ReedD · May 22, 2015 18:55 · May 22, 2015
diff --git a/luma.js b/luma.js
@@ -0,0 +1,52 @@
+/**
+ * @name Luma
+ * @description
+ * Calculate luma, the lightness of a color between absolute black and the brightest white. 
+ * 
+ * @author Reed Dadoune <[email protected]>
+ * @author Alnitak http://stackoverflow.com/a/12043228/3322075
+ *
+ * @param {float|string}
+ *  - {float} r The red value of the color
+ *  - {string} r The hex, rgb or rgba value of the color
+ * 	e.g. #fff, #fff, rgb(255, 255, 255) or rgba(255, 255, 255, 1)
+ * @param {float} g The green value of the color
+ * @param {float} b The blue value of the color
+ * @param {float} a The alpha value of the color
+ * 
+ * @returns {float} The luma value of the color
+ */
+function luma(r, g, b, a) {
+	if (arguments.length === 1) {
+		var match;
+		var colorString = String(r);
+		var hexRegex    = /^\#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$/;
+		var rgbRegex    = /^rgb\(([0-9]{1,3}),[ +]?([0-9]{1,3}),[ +]?([0-9]{1,3})\)$/;
+		var rgbaRegex   = /^rgba\(([0-9]{1,3}),[ +]?([0-9]{1,3}),[ +]?([0-9]{1,3}),[ +]?([0-9]{1}|(?:[0-9]{1})?\.[0-9]+)\)$/;
+		if (match = colorString.match(hexRegex)) {
+			var hex = match[1];
+			if (hex.length === 3) {
+				// Convert to 6
+				hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2];
+			}
+			var rgb = parseInt(hex, 16); // convert rrggbb to decimal
+			r = (rgb >> 16) & 0xff; // extract red
+			g = (rgb >>  8) & 0xff; // extract green
+			b = (rgb >>  0) & 0xff; // extract blue
+		} else if (match = colorString.match(rgbRegex)) {
+			r = parseFloat(match[1]);
+			g = parseFloat(match[2]);
+			b = parseFloat(match[3]);
+		} else if (match = colorString.match(rgbaRegex)) {
+			r = parseFloat(match[1]);
+			g = parseFloat(match[2]);
+			b = parseFloat(match[3]);
+		}
+	} else {
+		r = parseFloat(r) || 0;
+		g = parseFloat(g) || 0;
+		b = parseFloat(b) || 0;
+	}
+	var luma = 0.2126 * r + 0.7152 * g + 0.0722 * b; // per ITU-R BT.709
+	return luma;
+}