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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/**
* Given a color in the Lab space, return its chroma (colorfulness,
* saturation).
*
* @param lab
* The lab color to get the chroma from
*
* @return A number greater than zero that measures chroma in the image
*/
function labChroma(lab) {
return Math.sqrt(Math.pow(lab.a, 2) + Math.pow(lab.b, 2));
}
/**
* Given the RGB components of a color as integers from 0-255, return the
* color in the XYZ color space.
*
* @return An object with x, y, z properties holding those components of the
* color in the XYZ color space.
*/
function rgb2xyz(r, g, b) {
r /= 255;
g /= 255;
b /= 255;
// assume sRGB
r = r > 0.04045 ? Math.pow(((r + 0.055) / 1.055), 2.4) : (r / 12.92);
g = g > 0.04045 ? Math.pow(((g + 0.055) / 1.055), 2.4) : (g / 12.92);
b = b > 0.04045 ? Math.pow(((b + 0.055) / 1.055), 2.4) : (b / 12.92);
return {
x: ((r * 0.4124) + (g * 0.3576) + (b * 0.1805)) * 100,
y: ((r * 0.2126) + (g * 0.7152) + (b * 0.0722)) * 100,
z: ((r * 0.0193) + (g * 0.1192) + (b * 0.9505)) * 100
};
}
/**
* Given the RGB components of a color as integers from 0-255, return the
* color in the Lab color space.
*
* @return An object with lightness, a, b properties holding those components
* of the color in the Lab color space.
*/
function rgb2lab(r, g, b) {
let xyz = rgb2xyz(r, g, b),
x = xyz.x / 95.047,
y = xyz.y / 100,
z = xyz.z / 108.883;
x = x > 0.008856 ? Math.pow(x, 1/3) : (7.787 * x) + (16 / 116);
y = y > 0.008856 ? Math.pow(y, 1/3) : (7.787 * y) + (16 / 116);
z = z > 0.008856 ? Math.pow(z, 1/3) : (7.787 * z) + (16 / 116);
return {
lightness: (116 * y) - 16,
a: 500 * (x - y),
b: 200 * (y - z)
};
}
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