Get brightness from background color with jQuery

jquery.brightness.js

jQuery.fn.brightness = function() {
  var bg_color, rgba, y;
  bg_color = this.css('background-color');
  if ((bg_color != null) && bg_color.length) {
    rgba = bg_color.match(/^rgb(?:a)?\(([0-9]{1,3}),\s([0-9]{1,3}),\s([0-9]{1,3})(?:,\s)?([0-9]{1,3})?\)$/);
    if (rgba != null) {
      if (rgba[4] === '0') {
        if (this.parent().length) return this.parent().brightness();
      } else {
        y = 2.99 * rgba[1] + 5.87 * rgba[2] + 1.14 * rgba[3];
        if (y >= 1275) {
          return 'light';
        } else {
          return 'dark';
        }
      }
    }
  } else {
    if (this.parent().length) return this.parent().brightness();
  }
};

Usage: jQuery('.your-html-element').brightness(); // => return 'light' or 'dark' or undefined

Where do the numbers come from?

Even its not the exact values it might be related to this http://en.wikipedia.org/wiki/Luminance_(relative). The general idea is that green impacts us the most on the perception of what is "bright".

The Y in YIQ.

Hi, may I use this gist in a project? I couldn't find any licensing information.