Currently implemented switching from yuv to rgb, looking up rgb from the
table in the usual way, getting back to yuv. With luma lookup presets
(sepia, heat, xray) a color space conversion is saved directly looking
up rgb for a given Y and converting to yuv.
Probably this latter step can even be made faster precalculating a luma
to yuv table in an outer loop.
https://bugzilla.gnome.org/show_bug.cgi?id=625817
Implements a color lookup table filter with 4 presets:
- heat: fake heat camera effect
- sepia: sepia toning
- xray: invert + shade to blue
- xpro: cross process
https://bugzilla.gnome.org/show_bug.cgi?id=625817