© Springer International Publishing Switzerland 2015 A. Trémeau et al. (Eds.): CCIW 2015, LNCS 9016, pp. 81–90, 2015. DOI: 10.1007/978-3-319-15979-9_8 Development of a Dynamic Relighting System for Moving Planar Objects with Unknown Reflectance Ryosuke Nakahata, Keta Hirai, Takahiko Horiuchi, and Shoji Tominaga () Graduate School of Advanced Integration Science, Chiba University, Chiba, Japan horiuchi@faculty.chiba-u.jp Abstract. 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 ΔE * 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. Keywords: Relighting · Spectral reflectance estimation · Color reproduction · Dynamic system · Illuminant estimation 1 Introduction In general, when looking at an object, brightness and color in human perception de- pend on the type of the light source. Relighting is a technique to change the illumina- tion environment within an image. Relighting is used in industrial product design to simulate the appearance of objects under a variety of light sources. In previous studies, relighting has been implemented by various approaches. Zhen et al. [1] proposed a relighting method for human faces by changing the coefficients of the spherical harmonic function of the radiance environment map. This approach is based on the acquisition of three-dimensional model of a human face using a morph- ing model. Then the human face was relighted using this three-dimensional shape. The light source environments were approximated by a spherical harmonic function as a basis function. They performed this process in real time by only estimating the