Thanks guys. I'll try out the superimposing technique, and also exporting it to GIMP. I thought I would get an email when there were replies, that's why I took so long to respond.

Hi all, I was reading how to create lighting effects in an online book on Inkscape. As I understand, the lighting filters, use the objects alpha channel as the bump map for the lighting filter. I was wondering if it is possible to manipulate the alpha channel directly. For instance, setting a gray-s...