Is an xcf sourcecode? (according to GPL)

[gnalle@ruc.dk (Niels L. Ellegaard)]

Dear gurus :)

Suppose I use gimp to create graphics for a GPL'ed program. First I
use gimp to create a layered xcf-files of the graphics, and then I use
gimp to manually flatten the layers of the xcf files to create jpg's
for the game. Of course I keep the original xcf-files on my harddisk
to be able to correct spelling mistakes.

Do the xcf-files count as sourcecode? (according to the GPL)

Should Debian ideally offer free download of xcf-files corresponding a
large percentage of the graphics in the distribution?

Where can I read more about this? 

                   Thanks in advance

                          Niels


PS: GPL definition of sourcecode
http://www.gnu.org/copyleft/gpl.html

 The source code for a work means the preferred form of the work for
 making modifications to it. For an executable work, complete source
 code means all the source code for all modules it contains, plus any
 associated interface definition files, plus the scripts used to
 control compilation and installation of the executable.