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 ];
}






//      UTILITIES

// ------------------------------------------
// converts r,b,b to h,s,v
//  r,g,b are [0-255]
//  h,s,v are [0-1] X [0-1] X [0-255]
// Source :  Lol Software :  http://lolengine.net/blog/2013/01/13/fast-rgb-to-hsv
function RGB2HSV(r, g, b, hsv) {
    var K = 0.0,
        swap = 0;
    if (g < b) {
        swap = g;
        g = b;
        b = swap;
        K = -1.0;
    }
    if (r < g) {
        swap = r;
        r = g;
        g = swap;
        K = -2.0 / 6.0 - K;
    }
    var chroma = r - (g < b ? g : b);
    hsv[0] = Math.abs(K + (g - b) / (6.0 * chroma + 1e-20));
    hsv[1] = chroma / (r + 1e-20);
    hsv[2] = r;
}

// ------------------------------------------
//  r,g,b are [0-255]
//  h,s,v are [0-1] X [0-1] X [0-255]
// Source :  Lol Software :  https://github.com/kobalicek/rgbhsv
function hsvToRgb(rgb, hsv) {
    var h = hsv[0];
    var s = hsv[1];
    var v = hsv[2];

    // The HUE should be at range [0, 1], convert 1.0 to 0.0 if needed.
    if (h >= 1.0) h -= 1.0;

    h *= 6.0;
    var index = Math.floor(h);

    var f = h - index;
    var p = v * (1.0 - s);
    var q = v * (1.0 - s * f);
    var t = v * (1.0 - s * (1.0 - f));

    switch (index) {
        case 0:
            rgb[0] = v;
            rgb[1] = t;
            rgb[2] = p;
            return;
        case 1:
            rgb[0] = q;
            rgb[1] = v;
            rgb[2] = p;
            return;
        case 2:
            rgb[0] = p;
            rgb[1] = v;
            rgb[2] = t;
            return;
        case 3:
            rgb[0] = p;
            rgb[1] = q;
            rgb[2] = v;
            return;
        case 4:
            rgb[0] = t;
            rgb[1] = p;
            rgb[2] = v;
            return;
        case 5:
            rgb[0] = v;
            rgb[1] = p;
            rgb[2] = q;
            return;
    }
}