What Is the Set of Images of an Object Under All Possible Illumination Conditions?

13 years 4 months ago

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The appearance of an object depends on both the viewpoint from which it is observed and the light sources by which it is illuminated. If the appearance of two objects is never identical for any pose or lighting conditions, then – in theory – the objects can always be distinguished or recognized. The question arises: What is the set of images of an object under all lighting conditions and pose? In this paper, we consider only the set of images of an object under variable illumination, including multiple, extended light sources, shadows, and color. We prove that the set of n-pixel monochrome images of a convex object with a Lambertian reﬂectance function, illuminated by an arbitrary number of point light sources at inﬁnity, forms a convex polyhedral cone in IRn and that the dimension of this illumination cone equals the number of distinct surface normals. Furthermore, the illumination cone can be constructed from as few as three images. In addition, the set of n-pixel images of a...

Peter N. Belhumeur, David J. Kriegman

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