Hi,

if I use view.stage3DProxy.context3D.drawToBitmapData(this.bitmapdata), is there a way to get a png-File with alpha-Transparency?

Ofc yes. Use UNIQUE color for background, for example 0x330000. then just

image.bitmapData.threshold(original, rect, pt, “==”, 0xFF330000, 0x00330000, 0xFFFFFFFF, true);

As far as I know, it won’t be possible to do it “correctly” because unless I’m mistaken the backbuffer in Stage3D does not support alpha transparency (at least when rendering to the stage.)

The hack suggested by Shegl will work as long as you don’t have the 0x330000 color in your rendered objects, although it will likely not produce very nice-looking edges.

There’s a solution in:
http://away3d.com/forum/viewthread/1401/