High Precision Image Sensor Scale Factor Calibration

Abstract

A correlation method is described wherein the calibration accuracy of a commercial precision translator is transferred to the image plane of a camera system through the determination of normalized magnification and scale factor. For example, a commercial translator can have a calibration fractional error of between 10-4 - 10-6 or smaller. This calibration technique employs a simple experimental apparatus consisting of a camera system (CMOS detector and lens), linear translators and a large "random-dot" target. By correlating the shift in a sub-region of the image with the translation of the target over a sequence of translations, the fractional error of the normalized magnification was measured to be 10-4. For applications where the object size is of primary importance (industrial inspection, object tracking), this precision can be traded off for convenience or speed.