[FFmpeg-user] Filter for smoothening gradual luminance changes?

[Markku Tavasti]

Hi!

I have tried to find out proper way to smoothen luminance changes on 
videos of sunset. Cameras are action cameras where it is not possible to 
set manually exposure etc, and in fact, it is not desirable. Typically 
my video recordings are few hours, from full daylight, sun shingin 
towards camera, and endig to darkness. So exposure changes gradually, 
but problem is that on such cameras, change is annoying clear, sudden 
change. Therefore, I'd like to smoothen that so that it is not that sudden.

See example what I mean https://youtu.be/vOVYZAcWpZE?t=23s

Video is shot as normal video, and then speeded up with ffmpeg. If video 
would be done from pictures, then it is possible to change luminance of 
each picture to match to average of surrounding pictures, but cameras I 
use don't support taking pictures with given interval or provided 
intervals are too long. Therefore making 'timelapse' from video is needed.

Any suggestions?

--Tavasti