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Error Analysis of Surface Normals Determined by Radiometry
June 1983 (vol. 5 no. 6)
pp. 631-645
Rajarshi Ray, Object Recognition Systems, Inc., Princeton, NJ 08540.
John Birk, Hewlett-Packard Company, Palo Alto, CA 93303.
Robert B. Kelley, Robotics Research Center, University of Rhode Island, Kingston, RI 02881.
Surface normals can be computed from three images of a workpiece taken under three distinct lighting conditions without requiring surface continuity. Radiometric methods are susceptible to systematic errors such as: errors in the measurement of light source orientations; mismatched light source irradiance; detector nonlinearity; the presence of specular reflection or shadows; the spatial and spectral distribution of incident light; surface size, material, and microstructure; and the length and properties of the light source to target path. Typically, a 1° error in surface orientation of a Lambertian workpiece is caused by a 1 percent change in image intensity due to variations in incident light intensity or a 1° change in orientation of a collimated light source. Tests on a white nylon sphere indicate that by using modest error prevention and calibration schemes, surface angles off the camera axis can be computed within 5°, except at edge pixels. Equations for the sensitivity of surface normals to major error sources have been derived. Results of surface normal estimation and edge extraction experiments on various non-Lambertian and textured workpieces are also presented.
Rajarshi Ray, John Birk, Robert B. Kelley, "Error Analysis of Surface Normals Determined by Radiometry," IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 5, no. 6, pp. 631-645, June 1983, doi:10.1109/TPAMI.1983.4767454
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