Is it possible to cut away transparent areas of Gtk-pixbuf?

I am currently using rsvg in Python to separate Svggroups. I got it working so that 开发者_StackOverflow中文版rsvg loads a single group ... alas all the transparent space around that still remains.

Is there a gtk functionallity to cut away all this space?

Thanks for all the answers!

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There's nothing built-in but it's fairly simple to code it (walk over pixels, find the transparent ones). Unfortunately walking over pixels in python is probably slow.