Dynamically changing the palette of an image using Flash (AS3)

For the generative art framework ARTionscript I wanted to be able to dynamically change the colours of an image using actionscript. This can easily be done using Photoshop (or similar), but what about the latest uploaded Flickr image?

Having experimented with a few options, I settled on the following process:

• Load an external image
• Convert the BitmapData of the image to grey scale
• Perform a histogram equalisation on the BitmapData
• Posterize / limit the BitmapData to the number of colours in the new palette
• Swap the remaining colours in the BitmapData with the colours in the new palette
• Create some effect using the new BitmapData

And here is the code which takes advantage of the BitmapData.histogram, BitmapData.paletteMap & ColorMatrixFilter :

package com.artionscript.assistants
{
	import com.artionscript.palettes.Palette;
	import flash.display.BitmapData;
	import flash.filters.ColorMatrixFilter;
	import flash.geom.Matrix;
	import flash.geom.Point;
	import flash.geom.Rectangle;
	/**
	 * ...
	 * @author Trevor Boyle
	 */
	public class ImageAssistant
	{
		public static function convertBDToGreyScale(sourceBD:BitmapData):BitmapData {
			//BT.709-5 luminance constants

			var tempBD:BitmapData = sourceBD.clone();

			var greyScaleCMF:ColorMatrixFilter = new ColorMatrixFilter();
			greyScaleCMF.matrix = new Array(
			0.2125, 0.7154, 0.0721, 0, 0,
			0.2125, 0.7154, 0.0721, 0, 0,
			0.2125, 0.7154, 0.0721, 0, 0,
			0, 0, 0, 1, 0);

			tempBD.applyFilter(tempBD, new Rectangle(0, 0, tempBD.width, tempBD.height), new Point(0, 0), greyScaleCMF);

			return tempBD;
		}

		public static function equaliseGreyScaleBDHistogram(sourceBD:BitmapData):BitmapData {
			//concept by http://www.generation5.org/content/2004/histogramEqualization.asp

			var tempBD:BitmapData = sourceBD.clone();

			var v:Vector.<vector .<Number>> = tempBD.histogram();

			var adjustmentMultiplier:Number = 255 / (tempBD.width * tempBD.height);
			var tempAdjustedFreq:int;
			var cumulativeFreq:Number = 0;
			var adjustedRedFreqArr:Array = new Array();
			var adjustedGreenFreqArr:Array = new Array();
			var adjustedBlueFreqArr:Array = new Array();
			for (var i:int=0; i < 256; i++) {
				cumulativeFreq += v[0][i];

				tempAdjustedFreq = cumulativeFreq * adjustmentMultiplier;

				adjustedRedFreqArr[i] = tempAdjustedFreq << 16
				adjustedGreenFreqArr[i] = tempAdjustedFreq << 8
				adjustedBlueFreqArr[i] = tempAdjustedFreq
			}

			tempBD.paletteMap(tempBD, new Rectangle(0, 0, tempBD.width, tempBD.height), new Point(0, 0),
adjustedRedFreqArr, adjustedGreenFreqArr, adjustedBlueFreqArr, null);

			return tempBD;
		}
		
		public static function posterizeGreyScaleBD(sourceBD:BitmapData, depth:int):BitmapData {
			//concept by http://www.axiomx.com/posterize.htm

			var tempBD:BitmapData = sourceBD.clone();

			depth = Math.max(0, Math.min(255, depth));

			var colours:Array = [0x004358, 0x1f8a70, 0xbedb39, 0xffe11a, 0xfd7400];

			var numAreas:Number = 256 / depth;
			var numValues:Number = 255 / (depth - 1);

			var tempArea:int;
			var tempAdjustedFreq:int;
			var tempColour:uint;
			var adjustedRedFreqArr:Array = new Array();
			var adjustedGreenFreqArr:Array = new Array();
			var adjustedBlueFreqArr:Array = new Array();
			for (var i:int = 0; i < 256; i++) {
				tempArea =  Math.floor(i / numAreas);
				trace(colours[tempArea]);
				tempAdjustedFreq = Math.floor(numValues * tempArea);

				tempColour = colours[tempArea];

				adjustedRedFreqArr[i] = tempAdjustedFreq << 16
				adjustedGreenFreqArr[i] = tempAdjustedFreq << 8
				adjustedBlueFreqArr[i] = tempAdjustedFreq
			}

			tempBD.paletteMap(tempBD, new Rectangle(0, 0, tempBD.width, tempBD.height), new Point(0, 0),
adjustedRedFreqArr, adjustedGreenFreqArr, adjustedBlueFreqArr, null);

			return tempBD;
		}

		public static function posterizeGreyScaleBDToPalette(sourceBD:BitmapData, colours:Array):BitmapData {
			//concept by http://www.axiomx.com/posterize.htm

			var tempBD:BitmapData = sourceBD.clone();

			var depth:int = colours.length;

			depth = Math.max(0, Math.min(255, depth));

			trace(depth)

			var numAreas:Number = 256 / depth;
			var numValues:Number = 255 / (depth - 1);

			var tempArea:int;
			var tempAdjustedFreq:int;
			var tempColour:uint;
			var adjustedRedFreqArr:Array = new Array();
			var adjustedGreenFreqArr:Array = new Array();
			var adjustedBlueFreqArr:Array = new Array();
			for (var i:int = 0; i < 256; i++) {
				tempArea =  Math.floor(i / numAreas);
				tempAdjustedFreq = Math.floor(numValues * tempArea);
				tempColour = colours[tempArea];

				adjustedRedFreqArr[i] = ((tempColour >> 16) & 0xFF) < < 16;
				adjustedGreenFreqArr[i] = ((tempColour >> 8) & 0xFF) < < 8;
				adjustedBlueFreqArr[i] = (tempColour & 0xFF);
			}

			tempBD.paletteMap(tempBD, new Rectangle(0, 0, tempBD.width, tempBD.height), new Point(0, 0),
adjustedRedFreqArr, adjustedGreenFreqArr, adjustedBlueFreqArr, null);

			return tempBD;
		}

		public static function scaleBD(sourceBD:BitmapData, width:Number, height:Number, constrain:Boolean=true,
constrainToLargest:Boolean=false):BitmapData {

			var tempBD:BitmapData = sourceBD.clone();

			var scaleX:Number = width / tempBD.width;
			var scaleY:Number = height / tempBD.height;

			if (constrain) {
				if (constrainToLargest) {
					scaleX = scaleY = Math.max(scaleX, scaleY);
				}else{
					scaleX = scaleY = Math.min(scaleX, scaleY);
				}
			}
			var scaleMatrix:Matrix = new Matrix();
			scaleMatrix.scale(scaleX, scaleY);

			var scaledBD:BitmapData = new BitmapData(tempBD.width * scaleX, tempBD.height * scaleY, false, 0x000000);
			scaledBD.draw(tempBD, scaleMatrix);

			return scaledBD;
		}
	}
}