Neural Network Based Photometric Stereo with a Nearby Rotational Moving Light Source

Yuji IWAHORI  Robert J. WOODHAM  Masahiro OZAKI  Hidekazu TANAKA  Naohiro ISHII  

IEICE TRANSACTIONS on Information and Systems   Vol.E80-D   No.9   pp.948-957
Publication Date: 1997/09/25
Online ISSN: 
Print ISSN: 0916-8532
Type of Manuscript: PAPER
Category: Image Processing,Computer Graphics and Pattern Recognition
photometric stereo,  neural network,  principal components analysis,  cast shadows,  inter-reflection,  

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An implementation of photometric stereo is described in which all directions of illumination are close to and rotationally symmetric about the viewing direction. THis has practical value but gives rise to a problem that is numerically ill-conditioned. Ill-conditioning is overcome in two ways. First, many more than the theoretical minimum number of images are acquired. Second, principal components analysis (PCA) is used as a linear preprocessing technique to determine a reduced dimensionality subspace to use as input. The approach is empirical. The ability of a radial basis function (RBF) neural network to do non-parametric functional approximation is exploited. One network maps image irradiance to surface normal. A second network maps surface normal to image irradiance. The two networks are trained using samples from a calibration sphere. Comparison between the actual input and the inversely predicted input is used as a confidence estimate. Results on real data are demonstrated.