The Ditherize filter reduces the number of colors used in an image without actually performing the reduction to the image type. An RGB image will remain so, although appear to be indexed. The method and number of colors are able to be selected for this filter.
Ditherize Settings
The Dither type can be set to one of four options.
none: No dithering will be used.
fs: Floyd-Steinburg(Normal) dithering will be used.
fs/low-bleed: Floyd-Steinburg(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.