Gui Bitmap get blur

Hello, everybody,

I came across one problem about the bitmap in my display GUI. The Gui file is defined as below:

new GuiFadeinBitmapCtrl(StartupGui) {
profile = "GuiInputCtrlProfile";
horizSizing = "relative";
vertSizing = "relative";
position = "0 0";
extent = "800 600";
minExtent = "8 8";
visible = "1";
helpTag = "0";
bitmap = "";
wrap = "0";
fadeinTime = "600";
waitTime = "3300";
fadeoutTime = "400";
};

And then called:
StartupGui.setBitmap("mygame/client/ui/startupgui.jpg");

The size of startupgui.jpg is 800x600.

But the displayed bitmap is terrible: it seems that the pic has been scaled smaller(clear part), and the
edge of the displayed is very blur.

Do you have such problem?

Thanks for help.