Do you use transparent PNGs in Flash, Flex or AIR? Want to cut your application file size in half?

Embedding transparent PNGs dramatically increases the size of your Flash, Flex and AIR applications. Photoshop and Fireworks dot not have any compression available for transparent PNGs (that I am aware of).

Import your PNGs into Flash, give them a linkage id, and export the file as a SWF. Make sure to set your compression level in the publish settings (default is 80%). Using this method, I was able to cut the file size in half for a number of applications.

private var MyImage:Class;
private var myImage:Sprite = new MyImage() as Sprite;

rather than…

// Don't use this one 😉
private var MyImage:Class;
private var myImage:BitmapAsset = new MyImage() as BitmapAsset;

It is also much easier to manage your external assets from a SWF. Designers can set up a nice slice sheet using the stage in Flash. Much easier than managing tons of small PNGs in folders everywhere.

Image Manager

In addition to using the SWF it can also be very useful to set up an ImageManager to serve out images to your application. This prevents having to change code in multiple places to update the same image reference.

Image Manager Class:

package com.cb.utils
	import flash.display.Sprite;
	public class ImageManager
		public static const MY_IMAGE_ID:String = "my_image_id";
		public static var MyImage:Class;

		public static function getMovie(id:String):Sprite
			var result:Sprite;
				case MY_IMAGE_ID:
					result = new MyImage();
			return result;

To access an image from the manager class just make this call:

var myImage:BitmapAsset = ImageManager.getImage(ImageManager.MY_IMAGE_ID);

Importing PNGs into Flash

And for those of you that need a refresher on importing PNGs into Flash and setting up linkage IDs:

File->Import->Import to Stage...

File->Import->Import to Stage...

Right click on the image. Select ‘Convert to Symbol’…

Step 2


Step 3


Disclaimer: It may be obvious but you must be using transparent PNGs in your app to see a decrease in file size 😉 Most of the apps I work on have lots of transparent PNGs!

2 thoughts on “Compress Transparent PNGs with Flash

  1. If you create your library, export it to a swc (publish settings)
    Add that swc as a library to your as3 project>
    Now you can give your constant the value the name of your library classname for ex.:
    MY_IMAGE_ID:String = “image_class_libname”

    After that you can use reflection to retrieve it from that string.
    That way you can skip writing a big case switch for all your assets.

    reflection looks like this:

    public static function getLibClassInstance(libClassId:String):Class {
    var libClass : Class = getDefinitionByName(libClassId) as Class;
    return new libClass ();


    var clazz:Class = MyLib.getLibClassInstance(MyLib.MY_IMAGE_ID);

    by the way this is example code, untested


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