Will be useful for removing black edges (or any color) from rasters: http://docs.gimp.org/en/plug-in-colortoalpha.html
how could you configure it to apply from the edges (ala GDAL nearblack) rather than replacing a whole colour regardless of where it appears in the image?
Implemented over at #2023. @rcoup - this is generally interesting to me as an image effect at render time not really for collars since this is not something I've implemented at the gdal level and will work on tiles instead . Nearblack remains useful.