Question about GdkPixbuf initialization

[Geiger Ho <s997659 ee cuhk edu hk>]

Hi all,

  I'm using Gtk+ 1.2. I use GdkPixbuf to make an image viewer with zoom in
and zoom out functions. I create two GdkPixbuf. One is the source reading
from a picture file. One is the destination (the size is fixed) to show
the scaled version. It's ok to do zoom in. But when I do zoom out, the
previous image is being left behind with the scaled image (of coz smaller 
in size ) sitting on the top. I would like to know how I can make the
other area of the destination GdkPixbuf be black (or white) color arround
the scaled down image.

  Thanks in advance.

Regards,
Geiger