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@mjackson
Last active December 12, 2024 13:58
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RGB, HSV, and HSL color conversion algorithms in JavaScript
/**
* 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 ];
}
@gntlechaos
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If you have been looking for a variation that converts RGB to HSV with the hue ranging from 0 to 360 instead of 0 to 1, and the saturation and value ranging from 0 to 100, I have adapted this function, with this range re-mapping algorithm.

function mapMinMax(value,oldMin,oldMax,newMin, newMax) {
  return  (newMax-newMin)*(value-oldMin)/(oldMax-oldMin)+newMin;
}

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;
    }

    h = mapMinMax(h,0,1,0,360);
    return [h, s * 100, v * 100];
}

@kigiri
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kigiri commented Jun 18, 2020

working with css string here did:

const _rgbToHsl = rgbStr => {
  const [r, g, b] = rgbStr.slice(4, -1).split(',').map(Number)
  const max = Math.max(r, g, b)
  const min = Math.min(r, g, b)
  const l = Math.floor((max + min) / ((0xff * 2) / 100))

  if (max === min) return [0, 0, l]
  const d = max - min
  const s = Math.floor((d / (l > 50 ? 0xff * 2 - max - min : max + min)) * 100)

  if (max === r) return [Math.floor(((g - b) / d + (g < b && 6)) * 60), s, l]
  return max === g
    ? [Math.floor(((b - r) / d + 2) * 60), s, l]
    : [Math.floor(((r - g) / d + 4) * 60), s, l]
}

It takes a css rgb string and returns parts in a css ready scale.

I got results similar to chrome conversion.

@avisek
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avisek commented May 21, 2022

RGB, HSL, XYZ, LAB, LCH color conversion algorithms (ES6 Modules)
https://gist.github.com/avisek/eadfbe7a7a169b1001a2d3affc21052e

@RAFC-01
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RAFC-01 commented Mar 23, 2023

@isbyerley, came here to say the same thing. I think there's a mistake in the hsvToRgb. Here's my version:

function rgbFromHSV(h,s,v) {
  /**
   * I: An array of three elements hue (h) ∈ [0, 360], and saturation (s) and value (v) which are ∈ [0, 1]
   * O: An array of red (r), green (g), blue (b), all ∈ [0, 255]
   * Derived from https://en.wikipedia.org/wiki/HSL_and_HSV
   * This stackexchange was the clearest derivation I found to reimplement https://cs.stackexchange.com/questions/64549/convert-hsv-to-rgb-colors
   */

  hprime = h / 60;
  const c = v * s;
  const x = c * (1 - Math.abs(hprime % 2 - 1)); 
  const m = v - c;
  let r, g, b;
  if (!hprime) {r = 0; g = 0; b = 0; }
  if (hprime >= 0 && hprime < 1) { r = c; g = x; b = 0}
  if (hprime >= 1 && hprime < 2) { r = x; g = c; b = 0}
  if (hprime >= 2 && hprime < 3) { r = 0; g = c; b = x}
  if (hprime >= 3 && hprime < 4) { r = 0; g = x; b = c}
  if (hprime >= 4 && hprime < 5) { r = x; g = 0; b = c}
  if (hprime >= 5 && hprime < 6) { r = c; g = 0; b = x}
  
  r = Math.round( (r + m)* 255);
  g = Math.round( (g + m)* 255);
  b = Math.round( (b + m)* 255);

  return [r, g, b]
}

if h is equal to 360 this code shows NaN because you are not checking hprime for value 6 (360/60 = 6)
if (hprime >= 5 && hprime <= 6) { r = c; g = 0; b = x} "hprime <= 6" instead of "hprime < 6" fixes it

@SAKryukov
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SAKryukov commented Nov 6, 2023

It does work, but it is not good to do the comparison of floating point Number values as you do in your switch. If it works in your case, this is only a potentially unreliable special case. You could figure out the three cases of your switch before your /= expressions. With minimal modifications of your code, it would look like

const rgbToHsl = (r, g, b, a) => {
        let [r, g, b, a] = rgba;
        let max = Math.max(r, g, b), min = Math.min(r, g, b);
        const componentCase = max == r ? 0 : (max == g ? 1 : 2); // is max r g or b?
        r /= 255, g /= 255, b /= 255, min /= 255, max /= 255;
        let h, s, l = (max + min) / 2;
        if (max == min) {
            h = s = 0; // achromatic
        } else {
            let d = max - min;
            s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
            switch (componentCase) {
                case 0: h = (g - b) / d + (g < b ? 6 : 0); break;
                case 1: h = (b - r) / d + 2; break;
                case 2: h = (r - g) / d + 4; break;
            }
            h /= 6;
        }
        return [h, s, l, a];
};

Also, note that you should use const or let, but not var, to avoid the known risks related to the obsolete var.
Then, it is not nice that you accept separate r, g, and b on input but the function returns an array. Why RGB should be different from HSL? Note the line let [r, g, b, a] = rgba.

Finally, it is good to have the alpha channel as well. This work is done for the use in CSS, where the alpha channel is generally used everywhere.

@PEZ
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PEZ commented Nov 30, 2023

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.

@SAKryukov
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Thank you, Peter!

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

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