javascript compare 2 thresholds color

1typedef struct {
2     unsigned char r, g, b;
3} RGB;
4
5double ColourDistance(RGB e1, RGB e2)
6{
7    long rmean = ( (long)e1.r + (long)e2.r ) / 2;
8    long r = (long)e1.r - (long)e2.r;
9    long g = (long)e1.g - (long)e2.g;
10    long b = (long)e1.b - (long)e2.b;
11    return sqrt((((512+rmean)*r*r)>>8) + 4*g*g + (((767-rmean)*b*b)>>8));
12}
13