Photometric stereo

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Photometric stereo is a technique in computer vision for estimating the surface normals of objects by observing that object under different lighting conditions.

The technique was originally introduced by Woodham in 1980.[1] The special case where the data is a single image is known as shape from shading, and was analyzed by B. K. P. Horn in 1989.[2]

Methods[edit]

Under Woodham's original assumptions — Lambertian reflectance, known point-like distant light sources, and uniform albedo — the problem can be solved by inverting the linear equation I = n \cdot L, where I is a (known) vector of m observed intensities, n is the (unknown) surface normal, and L is a (known) 3 \times m matrix of normalized light directions.

Photometric stereo has since been generalized to many other situations, including non-uniform albedo, extended light sources, and non-Lambertian surface finishes.[3] Current research aims to make the method work in the presence of projected shadows, highlights, and non-uniform lighting. Surface normals define the local metric, using this observation Bronstein et al. [4] defined a 3D face recognition system based on the reconstructed metric without integrating the surface. The metric of the facial surface is known to be robust to expressions.

See also[edit]

References[edit]

  1. ^ Woodham, R.J. 1980. Photometric method for determining surface orientation from multiple images. Optical Engineerings 19, I, 139-144.
  2. ^ B. K. P. Horn, 1989. Obtaining shape from shading information. In B. K. P. Horn and M. J. Brooks, eds., Shape from Shading, pages 121–171. MIT Press.
  3. ^ "A Photometric Stereo Approach to Face Recognition". University of the West of England. Retrieved 2011-03-27. 
  4. ^ A.M. Bronstein, M.M. Bronstein, A. Spira, R. Kimmel. "Face recognition from facial surface metric". European Conf. Computer Vision-ECCV 2004. Retrieved 2004.