There are (combinations of) OpenCV functions/methods to find the difference between two frames of a video. After finding such areas I would then like to know the rate of change of brightness for those locations (between different frames). But I have yet to find an OpenCV function/method that given an area would return a value in proportion to the (average) brightness of that area. Did I miss something? Is there a set of OpenCV calls that might do this?
-thanks