Analyze Brightness in a Region of Pixels to drive Grade Node

‘There may be a tool that already does what I’m about to describe, but I’ve done something like what (I think) you want in the past by cropping to the small area that you want to analyse then put a sufficient blur on that small area to smooth it all out, then reformat the small crop up to a full size image.  Then, take a “frameHold” on that image on some reference frame, then divide the one by the other and you now have a full frame image that you can use to multiply against anything else to CC it in a way that will mimic the frame by frame difference of your little sampled area over the course of the shot, so you can (for example) reproduce flickering, or even remove flickering if you flip the order of the inputs on the “divide”.  Anyway, this may give you other ideas too.’

-from the nuke-l mailing list