Automatic Planning of Light Source Placement for an Active Photometric Stereo System

Abstract

Active sensing plays an important role in autonomous robot systems. This paper presents an automatic planning method of light source placement for an active photometric stereo system. Since photometric stereo systems normally use multiple light sources fixed to the environment, they cannot avoid shadows caused by surrounding objects. One remedy for this problem is to use a movable light source and to adapt its placement actively to the task environment. Candidate positions of a light source to avoid shadows are obtained initially based on a 3-dimensional model of the environment and image processing on a sphere assumed to be around the target objects. Then possible combinations are compared based on a criterion taking into accout of reliability and detectability of the measurement. We introduce a singular value analysis of the coefficient matrix to evaluate the reliability of the solution. As for the detectability criterion, size of a region which corresponds to a set of detectable surface normal vectors is evaluated on a Gaussian sphere. Experimental results, using a light source affixed to a manipulator, demonstrate usefulness of the sensor setup planning.