Patent ID: 7548270

Claim:
A method of exposure control for an imaging system, comprising: (a) capturing a predetermined number of images, wherein the images are defined by an image resolution matrix; (b) masking the images to establish a region of interest within the image resolution matrix; (c) analyzing brightness of the images within the region of interest, wherein the analyzing brightness step further comprises: determining brightness values of the images within the region of interest, averaging the brightness values to obtain an average brightness value, comparing the average brightness value to a target brightness range, wherein the method stops if the average brightness value is within the target brightness range, but otherwise the method continues, and subtracting the average brightness value from a target brightness value to establish a brightness differential; (d) calculating an exposure time for a subsequent image capturing step based on the analyzing brightness step; (e) adjusting an exposure time setting during the subsequent image capturing step based on the calculated exposure time; (f) again capturing a predetermined number of images; (g) again masking the images to establish the region of interest; (h) determining brightness values of the images within the region of interest; (i) averaging the brightness values to obtain a new average brightness value; (j) subtracting the new average brightness value from the target brightness value to establish a new brightness differential; (k) determining the sign of the new brightness differential; (l) comparing the sign of the new brightness differential to the sign of the brightness differential determined in an immediately preceding iteration of the method; (m) correcting an overadjustment condition when the sign of the new brightness differential is opposite the sign of the brightness differential, by dividing the new brightness differential by a predetermined factor to yield a corrected brightness differential; (n) calculating an exposure time for a further subsequent image capturing step based on the corrected brightness differential when the sign of the subsequent brightness differential is opposite that of the sign of the brightness differential, and based on the brightness differential when the sign is the same; and (o) adjusting exposure during the further subsequent image capturing step based on the calculated exposure time in step (n).