cross-domain and url

getColorFromUrl gets color from an image served from the same domain,
so you don't have to create an image element to get the color.

getColorAsync gets the color from another domain that has an open
cross-domain policy.

src/color-thief.js

@@ -137,6 +137,50 @@ ColorThief.prototype.getPalette = function(sourceImage, colorCount, quality) {
     return palette;
 };
 
+ColorThief.prototype.getColorFromUrl = function(imageUrl, callback, quality) {
+    sourceImage = document.createElement("img");
+    var thief = this;
+    sourceImage.addEventListener('load' , function(){
+        var palette = thief.getPalette(sourceImage, 5, quality);
+        var dominantColor = palette[0];
+        callback(dominantColor, imageUrl);
+    });
+    sourceImage.src = imageUrl
+};
+
+
+ColorThief.prototype.getImageData = function(imageUrl, callback) {
+    xhr = new XMLHttpRequest();
+    xhr.open('GET', imageUrl, true);
+    xhr.responseType = 'arraybuffer'
+    xhr.onload = function(e) {
+        if (this.status == 200) {
+            uInt8Array = new Uint8Array(this.response)
+            i = uInt8Array.length
+            binaryString = new Array(i);
+            for (var i = 0; i < uInt8Array.length; i++){
+                binaryString[i] = String.fromCharCode(uInt8Array[i])
+            }
+            data = binaryString.join('')
+            base64 = window.btoa(data)
+            callback ("data:image/png;base64,"+base64)
+        }
+    }
+    xhr.send();
+};
+
+ColorThief.prototype.getColorAsync = function(imageUrl, callback, quality) {
+    var thief = this;
+    this.getImageData(imageUrl, function(imageData){
+        sourceImage = document.createElement("img");
+        sourceImage.addEventListener('load' , function(){
+            var palette = thief.getPalette(sourceImage, 5, quality);
+            var dominantColor = palette[0];
+            callback(dominantColor, this);
+        });
+        sourceImage.src = imageData;      
+    });
+};