SunnyRed - 1 year ago 118
Javascript Question

# Change the Hue of a RGB Color in javascript

Similar to this (how to increase brightness) I want to change the Hue of a RGB (Hex) Color.

Say

`changeHue(#FF0000, 40)`
returns
`#FFAA00`

Here is the solution I found. I hope its usable and might help in the future. Any improvements or further solutions are very welcome.

## Change Hue

``````// Changes the RGB/HEX temporarily to a HSL-Value, modifies that value
// and changes it back to RGB/HEX.

function changeHue(rgb, degree) {
var hsl = rgbToHSL(rgb);
hsl.h += degree;
if (hsl.h > 360) {
hsl.h -= 360;
}
else if (hsl.h < 0) {
hsl.h += 360;
}
return hslToRGB(hsl);
}

// exepcts a string and returns an object
function rgbToHSL(rgb) {
// strip the leading # if it's there
rgb = rgb.replace(/^\s*#|\s*\$/g, '');

// convert 3 char codes --> 6, e.g. `E0F` --> `EE00FF`
if(rgb.length == 3){
rgb = rgb.replace(/(.)/g, '\$1\$1');
}

var r = parseInt(rgb.substr(0, 2), 16) / 255,
g = parseInt(rgb.substr(2, 2), 16) / 255,
b = parseInt(rgb.substr(4, 2), 16) / 255,
cMax = Math.max(r, g, b),
cMin = Math.min(r, g, b),
delta = cMax - cMin,
l = (cMax + cMin) / 2,
h = 0,
s = 0;

if (delta == 0) {
h = 0;
}
else if (cMax == r) {
h = 60 * (((g - b) / delta) % 6);
}
else if (cMax == g) {
h = 60 * (((b - r) / delta) + 2);
}
else {
h = 60 * (((r - g) / delta) + 4);
}

if (delta == 0) {
s = 0;
}
else {
s = (delta/(1-Math.abs(2*l - 1)))
}

return {
h: h,
s: s,
l: l
}
}

// expects an object and returns a string
function hslToRGB(hsl) {
var h = hsl.h,
s = hsl.s,
l = hsl.l,
c = (1 - Math.abs(2*l - 1)) * s,
x = c * ( 1 - Math.abs((h / 60 ) % 2 - 1 )),
m = l - c/ 2,
r, g, b;

if (h < 60) {
r = c;
g = x;
b = 0;
}
else if (h < 120) {
r = x;
g = c;
b = 0;
}
else if (h < 180) {
r = 0;
g = c;
b = x;
}
else if (h < 240) {
r = 0;
g = x;
b = c;
}
else if (h < 300) {
r = x;
g = 0;
b = c;
}
else {
r = c;
g = 0;
b = x;
}

r = normalize_rgb_value(r, m);
g = normalize_rgb_value(g, m);
b = normalize_rgb_value(b, m);

return rgbToHex(r,g,b);
}

function normalize_rgb_value(color, m) {
color = Math.floor((color + m) * 255);
if (color < 0) {
color = 0;
}
return color;
}

function rgbToHex(r, g, b) {
return "#" + ((1 << 24) + (r << 16) + (g << 8) + b).toString(16).slice(1);
}
``````

## Usage

``````changeHue("#FF0000", 40) --> returns #ffaa00
changeHue("#D61E1E", 180) --> returns #1ed6d6
changeHue("#2244BB", -80) --> returns #21bb66
``````

## References

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