Spatial filters provide a useful and efficient means of analyzing an input color image into components which capture different spatial properties. Representations based on spatial filtering have restricted usefulness for recognition, however, because the output of a spatial filter across an image depends on the scene illumination conditions. In this paper, we use a physically accurate linear model for spectral reflectance to derive invariants of distributions in spatially filtered color images that do not depend on the scene illumination. These invariants can be used for the illumination-invariant recognition of regions following an arbitrary linear filtering operation. We describe a method for illumination correction based on color distributions and introduce an illumination change consistency constraint which is useful for verifying matches obtained using the invariants. We show using a set of classification experiments that the filtered distribution invariants can significantly improve the capability of a recognition system in environments where illumination cannot be controlled.

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