Artifacts when using hue-chroma to increase chroma on gray areas of an image
The attached patch fixes artifacts when using GEGL hue-chroma in GIMP to add chroma to an image with gray portions:
0001-Fix-artifacts-in-gegl-hue-chroma-when-operating-on-g.patch
The patch has a simple check that doesn't alter hue or chroma in "sufficiently gray" portions of the image.
Here is a screenshot showing results before and after applying the patch:
It might, or might not, also be necessary to patch babl's extensions/CIE.c to not use SSE2. Or more likely it's necessary to completely erase all babl/GEGL/GIMP installed files and recompile/reinstall babl/GEGL/GIMP.
Or perhaps it's only necessary to create a new copy of the original layer to work on after the patch. The above screenshot is with default extensions/CIE.c. An odd problem with babl/GEGL/GIMP is the seeming "stickiness" of old artifacts in old layers.
Anyway, the patch works.