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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
Publication Date: 1997/09/25
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.