[tsarapkabel]

Имея некий sourceBitmapData:

var copyOfBitmapData:BitmapData = new BitmapData(100, 200); // (width, height)
var rectangleToCut:Rectangle = new Rectangle(111, 222, 100, 200); // (x, y, width, height)
copyOfBitmapData.copyPixels(sourceBitmapData, rectangleToCut, new Point());