[Therion] How to imbed cross-sections based on bitmaps

Hello, Generating and embedding cross-sections based on scraps is well described and works. My question: How do I imbed a cross-section which was not drawn using scrap editor, but is a scanned bitmap? Whatever parameters I use, it will not show, remains invisible. Can someone send me an example or point to the location where this is described? (Pls don't tell me I have to redraw 100's of cross sections using scrap-editor) Regards, Michael.