[flexcoders] Basic question about copying bitmap Data to a display object.

[atlantageek]

Currently I am copying bitmap data to an image using 
matrix=new Matrix()
matrix.scale(img.width/_bitmap.width)
img.graphics.beginBitmapFill(_bitmap,matrix,false,false)
img.graphics.drawRect(0,0,img.width,400)
img.graphics.endFill

any suggestions. This is a update that happens several times a second.
It gets slower over time.