How to convert "background-color" to rgb() format?

I want to change the opacity of background-color of one of the elements on my page. In order to do this I need to first convert the color to rgb() format (or extract r, g and b elements).

• From this I can see how to convert a hex string to numeric format...
• but colors are not always in hex format. They can also be named colors like "red"

    red     ---> rgb(255, 0, 0)
    #ff00ff ---> rgb(255, 0, 255)

How can this b开发者_开发知识库e done?

To convert a colorName to RGB or HEX, you'll first need a dictionary of color names and the respective values, than you can do:

function nameToHex(name) {
  return {
    "aliceblue": "#f0f8ff",
    "antiquewhite": "#faebd7",
    "aqua": "#00ffff",
    "aquamarine": "#7fffd4",
    "azure": "#f0ffff",
    "beige": "#f5f5dc",
    "bisque": "#ffe4c4",
    "black": "#000000",
    "blanchedalmond": "#ffebcd",
    "blue": "#0000ff",
    "blueviolet": "#8a2be2",
    "brown": "#a52a2a",
    "burlywood": "#deb887",
    "cadetblue": "#5f9ea0",
    "chartreuse": "#7fff00",
    "chocolate": "#d2691e",
    "coral": "#ff7f50",
    "cornflowerblue": "#6495ed",
    "cornsilk": "#fff8dc",
    "crimson": "#dc143c",
    "cyan": "#00ffff",
    "darkblue": "#00008b",
    "darkcyan": "#008b8b",
    "darkgoldenrod": "#b8860b",
    "darkgray": "#a9a9a9",
    "darkgreen": "#006400",
    "darkkhaki": "#bdb76b",
    "darkmagenta": "#8b008b",
    "darkolivegreen": "#556b2f",
    "darkorange": "#ff8c00",
    "darkorchid": "#9932cc",
    "darkred": "#8b0000",
    "darksalmon": "#e9967a",
    "darkseagreen": "#8fbc8f",
    "darkslateblue": "#483d8b",
    "darkslategray": "#2f4f4f",
    "darkturquoise": "#00ced1",
    "darkviolet": "#9400d3",
    "deeppink": "#ff1493",
    "deepskyblue": "#00bfff",
    "dimgray": "#696969",
    "dodgerblue": "#1e90ff",
    "firebrick": "#b22222",
    "floralwhite": "#fffaf0",
    "forestgreen": "#228b22",
    "fuchsia": "#ff00ff",
    "gainsboro": "#dcdcdc",
    "ghostwhite": "#f8f8ff",
    "gold": "#ffd700",
    "goldenrod": "#daa520",
    "gray": "#808080",
    "green": "#008000",
    "greenyellow": "#adff2f",
    "honeydew": "#f0fff0",
    "hotpink": "#ff69b4",
    "indianred ": "#cd5c5c",
    "indigo": "#4b0082",
    "ivory": "#fffff0",
    "khaki": "#f0e68c",
    "lavender": "#e6e6fa",
    "lavenderblush": "#fff0f5",
    "lawngreen": "#7cfc00",
    "lemonchiffon": "#fffacd",
    "lightblue": "#add8e6",
    "lightcoral": "#f08080",
    "lightcyan": "#e0ffff",
    "lightgoldenrodyellow": "#fafad2",
    "lightgrey": "#d3d3d3",
    "lightgreen": "#90ee90",
    "lightpink": "#ffb6c1",
    "lightsalmon": "#ffa07a",
    "lightseagreen": "#20b2aa",
    "lightskyblue": "#87cefa",
    "lightslategray": "#778899",
    "lightsteelblue": "#b0c4de",
    "lightyellow": "#ffffe0",
    "lime": "#00ff00",
    "limegreen": "#32cd32",
    "linen": "#faf0e6",
    "magenta": "#ff00ff",
    "maroon": "#800000",
    "mediumaquamarine": "#66cdaa",
    "mediumblue": "#0000cd",
    "mediumorchid": "#ba55d3",
    "mediumpurple": "#9370d8",
    "mediumseagreen": "#3cb371",
    "mediumslateblue": "#7b68ee",
    "mediumspringgreen": "#00fa9a",
    "mediumturquoise": "#48d1cc",
    "mediumvioletred": "#c71585",
    "midnightblue": "#191970",
    "mintcream": "#f5fffa",
    "mistyrose": "#ffe4e1",
    "moccasin": "#ffe4b5",
    "navajowhite": "#ffdead",
    "navy": "#000080",
    "oldlace": "#fdf5e6",
    "olive": "#808000",
    "olivedrab": "#6b8e23",
    "orange": "#ffa500",
    "orangered": "#ff4500",
    "orchid": "#da70d6",
    "palegoldenrod": "#eee8aa",
    "palegreen": "#98fb98",
    "paleturquoise": "#afeeee",
    "palevioletred": "#d87093",
    "papayawhip": "#ffefd5",
    "peachpuff": "#ffdab9",
    "peru": "#cd853f",
    "pink": "#ffc0cb",
    "plum": "#dda0dd",
    "powderblue": "#b0e0e6",
    "purple": "#800080",
    "red": "#ff0000",
    "rosybrown": "#bc8f8f",
    "royalblue": "#4169e1",
    "saddlebrown": "#8b4513",
    "salmon": "#fa8072",
    "sandybrown": "#f4a460",
    "seagreen": "#2e8b57",
    "seashell": "#fff5ee",
    "sienna": "#a0522d",
    "silver": "#c0c0c0",
    "skyblue": "#87ceeb",
    "slateblue": "#6a5acd",
    "slategray": "#708090",
    "snow": "#fffafa",
    "springgreen": "#00ff7f",
    "steelblue": "#4682b4",
    "tan": "#d2b48c",
    "teal": "#008080",
    "thistle": "#d8bfd8",
    "tomato": "#ff6347",
    "turquoise": "#40e0d0",
    "violet": "#ee82ee",
    "wheat": "#f5deb3",
    "white": "#ffffff",
    "whitesmoke": "#f5f5f5",
    "yellow": "#ffff00",
    "yellowgreen": "#9acd32"
  }[name.toLowerCase()];
}

