This effect converts all colors except a single one to
grey. The color is selected by an RGB triple and a
tolerance for the color matching in hue degree can be specified.
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
