Development of an inspection system for planar steel surface using multispectral photometric stereo

We address the methodology and hardware design for detecting defects on a steel surface. The goal of this work is to develop a surface inspection system for defects with three-dimensional (3-D) characteristics on planar steel surface using multispectral photometric stereo technique. First, the reflections of multispectral illuminations from a steel surface are captured by a multi-channel camera system. Then, a 3-D reconstructed surface profile is extracted from estimated gradient fields. The developed system is applied to real steel specimens and the experimental results show that it can reliably detect tiny defects on the surface.