(05-16-2017, 03:28 PM)DcNdrew Wrote: ....And of course I'd like to make less colors to work with them easier....
You can use Colors -> Info -> Colorcube Analysis
lots of screenshots so not inline http://i.imgur.com/nEKI3WZ.jpg
That is straight from the site you referenced - 56 colours although there are options on that site for different color schemes.
Looking at your request on how to reduce the number of colors.
1. Posterize sort of works.
Give the image a small gaussian blur Filters -> Blur -> Gaussian Blur
Apply Colors -> Posterize can get you down to 16 colors, depending on original image. http://i.imgur.com/WITxBqT.jpg
2. An alternative is
Apply a gaussian blur
Convert the image from RGB mode to Indexed mode. Image -> Mode -> Indexed http://i.imgur.com/JauAZf5.jpg with a small number of colors (using 8) here.
That gives an image with a color map Windows -> Dockable Dialogs -> Colormap that looks like this http://i.imgur.com/fnGUVIz.jpg (7 colors + white)
The colormap can be edited to further reduce colors, the sea for example http://i.imgur.com/2iRp1Dk.jpg
Set the image back to RGB mode Image -> Mode -> RGB and a check gives 6 colours. http://i.imgur.com/jU8amzS.jpg