproduce accurate colors on a display device. In the reflectance acquisition, we use a programmable light source that can produce any spectral curve. The surface spectral reflectance of an object in a darkroom is obtained based on the lighting technique with five spectral basis functions that are generated by the programmable light source. The acquired reflectance and user-input illumination information are used to calculate accurate CIEXYZ values of the relighted image. Finally, CIEXYZ values are accurately transformed to RGB values. In the experiment, illuminant A and D65 are used as the illuminants for relighting. As a result, by comparing a computer simulation with actual experiments with real objects, we observe an average color difference \( \Delta {\text{E}}^{*}_{\text{ab}} \) of approximately 7. This system operates at a rate of 1 frame per second. In addition, in this study, we have implemented another relighting system for objects under an environmental lighting condition by determining the spectral power distribution of the illumination source.