How to convert “background-color” to rgb() format?

Question

Here is my problem:

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() fo

Answer 1

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).

Answer 2

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

Answer 3

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>