scrolledWindow's scrollbars

[jody <jody xha gmail com>]

Hi
I use a ScrolledWindow to display an image. The ScrolledWindow is the only
child of the main window.
If the image is small enough, i want to size my window in such a way that
the ScrolledWindow tightly encloses the image (all of the image but no
more can be seen).
When i set the policy to automatic for both scrollbars and use the
size of my image to set
the window size, the scrollbars still appear. Apparently i need to add
2 pixels to
the width and the height of the image size so the scrollbars don't appear.
I.e. for an image with size 400x300 i have to do resize(402,302) to get
a ScrolledWindow without scrollbars. resize(401,301) already gives rise to
the scrollbars.
I guess those 2 pixels are some part of a border of the viewport, the
ScrolledWindow, or the main window.

Is there any way to get this "border" size?

Thank you
  jody