If you install my
Toolbox of Lua-scripts there are several options dedicated to palette reduction/optimization, f.ex.
* Palette-->Analyze & Optimize-->
Median CutClassic and effective reduction to a desired # of colors.
* Palette-->Analyze & Optimize-->
Optimize ColorsA script that identifies clusters in colorspace (redundantly similar colors) and fuses them. Adjustable strength/radius. Great for weeding out all those accidental near duplicates.
* Image-->Optimize & Remap-->
Reduce (rare) colsProcesses both the image and palette to remove the least useful colors. Can reduce to a desired amount of colors (set "Removal Tolerance" to 100% and select how many colors to remove). A very effective algorithm.