[FFmpeg-user] filter guidance needed: persisting one colour

[Zedsquared]

Hi Folks,
    I'm looking for a suggestions as to a pipeline to achieve this effect
for a public art project ( I don't need a full pipeline, just suggestions as
to where to start looking among the filters and the general way to approach
things would be appreciated ).

The situation is a static overhead camera video of a crowd, in the dark, 
wearing flashing devices. I'd like to be able to produce a live video feed
whereby the flashes (which can be a specific colour that I control, they'll
probably be bright green in this case) are persisted for a while (or
permanently until the pipeline is restarted if that's easier).

I can see something like a heavily quantised (or posterised) green channel
only extraction of the input feeding an overlay image that is additively
updated every frame working, but I'm not sure what filters can do this. I'm
up for modifying existing filters if that's what it takes. It's sort of a
backwards chroma key situation... maybe maskfun?

All help much appreciated!  

Cheers,
        Robin.



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