ActionScript 3.0 :: BitmapData - SetPixels / SetVector Difficulties?

I'm trying to get my head round bitmapData and everything you can do with it. I'm using pure AS3 at the moment.I've been playing with some Perlin noise examples - worked ok - and tried writing another image (png) onto the bitmapdata.The new image is EMBEDed in the as3 code:

Code:
[Embed(source='icon.png')]
private var ImageClass:Class;
private var img:Bitmap = new ImageClass();

I write the perlin noise to the BitmapData thus:

Code:
var bmd:BitmapData = new BitmapData(200, 200, true, 0x00000000);
bmd.perlinNoise(baseX, baseY, octaves, seed, stitch, fractal, channels, grayscale, offsets);
var bm:Bitmap = new Bitmap(bmd);