This is a simple and straightforward converter between RGB and HSV values, with RGBs from 0 - 255 and HSV values with hue from 0 - 359 and S/V from 0 - 1. I wrote it for an as yet unfinished HTML5 red-eye correction tool, but I'll be unable to devote much time to side-projects until after the holidays, so I thought I'd put this up now in case someone found it useful.

Enjoy!

function getHSV(r, g, b) {
var h, s, v, max, delta;
// v (value) is the highest of the RGB values scaled to [0-1]
max = Math.max(r, Math.max(g, b));
if (max == 0) return [0, 0, 0];
v = max / 255;
// delta is the difference between the largest and smallest of RGB
delta = max - Math.min(r, Math.min(g, b));
if (delta == 0) return [0, 0, v]; // No delta = grey, only v is significant
// s (saturation) is delta divided by max
s = delta / max;
// h (hue) is a number in degrees describing the color's angle on the hsv color wheel
if (r == max) h = (g - b) / delta;
else if (g == max) h = 2 + (b - r) / delta;
else if (b == max) h = 4 + (r - g) / delta;
// convert hue to degrees
if (h < 0) h += 6;
h *= 60;
return [h, s, v];
}
function getRGB(h, s, v) {
var quadrant, max, mid, min, fraction;
max = Math.round(v * 255);
if( s == 0 ) return ([max, max, max]); // Greys
// Quadrant is between 0 and 5, where 0, 2, and 4 are red, green, and blue
h /= 60;
quadrant = Math.floor(h);
// fraction is distance away from quadrant representing hue's primary color
fraction = (quadrant % 2 == 0) ? (1 - h % 1) : h % 1;
// min and mid are the smaller two RGB colors in the final return array
// We don't know what primary colors they represent...
min = Math.round(max * ( 1 - s ));
mid = Math.round(max * ( 1 - s * fraction ));
// ...until we check what quadrant we're in
switch (quadrant) {
// reds
case 5: return [max, min, mid];
case 0: return [max, mid, min];
// greens
case 1: return [mid, max, min];
case 2: return [min, max, mid];
// blues
case 3: return [min, mid, max];
case 4: return [mid, min, max];
}
}