The Ditherize filter reduces the number of colors used in an image without changing the image type. An RGB image will remain so, although appear as if indexed. The method and number of colors can be selected.
Ditherize Settings
The Dither type can be set to one of four options.
none: No dithering will be used.
fs: Floyd-Steinberg(Normal) dithering will be used.
fs/low-bleed: Floyd-Steinberg(Reduced Color Bleeding) dithering will be used.
ordered: Positioned Color Dithering will be used.
The Colors slider sets the number of colors to reduce the image to.