A Practical Face Relighting Method for Directional Lighting Normalization

We propose a simplified and practical computational technique for estimating directional lighting in uncalibrated images of faces in frontal pose. We show that this inverse problem can be solved using constrained least-squares and class-specific priors on shape and reflectance. For simplicity, the principal illuminant is modeled as a mixture of Lambertian and ambient components. By using a generic 3D face shape and an average 2D albedo we can efficiently compute the directional lighting with surprising accuracy (in real-time and with or without shadows). We then use our lighting direction estimate in a forward rendering step to r̈elightärbitrarily-lit input faces to a canonical (diffuse) form as needed for illumination-invariant face verification. Experimental results with the Yale Face Database B as well as real access-control datasets illustrate the advantages over existing pre-processing techniques such as a linear ramp (facet) model commonly used for lighting normalization. This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories, Inc.; an acknowledgment of the authors and individual contributions to the work; and all applicable portions of the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories, Inc. All rights reserved. Copyright c ©Mitsubishi Electric Research Laboratories, Inc., 2005 201 Broadway, Cambridge, Massachusetts 02139