as2背景画像をステージサイズに

background._xscale = Stage.width / 1024 * 100;
background._yscale  = Stage.height / 768 * 100;
if(background._xscale >= background._yscale)
{
background._yscale = background._xscale;
}else{
background._xscale = background._yscale;
}