Abstract
This paper describes a method for estimating the spatial distribution and the spectral distribution of omnidirectional illuminations in natural scenes, and an application of the method to image rendering in computer graphics. First, we introduce an imaging system using a spherical steel ball and a normal color CMOS camera. In order to get precise omnidirectional illumination distribution, we develop a mechanism for rotating the camera around the ball in a natural scene. We determine the mapping between the coordinates on the ball and the directional vectors of light rays in the world. Next, illuminant spectral distribution at each direction is estimated from RGB sensor data by using the linear finite model and the camera sensitivity functions. Moreover, the estimated spectral radiance distribution is used for image rendering of virtual objects. In experiments, an omnidirectional illumination is estimated in an indoor scene, and an CG image of metallic objects is created using the estimated illuminant.
