lossy-LowLess Codec

[esby]

I don't know how to explain the idea,
but is there a lowsy codec that have a low-less part...

I explain:
(I'm still thinking about encoding subs & effects as a stream)

If we need to encodes subs in it, we need an overlay color,
for this color we need the codec to be lowless,
For the rest, subs, we can be lowsy...

in other words:
Once we determined the subs' contours, using lowless compression,
we can compress the content using lowsy compression.

esby

Thanks in advance for any idea