Couple of precision issues here:
- Interpolation was rounding trunkcating colors, and because
of some precision issues value 254.999 became 254 leading
to troubles later.
Now color interpolaiton will do rounding to nearest int.
- Subtract was setting channels to something negative which
confused color management (especially negative alpha),
Now subtract effect will clamp channels to 0 from bottom
and also do some tricks to prevent small alpha which
could also confuse color management.
c5c34ca65f