RGB, HSV, and HSL color conversion algorithms in JavaScript

color-conversion-algorithms.js

/**
 * Converts an RGB color value to HSL. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSL_color_space.
 * Assumes r, g, and b are contained in the set [0, 255] and
 * returns h, s, and l in the set [0, 1].
 *
 * @param   Number  r       The red color value
 * @param   Number  g       The green color value
 * @param   Number  b       The blue color value
 * @return  Array           The HSL representation
 */
function rgbToHsl(r, g, b) {
  r /= 255, g /= 255, b /= 255;

  var max = Math.max(r, g, b), min = Math.min(r, g, b);
  var h, s, l = (max + min) / 2;

  if (max == min) {
    h = s = 0; // achromatic
  } else {
    var d = max - min;
    s = l > 0.5 ? d / (2 - max - min) : d / (max + min);

    switch (max) {
      case r: h = (g - b) / d + (g < b ? 6 : 0); break;
      case g: h = (b - r) / d + 2; break;
      case b: h = (r - g) / d + 4; break;
    }

    h /= 6;
  }

  return [ h, s, l ];
}

/**
 * Converts an HSL color value to RGB. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSL_color_space.
 * Assumes h, s, and l are contained in the set [0, 1] and
 * returns r, g, and b in the set [0, 255].
 *
 * @param   Number  h       The hue
 * @param   Number  s       The saturation
 * @param   Number  l       The lightness
 * @return  Array           The RGB representation
 */
function hslToRgb(h, s, l) {
  var r, g, b;

  if (s == 0) {
    r = g = b = l; // achromatic
  } else {
    function hue2rgb(p, q, t) {
      if (t < 0) t += 1;
      if (t > 1) t -= 1;
      if (t < 1/6) return p + (q - p) * 6 * t;
      if (t < 1/2) return q;
      if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
      return p;
    }

    var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
    var p = 2 * l - q;

    r = hue2rgb(p, q, h + 1/3);
    g = hue2rgb(p, q, h);
    b = hue2rgb(p, q, h - 1/3);
  }

  return [ r * 255, g * 255, b * 255 ];
}

/**
 * Converts an RGB color value to HSV. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSV_color_space.
 * Assumes r, g, and b are contained in the set [0, 255] and
 * returns h, s, and v in the set [0, 1].
 *
 * @param   Number  r       The red color value
 * @param   Number  g       The green color value
 * @param   Number  b       The blue color value
 * @return  Array           The HSV representation
 */
function rgbToHsv(r, g, b) {
  r /= 255, g /= 255, b /= 255;

  var max = Math.max(r, g, b), min = Math.min(r, g, b);
  var h, s, v = max;

  var d = max - min;
  s = max == 0 ? 0 : d / max;

  if (max == min) {
    h = 0; // achromatic
  } else {
    switch (max) {
      case r: h = (g - b) / d + (g < b ? 6 : 0); break;
      case g: h = (b - r) / d + 2; break;
      case b: h = (r - g) / d + 4; break;
    }

    h /= 6;
  }

  return [ h, s, v ];
}

/**
 * Converts an HSV color value to RGB. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSV_color_space.
 * Assumes h, s, and v are contained in the set [0, 1] and
 * returns r, g, and b in the set [0, 255].
 *
 * @param   Number  h       The hue
 * @param   Number  s       The saturation
 * @param   Number  v       The value
 * @return  Array           The RGB representation
 */
function hsvToRgb(h, s, v) {
  var r, g, b;

  var i = Math.floor(h * 6);
  var f = h * 6 - i;
  var p = v * (1 - s);
  var q = v * (1 - f * s);
  var t = v * (1 - (1 - f) * s);

  switch (i % 6) {
    case 0: r = v, g = t, b = p; break;
    case 1: r = q, g = v, b = p; break;
    case 2: r = p, g = v, b = t; break;
    case 3: r = p, g = q, b = v; break;
    case 4: r = t, g = p, b = v; break;
    case 5: r = v, g = p, b = q; break;
  }

  return [ r * 255, g * 255, b * 255 ];
}

Here's a version of hslToRgb for Clojure (and ClojureScript and whatever Clojure implementation):

(defn hsl->rgb [h s l]
  (let [hue->rgb (fn hue->rgb
                   [p q t]
                   (let [t (if (< t 0) (inc t) t)
                         t (if (> t 1) (dec t) t)]
                     (cond
                       (< t (/ 1 6)) (+ p (* (* (- q p) 6) t))
                       (< t (/ 1 2)) q
                       (< t (/ 2 3)) (+ p (* (* (- q p) (- (/ 2 3) t)) 6))
                       :else p)))
        [r g b] (if (= s 0)
                  [l l l]
                  (let [q (if (< l 0.5) (* l (+ 1 s)) (- (+ l s) (* l s)))
                        p (- (* 2 l) q)]
                    [(hue->rgb p q (+ h (/ 1 3))) (hue->rgb p q h) (hue->rgb p q (- h (/ 1 3)))]))]
    [(* r 255) (* g 255) (* b 255)]))

(comment
  (hsl->rgb (/ 120 256) 1.0 0.5)
  ;; => [0 255 207.18750000000003]
  :rcf)

It's a straight port. There may be dragons such as boxed math and things? I haven't considered.

Thank you, Peter!

Here's a version of hslToRgb for Clojure (and ClojureScript and whatever Clojure implementation):