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# mjackson/color-conversion-algorithms.js

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RGB, HSV, and HSL color conversion algorithms in JavaScript
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 /** * 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 ]; }

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 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 commented Nov 30, 2023

Thank you, Peter!

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