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Technical Report HW-MACS-TR-0020

TitleHow do joint image statistics change with illumination?
AuthorsOndrej Drbohlav, Mike Chantler
AbstractThe dependence of statistical properties of an image as a function of illumination direction is an exciting topic which was so far investigated experimentally, and also addressed theoretically for a special case of low-order moments of image features. In this paper we observe the principal relationship between the joint (co-occurrence) distribution of surface properties and the corresponding joint distribution of local image features. We focus on two kinds of statistics computed from local image neighbourhoods: (a) the joint distribution of pixel intensities, and (b) the joint distribution of binary patterns obtained by taking the signs of intensity differences between a selected reference pixel and all other pixels. We work with a non-parametric histogram representation of the probability distribution functions, and show how the frequencies in a histogram bin depend on illumination. Finally, we focus on approximating the illumination dependence of image statistics by a harmonic series. Experimental results obtained using a real surface are presented.


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