Patent ID: 7324688

Claim:
A method for determining a direction of a principal light source in an image, comprising: acquiring, with a camera, an input image I of an object illuminated by a principal light source from an unknown direction s, the input image including an array of pixels, and each pixel having an intensity I(x, y); constructing an intensity vector {right arrow over (I)} from the intensities of the input image; defining an albedo map ρ for the object; constructing an albedo vector {right arrow over (ρ)} from the albedo map; generating a shape matrix N for the object; multiplying the albedo vector {right arrow over (ρ)} by the shape matrix N to obtain a shape-albedo matrix A; determining an estimated direction s* to the principal light source from the intensity vector {right arrow over (I)}, the albedo vector {right arrow over (ρ)} and the shape-albedo matrix A according to an optimization s * = arg ⁢ ⁢ min s ⁢  I → - ρ → - As  . ⁢