Illumination: a directional filter of texture?

This paper uses theory, simulation, and laboratory experiment, to show that directional illumination, used during the image acquisition process, acts as a directional filter of three dimensional texture. It is shown that the directional characteristics of image texture are not intrinsic to the physical texture being imaged, as they are affected by the direction of the illumination. This result has important implications for texture classification schemes: as many use directional characteristics for discrimination purposes. Variation of illuminant direction is shown to significantly affect a common texture measure : the Laws' L5E5 operator [1]. 1. Introduction Texture classification normally involves three processes. First, the subject texture must be illuminated and its image acquired. Second, feature operators are applied to the digitised image to produce a set of feature images. It is these images that provide the numerical descriptions of the textures. Third, a set of discriminant rules (for instance, a set of statistically derived discriminant functions) are applied to classify the image into texture classes.