Deoldify Vapoursynth filter

[Dan64]

I'm struggling in getting the proper dark color in colored images. 

In images where there is darkness, deoldify/ddcolor not being able to understand what it is the dark area and what color to give it, they often decide to color these dark areas with blue which then becomes red and then returns to blue introducing a psychedelic effect. 

I end-up taking a draconian decision to add a post-process filter called "dark_darkness", that makes dark images really dark (and not flashing blue/red). 
This effect is achieved by de-saturating (via parameter "dark_sat") and reducing the brightness (via parameter "dark_bright")  that parts of the image with a low luma value (below the "dark_threshold").

I attached a new version of the filter.

Thanks,
Dan