A study on the flexible camera calibration method using a grid type frame with different line widths

With 3D vision measuring, camera calibration is necessary to calculate parameters accurately. In this paper, we present an algorithm for camera calibration using perspective ratio of a grid type frame with different line widths. It can easily estimate camera calibration parameters such as the focal length, scale factor, pose, orientations, and distance, but the radial lens distortion is not modeled. The advantage of this algorithm is that it can estimate the distance of the object. To validate the proposed method, we set experiments with a frame on a rotator at a distance of 1.2 m from the camera and rotate the frame from 60 to 60 degrees. We investigated the distance error affected by the scale factor or different line widths and experimentally found an average scale factor that includes the least distance error with each image. The average scale factor tends to fluctuate with small variation and decreases the distance error. Compared with classical methods that use stereo camera of two or three orthogonal planes, the proposed method is easy to use and flexible.