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library to determine if the color parameter is a 'light' or a 'dark' color
此脚本不应直接安装。它是供其他脚本使用的外部库，要使用该库请加入元指令 // @require https://update.greasyfork.icu/scripts/491888/1355841/Light%20or%20Dark.js
// ==UserScript==
// @name Light or Dark
// @namespace http://greasyfork.icu/en/users/906106-escctrl
// @description library to determine if the color parameter is a 'light' or a 'dark' color
// @author escctrl
// @version 1.0
// @grant none
// @license MIT
// ==/UserScript==
// helper function to determine whether a color (the background in use) is light or dark
// https://awik.io/determine-color-bright-dark-using-javascript/
function lightOrDark(color) {
var r, g, b, hsp;
if (color.match(/^rgb/)) { color = color.match(/^rgba?\((\d+),\s*(\d+),\s*(\d+)(?:,\s*(\d+(?:\.\d+)?))?\)$/);
r = color[1]; g = color[2]; b = color[3]; }
else { color = +("0x" + color.slice(1).replace(color.length < 5 && /./g, '$&$&'));
r = color >> 16; g = color >> 8 & 255; b = color & 255; }
hsp = Math.sqrt( 0.299 * (r * r) + 0.587 * (g * g) + 0.114 * (b * b) );
if (hsp>127.5) { return 'light'; } else { return 'dark'; }
}