What's the best way to “round” a Color object to the nearest Color Constant?

Question

I will be retrieving the exact color of a pixel and would like to relate that exact color to a constant like Color.blue. Is there an easy way to \"round\" to the n

Answer 1

The basic approach is to find the closest standard color to your sample by simply comparing the sample to each of them. The problem, of course, is in defining "closest." The most obvious would be use the Euclidean distance in RGB space. The problem is that this distance does not correspond very well with our perceptual sense of "closest color". A discussion of this problem, along with a nice (easily computed) metric (including pseudocode!) can be found in this paper.

EDIT: Just in case the link to that paper goes dead (or if you're lazy and are willing to use code without understanding what it does), here's my Java version of the "color distance function" the paper suggests as a "low-cost approximation" to their recommended distance function (a weighted Euclidean distance in RGB space):

double colorDistance(Color c1, Color c2)
{
    int red1 = c1.getRed();
    int red2 = c2.getRed();
    int rmean = (red1 + red2) >> 1;
    int r = red1 - red2;
    int g = c1.getGreen() - c2.getGreen();
    int b = c1.getBlue() - c2.getBlue();
    return Math.sqrt((((512+rmean)*r*r)>>8) + 4*g*g + (((767-rmean)*b*b)>>8));
}

Note that if you're just going to rank color distances, you can dispense with the call to Math.sqrt(), saving some computation costs.