I have some code that generates image of a pie chart. It's a general purpose class, so any number of slices can be given as input. Now I have problem picking good colors for the slices. Is there some algorithm that is good at that?
Colors need to follow some rules:
Some algorithm manipulating with RGB values would be a preferred solution.
I would pre-compile a list of about 20 colors, then start repeating with the 2nd color. This way you won't break your second rule. Also, if someone makes a pie chart with more than 20 slices, they have bigger problems. :)
Take a look at Color Brewer, a tool that helps to define a coloring scheme to convey qualitative or quantitative information: maps, charts, etc. Out of three "types" of palettes that this tool can generate - sequential, qualitative, and diverging - you probably need the latter, diverging...
You can even download Excel files with RGB definitions of all the palettes.
There is a generator here. It is intended for web design, but the colours would look great on a pie chart, too.
You could either pre-compile a list of nice colours, or examine the logic behind the generator and do something similar yourself.
I found this pseudocode formula that might help. You could start with a set to seed it.
Colour Difference Formula
The following is the formula suggested by the W3C to determine the difference between two colours.
(maximum (Red value 1, Red value 2) - minimum (Red value 1, Red value 2)) + (maximum (Green value 1, Green value 2) - minimum (Green value 1, Green value 2)) + (maximum (Blue value 1, Blue value 2) - minimum (Blue value 1, Blue value 2))
The difference between the background colour and the foreground colour should be greater than 500.