/////////
function hex2rgb(c) {
  if (c[0] === '#') c = c.substr(1);
  var r = parseInt(c.slice(0,2), 16),
      g = parseInt(c.slice(2,4), 16),
      b = parseInt(c.slice(4,6), 16);
  return 'rgb('+ r +','+ g +','+ b +')';
}

/////////
document.querySelector("#btn").addEventListener("click", function(){
  var hex = nameToHex( document.querySelector("#colorName").value );
  if(!hex) return;
  document.querySelector("#rgb").textContent = hex2rgb(hex);
  document.querySelector("#hex").textContent = hex;
});

<input id="colorName" type="text" size="8" value="cyan">
<input id="btn" type="button" value="Convert">
<div id="rgb">RGB result</div>
<div id="hex">HEX result</div>

Use window.getComputedStyle(elem, null).getPropertyValue("background-color"); to get the background-color string. Then, check if it's in a desired format.

• rgb(n, n, n)
• Others, such as hsl, rgba, hsla, ... convert these using an easy-to-find algorithm
• Color names: Create a map of colornames-to-rgb (such as: var name2rgb = {red: "rgb(255, 0, 0)"};)

A list of color names can be found on the web. Visit this site for a list of colornames (which is probably not complete).

This function will get you the r and g and b that you can use to create any format you want:

color_1 = resolve_color('#FFCC00');

color_2 = resolve_color('#FC0');

color_3 = resolve_color('rgb(255, 204, 0)');

color_4 = resolve_color('rgb(100%, 80%, 0%)');

In all examples, color_N is:

/* color_N is an array
 *   - color_N['red']    : 255
 *   - color_N['greenn'] : 204
 *   - color_N['red']    : 0
 */

Function

function resolve_color(color){
    // return an array containing R, G and B values
    if(color === 'transparent')// IE (6 and ?)
        color = '#FFF';
    var r,g,b;
    var hex_color_pcre = new RegExp("^#[0-9a-f]{3}([0-9a-f]{3})?$",'gi');
    var rgb_color_pcre = new RegExp("rgb\\(\\s*((?:[0-2]?[0-9])?[0-9])\\s*,\\s*((?:[0-2]?[0-9])?[0-9])\\s*,\\s*((?:[0-2]?[0-9])?[0-9])\\s*\\)$",'gi');
    var rgb_percent_color_pcre = new RegExp("rgb\\(\\s*((?:[0-1]?[0-9])?[0-9])%\\s*,\\s*((?:[0-1]?[0-9])?[0-9])%\\s*,\\s*((?:[0-1]?[0-9])?[0-9])%\\s*\\)$",'gi');
    if(color.match(hex_color_pcre)){
        if(color.length == 4){
            r  = color.charAt(1)+""+color.charAt(1);
            g  = color.charAt(2)+""+color.charAt(2);
            b  = color.charAt(3)+""+color.charAt(3);
        }
        else{
            r  = color.charAt(1)+""+color.charAt(2);
            g  = color.charAt(3)+""+color.charAt(4);
            b  = color.charAt(5)+""+color.charAt(6);
        }
        r = h2d(r);
        g = h2d(g);
        b = h2d(b);
    }
    else if(color.match(rgb_color_pcre)){
        r = RegExp.$1;
        g = RegExp.$2;
        b = RegExp.$3;
    }
    else if(color.match(rgb_percent_color_pcre)){
        r = parseInt((RegExp.$1)*2.55);
        g = parseInt((RegExp.$2)*2.55);
        b = parseInt((RegExp.$3)*2.55);
    }
    else
        return false;

    var returned =[];
    returned['red'] = r;
    returned['green'] = g;
    returned['blue'] = b;
    return returned;
}

function h2d(h) {
    // hex to decimal
    return parseInt(h,16);
} 

source: http://www.kadimi.com/en/javascript-tween-function-368

Or you could just bring up the color pallet using word, excel or powerpoint and one of the color option (eg fill) and enter the hex value ... it will give you the RGB values.