Convert images to simulate palettes of ancient displays

if you have GEGL 0.4 or higher rather use Tools -> GEGL Opereation -> Color Reduction

The following can be simulated

Regular RGB palettes

• 3-bit RGB 2 colors per channel 8 colors in total
• 6-bit RGB 4 colors per channel 64 colors in total
• 9-bit RGB 8 colors per channel 512 colors in total
• 12-bit RGB 16 colors per channel 4,096 colors in total
• 15-bit RGB 32 colors per channel 32,768 colors in total
• 18-bit RGB 64 colors per channel 262,144 colors in total
• change any number of colors per channel 2-256 colors

Non-regular RGB palettes

• 3-3-2 bit RGB 8 8 4 colors, 256 colors in total
• 5-6-5 bit RGB 32 64 32 colors, 65,536 colors in total (16-bit RGB)
• 3-level RGB 3 3 3 colors, 27 colors in total

To do

• greyscale (can be simulated by first converting to Greyscale and then to RGB.
• intensity (cannot do 4-bit RGBI)
• dithering
• custom palettes
• maximum simultaneous colors

Prerequisites

• Gimp 2.8
• Python

Installation

• copy palette_change.py to your ~/.gimp-2.8/plug-ins directory.
• make sure that palette_change.py is marked as executable (sudo chmod +x palette_change.py)

References

• https://en.wikipedia.org/wiki/List_of_monochrome_and_RGB_palettes
• https://en.wikipedia.org/wiki/List_of_color_palettes
• http://gimpbook.com/scripting/
• http://www.gimp.org/docs/python/index.html