Extract image from Gtk::Image

[Andreas Bauer <baueran rsise anu edu au>]

Hi together,

I have a somewhat largish Gtk::Image in my program, and would like to
take out rectangular areas from it, which in turn should be
represented as Gtk::Images for later use.

Does someone have any idea on how to achieve this with gtkmm? 

I assume I need to do something with a Pixbuffer as intermediate step,
but it wasn't obvious to me on how to actually proceed.

Many thanks,

Andreas.