I don't know if it continues in Poser 7, but Poser 5 and Poser 6 have provision for two different sorts of Bump Map. Bump is a greyscale, and works in the firefly render engine. Gradient Bump, at least according to the manual, is a compatibility mode which allows use of P4 bumpmaps when rendering the the P4 render engine. But what do bump maps actually do? I've seen various descriptions, but some of those descriptions seem broken. For instance, changing the direction of the normal. You have the normal vector, a direction in 3D space, and to shift that you need two numbers, whether polar coordinates or local cartesian. And a greyscale only gives you one. So is there a more technical description, preferably not depending on math equations, which can tell us what actually happens. (And why do people just greyscale the texture and use that as a bumpmap?)