[help] get the alpha channel value from external .png

programming flash
1

[LEFT]i can now getPixel() from a external jpg
but what i finallly want to achieve, is getPixel32()
the alpha value is always FF(255)
i don’t know why …
can anyone see the problem?

[COLOR=#22229c]http://www.senocular.com/flash/source.php?id=0.168[/COLOR]
take a look on this sample~
in this sample the photo is partially transparent, i can see that in photoshop
if i put my code in this file, the color picker can tell the alpha changes.
that why i still think there is a chance for getting the alpha value from external .png~
just don’y know how to achieve it T_T
(i’ve try transparent png and also alpha channel added png, doesn’t work like the sample)

 [LEFT]import flash.display.BitmapData; 
import flash.geom.ColorTransform; 
import flash.geom.Matrix; 

Stage.scaleMode = 'noScale'; 
Mouse.hide(); 

pixData_xml = new XML(); 
pixData_xml.onLoad = startGetPix; 
pixData_xml.load("pixData.xml"); 
pixData_xml.ignoreWhite = true; 

picListener = new Object(); 
picLoader = new MovieClipLoader(); 
picListener.onLoadInit = function(target_mc:MovieClip) { 
   getPix(); 
}; 
picLoader.addListener(picListener); 

function startGetPix(success) { 
   imgPath = pixData_xml.childNodes[0].firstChild.attributes.imgURL; 
   picLoader.loadClip(imgPath,img_mc); 
} 
var image_bitmap; 
function getPix() { 
   image_bitmap = new flash.display.BitmapData(img_mc._width, img_mc._height); 
   image_bitmap.draw(img_mc,new Matrix()); 
   var channelBitmap = image_bitmap.clone(); 
   channel_mc.attachBitmap(channelBitmap, 1); 

var sourceRect = image_bitmap.rectangle;
var offset = new flash.geom.Point(0,0);
   channelBitmap.copyChannel(image_bitmap, sourceRect, offset, 8, 8); 

} 

onMouseMove = function () { 
   picker_mc._x = _xmouse; 
   picker_mc._y = _ymouse; 
   var curr_color:Number = image_bitmap.getPixel32(img_mc._xmouse, img_mc._ymouse); 
   var preview_colortansform = new flash.geom.ColorTransform(); 
   preview_colortansform.rgb = curr_color; 
   color_mc.transform.colorTransform = preview_colortansform; 
    
   var alpha:String = (curr_color >> 24 & 0xFF).toString(16); 
   trace(">> alpha: "+alpha); 
   // ff 
   var red:String = (curr_color >> 16 & 0xFF).toString(16); 
   trace(">> red: "+red); 
   // aa 
   var green:String = (curr_color >> 8 & 0xFF).toString(16); 
   trace(">> green: "+green); 
   // cc 
   var blue:String = (curr_color & 0xFF).toString(16); 
   trace(">> blue: "+blue); 
   // ee 
   trace("0x"+alpha+red+green+blue); 
   // 0xffaaccee 
   hex_txt.text = "0x"+alpha+red+green+blue; 
   updateAfterEvent(); 
};[/LEFT]

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