METHOD AND SYSTEM FOR AUTOMATICALLY CALIBRATING A COLOR-BASED MACHINE VISION SYSTEM

摘要

A calibration algorithm is provided for calibrating a machine vision system including a color camera (22), a framegrabber (12) and an illumination source (26) wherein subsequently acquired images are processed on a pixel-by-pixel basis. After framegrabber offsets are measured to obtain initial or offset calibration data, the camera is pointed at a target (28) monotone patch of known reflectance such as pure white and the camera outputs for red, green and blue are determined while observing the monotone patch to obtain spatial calibration data. The gain for each of the output channels of the color camera is automatically determined from the initial calibration data. Applying the three gain factors to a subsequent image on the pixel-by-pixel basis allows one to end up with a color-corrected image without incurring any time performance penalty. At any time during an inspection process, a small area of white reflectance can be observed. The resulting dynamic white calibration data is used to correct for any medium-to-long term temporal variation in imaging conditions.