how to use gdk_image_get(..)?

[Jiang XU <jiang xu echostar com>]

This one drives me crazy!!!   =:-(


|I don't know what is wrong about that:

window1 is a GtkWindow and has been realized by
gtk_widget_realize(window1)

1.  GdkImage *image;
2.
image=gdk_image_new(GDK_IMAGE_NORMAL,gdk_window_get_visual(window1->window),100,100);

3.  image=gdk_image_get(window1->window,0,0,100,100);

Always failed on step 3, show error message:
    Gdk-ERROR **: BadMatch (invalid parameter attributes)
      serial 127 error_code 8 request_code 73 minor_code 0

I wonder why???
If somebody knows, please tell me ASAP!!, thanks!!!