Camera Calibration In the field of machine vision

Camera Calibration • In the field of machine vision, camera calibration refers to the experimental determination of a set of parameters which describe the image formation process for a given analytical model of the machine vision system. • Ideally, camera calibration is performed without specialized optical equipment, without modifications to the hardware, and without a priori knowledge of the vision system. • Most calibration techniques are based on the observation of planar (2 D) targets with a large number of control points. Memorial University of Newfoundland October 5, 2006. 1

Camera Calibration is critical in many machine vision applications: • Photogrammetry: determining geometric properties of objects from photographic image • Stereoscopy: determining the 3 D coordinates of points of an object taken from two different positions • Dimensional metrology: the science of calibrating and using physical measurement equipment to quantify the physical size of or distance from any given object • Multisensor Image fusion: the process of combining relevant information from two or more images into a single image • Robotics, navigation, reverse engineering Memorial University of Newfoundland October 5, 2006. 2

Camera Calibration 3 D Calibration target proposed by Prof. Janne Heikkilä Memorial University of Newfoundland October 5, 2006. 3

Camera Calibration Orthogonal (Fig 8) versus perspective (Fig 9) projection of a circular control point: Memorial University of Newfoundland October 5, 2006. 4

Camera Calibration Checkerboard calibration target proposed by Jean-Yves Bouguet (Caltech) Memorial University of Newfoundland October 5, 2006. 5

Camera Calibration The machine vision parameters which must be identified include: a) b) b) c) d) e) The scale factor (negligible on solid-state cameras) The principal point (i. e. , the coordinates of the image center) The skew coefficients (negligible? ) The effective focal length of the lens-camera assembly The radial and tangential lens distortion coefficients The pose (position and orientation) of the camera Parameters a) through d) are classified as intrinsic, e) as extrinsic. Memorial University of Newfoundland October 5, 2006. 6

Camera Calibration Memorial University of Newfoundland October 5, 2006. 7