Constructing colours for maximum contrast

Question

I want to draw some items on screen, each item is in one of N sets. The number of sets changes all the time, so I need to calculate N different colours which are as different as possible (to make it easy to identify what is in which set).

So, for example with N = 2 my results would be black and white. With three I guess I would get all red, all green, all blue. For all four, it's less obvious what the correct answer is, and this is where I'm having trouble.

EDIT:: The obvious approach is to map 0 to Red, 1 to green, and all the colours in between to the appropriate rainbow colours, then you can get a colour for set N by doing GetRainbowColour(N / TotalSets), so a GetRainbowColour method is all that's need to solve this problem

Answer 1

You can read up on the HSL and HSV color models in this wikipedia article. The "H" in the acronymns stands for Hue, and that is the rainbow you want. It sounds like you want saturation to max out. The article also explains how to convert to RGB color.

Looks like a similar question has been asked before here.

Answer 2

The answer to this question is subjective - what is best contrast to someone with full vision is not necessarily best contrast to someone who is colour blind or has limited vision or someone with normal eyesight who is operating the equipment in a dark environment.

Physiologically, humans have much better resolution for intensity that for hue or saturation. That is why analogue TV, digital video and photo compression throw away colour information to reduce bandwidth (4:2:2) - if you put two pixels which are different intensities together, it doesn't matter what colour they are - we simply can only sense colour differences on large areas of like intensity.

So if the thing you are trying to display has lots of small areas of only a few pixels, or you want it to be used in the dark (in the dark the brain boosts the blue cells and we don't see colour as well) or by the 10% of the male population who are colour blind, consider using intensity as the main differentiating factor rather than hue. GetRainbowColour would ignore the most important dimension of the human visual sense, but can work quite well for continuous data.