That isn't really what I meant. How are you scanning this? Are you scanning it as JPG directly?
Make sure you scan it as a TIFF or BMP. I don't recommend using JPG for greyscale pages at all, but if you must use JPG, it should only be done as the very final step. Whatever you do to edit your scans, it should be kept as a bmp, tiff, png, or psd until the very end.