Bitmap Alpha Problem

Hi;
I'm trying to tweak a script I found online to work for my application. The problem I am having is to make a certain part of the bitmap that is created by code transparent...but only a certain part of it. The code has the following:

_fire = new BitmapData(865, 92, false, 0xffffff);

Note
the alpha flag must be set to false, which is the source of my problem,
or nothing prints to screen at all. I need to make certain pixels
transparent. _fire is added to the stage and then called thus:

_fire.paletteMap(_grey, _grey.rect, ZERO_POINT, _redArray, _greenArray, _blueArray, _alphaArray);

at the end of the script. The colors for the arrays are created thusly:

code:

---

private function _createPalette(idx:int):void {

_redArray = [];

_greenArray = [];

_blueArray = [];

_alphaArray = [];

for (var i:int = 0; i < 256; i++) {

var gp:int = new int();

gp = _fireColor.getPixel(i, 0);

if (gp < 1050112)

{

_redArray.push(255);

_alphaArray.push(255);

} else {

_redArray.push(gp);

_alphaArray.push(0);

}

_greenArray.push(0);

_blueArray.push(0);

}

}

---

I added that if clause to capture when the color is black because that's
where I need to make it transparent. The problem is that where I need it
to be transparent, it's blue (why blue I don't know). Is there any way
to make it transparent? The entire code follows.
TIA,
George

code:

---

package {

import flash.display.Bitmap;

import flash.display.BitmapData;

import flash.display.BlendMode;

import flash.display.DisplayObject;

import flash.display.Loader;

import flash.display.LoaderInfo;

import flash.display.Sprite;

import flash.display.StageQuality;

import flash.display.StageScaleMode;

import flash.events.Event;

import flash.events.MouseEvent;

import flash.filters.ColorMatrixFilter;

import flash.filters.ConvolutionFilter;

import flash.geom.ColorTransform;

import flash.geom.Point;

import flash.system.LoaderContext;

import flash.net.SharedObject;

import flash.net.URLRequest;

import flash.text.TextField;

import flash.text.TextFieldAutoSize;

import flash.text.TextFormat;



[SWF(width=465, height=92, backgroundColor=0xffffff, frameRate=30)]



public class Fire extends Sprite {



private static const ZERO_POINT:Point = new Point();



private var _fireColor:BitmapData;

private var _currentFireColor:int;



private var _canvas:Sprite;

private var _grey:BitmapData;

private var _spread:ConvolutionFilter;

private var _cooling:BitmapData;

private var _color:ColorMatrixFilter;

private var _offset:Array;

private var _fire:BitmapData;

private var _redArray:Array;

private var _zeroArray:Array;

private var _greenArray:Array;

private var _blueArray:Array;

private var _alphaArray:Array;



public function Fire() {

//            stage.scaleMode = StageScaleMode.NO_SCALE;

//            stage.quality = StageQuality.LOW;

var loader:Loader = new Loader();

loader.contentLoaderInfo.addEventListener(Event.CO  MPLETE, _onLoaded);

loader.load(new URLRequest('images/fire-color.png'), new LoaderContext(true));

}



private function _onLoaded(e:Event):void {

_fireColor = Bitmap(LoaderInfo(e.target).loader.content).bitmap  Data;



_canvas = new Sprite();

_canvas.graphics.beginFill(0xffffff, 0);

_canvas.graphics.drawRect(0, 0, 865, 465);

_canvas.graphics.endFill();

_canvas.addChild(_createEmitter());



_grey = new BitmapData(865, 465, false, 0xffffff);

_spread = new ConvolutionFilter(3, 3, [0, 1, 0,  1, 1, 1,  0, 1, 0], 5);

_cooling = new BitmapData(865, 465, false, 0xffffff);

_offset = [new Point(), new Point()];

_fire = new BitmapData(865, 92, false, 0xffffff);

addChild(new Bitmap(_fire));



_createCooling(0.16);

_createPalette(_currentFireColor = 0);



addEventListener(Event.ENTER_FRAME, _update);

//            stage.addEventListener(MouseEvent.CLICK, _onClick);

}



private function _onClick(e:MouseEvent):void {

if (++_currentFireColor == int(_fireColor.height / 32)) {

_currentFireColor = 0;

}

_createPalette(_currentFireColor);

}



private function _createEmitter() [Very Happy] isplayObject {

var tf:TextField = new TextField();

tf.selectable = false;

tf.autoSize = TextFieldAutoSize.LEFT;

tf.defaultTextFormat = new TextFormat('Verdana', 80, 0xffffff, true);

tf.text = '__________________________________________';

tf.x = (465 - tf.width) / 2;

tf.y = 0;

//            tf.y = (465 - tf.height) / 2;

return tf;

}



private function _createCooling(a:Number):void {

_color = new ColorMatrixFilter([

a, 0, 0, 0, 0,

0, a, 0, 0, 0,

0, 0, a, 0, 0,

0, 0, 0, 1, 0

]);

}



private function _createPalette(idx:int):void {

_redArray = [];

_greenArray = [];

_blueArray = [];

_alphaArray = [];

for (var i:int = 0; i < 256; i++) {

var gp:int = new int();

gp = _fireColor.getPixel(i, 0);

if (gp < 1050112)

{

_redArray.push(255);

_alphaArray.push(255);

_greenArray.push(255);

_blueArray.push(255);

} else {

_redArray.push(gp);

_alphaArray.push(0);

_greenArray.push(0);

_blueArray.push(0);

}

}

}



private function _update(e:Event):void {

_grey.draw(_canvas);

_grey.applyFilter(_grey, _grey.rect, ZERO_POINT, _spread);

_cooling.perlinNoise(50, 50, 2, 982374, false, false, 0, true, _offset);

_offset[0].x += 2.0;

_offset[1].y += 2.0;

_cooling.applyFilter(_cooling, _cooling.rect, ZERO_POINT, _color);

_grey.draw(_cooling, null, null, BlendMode.SUBTRACT);

_grey.scroll(0, -3);

_fire.paletteMap(_grey, _grey.rect, ZERO_POINT, _redArray, _greenArray, _blueArray, _alphaArray);

}

}

}

---