Two-image photometric stereo method
Jun An Yang, Noboru Ohnishi, Noboru Sugie · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1992
In the photometric stereo method, the surface orientation of an object is determined by using multiple images (at least three images). The multiple images are obtained by changing the position of a light source, and the surface orientation of the object can be determined only in the area of the object illuminated by all light sources. So it is desirable that the number of light sources should be reduced. We propose a method for determining surface orientation along with reflectance, in which only two light sources are used. It is assumed that an object is convex and has a smooth Lambertian surface with locally constant reflectance. We have found the following: there exists a 'separation line' in the image, along which the surface normal is represented as a linear combination of two vectors pointing toward the direction of light sources, and the separation line separates the surface into two regions. Not only when the reflectance is known, but even though the reflectance is unknown, we can determine the surface orientation of the object using the property of the separation line. Here we use the constraint of convexity. Simulations carried out under various situations yielded satisfactory results.