It is possible to revert a BUM to grayscale. There is a plug on the Mac Classic version of GraphiConverter that will convert a BUM to grayscale in any format that you like. The real trick is nullifying the emboss. Other than that, it's a straightforward (done backwards) process to convert it. Since an emboss can't be perfectly undone, the process averages the red and green channel after de-embossing and then writes that to all three channels. Once that is done, the grayscale is inverted (provided that the grayscale was properly inverted in the first place) and saved. The result is a little fuzzy, so sharpening might be needed to make it more usable. Keep in mind that BUM isn't a real format. A BUM can be any RGB file format, BMP, PICT, TIFF, JPEG, etc. The extension is just changed to give Poser 4 a proper handle on it.