TECHNIQUES FOR CALIBRATION OF THE SCALE FACTOR AND IMAGE CENTER FOR HIGH ACCURACY 3D MACHINE VISION METROLOGY.

Abstract

Techniques are described for calibrating certain intrinsic camera parameters for machine vision. The parameters to be calibrated are the horizontal factor, i. e. the factor that relates the sensor element spacing of a discrete array camera to the picture element spacing after sampling by the image acquisition circuitry, and the image center, i. e. the intersection of the optical axis with the camera sensor. The scale factor calibration uses a one-dimensional (1-D) FFT and is accurate and efficient. It also permits the use of only one coplanar set of calibration points for general camera calibration. Three groups of techniques for center calibration are presented: Group I requires using a laser and a four-degree-of-freedom adjustment of its orientation, but is simplest in concept, and is accurate and reproducible. Group II is simple to perform, but is less accurate than the other two. The most general, Group III, is accurate and efficient, but requires accurate image feature extraction of calibration points with known 3-D coordinates. A feasible setup is described.