ditherize - Dithers current selection
This script takes the current selection and dithers it just like convert to indexed.
[PF_RADIO, "dither_type", "The dither type (see gimp_image_convert_indexed)", 1, [none => 0, fs => 1, "fs/low-bleed" => 2, ordered => 3]], [PF_SLIDER, "colours", "The number of colours to dither to", 10, [0, 256, 1, 1]],
This is quite convoluted, but I found no other way to do this than:
create a new image & one layer copy & paste the layer ditherize new image copy & paste back
Distributed under the same terms as Gimp-Perl.