The hassle is with Poser 5. It uses JPEG, and does not convert JPEG to BUM as an outside step, the Poser 4 renderer will use a BUM directly, or convert a JPEG to BUM inside its internal brain as it needs it. The FireFly bump only use JPEG (or other std. greyscale formats). If a BUM is the only format supplied, it is difficult to get an accurate un-conversion back to the original greyscale.