[Therion] Embedding cross-sections based on bitmaps

Hello, I'm familiar with the method of embedding cross-sections made using scrap editor. That works. For our 10km - cave, we have 100's of cross-sections scanned from paper (i.e., bitmaps), drawn decades ago. How can I embed those? The method used for scanned paper surveys seems not to work. Whatever parameters I use, the cross-section scrap remains invisible. (Pls don't tell me we have to re-draw all the cross-sections) Regards, Michael.