[FFmpeg-user] Normalize video on a section of the video

[Benjamin Hill]

I have a time-lapse of a beach scene.  The exposure wasn't locked.  So, I'd
like to keep the exposure as constant as possible, likely from using the
"normalize" filter. <https://ffmpeg.org/ffmpeg-filters.html#normalize>

The problem is that it takes the entire frame into account - including the
palm tree that is waving in the wind and messing everything up.  Is there a
way to normalize on the upper-left quadrant of the scene (which is all blue
sky) and ignore the right side?  Maybe a way to temporarily mask out the
tree when picking normalization adjustments?