Quote - When you say "not from a grayscale image", now the words are being twisted. Forget the term grayscale image. Instead, think "topology delta matrix". Given a topology delta matrix, i.e. the difference between two meshes as measured along the surface normal vector from one to the other, you end up with exactly the data found in a bump map.

See what I mean? From that, you can construct all the normals.

There is a technical difference in that normal maps make use of three color channels (RGB) to disturb the normal on X, Y and Z axes, whereas bump maps only use one to disturb the normal on Y.  So what he's saying about grayscale vs. not-grayscale does matter, at least on paper.  However you're still stuck with not being able to disturb the actual profile of the geometry; both techniques just give you a shading effect.  Raytraced shadows will ignore bump maps for sure, and any place where the horizon of a model is visible, it will still be perfectly smooth.

Here's a good example I found of what MIGHT be possible:
http://www.game-artist.net/forums/support-tech-discussion/7756-bump-maps-vs-normal-maps.html

I don't know if Poser's shadows (raytraced or depthmapped) will accurately reproduce the kind of self-shadowing demonstrated there, I tend to doubt it.  I don't have anything normal mapped handy to test it with.

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