Drawable to byte[]

I have an image from the web in an ImageView. It is very small (a favicon) and I'd like to store it in my SQLite database. I can get a Drawable from mImageView.getDrawable() but then I don't know what to do next. I don't fully understand the Drawable class in Android.

I know I can get a byte array from a Bitmap like:

Bitmap defaultIcon = BitmapFactory.decodeStream(in);

ByteArrayOutputStream stream = new ByteArrayOutputStream();
defaultIcon.compress(Bitmap.CompressFormat.JPEG, 100, stream);

byte[] bitmapdata = stream.toByteArray();

But how do I get a byte array from a Drawable?