The  Weizmann  Institute  of  Science
Faculty of Mathematics and Computer Science

Vision and Robotics Seminar

Ronen Basri

will speak on

Lambertian Reflectance and Linear Subspaces

Variations in lighting can have a significant impact on the appearance of an object.  In this talk I will provide a novel characterization of this variability for the case of Lambertian objects. In particular, I will show that the set of all reflectance functions (the mapping from surface normals to intensities) produced by Lambertian objects under distant lighting lies close to a 9D linear subspace.  This implies that, in general, the set of images of a convex Lambertian object obtained under a wide variety of lighting conditions can be approximated accurately by a low-dimensional linear subspace, explaining prior empirical results. We also provide a simple analytic characterization of this linear space. These results are obtained by representing lighting using spherical harmonics and describing the effects of Lambertian materials as the analog of a convolution.  We use these results to develop novel algorithms for object recognition and photometric stereo that work under complex lighting that include unknown combination of point and extended light sources.

Joint work with David Jacobs of NEC Research Institute.

The lecture will take place in the
Lecture Hall, Room 1, Ziskind Building
on Thursday, June 13, 2002
at noon