an automatic process for calibrating the optical image exposure value to compensate for changes in machine vision systems to maintain optimal exposure of captured images and adjust for the different characteristics among cameras components , such as imaging sensor sensitivity , led strength , external lighting , reflective functions of any background material , different external lighting conditions , possible changes or updates of the systems over the years , such as led changes , and even the aging of camera sensor and leds over time . a series of images of a target are captured with a predetermined sequence of exposure values , the saturation exposure percentage of a region of interest is calculated in each of the images , and the saturation exposure percentages are compared to determine the exposure value that has a saturation exposure percentage that varies the least from the saturation exposure value of the preceding and following exposure values .