Generate unique colours

Question

I want to draw some data into a texture: many items in a row. They aren't created in order, and they may all be different sizes (think of a memory heap). Each data item is a small rectangle and I want to be able to distinguish them apart, so I'd like each of them to have a unique colour.

Now I could just use rand() to generate RGB values and hope they are all different, but I suspect I won't get good distribution in RGB space. Is there a better way than this? E.g. what is a good way of cycling through different colours before they (nearly) repeat?

The colours don't have to match with any data in the items. I just want to be able to look at many values and see that they are different, as they are adjacent.

I could figure something out but I think this is an interesting question. :)

Answer 1

Using the RGB color model is not a good way to get a good color mix. It's better to use another color model to generate your color, and then convert from that color model to RGB.

I suggest you the HSV or HSL color model instead, in particular you want to vary the Hue.

If you want X different color values, vary them from 0 to 360 with a step size of 360 divided by X.

Answer 2

In general RGB isn't a great color space for doing these sorts of things because it's perceptually nonlinear, for starters. This means that equal distances moved between RGB triplets do not look equally different to our eyes.

I'd probably work in the L*c*h* space (see also) space, or HSL space, and just generate a uniform spacing in hue. These spaces have been designed to be approximately perceptually linear.

Answer 3

Whats your sample space... how many items are we talking.

You could build up an array of RGB Triples from

for(int r = 0; r < 255; r = r+16)
   for(int g = 0; g < 255; g = g+16)
      for(int b = 0; b < 255; b = b+16)
           // take r, g, b and add it to a list

Then randomise your list and iterate through it. that'd give you 16^3 (4096) different colors before a repeated color.

Answer 4

Google "delta e cie 2000"; the colour-difference formula is useful for determining apparent (visual) distance between 2 colours. (On a monitor; there's a different formula for pigments.) It operates on colours in Lab space (props to simon), but applies a perceptual calculation of difference.

We found that a number around 1.5 was sufficient to ensure visually distinct colours (i.e. you can tell the difference if they are near one another), but if you want identifiable colours (you can find any colour in a legend) you'll need to bump that up.

As to creating a set of colours... I'd probably start at some corner of Lab space, and walk around it using a step size that gives large enough visual differences (note: it's not linear, so step size will probably have to be adaptive) and then randomize the list.

Answer 5

This is very similar to the four-colour problem relating to colouring maps, this might yield some interesting solutions for you:

Four colour theorem

Answer 6

If you just need a set of perceptually-distinct colors (and not an algorithm to generate them) I have created a free tool on my website that does just that:
http://phrogz.net/css/distinct-colors.html

Instead of just using even spacing in RGB or HSV space (which are not uniformly distributed with respect to human perception) the tool allows you to generate a grid of values in HSV space and it then uses the CMC(I:c) standard for color distance to throw out colors that are perceptually too close to each other. (The 'threshold' slider on the second tab allows you to control how visually distinct the colors must be, showing you the results in realtime.)

In the end, you can sort your list of generated colors by various criteria, and then evenly 'shuffle' that list so that you are guaranteed to have visually-distinct values adjacent to each other in the list. (I recommend an 'Interleave' value of about 5.)

As of this writing the tool works well with Chrome, Safari, and (via a shim) Firefox; IE9 does not support HTML5 range input sliders, which the UI uses extensively for interactive exploration.