Sort list of colors by HSV/HSB

Question

I am looking to sort a very long list of colors by their HSV/HSB values. I would like to sort them by Hue, then Sat, then Bright. Really all I need is a way to tell if one color comes "before" or "after" based on that order of HSV since I am just going to make a compareTo() in Java and use a TreeSet to do the ordering. In Java, HSV values are all stored as floats.

I am terrible at algorithms like these so any help would be appreciated!

Answer 1

The brute force way:

public final class ColorComparator implements Comparator<Color> {
    @Override
    public int compare(Color c1, Color c2) {
        float[] hsb1 = Color.RGBtoHSB(c1.getRed(), c1.getGreen(), c1.getBlue(), null);
        float[] hsb2 = Color.RGBtoHSB(c2.getRed(), c2.getGreen(), c2.getBlue(), null);
        if (hsb1[0] < hsb2[0])
            return -1;
        if (hsb1[0] > hsb2[0])
            return 1;
        if (hsb1[1] < hsb2[1])
            return -1;
        if (hsb1[1] > hsb2[1])
            return 1;
        if (hsb1[2] < hsb2[2])
            return -1;
        if (hsb1[2] > hsb2[2])
            return 1;
        return 0;
    }
}

A really easy, no-thought way to do it if you can use the Google Guava libraries is:

public final class ColorComparator extends Ordering<Color> {
    @Override
    public int compare(Color c1, Color c2) {
        float[] hsb1 = Color.RGBtoHSB(c1.getRed(), c1.getGreen(), c1.getBlue(), null);
        float[] hsb2 = Color.RGBtoHSB(c2.getRed(), c2.getGreen(), c2.getBlue(), null);
        return ComparisonChain.start().compare(hsb1[0], hsb2[0]).compare(hsb1[1], hsb2[1])
            .compare(hsb1[2], hsb2[2]).result();
    }
}

I would say just loop over the arrays and compare them (or use lexicographical ordering in Guava), but you might want to change the sort ordering around.