Imaging Systems

Polarization imaging for material classification

[+] Author Affiliations
Shoji Tominaga

Chiba University, Graduate School of Advanced Integration Science, Department of Information Science, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Akira Kimachi

Osaka Electro-Communication University, Department of Engineering Informatics, Neyagawa, Osaka 572-8530, Japan

Opt. Eng. 47(12), 123201 (December 23, 2008). doi:10.1117/1.3041770
History: Received March 02, 2008; Revised October 04, 2008; Accepted October 24, 2008; Published December 23, 2008
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A simple and stable method is proposed for distinguishing dielectric and metal material surfaces from the polarization images captured by a vision system consisting of a linear polarizer and a digital camera. The polarization state is determined by the transmitted light intensity through the polarizer as a function of polarizing orientation. The degree of polarization (DOP) is estimated from the image intensities through the polarizer. The DOP map is quite effective for material classification around specular highlight on an object surface. We prove that the DOP map is convex for a dielectric surface and concave for a metal surface. The problem of material classification is then reduced to a simple judgment of the convexity of the DOP map obtained around the highlight peak. The proposed method is not a pixelwise local method based on thresholding the Fresnel ratio computed at each pixel but an area-based method based on the DOP map in a highlight area. The feasibility of the method is confirmed in experiments under a variety of conditions.

© 2008 Society of Photo-Optical Instrumentation Engineers

Citation

Shoji Tominaga and Akira Kimachi
"Polarization imaging for material classification", Opt. Eng. 47(12), 123201 (December 23, 2008). ; http://dx.doi.org/10.1117/1.3041770


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