Techniques for calibration of the scale factor and image center for high accuracy 3D machine vision metrology

Abstract

This paper describes techniques for calibrating certain intrinsic camera parameters for machine vision. The parameters to be calibrated are the horizontal scale 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 1D-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 11 is simple to perform, but is less accurate than the other two. The most general Group I11 is accurate and efficient, but requires accurate image feature extraction of calibration points with known 3D coordinates. A feasible setup is described.Results of real experiments are presented and compared with theoretical predictions. Accuracy and reproducibility of the calibrated parameters are reported, as well as the improvement in actual 3D measurement due to center calibration.

Camera Models and Fundamental Concepts Used in Geometric Computer Vision

“…Before this, that model was already used by Lenz and Tsai [305,306] (see also the textbook [253,254] by Jähne); however, they used it as forward model, i.e., in the below equations, one would swap the forward and back-projection equations. The division model as defined by Fitzgibbon and Bräuer-Burchardt and Voss, is given as:…”

A comparative review of camera calibrating methods with accuracy evaluation

“…(2) Intrinsic versus extrinsic camera calibration. Intrinsic calibration is concerned only with obtaining the physical and optical parameters of the camera [16,17]. Besides, extrinsic calibration concerns the measurement of the position and orientation of the camera in the scene [18,19].…”

Calibration of Convex Lenses with 2nd Order Radial Distortion Model

“…Much research has been made in the region of distortion calibration on wide-angle [5][6]. Huge numbers of these techniques utilize calibration patterns [7][8][9], while other nonmetric techniques rely on upon the attendance of certain features in the scene [2,[8][9][10]. The limitation of the greater part of these strategies is that they are interested in modifying the distortion and leaving parameters (intrinsic and extrinsic) to be evaluated with different strategies.…”

“…Choosing the right model and trials could provide accurate result. Simpler methods used by the computer vision community, have been developed due to the complexity of the evaluation trials and advances in the use of computers for analytical analysis [1,2,3].…”