Added setting "ignoreFrequentColors"

lib/colorStatistics.js

@@ -0,0 +1,80 @@
+/* jslint moz: true */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+(function(){
+	"use strict";
+	
+	
+	var scope;
+	if ((typeof exports) !== "undefined"){
+		scope = exports;
+	}
+	else {
+		window.scope.colorStatistics = {};
+		scope = window.scope.colorStatistics;
+	}
+	
+	class Statistic{
+		constructor(){
+			this.colors = Object.create(null);
+			this.numberOfColors = 0;
+			
+			this.minBoundary = {count: Number.NEGATIVE_INFINITY};
+			this.maxBoundary = {count: Number.POSITIVE_INFINITY, previousColor: this.minBoundary};
+			this.minBoundary.nextColor = this.maxBoundary;
+		}
+		addColor(r, g, b, a){
+			var index = String.fromCharCode(r, g, b, a);
+			var color = this.colors[index];
+			if (!color){
+				color = {index, color: [r, g, b, a], count: 0, previousColor: this.minBoundary, nextColor: this.minBoundary.nextColor};
+				this.numberOfColors += 1;
+				this.minBoundary.nextColor = color;
+				color.nextColor.previousColor = color;
+				this.colors[index] = color;
+			}
+			color.count += 1;
+			if (color.count > color.nextColor.count){
+				// swap colors to remain in right order
+				// a -> b -> c -> d becomes a -> c -> b -> d
+				var a = color.previousColor;
+				var b = color;
+				var c = color.nextColor;
+				var d = color.nextColor.nextColor;
+				
+				a.nextColor = c;
+				c.previousColor = a;
+				
+				c.nextColor = b;
+				b.previousColor = c;
+				
+				b.nextColor = d;
+				d.previousColor = b;
+			}
+		}
+		getMaxColors(n){
+			var n = Math.min(n, this.numberOfColors);
+			var colors = Object.create(null);
+			var current = this.maxBoundary;
+			for (;n && current;n -= 1){
+				current = current.previousColor;
+				colors[current.index] = current;
+			}
+			return colors;
+		}
+	}
+	
+	scope.compute = function computeColorStatistics(rawData){
+		var statistic = new Statistic();
+		for (var i = 0, l = rawData.length; i < l; i += 4){
+			statistic.addColor(
+				rawData[i + 0],
+				rawData[i + 1],
+				rawData[i + 2],
+				rawData[i + 3]
+			);
+		}
+		return statistic;
+	}
+}());