Minor Bug with Bitmap Smoothing in AS3

We recently encountered a problem where bitmap images that we created dynamically were not being properly smoothed when rotated and scaled. We couldn’t see any obvious reason for it – we were setting the container bitmap to smooth, tried every quality setting, but it still looked terrible.

The answer turned out to be super simple, if not immediately obvious. The Bitmap object in ActionScript 3 reverts its .smoothing property to false whenever you change it’s .bitmapData property. Because we were setting up our Bitmap objects in advance, then assigning BitmapData objects to them when they were created, it simply appeared as though smoothing just didn’t work in our project.

Here’s a quick code example:

var bmp:Bitmap = new Bitmap(null,true);
trace(bmp.smoothing); // true
bmp.bitmapData = bmpd;
trace(bmp.smoothing); // false

And here’s what it looks like with smoothing on (top) versus off (bottom).

You can definitely see how our project wasn’t looking too good prior to fixing this issue.

Grant Skinner

The "g" in gskinner. Also the "skinner".



  1. Thanks for mentioning! Will safe me a lot of time!

  2. Off topic: When I right click the SWF and select “Zoom In” the browser (FF) wants to add and entry “[Folder Name]” to my bookmarks… huh? I’m on a Mac right now, maybe thats it. Quirky little machines those Mac’s…

  3. @pan69

    I ran into this problem yesterday afternoon while in development. It seems to be a Mac only bug with Firefox It doesn’t look like a Flash bug, but a browser bug. Hopefully it will be resolved in the next release/build of Firefox.

    Quirky perhaps, but I still love my mac 🙂

  4. workaround in mxml

    ViewHelper Class:

    public static function smoothImage(event:Event):void


    var bitmap:Bitmap = ((event.target as Image).content as Bitmap);

    if (bitmap != null)


    bitmap.smoothing = true;



  5. on complete not creationComplete

  6. Just came across with this bug. Thanks for the post.

  7. Thanks for the tip. I just couldn’t work out why my bitmaps looked so rubbish.

  8. Can anyone explain my bitmap smoothing woes? Is it really just a limitation of Flash?


    (watch small thumbnail when toggling quality)

    and the thread on actionscript.org:


  9. Thanks:)

    I was crazy for few hours, almost thinking to switch project to HTML because of that 🙂

    Than i run into this post

  10. SWEET, this explains everything…

  11. Claudius – re your FLEX fix above (and just in case it helps anyone else) – works on Flash with the following var replaced:

    var bitmap:Bitmap = (event.target.content as Bitmap);

    I was going nuts trying to smooth dynamically loaded images – your function worked a treat!



  12. This wasn’t working for me with super small scaling (thumbnails) until I added this once my class was added to the stage:

    stage.quality = StageQuality.BEST;

  13. I ran into the same problem, and I noticed that works if you initiate another object (Bitmap) set the new object bitmaData = yourBitmapData and then add smooting = true to Bitmap object

    var bitmapOver:Bitmap = Bitmap(new OverFinal());

    bitmapOver.smoothing = true;


    //end adding png OVER

    actualBMD = new BitmapData(ui11.width, ui11.height, true, 0xFFFFFFFF );

    actualBMD.draw(ui11, new Matrix(), null, null, null, true );

    var smoothTRY:Bitmap = new Bitmap(actualBMD);

    smoothTRY.smoothing = true;

    actualBMD = smoothTRY.bitmapData;

  14. This is working if you do:

    var bitmap:Bitmap = new Bitmap(yourBitmapData)

    bitmap.smooting = true;

    now it works

  15. Nothing else seemed to work for me. If you apply a filter to the bitmap with 0 alpha, smoothing is added:

    _bmp.filters = [new GlowFilter(0x000000, 0, 5, 5)];

  16. what about bitmaps in the library nested in custom-class movieclips that are initiated dynamically?

    do i need to acces the bitmap through code (movieclip.getchildat()) and re-assign smoothing = true?

  17. ok i tested that and the answer is yes: you do have to reassign smoothing to library bitmaps like this:

    Bitmap(myMovieClip.getChildAt(~)).smoothing = true;


  18. How can I make smooth my movie clip¿?
    This is my code.

    imageCentral_3._x = 700;
    imageCentral_3._y = 150;
    imageCentral_3._alpha = 100;
    imageCentral_3._rotation = -4;

  19. Thanks folks! I am using two static BitmapData objects and swapping them out from under the displayed Bitmap when some action is performed. The same problem occurs. The first load looks nice, the subsequent ones look horrible. By resetting the smoothing property to true just after the swap, everything starts to spin right! Annoying little gremlin is quashed thanks to your post here.

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