[转]求解！怎么将JPG图片的黑底去掉换成透明底

[转]求解！如何将JPG图片的黑底去掉换成透明底？
http://bbs.9ria.com/viewthread.php?tid=76207&extra=page%3D2%26amp%3Borderby%3Ddateline%26amp%3Bfilter%3D2592000



求解！如何将JPG图片的黑底去掉换成透明底？

在线等答案~ 请各路大侠们帮忙哈！

package
{
        import flash.display.Bitmap;
        import flash.display.BitmapData;
        import flash.display.Sprite;
        import flash.events.Event;
        import flash.utils.ByteArray;
       
        /**
         * ...
         * @author sailor
         */
        [SWF(backgroundColor=0x550055)]
        public class Main extends Sprite
        {
               
                [Embed(source = '../lib/2.jpg')]
       
                public var bmp:Class;
                public function Main():void
                {
                        var bmpd:BitmapData = Bitmap(new bmp()).bitmapData;
                       
                        var newbmpd:BitmapData = new BitmapData(bmpd.width, bmpd.height, true, 0);
                        var buffer:ByteArray = bmpd.getPixels(bmpd.rect);
                       
                        buffer.position = 0;
                        for (var i:int = 0, len:int = buffer.length ; i < len; i += 4 )
                                buffer[i] = (buffer[i + 1] + buffer[i + 2] + buffer[i + 3]) / 3;

                        newbmpd.setPixels(bmpd.rect, buffer);
                       
                        addChild(new Bitmap(newbmpd));
                       
                }
               
               
        }
       
}