Please help me to center a image

I did as below but it's not on the center

_screen.AddObject("splashimage", "Image")
_screen.splashimage.Picture = path_screen
_screen.splashimage.Visible = .T.

_screen.splashimage.left = (_screen.Width - _screen.splashimage.left) / 2
_screen.splashimage.top = (_screen.Width - _screen.splashimage.top) / 2