luminosity.js
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var utils = require('../utils')
, nodes = require('../nodes');
/**
* Returns the relative luminance of the given `color`,
* see http://www.w3.org/TR/WCAG20/#relativeluminancedef
*
* Examples:
*
* luminosity(white)
* // => 1
*
* luminosity(#000)
* // => 0
*
* luminosity(red)
* // => 0.2126
*
* @param {RGBA|HSLA} color
* @return {Unit}
* @api public
*/
module.exports = function luminosity(color){
utils.assertColor(color);
color = color.rgba;
function processChannel(channel) {
channel = channel / 255;
return (0.03928 > channel)
? channel / 12.92
: Math.pow(((channel + 0.055) / 1.055), 2.4);
}
return new nodes.Unit(
0.2126 * processChannel(color.r)
+ 0.7152 * processChannel(color.g)
+ 0.0722 * processChannel(color.b)
);
};