A method for estimating colors of scene illuminants under spatially non-uniform environments

摘要

This paper proposes a method for estimating illuminant colors that have two different light sources, i.e. fluorescent light and daylight. The conventional methods assume that one light source exists in a scene or in a small region and that it spans a scene uniformly. Therefore the methods cannot estimate illuminant colors when two different light sources are illuminating the scene or the region. Our method formulates the relationships among the colors of two regions that have the same surface reflectance but are in different locations and have different illumination rates (which vary from location to location). In order to clarify the unknown surface reflectance common to each color region, the method uses the property that the colors derived in the regions comprise the plane through the origin in a three-dimensional color space. By determining the normal of the plane, which is unique to the surface reflectance, the coefficients of the basis function of surface reflectance are derived. In this way, we can estimate illumination rates, that is, the colors of the scene illuminants. The results of numerical simulations using the reflectance dataset from the ISO-TR 16066 database and two illuminants (a typical fluorescent lamp and sunlight) show that the estimated illumination rates are similar to the ground truth.