Retro Pixel Pro is a fullscreen image effect that reduces the number of colors to up to 256 specific colors and can also lower the resolution to any width and height, creating a retro look.
Another possible way to use it is to keep the resolution high and only reduce the colors for a posterization-like effect.
Includes a number of preset palettes and also the option to extract a palette from an images.
Compatibility:
This image effect will probably not work on your mobile device because of shader incompatibility.
Link to documentation
Link to YouTube video